Some aspects of the coordination chemistry of iron(III)

Coordmatlon Chmmtrv Rtwews Elsevter Pubhshmg Company, Amsterdam - Prmted m The NetherlAnds

SOME ASPECTS OF THE COORDINATION

CHEMISTRY

OF IRON(III)*

S A COTTON Departtmwt

of Chemrstr~. Queen Mar? Coliege. Mile End R_oad I ondon E I (Gt BRUNEI)

(Recewed October Sth, 1971)

CONTENTS Clocurl

185

ot symbols Introduction

186

Physwal techniques applicable to lrzn( III) complewx Magnetism (0 Electromc spectra \iI) (111) Electron paramagnetlc resonance blos\bauer spectroscopy (Iv)

186 187 187 189 191

Complews ot oxygen-cont.nnmg hgands hlonodcntate (0 BI- and terdentate (10 (111) XIl\ed 0,N donors Acids (carboxyhc and ammo) (Iv)

192 192 196 197 198

Complews-of nttrogendonor hgands hlonodentate (0 Bldentdte (and other) hgands (11)

199 199 201

Complexes ot hahdex

202

Complexes ot sulphur donors

‘05

Complexes of phosphorus and arsemc donors hlonodentate (1) Polydentate donors (II)

2r1 211 ‘12

Complexes of carbon donor5

211

Conclusion

214 215

Acknowledgements Appendlv

316

References

218

GLOSSARY peff V

6 sh H D. E

OF SYhlBOLS

effective magnetic moment (m Bohr magnetons, B \l ) vibrattonal stretchmg mode vibrational bendmg mode shoulder applied field zero-field spltttmg parameters

* No reprmts avadable Coot-d Chetn Rev,

8 (1972)

i-f firs s IlV B. C k

Hamdtoman operator spm quantum number total spm of ss stem mxrowave quantum Racah parameters orbital reduction factor

5 A COTTON

186

A INTRODUCTION Despite nation

,md blologlCdl

the mdustnal

chemistry

then, a number

unportdnce

of iron-contdmmg

of the metal hds been sadly neglected, of groups

hdd studled

a conslderable

systems,

the coordl-

especially m recent years

number

of complexes,

Before

the relevant

ref-

erences may be found m the book by SldgwlLk ’ and tn the treatises by Gmelm 2, Mellor 3 and Pascal 4 This comparative lack of Interest has been espeLra1ly mdrked m the case of ~ron(IlI),

largely owing

to the propertres

of the d’ Ion

Two of the prmcrpal physical techniques currently used for studying coordrndtron complexes are eiectromc absorption spectroscopy dnd pdrdmagnellc sus_eptlblhty measurements, for the high-spin Fe” ion, the free ion ground stdte IS 6S, becoming 6Al m a weak crystal tield There are no other sextuplet states, so that all exerted states of the c/s Ion hdve d dlfferent spm multlphcrty to the ground state, and transrtions to them arc spin-forbidden Hence the dbsorptlon bands due to V-4” transitrons are extremely weak dnd dre frequently obscured by charge-transfer bands trallmg mto the vrslble region of the spectrum A further consequence

of the ground state bemg an orbltal

smglet 12 that there 1s no orbltal

contrlbu-

tron to the mdgnetrc moment and thus the observed moments scarcely vary from the spmonly value It IS sometimes possible to dlstmgulsh between tetrahedral and octahedral coordination on the basis of electromc spectra, but no such dlstmctlon can be made as a result of mdgnetlc

measurements

that the study of rron(lI1)

It 1s probably mamly for these and certain chemical reasons complexes has been neglected until quite recently_

Thus IS unfortunate, as S = 112,312 and S/2 ground states are hnown to exist, and other physlcal teLhmques such as EPR, Mdssbauer and vlbratlonal spectra can grve a good deal of information about the electronic and molecular structure of ferric complexes. This review IS mainly concerned with describing complexes that have been Isolated m the sohd state, and solution data are only mentroned when they have a bearmg upon the species present m the sohd phase. All basic complexes have been excluded, as have polynuclear systems, which merit a separate, more theoretrcal, tredtrnent In dddrtron to the sources l-4 referred to earlrer, Colton and Canterford’s splendid book ’ also covers some of the ground considered here Before proceeding varrous spectroscopic

to the drscussron techniques

of complexes,

for studying

iron(lI1)

we briefly

consider

the usefulness

of

systems

B PHYSICAL TECHNIQUES APPLICABLE TO IRON(II1) COMPLEXES

-

Good treatments of EPR, Mdssbauer, electronic and vIbratIonal spectra are, for example, avdilable m Hill and Day’s text6 whilst numerous books and review volumes have dealt with magnetism and electromc spectra At a sampler level, Greenwood’s review ’ 1s probably still the best simple mtroductlon to Mossbauer spectra No really good simple mtroductlon to EPR exists although Goodman and Raynor have assembled ’ an excellent combmatlon of theoretical and experimental data and togethkr with d suitable text such as that by Atkms

187

COORDINATION CHI-WSTRY 01 IRON(II1)

and Symons”

this constitutes

a reasonable mtroduLtlon

to EPR

The ferric ion has five 3d electrons so that it IS evident that t&e: (S = _5/2), t&e: (S = 3/2) and t:g (.S = l/2) ground states might arlse. In tact, the t&e; configuration cannot be the ground are known

term m an octahedra1

in relatively

1 1 and 12) Mdgnetlc

or tetrahedral

few cases, normally susceptlblhty

where

measurements

&and

field lo and S = 3/2 systems

there is a strong (preferably

tetragonal

field (cf

over a temperature

refs.

range)

afford excellent means of determlmng the ground term Ions with a 6A 1 ground state (S = S/2) have moments close to the 5 92 6 M predlcted by the spm-only formula for an orbltdl singlet As there are no other states with the same spin multlphclty, large devlatlons cannot be due to the mixing-m of excited states into the ground state (as IS usually m the case of A or E ground srates) although h&-order perturbations are probably sible for slight devlatlons frequently noted.

invoked respon-

Any significant deviations are probably due either to impure materials (even a small amount of Fez O3 can cause slgmfkan t devlatlons) or to possible dlmer formatlon, where antlferromagnetlc interaction can lead to low pet7 values Little can be said about the magnetism of complexes with S = 3/2 ground to the paucity

of experimental

data. Generally

moments

states,

owmg

are close to 4.0 B,M , the spm-

only value being slightly less than thu, thus the ground term In these systems IS probably 4A2, for which only a small orbital contrlbutron to the moment 1s expected, m agreement with EPR results ” For a system with one unpaired electron, the ground state in an octahedra1 field is 2 Tzg, thus the preseme of an ‘orbital’ contrlbutron to the moment, which should thus be temperature-dependent, IS expected_ F~gg~s I3 has calculated the variation of peff with temperature as a function of the axial field, also makmg allowance for covalency F~gg~s and co-workers results and have, however, more recently shown l4 that this method can @ve ambiguous therefore the hmltatrons Inherent should be borne m mmd when mterpretmg results Moments reported he m the range 2 O-2 6 B M at ambient temperatures and decrease upon coolmg The presence of high-spm impurities even in very small amount can easdy inflate measured susceptlbrlltles, as has been noted for [Fe(S2Cz O,),] 3- (see p. 208) m particular This pomt 1s even more important m vrew of the mstablhty of many low-spm iron(ll1) complexes

(li) Electronrc spectra Although the basic features of the ‘W-d” spectra of high-spm ferric complexes to be reasonably well understood, much work remains to be done in this field.

appear

In a cubic crystal field, the ‘S free ion term transforms as 6A1 ; no other spm-sextuplet state exrsts (see Fig I), so that all d-d

Coord Chetm Rev, 8 (1972)

transltions

are spin-forbidden

and hence

rather

weak,

S

188

(typically, probably spur-orbit

extinction coefficients E N 0.01 - 0 1 m octahedral made possrble by admrxture of spm-quartet character coupling

Certain

free ran terms are independent nephelauxetrc effect

states originating

systems) These bands are mto the ground state vra

from the 4F(4A2),

of 1ODq thus gives an unusually

A_ CO-t-l-ON

aD(4E) direct

and 4G(4E,

measure

4A ,)

of the

Despite this however, certain problems arise and high-spin Fe3’ d-d spectra are generally more drfficult to assign than those of the rsoelectromc bin*+ complexes The mam reason for this IS that charge transfer absorptron occurs at lower energy ID the ferrrc complexes, and often most of the d-d bands are obscured No defimte assrgnment of the d-d bands in the electromc spectrum of the hexaquo ran seems yet to have been made, owing to the ready formatron of hydroxy complexes The best results we have are probably those of 3+ ion (see p_ 193) although even these authors felt Holt and Dmgle44 for the [Fe(urea)6] drsmchned to make defirnte assignments Few data are available for S = 3/2 systems, many transrtrons are spur-allowed so that extmctron coeffictents m the range l-100 may be expected, especrally as there 1s hkely to

be d good dedl of enhanLenlent through overlap wtth Lharge transfer bands

189

COORDINATION CHEhlISTRY OF IRON(III)

Ewald et When ’ T2 becomes the ground state we expect some spm-allowed transItIons al l5 have examined the spectra m the vlslble and UV regions of a number of iron-sulphur complexes_ They obtam reasonable 1ODq values of ca 20,000-25,000 cm-’ although the E values (up to 103) are unusually of charge correct.

transfer

(ui) Electron

transitions

paramagnetrc

high

mlxmg

However,

with “&d”

resonance

we know bands

httle at present

about

so that their assignments

the effects are probably

(EPR)

(a) S = .5/Z Whdst most early EPR work on high spm systems was concerned with the elucldatlon of the quartlc terms m the spm Hamlltoman for virtually cubic systems, we find that many of the parameters m the complete spm Hamdtoman l6 17, VIZ

-6S(S+

1)+3S’(S+

I)*]

+S;

+S”]

+A SI

may be neglected

for D values > ca 0 01 cm- ’ The terms m a and b are only really important m near-cubic fields whilst we usually neglect the hyperfine term because of the low abundance of “Fe (I = l/2, abundance 2 2%) We therefore rewrite the spm Hamdtoruan as f./=&HS+D[s;-35/12]

+EESC

-$I

where D 1s the ‘out-of-plane’ zero field sphttmg parameter and E- the ‘m-plane’ zero field sphttmg parameter_ The real g value 1s generally taken ‘* to be very close to 2 00 Real ami effectrve g values At this stage It IS very convenient to define the difference between real and effective g values. This IS necessary for systems where S > l/2, where It

IS often expedient to refer to features of the spectra by geft values rather than field values For high-spm Fe3’ at X-band frequencies (9 3 GHz) signals are often found which can be analysed

m terms of gl ca

Hamlltoman &f

1 100 gauss and g,, ca 3300 gauss

Takmg

a fictltlous

spm

with S = l/2, we define

hV =pHres

so that this signal can be described m terms of the effectme g valuesg, N 6 g,, N 7 In fact, this type of signal arlses from D (large) (2 ca 0 2 cni’ ), h (= EYD) N_O m the spm Ham&

toman, correspondmg to a strong trlgonal or tetragondl dlstortlon I9 (lt 1s Important to note that real g values are independent of microwave frequency whdst “effectlve”g values are frequency-dependent ) Coord

Cirem Rev, 8 (1972)

S A COTTON

190

Lrkewlse, d nearly rsotroptc resonance 1s sometimes found ca 1500 gauss at X-band and IS described as geff N 4 3, arising I9 from D > ca 0 2 cm-‘, X N l/3. Because of its isotropic nature and statIstica effects rt generally appears much more intensely than other transttrons and usually

domtnates the spectrum_ For near-cubrc systems (D N 0.00 1-O 05 cm-‘, h N 0) five transttrons appear, centred on g N 2.00, these are 15/2 > + 13/2 > ,13/2 > + I l/2 >, I l/2 > +1-l/2 > ,1-l/2 > *l-3/2 > and I-3/2 > -+I-5/3 > transitions Much of the EPR behaviour of high-spm dS systems 1s summarlsed in Dowsing and Gibson’s paper ” (b) S = 3/-3 The spin Hamtltonian H =/3gHS+

D[S;

is -

15/12]

+E[S;

-S;]

Typically for D large and h ca. 0, effective values g1 N 4, g,, N 2 are obtained as m the case ” of distorted Cr**Lcomplexes such as Cr(acac) s However, few data are available (c) S = 1/z The theory has been developed simple

spur Hamrltoman

H=P[gx is taken

H,.S,

by Bleaney

and O’Brien

and modtfied

by Grtffith*r

a

of the form

+g,,

HY S, +gr

and a low-symmetry

Hz Sri

perturbation

c(q), q(xz) and t@z) so that then form of the ground doublet to be

considered

energies

to split the one-hole

real functions

are A, - v/2 and v/2 respectively

Takmg

the

x=A4 Il+>-tBl~;>+cI-l+> x’=

AI-l->--f?I~;>+CIl->

where A, B and C are the coefficients of the wave functions of the ground doublet, the mteractton of these states with the magnetic field, the g values dre obtained

from

gx = 2[324C - B* + kB(C-A)&] g,, = 2[2AC gz = 2[A2

+ B* + kB(C+A)fi] -B*

+ C* + k(.4*-C*)]

and A*

+B*

+C*

= 1

where r’c1s the orbltal

reductron

factor.

The values

of V and A are related*’

to the coeffi-

cients A. B and C and hence V and A may be obtamed This, of course, 1s a shghtly modlfied crystal field approach and makes no allowance for mteractlon with charge-transfer states or configuratrons such as figeg The general effect of not mcludmg these terms 1s that inflated k values (often > 1 0) are obtamed A molecular orbrtal approach would be

COORDINATION TABLE

CHEMISTRY

Or

IRON(‘!I)

1

Reported

prmcrpal values of theg-tensor

Complex

kl

for low-spm Iron(II1)

I

iIT2I

complekes k3

I

hlednnn ’

Ref 199.219

(Ph4P)31Fe(SzC2(CN)2)31

2 225

2 114

1 986

a

Fe(SzCOEt)3

2 193

2 143

1 992

b

199

Fe(S2CSEt)3

2 178

2 131

1998

b

199

FdS2CPh)3

2 155

2 094

2 008

C

Fe(hIcCSCHCShle)3

2 14

2 09

2 01

.I

213

Te(MeCSCHCOUe)3

2 341

2 182

1 930

d

199

Fe(PhCSCHCOPh)s

2 330

2 171

I 950

e

199

re(PhCSCHC0MeJ3

2 333

2 175

1 933

e

199

Fe(MeCSCHCOPh)

3

Fe(S2Chhle2)3 IFe(py)2&C2002)2

Ied

199

2 308

2 177

1 938

e

199

2 111

2 076

2 015

f

197

2 13”

1 99 b

g

199

7- 13L’

199b

3

199

I+(blpy)3(Pf6)3

261

1 61 b

!

149

Fe(4,4’-dmb)3(PT6)3

2 64 a

1 3Sb

f

149

Fe(5,5’-dmb)3(PI-&

260”

160b

f

149

Fe(phen)s(PF,)3

2 69 a

1 lgb

f

149

&i-c(CN)6

2 35

092

f

21

] %HzO

KBalFe&C202)3

a

2 10

’ The followng abbrewatlons are used II, solid b, CHCI,, c PhMe d, CHZt&, e C6&,, f. CoIfl analague, g, py (all solvents frozen) d The followmg abbrevlatlons for hgands are used py = p\ rldme hip) = 3_.2-blpvrld>l 4 4 -dmb = 4.4 -dunethylblpy, 5.5’-dmb = 5 S’dlmeth) Iblp) , phen = 1, IO-phcnatthrolme

but so little IS known about the excited states that thrs 1s not at present possible Assignments of the electromc spectra are a prerequisite Prmclpal g values for low-spm

preferred

Iron(IIl) complexes are listed m Table 1

(IV) Mussbauer spectroscop) A conventent 6 = const

expression

F [ ix(o)

for the Isomer shift, 6, IS

12abwrber - Ix(O) IL”,1

- where Sr IS the difference m radu between the excited and ground states and the terms 111 x(O) refer to the S-electron density at the nucleus S-electron density depends upon both oxldatton state dnd co-ordmatlon number, m fact, a comept of “partial isomer shift”, whereby the total isomer shift may be regarded as the Coorri

CXem Rev , 8 (1972)

S A COTTON

192

sum of the partial Isomer shifts for the donor atoms (for the same oxldatlon state of t’le see so ref 149) A second parameter frequently obtained al metal) has been developed** ( from Mossbauer

spectra

IS the quadrupole

sphttmg,

A or AiE This occurs

when

there IS an

electric field gradlent (EFG) at the nucleus, there exist both ‘valence’ dnd ‘latttce’ contnbutlons to the EFG, the former arising from an uneven electron dlstrtbutlon. Thus, neglectmg lattice contnbutlons. octahedral high spm Fe3* (fzgei) should give rise to no quadrupole sphttrng,

whilst octahedral

low-spin

Fe3’ (tGg) should

exhlblt

such sphttmg

Experimental

results generally bear out these expectations, high-spm species have AE values of cd O-O 5 mm set-’ (g enerdlly at the lower end of the range) whilst A E values for low-spin system5 are frequently as much as 3 mm set’ A notable exceptlon to this IS the S = S/2 system ‘43 Fe [N(SIMe3)2] 3 where the quadrupole sphttmg 1s 5 12 mm set-’ This mdy drlse from dn exceptIonally large contrlbutlon from the ‘valence’ part, due to the strong tngondl field, and also the ‘valence’ and ‘lattice’ contrlbutlons having the same sign C -COMPLCXLS

DI- OXYGCNCONTAINING

LIGANDS

(I) Mormdentate (a) IVater

The salts of the oxydclds

Fe( NO3 )3 -9H2 0,

Fe(C104)3

1OH2 0 and Fez (SO4)3

1OH20

are well known, bemg obtained from acid solution as pale pmk soltds The nitrate appears, from EPR results to contain trlgonally dlstorted hexaquo-fernc Ions 23 with D z 0 08 cm-’ D values up to 0 2 cm-’ have been reported 24 for the hexaquo ion m several ferric nlums X-ray structural locate v(Fe-OH*)

study

would

be welcomed

m the perchlorate

for a hexaquo

and nitrate

complex,

Raman

study

falled to

complexes

The yellow ferric chloride hexahydrdte has been shown 25 to possess the structure trarzs-[FeC12(0H2)4]+C1--2H20, analogous to FeCl, -4H20 (ref 26) The far-IR spectrum of this compound has been reported 27 to Lontam absorption bands at 374-358 cm-’ and 305 cm-’ (possibly v(Fe-0H2) and v(Fe-Cl) respectively) wlulst the Raman spectrum 23 shows bands at 418 cm-’ and 298 cm-’ (v(Fe-OH,)) and 255 cm-’ (v(Fe-Cl)) The nature of the s?ecles present m aqueous solutions of ferric chlonde IS m some doubt, despite the amount of work done 2s-31 , solutions dilute m Fe3+ and concentrated m HCl contam largely FeCli, but at h&er Fe3’ concentrations octahedral and polymeric species are present EPR of FeC l3 *6H2 0 m AlC13 *6H2 0 has been studled 23 s2 and Interpreted m terms of the spin Hamiltomdn parameters D N 0.15 cm’ and X = 0 It has been suggested 23 that these parameters may be accounted for by the ferric Ion havmg assumed the configuration tram[ Fe(OH2 )4C12 !’ Treatment of FeC13 .6H2 0 with SbCls yields 33 the complex fraiu-[Fe(OH,), Cl2 ] +SbCl,.4H, 0, the crystal structure 34 and Raman spectra 23 h&ve been nnestlgated Another compound 1s (NH4j2 [FeCls -OH2 1, which forms beautiful red crystals when an aqueous solution of ferric chloride and ammonium chloride IS allowed to evaporate slowly The crystal structure has been reported 35 as has that of the mdrum

COORDINATION

CHEMISTRY

01- IRON(111)

193

analogue 36, the EPR spectrum of the drluted terms of D = 0 086 cm-’ , h = 0 1 1, conststent

icon complex wrth sltghtly

to be more fully mvestrgated are the mrxed hahde

has been Interpreted ” m dtstorted C4, symmetry Stall

specres 37 Ma [FeCl,

Brs -OH,]

and

Ma [ FeCla Bra OH2 ] (M = Rb. Cs). Other hydrates mclude FeBra -6Ha 0, about which httle ts known owing to tts tendency to decompose on heating There IS, of course. the possrbrhty that tt has a structure srmrlar to Fe& *6H20 Ferric fluortde forms two hydrates, FeF3 -3Ha 0 and FeFs -4tH20. the trthydrate

adopts

a nearly

regular

octahedral

structure

” m whtch

adjacent

octdhedra

share apices tn the direction of the c-axts The d-d spectr.t of ferric bromtde and fluortde species in aqueous solutton have been studied recently 3y, but JS with the chloride complexes more work IS requtred to clear up the sttudtton No complex ton [FeBrs OHa] ahas been reported, unlike [lnBrs OH2 ] *- (rets _ 23,40), a number of terrttluorrde complexes are known which contain water that IS possrbly coordmated4r They are of two types M2 FeFs xH2 0 (M = Na K, x = $.M=K,_Y= 1,M=Ti._r=3,~1=Ag,x=3)and MFeFs 7H20 (M = Cd Fe. Co, NI), the latter probably ions Further mvestrgdtron of these systems by modern welcome. (6) Ureas The complexes

contammg octahedral spectroscoptc methods

M(OH2 )c would be

(X = Cl04 N03, Cl) readily crystalhse from aqueous solutron 42 , EPR results 43 indicdte that they contain slightly dtstorted [Fe(urea)6] ‘+ tons, m accordance with the poldrised single-crystal electronic spectra of [Fe(uredje] 3*(C104)a, which is reported to be trrgondlly distorted 4. bands were noted at 12,500, 17,000, 23 030 and 23,320 cm-’ _ The sphttmg between the two htghest bdnds comcrdes wtth v(Fe-0) reported for these compounds by two groups of workers 43V45 The cychc ureas, ethylene urea (EU) and propylene (PU) form complexes 4G FeC13-2EU and FeC13 -2PU whtch may be of the type [FeLJCI,]‘FeCIZr Fe(urea),Xs

(L) Sulplloxlcles Most of the work has been concerned with dtmethylsulphoxtde (DMSO),Cotton and Francrs reported47 the yellow Fe(C104)s 6DMS0, red-brown FeBra 6DMS0, and FeC13 ‘?DMSO (yellow) FeC13 4DMSO (which IS converted mto FeC13 2DMSO at 50” C) was reported at thts time4’ whtist Fe(N03)3 6DMS0 has been prepared more recently49 The 2 1 ferric chloride complex has been shown So to possess the structure fratzs[Fe(DMS’3)4C12]‘FeC14. The hexacoordtnate chromophore possesses approximately 041, assigned the far-JR spectrum of Fe(DMS0j2C1a on local symmetry_ Johnson and Walton” the basis of a pentacoordmate structure, correctly, they assigned the bands at 463 and 290 cm’ to v(Fe-0) and v(Fe-Cl) respectively, but ignored ~3 of FeCli at 377 cm-’ A more whtlst EPR recent study of DMSO complexes has confirmed43 the asstgnment of Y(Fc-0) spectra have shown that the hexakls-DMSO Fe3+ Ions are shghtly dlstorted from effectwe O,, symmetry,

m accordance

with the predlctlons of Berney and Weber**

of ferric chloride with tetrahydrothlophen

been prepared, Coord

oxide 53 and dlphenylsulphoxlde

these are thought to possess stmtlar structures

Chern Rev,

8 (1972)

2 1 complexes 54 have also

to the DMSO dnalogue

S A COTTON

194

(d) @ndrue

.V-mrdes

A number of complexes

Fe(py0)6(C10,1)3

of pyridme N-oxide Itself have been prepared, the first bemg where IR spectra and conductance results ” + indicated the formula

bemg assrgned at 385 cm’ m the far-IR Fe(pyO),& [Fe(pyO), I 3+ ((3% 13, v(Fe-O) was first reported at about the same time 57. this complex affords an example of how an Incorrect structure can be asstgned on the basrs of mcomplete data Purely upon the basts of cryoscopic me,tsurements, a monomerrc, pentacoordmate structure was assrgned Later workers ” suggested the fonnulatron [Fe(pyO)? Cl2 ] +Cl-. based upon an incorrect mterpretatton of the far-IR spectrum As a result of exammmg the far-IR,Raman, and electromc mm- [Fe(pyO),Cl,] ‘(FeC14)-, slmllar spectra, most recent work 59 assigned tt the structure to that adopted by Fe(DMS0)2 Cl3 (ref 50) This evrdence was supported wrth the observatton that the complex is d 1 1 electrolyte m mtrobenzene and that, on treatment wth methanohc hthmm perchlorate, a complex [Fe(pyO),,C12]+ ClOi-HZ0 was formed The ferric bromide complex Fe(pyO)* Br3 was also prepared whilst a monomeric chloro complex Fe(pyO),CIJ could Jso be tsolated from ethereal solutton Fe(py0)3(NCS)3 was first reported sltghtly earl.er 6o and two nitrate complexes, Fe(pyO)B( NO3 )3 *2H2 0 and Fe(py0)4(N03)3 *HZ 0 have been made i9 The latter IS belteved to contam two mono-

dent&e nitrate groups Conbwtent rtsslgnment of v(Fe-0)

can be made ” to infrared bands m the region 320-

350 cm-‘. but the non-observatron of Raman bands asstgnable to v,,(Fe-0) m the hex&s-(py0) complexes has led to the suggestion that the [Fe(pyO),] 3+ ton IS very dtstorted, J theory supported by the observatton of a strong signal wtth getf ca 4 3 m the Xband EPR spectra of the 6 1 nitrate dnd penhlorate complexes The spin-HamIltomdn parameters D = 0.36 cm- _ h = 0 233 have been awgned to the [Fe(pyO),] 3+ Ion m the perchlorate

complex

59

A series of complexes of the type [FeC4-RC, HqNO)6] (C104)3 have been studred 6’ (R = OMe. Me, H, Cl, or NO, ), Y(Fe-0) being dsslgned to bands ca 400 cm-’ m the IR, &tTvalues lay m the range 5 97 - 6 07 B M (e) Anudes and related Iigands Drmethylformamtde (DMF) readtly complexes wrth rron(IlI), EPR and vrbrdtronal studies on Fe(DMF)6(C104)3 imply 43 that the complex IS structurally very srmdar to the I I dmrethylsulphoxtde analogues The hgand phenazone (pn) (PhN*CO-CH C(Me)N-Me) coordmates VU d carbonyl oxygen, and complexes Fe(pn)6(C’104)3, [Fe(pn)6] 3+ (FeX.& (X = Cl, Br) and Fe(pn)s(NCS)s are known 62 Far-IR Raman, and EPR support these structures 43 Yet another example of a complex contammg a FeL? Fe(HMPA)6(C104)3 (HMPA = hexamethylphosphoramrde OP(NMe2)3), reported IS 6 25 B M , whrch seems Donoghue and Drago 63, the reported magn etrc moment

results ion 1s

by rather

htgh The hexakts complex of trtmethylphosphate wtth ferric perchlorate has ,u,ft = 6 04 B M , and IS a 1 3 electrol) te in mtrobenzene 64. electromc spectral measurements imply that this hexacoordlnate species 1s also present m solutton Wtth N,iV-dunethylacetamlde

COORDINATlON

CHEMISTRY

(DMA) the complexes formed

195

OI- IRON(III)

Fe(DMA)6 (C104)3, Fe(DMA)2 Cl3 and Fe(DMAJ2 Cl3 - 2H2 0 are chloride complex IS a 1 1 electrolyte m DMA dnd thus IS prob.!-

65, the anhydrous

bly [Fe(DhlA)+Clz]+FeC1~

e-Caproiactam

(HNm=O)

Fe(Laprolacta!n)6(CIOa)3 dnd Fe(caprolactam)2C13 electrolytes !n nltromethdne and thus are probably (FeC14C12)+(FeCi4)

forms complexes66

which are. respeLt!vely. I 3 and I- I of the usual (FeL6)‘+(C10;)3 and

types

(j)Pf~ospfm~cand arsule oxides Conlpared to the l!gands discussed earlier, where SIX ligdnd molecules can coordinate to the metal ion, dt nlost only four phosphrne ox!de l!gands cdn coordmate to the ferric Ion Fe(Ph3P0)4(C104)3 was first prepared from alcohol!c soiut!on by Bann!ster dnd COttOn6’ from benzene solution 68 Fe(Ph3AsO),(C10q)3 whrlst Fe(Ph3 POj2 Cl3 was later prepared was or!g!nally prepared by d shghtly more !nd!rect method frotn ferric nitrate sod!um perchlorate and tr!pbenyldrs!ne oxide !n ethanol 69 although !t may be prepared by the direct react!on of ferric perchlorate and the l!gand 7fl Fe(Ph3 AsO)* Cl3 WJS prepared s!m!iar react!on to that utd!sed for the Ph3P0 dnalogue Pb!lhps and Tyree suggested that

the trlphenyl

and

[Fe(Ph3AsO)jC12]+FeCl~,

dence

arsme

oxide

‘O m the IR spectra

coOr&nattOn,

but In

complexes

should

be formulated

ds d result of conduct.mce

Fe(Burz3P0)4(C10~)3,

[Fe(Ph3As0)4r*(C104)a

!neasure!nents

of erther of the above perLhIorate

two perLh!orate

by cl 69

There

complexes

groups

IS no evi-

for perchlordte

are thought

to coordl-

nate 7! This reflects the lessened ster!L effect of Iz-dll\yl Lompared with phenql groups Far-IR asslgnrnents were v(Fe-OPBu”3) at 410 cm-’ and v(Fe-0CI03) at 315 ~ni’ Further studies of the tr!phenyl phosphine Jnd ars!ne ov!de systenis have been made 7o utlhsmg Raman IR dnd EPR spectroscopy !n re-euam!n!ng the perchlorate and recently chloride complexes. and !n character!s!ng the complexes FeL2 Br3 FeL2(N03 )3 a!!d complexes gave the (gl = 6. g,, = 3) type of EPR Fe(Ph3 PO), (NCS)3 Th e p erchlorate spectrum and were thus assigned square-planar rather thdn tetrahedral structures Fo! the D = phosphlne oxide complex. D = 0 84 cm-’ , h = 0 005 and for the arserlc analogue,

1 05 cm-’ h = 0 IR ddta md!cated

thdt the nitrate

Lompleucs

d!d not tontdin

‘!on!c

nitrate groups, and the EPR results suggested a tngonal-b!pyram!dal structure w!th monodentdte nitrates (D3~1) At the X-band, the EPR s!gnals were of the Cgl = 6.g,, = 2) type with a sl!gbt spI!tt!ng !n the g = 6 resonance this wds interpreted m terms of the signal re-

flecting the overall rather than the local symmetry

The D values are Cd_ 0 6 cni’

and X value

the D values ca 0 05 Fe(Ph3 PO)2 (NCS)3 wds thought to hdve d s!!i!!ldr structure of 0 07 cni-’ compared to 0 5.5 cni’ for the nitrate dnalogue shows th,!t the trrgondl tortion IS quite small here reflecting the s!!n!lar Dq values that NCS The halide complexes ev!dently possess the rrarls-[Fe(Ph3RO)JX-,

d!5-

and PhsPO create 1’ (FeX;) structure

the character!st!c v!brat!onnl fund,!mentals ot the FeX; ions were noted m both the tk-IR and Raman spectra and the EPR spectra evh!b!ted (get* = 2) resonances from the t-eX,, Ions and (gL = 6) resonances [Fe(Ph3R0)4X,]+,forR=P,X=C1

from the hexdcoordlnate chromophores in the ions the!!D=O63,X=OOl .mdforX=Br,D=

cm~‘,X=0.forR=As,X=Ci,D=O55c!ii~’.h=O01 Coord

Chem Rev.

8 (1972)

dndforX=Br.D-~.50cnl-‘=O

I90

196

S A COTTON

A!though v(Fe-0) spectra

may be assrgned to a band of medium-to-strong

of the arsine oxide complexes

m the region 400-435

cm-‘,

intensity m the IR no such consistent

as-

stgnment is possible for the phosphme oxide complexes_ Thus IS a good example of the lmutations of far-IR spectroscopy as a stereochemrcal tool It would be interesting to study the effects of small alkyl groups, unlike Fe(pyO)sCIs (ref 59) no complex Fe(PhsPO)sCls can be prepared ‘O, it appears, however, that alkyl substrtuents are less stereochemtcally demanding than phenyl groups’l (g) Mix ellarrems FeC13-ttz 0 and related systems were prepared many years ago * but httle IS known about them.

1 1 adducts

of ferric chloride

with benzophenone

and acetophenone

are known ’

whilst with benzanhrone,

C1,HloO, FeX3 benzathrone complexes (X = Cl, Br) have been values bemg 5.73 B M (X = Cl) and 6 02 B M. (X = Br) The dark brown ethoxtde Fe(OEt)s has been prepared from FeCls and NaOEt m ethanol ’ or from ferric chlorrde m ether-benzene on treatment with excess ammonia 76 Fe(Ohfe)3 IS also known The magnetic properties of these systems, which are hrgh-spur wtth abnormally large Curtc-Weiss constants. have been Interpreted “*” m terms of a trmuclear reported

7’ , petI

structure

mvolvmg

The alcoholates

Fe04

tetrahedra.

FeC13 *2ROH

(R = Me, Et, Pr”, Pr’, Bu”, Bul) have been reported

they are prepared from ferric chlorrde and the appropriate (II) BP and ter-dentate

“,“,

alcohol m benzene

hgands

Iron(III) forms three complexes with acetylacetone (acac), of whrch Fe(acac)s IS the best known It IS readily prepared as red crystals by the reaction of aqueous ferrtc chlortde wtth urea and excess acetylacetone The crystal structure “shows that the ferric Ion IS at the centre of a nearly perfect octahedron of oxygen atoms The ferric tris(tropolonate) complex, Fe(C, Hs O2 )s contains a much more distorted octahedron “, as one might expect from the more rrgrd nature of the hgand Smgle-crystal magnetrc susceptrbrhty measurements 83 on Fe(acac)s have determmed D to be -0 11 2 0 01 cm* whilst v(Fe-0) has been asstgned to far-IR bands at 434 and 300 cm-’ wrth the ard of metal Isotope substrtutron s4 q8’ Smgle-crystal electromc spectra have also been reported 86 Fe(acac)2 Cl and Fe(acac)Cls can be prepared either by refluxmg the appropriate quantities of FeCls and acac m benzene “, or by reaction of the stotchtometrtc amounts of FeCl, and Fe(acac)j _ Fe(acac), Cl has been shown 88 to possess a shghtly drstorted squarepyramtdal structure, with the Fe atom raised 0 51 A above the basal plane. The Mossbauer parameters are ” 6 = 0 60 mm see-r and AE = 1 mm set-’ , for Fe(acac)Cla , AE is go 0.44 mm set-’ Fowles et al. ” have reported camp lexes of 1,4-dtoxan which mclude Fe& -droxan, thus may have a polymeric structure mvolvmg bridging droxans and hence pentacoordmate

COORDINATION

ferric iron

d-d

197

CHEMISTRY OF IRON(II1)

bands

occur at 12.0, 15.2, 17.1, 19.0, 24-6,30-O,

cm-’ , it IS. however, not improbable that the structure is cause of the richness of d-d bands and also since Y(Fe-Cl) 1s htgh for Y(Fe-Cl) m a five-coordmate environment report ‘* concerned thus compound and two others, (droxan)3 -HCl, which are not well defined

More recently,

37 0 and 45.0 (x 103)

[Fe(droxan)~Cl~]‘(FeCl4)- beat 380 cni',whrch

was noted

but Lorrect for (FeC14)-. An earlter FeC!3(droxan)2

-2H2 0 and Fe&

(CaHlo02)

the 1 1 complex of ferric chlorrde with dlmethoxyethane

was reported Q3, this possibly involves pentacoordmate

rron(III), v(Fe-Cl) occurrmg at 1 I-0, 14 4,23

at 355 and 375 cm-’ and d-d bands 36.0 (x 103) cm-‘. Walmsley and Tyree 94 have mvestrgated some complexes to bands

formed

-

being

assigned

0,28.4,3

wrth liquids

1 5 and of the type

R = Bu” (Lr

) or Pr”O (L2)) preparmg [Fe(Lr )s] 3+(FeCl,I)s, 413 and [Fe(L2)* Cl2 ]+(FeCI,)- all of wh;ch have pcff values of ca. 6 1 PW-~)S13+(C10

R2 PO*CHa .PORa

(where

B.M at ambrent temperatures_ A related complex, [Fe(OMPA)3] 3f(FeC1;)3 (OMPA = octamethylpyrophosphoramide, (Me2 N), 0POPO(NMe2 )2) was reported by Joesten and Nykerk who found rt to be a 1 3 electrolyte m mtrobenzene 95 They report peff to be 12 8 B M., evidently

this 1s not pet- per Fe, which would

h&r_ The complex 1_c,~=6 13 BM

[Fe(btpyOz)s] (C104)s *3H2 0 (brpyO? at room temperature Q6 whilst v(Fe-0)

bands at 408 and 377 cm-’ 2,2’,2”-Terpyrrdme-l.l’,l”-trroxrde have prepared hrgh-spur complex

seem to be 6 4 B-M , which

the complexes

Because should

(terpy03) Fe(terpy03)C13

of the stereochemical

adopt

the mertdronal

= 2,2’-brpyrtdyl-2,2’-droxrde) has has been assrgned ” to far-IR

IS a terdentate

hgand.

and Fe(terpy03)2(C104)3,

requuements

IS strll very

of the hgand,

Rerff and Baker9’ which

are both

the ferric chloride

configuration

(m) Mcxed 0.N dorzors

Some of the most mterestmg

complexes

of this kmd of donor

ethylenebrs(sahcylrdenermmato)) and related hgands, by Pferffer and Tsumakr 99 Two forms of Fe(salen)Cl

are formed

by salen (N.N’-

the first examples being prepared have been xsolated, one being mono-

meric and having a molecule of mtromethane m the lattrce ‘00 whrlst the other 1s drmerrc lo1 _ The monomers follow Curie-Weiss behavlour, with peff values of 5.7-6 0 B M at 300°K and 0 values of 2-6O whilst the drmers have moments whrch drop from 5.1-5 4 B-M. at 300°K to 3.6-3.9 I3 M at 77°K (ref. 102) The latter results have been interpreted m terms of a bmuclear spm-free rron(II1) model, with J values of 6 5 -8 cm-’ Mossbauer spectra have been recorded for a number of these systems ‘03. as a result of this, certam reclassrfrcatrons were suggested. The pentacoordmate monomers generally give smaller Isomer shafts than the drmers, as one might expect More recently, adducts of the type Fe(saIen)*RCOz have been

studled lW, these exhibrted slmllar magnetic behaviour to the other systems, so it appears that both monomers and dlmers ex!st here too Coord Chem Rev

8 (L972)

S

198

A COTTON

Further examples of complexes mvolvmg 0-N donors are provided by complexes of IIf-substituted sahcyldldmunes (salHNR) whrch grve complexes FeC&(salNHR), (probably Fe(salNR)3 and Fe(salNR)2 X (X = Cl, five-coordmate [FeCl(salHNRj~ I “Cl;), octahedral Br) whrch may be dlso five-coordmate xylphenyl) sahcylaldrmme 5.0 + 0 05 B M at 29S°K,

‘OS The terdentate

bgand

derived

from N-(Z-hydro-

(LH,) gives complexes FeLX (X = CI, Br) wrth ~,t, values of so that they are probably drmertc ‘06 On refluxmg these m

pyrrdme, complexes FeLX(py)J are obtamed, which have ‘normal’ moments of 6 0 f 0 05 B-M. and are thus probably monomers, wrth one mole of lattice pyrrdme N,~.Dm~ethylethylenedn.tmme N-oxrde grves a rather unstable brown complex lo’, Fe(Me2 NO-CM2 -CH2 -NH2 )3(CIOd)3, which IS d 1 3 electrolyte and has flUerr= 5 80 B M , the hgand

IS presumably

brdentate

(IV) Acids One of the consprcuous ammo

dcrd complexes,

gaps m our knowledge

constdermg

of coor$inatron

the importance

too bttle attentron has been paid to then metal carboxylic dnd ammo actds m thus sectron

of ammo

complexes

compounds

concerns

acids m brologtcal We drscuss complexes

systems, of both

(a) Car3uxyktes Generally, rron(III), hke chromium(IlI), does not form monomerrc carboxyldtes, rnstead, specres based on a trtangular Fe30 chromophore are formed The magnehsm of a number of these systems has been mvestrgeted in both the solid state and solutron lo*, and interpreted m terms of antrferromagnettc behavrour A complex [Fe(en)(OHj2 (PhC02 )] has been Isolated ‘09 dnd the magnetrc behavrour on the bdsls of a spm-equd~brnrm The com%a296 = 2 74 B-M.; p;;r = 2 32 B M ) interpreted plex may not be monomeric, however The red crystallrne FeCI(MeC02 )2 IS reported to be formed from the reactron of anhydrous Fe& wrth anhydrous acettc actd, the dark brown bromide dnalogue FeCI(HCO,), 312 H20). Are these monomers9 By extractmg a mrxture of Fe(MeCO,), and [Fes(MeC02)80H]

IS known,

as IS rl’

w~tb acetrc acrd ‘I’, a

dark compound Fe2(MeC02)5 was obtamed, thus 1s presumably dtmeric Starke ‘12 has reported that reactron of forrmc or acetrc acid with non, in methanol m the presence of oxygen, produces species Fe(RC02)(OMe), However, more simple complexes are formed with oxalate and related Ions M3Fe(oxalate)3 lnHz 0 (M = Lr, Na, 22 = 0, M = K, t2 = 3) are typical. The structure of the potassmm salt has been determned ‘I3 : the stx oxygen atoms coordinated to the non atom form an approxrmate!y octahedral array, the O-Fe-O angles averaging ca 85” Smgle-crystal magnetic susceptrbrhty measurements have determined D. the zero-field splitting parameter, to be -0 55 cm’, reflecting the strong tngonal field 83 _ Lrttle mvestigatron seems to hdVe 5H20 where interestmg possrbrhbeen made of complexes 1I4 of the type Fe(D-tartrate), ties arrse.

COORDINATION

CHEMISTRY

199

OF IRON~III)

(b) Anmo acid complexes The amino acid DL-metionine [MeS(CH2)2 CH(NHI)C02 H] forms a tns-complex with occrlrs via the iron(III) having peff = 5 63 B M , it was suggested ‘I5 that coordmation amine and carboxylate functions More recently, It has been found that react:on between Fe3+ and L-cysteine m alcohol gives labde red, blue, and violet co‘nplexes ‘I6 _ The violet *2H2 0, It is uut:ally produced at -78” as a green complex was found to be Fe(cysteme)a

complex which changes lrreverslbly mto the purple complex on raising the temperature. Electromc spectral, ORD and CD measurements Indicated the blue species to be a 1 1 complex, the red species to be a 1 2 complex and the violet species I-3, all rnvolvmg S,Ocoordmatlon. It was suggested that the unstable green complex 1s an isomer of the violet tris-complex, havmg S,N-coordinatton Rdder and Bayer have reported Ii7 the EPR specrrum of an tron(III)-cysteme complex of unspecified compontton, havmggl = 2.33, gll = 1.94; evidently it 1s an (S = l/2) species, involvmg conslderable axial dlstortlon Iron salts give a deep purple colour with thloglycolhc acid m ammoniacal solution; no stable iron(llI) complex exists, but the species present 1s thought to contam iron “* EPR measurements on frozen solutions might be of value here (c) Cow~pkxes of EDT,!

only ferric

and related lrgarlds

Two types of EDTA coordmatlon have been discovered by X-ray dlffractlon studies, m the complexes Rb [Fe(EDTA)H2 0] *Hz 0 and Lt [Fe(EDTA)H* 0] l2Hz 0, ferric tons are surrounded by a hexadentate EDTA molecule and a water molecule, m Whdt may be regarded as a distorted penTagonal-blpyramldal configuration ‘I9 In Fe(HEDTA)-Hz 0, one carboxyhc group 1s protonated, and thus does not coordmate, so that the ethylenedtammetetraacetlc actd group IS pentddentate, 3 water molecule completes the distorted octahedral coordmation of the metal Izo The EPR spectrum of Fe(HEDTA)*H*O, doped into the isostructural Ga analogue, has m terms of the parameters been investigated “I , at 1 lOoK, the spectra were interpreted D=O69cK’,h=0.267( on coohng further, h appears to increase) The EPR of Fe3* doped into a NH,‘[Co(EDTA)*H,O] host has been reported I** and interpreted 123 m terms of the parameters

D = 0 769 cm-‘, X = 0.307.

-xH20 (0
-

as m the EDTA analogue. OF NITROGEN-DONOR

LICANDS

(I) Monodentate (a) Thiocyanate and cyanate Reaction of Fe(NCS)s and alkylammomum coord_ Chern.Rev, 8 (1972)

thlocyanates

m alcohol leads to the formatIon

S A COTTON

200

of the hexakrs

salts (R4N*)3 [Fe(NCS)6]

‘-

In the e]ectromL

spectrum

of the tetramethyl-

bands are noted at 10,640 cm-’ and 17,500 cnri’ , most of the specby the usual Fe-NCS charge-transfer absorption 126 Far-IR absorpt.ons assrgnabie to V(Fe-NCS) were noted r2’ at 298sh, 272 and 233 cm’, m the ethyl at 370 cxti'and G(Fe-NCS) at 98 cm’ iron(III)analogue, others 128 assign u(Fe-NCS) throcyanate complexes are all probably IV-bonded, the occurrence of a medium mtensrty

ammonium salt, d-d trum bemg obscured

band at ca 470 cm-’

m the IR being regarded

(Ph4As)“[Fe(NCO)s]

has been prepared

as dragnostrc

of thus 129_

from AgNCO and Fe&

m acetone

13’,

v(Fe-b CO) was assigned to a far-JR band at 4 10 cm-’ The coordmatron rs presumably terrhedrdl and thus rt IS likely to be N-bonded The h&-spur complex [Fe(N3)5 ] ‘- has been reported,

the structure

of the tetraphenylarsomum

salt shows the ferrrc ron to have

nedr-Da/, local symmetry Equatorral Fe-N distances, at 1 963-l 971 8, are shorter the axial Fe-N distance 261 , presumably due to &and-hgand repulston fb) Attitttottta No simple complexes merely

exist m aquous

solution,

dddition

of ammonia

to ferric

than

Salts

precipitating

the hydrous oxide However, treatment of anhydrous ferrrc chloride r3? wrth ammonia gas produces the very hygroscoprc, unstable comdnd ferric bromrde plexes FeCla -6NH3 and FeBrs -6NH3, about whrch very little IS known

A larger number of basic complexes have been Isolated. as well as species of the type (pyH)+(Fe&)and (pyW)s(Fe2 C19)3- (refs 133, 134) The ldtter complexes have all been shown I35 to contain FeC& 1011s On the other hand, some genume pyrrdme complexes have been made Fe(py),(NCS)s crystdls from alcohohc solution fdr-IR assrgnments ofv(Fe-NCS)

and Fe(qumohne)s(NCS)s were prepared as rrrdescent of the pyrrdme complex 13’ led to 136 A remvestrgdtron at 300 cm’ and v(Fe-py) at 249 cm-‘, the paucity of

far-IR bands suggests that this 1s the Jzc-isomer The complex Fe(py),C13 was also prepared by refrrgeratmg a drlute solutron of anhydrous ferric chlonde In pyrxdme 133Y*34. it forms very hygroscoplc red crystals A more recent investrgatron I38 suggests that rt rsfac-Fe(py)3C1s spy, the spur Hamrltoman parameters are D N 0 164 cm-‘. h = 0 100 whilst v(Fe-Cl) is dssigned to 300 and 250 cm-’ and v(Fe-N)

at 333 and cd 200 cm-’

Whrlst no characterrsable

product

could

be obtained

from the reactron of FeBrs and pyrrdme, the parameters D = 0 665 cm-‘, X = 0 033 were obtained from In(Fe)pysBr3 rmplymg afac structure Spectrophotometrrc studies of FeC13 m pyrrdme I39 suggest that three specres are present, FeCI;, an uncharged species [Fe(py),,Cls] and a metastable species of IOW Cl- Fe” ratio, possibly [Fe(py),& ]+

(d)Pyrazoles In an early study I40 of the complexmg ability of pyrazole, a complex Fe(pyrazole)4Cls was reported It was claimed, purely on the basrs of halogen analysis, that this was the correct formula for a complex which could not, however, be obtained m a pure state More r3’ has shown that thrs IS m fact Fe(pyrazole)3C13. EPR spectra (D = recent investigation

13’

COORDINATION

0 24 cm’,

CHCXIISTRY

201

Oi- IRON(II1)

h = 0 13). far-IR and Raman

results

imply

it IS m fact thejac-isomer.

A similar

complex Fe(3-methylpyrazole)3C13 may be Isolated. this ha> more Raman and far-IR bdnds than the pyrazole analogue, and m view of the EPR data (D cd 0.90 cn-’ , X = 0 3 I), d meridional

polydentate,

structure

wds assigned

the complex

dme)z Cl3 IS probably

The hgdnds pyrazme

Fe(pyrazme)s,2C13

a polymer

IS thought

dnd pyrimidme to be dmlen

are potentially *, whilst

Fe(pyrmn-

I38

This compound exhibits a number of interesting features, first prcpdred by Burger and Wannagat *‘I. the crystal structure shows that the Iron atom IS three-coordinate 14’ - The FeN3 and FeNSi units are pl,mdr, and the symmetry of the environment of the iron atom may be regarded as 031~) although the molecule hds only D3 symmetry overdll A prelnnmary study of the magnetlL dnd speLtros_opic properties of this complex showed that it obeyed the Cune-Weiss Idw to liquid nitrogen B-M _0 = - 10”) The Isomer shrft m the Mossbauer spectrum

temperatures (.u,~~ = 5 9 1 IS of the order expected for

a tercoordmate Fe3’ Ion (6 = 0 43 mm seL’ relative to nltroprusslde) but the quJdrupole splitting is extremely large (~Lz = 5 12 mm set-’ ) and this hds not yet been explamed The EPR spectra at X-bdnd (9 3 GHz) and Q-band (36 0 GHt) were interpreted m terms of the parameters D = 1 00 cm-‘. X = 0 Crystal field calculations m D3/, symmetry afford the d orbttal sequeme e’ +I 2370, cz’ -6980. err -8800 ‘m-l _ unplymg strong Interaction m the _u_lplane ‘43 (II) Bdettrate

(atrd other) hgatxis

Much preparative work has beep carried out with the llgdnds 1.10.phendnthrolme (phen) dnd 2,2’-blpyndfl (blpy) Addltlon of these hgands to aqueous solutions of ferric salts leads to the formdtlon

of brown hydroxy-brtdged dmers of the type ‘~4 If the tris-complexes of Fe” dre first prep,tred, [(phen )Z Fe(QH)z Fe(phen)z 1 4+ However they can be smoothly oxrdlsed to the blue [Fe(phen)J] ‘+ dnd [Fe(blpy),] 3+ complex ions “’ These systems are low-spm the magnetic moments ‘4611’7, hlossbauer parameters I’9 Is8 I50 (Table 1) have been obtamed F~ggls 146 Interprets the vana(Table 2) and-EPR spectra tion of magnetic

susceptlblhty

with temperature

m terms of dn axial field of ca #JO-600

cm-’ On the other hand, the EPR spectra are interpreted Iso m terms of a dtstortlon of SOO- I200 cni’ and postulate an E ground term. m contradlctron to the inferences of Ftgg~s The hmltatlons of the simple crystal field approach IS revealed by the rnagmtude ofk, the orbital reduction factor cdculated. 0 93-I 07 this results from the neglect uf factors such as configuratlon mteractlon ] ‘CIO; expected to be Other Iow-spm systems 14’ are of the type [Fe(bipy)2(CN), CIS (C,, ), which exhtblt a quadrupole sphttmg m the Mossbduer spectrum comparable to results have also been reported 14’. pcff values that of the tns-complex “’ Susceptibility of 2 40-2 00 B M were noted over the range 3,95--79°K and were interpreted in terms of a low-symmetry field of ~3: 500 cm-’ dnd a k value of 0 9-l 0 EPR results would be Coord

Chem Rev

8 (1972)

202

S A CO-ITON

welcome

Reaction of ferric chloride in ddute HCI wth phenanthrohne Bves 14’ a complex Fe, phen,Cl, whdst slmllar reactions in acetic acid lead “’ to Fe, phen, Cl6 iMeCO* H. This latter complex IS part of a series [Fe(phen)* Cl, ]‘X- nMeCOp H (X = C104, n = 1, X = as Cl, n = 2, X = FeC!&, n = 0.5). A complex Fe(phen)CfS was orlgmally Is2 formulated l

[Fe(phen)* Cl,, 1’ [FeC14 ] - as it gave a perchlorate [Fe(phen)z Cl2 ]'ClO; . Later studies 14’ indicated that this comp!ex (whrch could be Isolated m two crystalline modlficatrons) :s probably a chloro-bndged dlmer Fel(phen)3Cld is thought to be [Fe(phen)* Cl2 ]+[Fe(phen)C14] -; on treatment with methanohc LlC104, [Fe(phen)* Cl2 ]+ClO< IS obtained, whdst reaction with tetraethylammomum chloride yields [Et4N]+[Fe(phen)C14], which can also be prepared directly from (Et4N)+(FeC14)and phen m acetone. Clearly more work on these systems 1s desirable. Fe(en)3C13 has been prepared by direct reaction in absolute alcohol ls3, It IS low-spm, 2s might be expected

If the ethylenedrammes

are chelating.

The electromc

spectrum

was

anaiysed in terms of the parameters B = 500, C = 2000, Dq = 1950 cm-’ , B IS reduced to about 50% of the free ion value 2-(2’-Pyrldyl)umdazole (pyimH) and 2-(2’-pyndyl)benzirmdazole (pybelmH) form lowspin tris-complexes Is4 Fe(pylmH)3(C104)3 and Fe(pybelmH)3C13 as well as an ‘inner’ complex Fe(pyrm)3 m&H20 Two terpyrldyl

complexes

have been reported

as m the case of the analogous from the Iron(U) complex. thought to be Is6 One class of complexes

phenanthrohne

The chloride which IS rather

Is5 , Fe(terpy)C13 and Fe(terpy)* (ClO,), , complex, the perchlorate had to be prepared

complex

should

hard to classlty

be merrdlonal, is the rsocyamde

as InC13-terpy complexes

IS re-

ported over 60 years ago Is’. FeC13_2EtNC, FeC13*3EtNC and FeC13 -3PhNC were obtamed tmtlally ds 011s from ether, eventually yellow crystals were obtamed. No further work seems to have been reported on these complexes A rather exotic example of a ferric complex with only mtrogen-donor hgands IS a heptacoordinate complex whose structure has been reported by Flelscher and HawkInson Is’, a pentadentate macrocycle and two N-bonded thlocyanates make up the coordmatlon sphere, where Fe-N(macro) = 2 23 + 0 05 A and Fe-NCS = 2.01 f 0 02 A. This IS one of a series of complexes

form [FeBX*] ‘Y-, where B = 2,13-dimethyl-3, octadeca-1(18)2,12,14,16-pentaene, where X= Cl, Br,

160 which are of the general

6,9,12,18-penta-azablcyclo[12,3,1]

I or NCS, and Y = C104, BF4 or NCS They are S = 5/2 systems whrch are 1: 1 electrolytes - of especial interest IS the Felxl--I linkage, one of the few known Further study of this type of system would be mterestmg E COMPLEXES Ol- HALIDES

The specres considered m this sectron are those which contain only hahde ions coordlnated to iron(IlI), other ferric hahde complexes are discussed in other sections, especrally m sect. C

COORDINATION CHEhIISTRY OF IRON(II1)

203

t TABLE 2 iMossbauer parameters and magnenc moments a Temp

6 (mm set’)

Fe(phen)3(ClO4)3.3H20

80 80 300

1 e(bqw)3(C104)3-3HzO IFe(bw)tCCN)2

ICI04

jTe(phen)t(CN)2

I Cl04

0 36 0 32 0 24

AE b (mm scf_Ti)

171 1 80 I 63

I;ge% )’ 2 40 240 2 34 (294) 2 01 (81) 2 42 (300) 2 03 (80)

[Te(phen)zClz j+[Fe(phen)C14 j[Et4Nj+[Fe(phen)Ci4]-

80

0 63 065

0 05

80

0 05

5 57

[Te(phen)K12

80

06.5

0 05

5 91

77

040

1 36

fe( en)

j+ClO4-

3C13

2 45 (285) i 17 (80)

Te( terp) K13

80

ca 071

0 54

5 85

Fe( terpy)2(C10&

80

c3 033

343

2 16 (286) 191 (78)

Fe(pyimHMClO&

2 47 (295)

l-.e(p)un)s-*H20

2 52 (295)

d Data from rets 146, 148, 149. 151, 153 and 158 b Relative to sodium mtroprusslde ’ At ca 300%

unless otherwsc

stated

The tetrachloroferrate ion occurs nature of the Ion has been confirmed

m a number of complexes; the essentially tetrahedral by crystallographic mvestlgatlon, although lt 1s usually

shghtly dlstorted In (Ph4As)“(FeC14)‘the Cl-Fe-Cl angles are 16’ 107” and 1 14.5” whdst m [Fe(DMS0)4C12 ] ‘(FeCl.+)- they are 162 108.2” and 112 2”. Similar values have been reported for Na’FeC14- (ref 163) and (PC14)+(FeC14)- (ref lG4) Mcissbauer studies have also been made ‘35-“‘, reported isomer shifts are 0.45 mm set-’ for (FeCL)- and 0 5 I mm set -1

for (FeBr4)- Gmsberg and Robm 13’ showed that salts of the type (pyH+)s(Fe2 C19)3- are m fact composed of (FeC14)- ions, but they did prove that one form of Cs3 Fe2 Cl9 fact contam dlmerlc (Fe,C19)3- units The assignments of the d-d bands m the electronic spectrum of the tetrahaloferrate Ions IS still the subject of uncertainty as fine structure has been found at low temperatures 13’ unsuspected by others ‘M The mixed tetrahaloferrate ions also exist, FeC13 Br- and FeBr3C1- were prepared by Kraus and Heldlberg 37 and reexamined by Clausen and Good ‘67 who treated an alcoholic solution of the appropriate ferric halide with a tetraalkylammoruum hahde. FeC12 Brz- has also been Isolated 167 from bromine oxidation of alcoholic FeCl, , followed by addition of Coord

CIIem Rev,

8 (1972)

S A COTTON

104

TABLF 3 Vlbratiozul IundsrnentJls I65 for reCI;

raq

I-eBrj-

"1

330

700

"2

114 378 137

785 95

“3 v4

and FeBrq- (In cm-‘)

the Jkylammomum h&de The Mossbauer spectra 16’ show a gradual Increase m isomer shift as chlor’de IS replaced by bromide. no quadrupole sphttmg wds seen The far-IR spectra showed v(Fe-Cl) ‘n the region 350-390 cm-’ and Y(Fe-Br) ‘n the reg’on 260-300 cm-‘, J number of unass’gndbfe bands were, however, noted Fundamentals for Fet&- and FeBraare tabulated “’ ‘n Table 3 No <‘nlomc pentachlorldes

or bromides

h,jve been reported

but some pentafluortdes

known In the ease of mdmm(IlI) both InC14- and I&l:can be obtained, depend’ng t!le cho’ce of cond’t’ons (espeL’ally solvent), so that ‘t IS poss’ble that the unsolvated

are upon FeClg-

ion mtghht be obtamed In contrast, the stable dn’on’c spec’es for fluor’de IO’I IS 4’ FeFz-, v(Fe-F) has been asslgned m the 450-500 cm-’ m the IR ‘69,‘70 A number of tetra- and penta-fluor’des have been prepdred, but these are probably LI, Na) have pett values of 5 SO-S.95 have moments

of ca 4 8 B M (ref

polymers with fluor’de bndges, M3 FeFs B M at room temperature whilst CsFeF4

171) These ‘low’ moments

may reflect

(M = NH4, and K2 FeFs

antlferromagnetlc

mteractlon via br’dgmg fiuurmes. On heatmg (NH4)3 FeF6 to 140°C, NH4 FeF4 IS formed A detailed study IT3 of M, FeF, systems (M = LI, Na. K, Rb, Cs, Ag, T1 and NH4) showed that they contamed FeFz- octahedra, having Curre-Weiss magnetic behavlour to hquld

“*

mtrogen temperature v(Fe-F) was assigned at 450-500 cm-’ and G(F-Fe-F) at 270350 ‘In-’ m the fdr-IR A reLent EPR study ” has been made of the FeFz- ‘on m aqueous solution showmg the strength of fluor’de Loordmatlon to iron, the expected seven-hne spectrum was obtamed, Lharactensed by g,, = 2 0036 and aF ca 23 0 gauss it IS evident from the value of the isomer shift (0 69-O 71 mm set-’ ) m the Mossbauer but it was not spectra ‘35*‘65 of FeC13 and FeBr3 that the ferric ‘on IS hexacoordmate, It IS preclp’tated from sountil recently that the FeCIz- ‘on was isolated and charactensed. over the electronic lution “’ by large cdt’ons such as ICO(NH~)~] 3c There IS controversy spectral assignments, early workers 176 assqp a band at 18,730 cm-’ to 6A1 4 4 Tz and a band) whilst bdnd dt 22,080 cm-’ to 6A1 + 4A ‘, 4E (this IS probably a charge-transfer others 3’ assign bands at 9100, 11,550and 13,15Ocm-’ to 6AI +4A1, 6Al+4T2 and 6A I --f 4A,, 4E respectively, glvmg Dq values which appear rather low. More recently I”, these transtttons have been ascribed to bands at 8900, 12,800 and 18,000 cm-‘, g’vmg 1ODq

205

COORDINATION CHEMISTRY OI- IRON(II1) values m accordance at 9800,

13,600

with theory

and 17.900

178 and are consistent with the d-d bands of Cs:FezCb cm-’ The reported Isomer shift ‘G lI79 for FeClz- 1s ca. 0.75

mm set-* ; the absence

of a quadrupole

low-energy

spectrum

vibrational

splitting

of (FeC16)3-

lmphes

near octahedral

has been investigated

“’

symmetry_

The

I*‘, vJ(v,,Fe-Cl)

occurs in the range 248-257 cm-‘. v4(6Cl-Fe-Cl) at 181 cm-’ and vl (~~~Fe-cl) at 283 cm-’ _ One expects that (FeBr6)3- would be more unstable, owing to steric factors, it might be formed

m mel?s

No lodlde

complexes

are known

F COMPLEXES Or SULPCIUR DONORS Most of the recent “spin-equlllbna” dlthlocarbamate

interest

m fernc

complexes

m due to the posslblhty

complexes, especially with sulphur-contammg system, doyen of “spm-equlhbrla” compounds,

of obtaining

hgands In this section the will be dealt with first,

followed by dlscusslon of the other systems Metal complexes of sulphur-contdmlng hgands have been revlewed generally by Llvmgstone ‘*I, MKleverty “’ and Coucouvdnis’83 Mdgnetlc moments and hfossbauer parameters for some of these complexes are presented m Tables 4 and 5. (a) Dl~fzmcai-barnates

These black solids were mltldlly

prepared

by DeGpme

IfiJ ““,

but It was Cambl

et al

186-1go who studled a wide range of these compounds at 84, 194, 391 and 350%. They found that room temperature moments varied between 2 3 and 5 9 B M per ferric ion, depending upon the nature of the substltuent R m (R, NCSz)sFe Furthermore, the varlatlon

of susceptlblhty the moments Despite

all

regarded

with temperature Involved complete departure from Curie-Weiss behavlour, geneTally tended towards “low-spm” values as the temperature wds lowered

the inherent

as the correct

Cambl’s mterpretatlon equlhbrlum between S = l/2.

spin”,

lrmltatlons interpretation

m research

at this period,

of the results.

Cdmbl presented

m the words of Martin

what IS still

dnd co-workers’g’,

of thts rather confusing and novel behavlour in terms of”a thermal two magnetlcally lsomerlc forms” (currently termed “low-” dnd “high-

S = 512) was “remarkably

studied a series of N.fV-duubstltuted solution, finding that the anomalous

perceptive”

Martin

dlalkyldlthlocarbam~tes magnetism perslsted

dnd his co-workers

lmtlally

m both the solid state and in benzene and chloroform_ so

that, together with mol wt determmatlons, it WISestabhshed that the magnetic phenomena were not due to antlferromagnetlc (whether inter- or mtra-molecular) effects. It was found that four of the mneteen complexes then studied exhIbIted discrepdncles between the solid and solution magnetochemlstry results These were explamed “I as bemg due to the relaxatlon

of lattice forces !n solution which %mpress distortions on the Fe& octahedra m the sohd state”. The magnetic effects were ratlonahsed In terms of a thermal equlhbrmm between the two possible ground states, 2 T2 and 6A I, with the ’ T2 state being the ground state and the 6A 1 state bemg mLrea.srngly populated as the temperature rose lg2 _ The most reLent publication from these workers Is discussed magnetic measurements made Coord

over a range of temperatures and pressures, A V, the volume difference between the Cixm

Rev,

8 (1972)

206

S A COTTON

Msgnetlc moments of some low-spm compbes

of Sdonors

Complcv

wl (BM

Temperature 1

Ref

&I

Fe&CNButz2)j

2 46

300

207

Fe&CSEt)3

2 19 2 57 2 11 2 26

109

205

Fe(S2CPh)3

2 11 2 45

l-e(S2COhfe)3

Fe(hfcCSCHCS\fe)3 KBa[I-‘c(S2C20~)3j (PW%[I

301

6?C2(CN)2)3]

209

91

15

7 ‘8 __

293 100 293 100 297

2 50

293

1 73 2 00 20-t

-6H2O

103 295

2 2.5

215 218

94

(P~JP)z [ I e(S2C2(CN)2)2(S2CNhle2)]

‘-

2 53

Cd 290

(PhJP),[I-e(S2Cz(CN)2)2(S2CNCtt)l

*

2 60

cn 290

(P~~P)[~c(S~C~(CN)~)(S~CNE~~)~J

2 36

ca 290

(Ph403[Fe&C

2 50

ci3 290

C(CN)2)(S2C2(CN)2)2]3-

213

222

twc St&es, was found to correspond to a contraction of ca 0 1 A m the Fe-S bond on passing from high-spin to low-spm behavrour. The only published crystal structure IS of Fe(S2 CNBU’~~ )a, where

the configuratlon

1s rptermedrate

trrgonal

may be regarded

between

prismatic

as bemg at the corners

of the SIX sulphur and trlgonal of two parallel

atoms

antlpnsmatlc equrlateral

around

the iron atom

lg3 _ The sulphurs triangles,

whrch are ro-

tated by 32” from the trlgonal prlsmatlc configuration The Mossbauer spectra of a number of these compounds have been studled by several workers 144-1g7,the observed quadrupole splittings typically lay III the range 0.4-O 7 mm set-’ It is Important to note that only d smgle spectrum is noted at all temperatures that IS, not one that cdn be analysed as a supermlposltlon of spectra from both high- and low-spm specres This means that the relaxation time from one spm state to another 1s shortel than the hfetrme of the “Fe exctted state, and hence the Isomer shift and quadrupole splitting are functions of the proportions of high- and low-spm species at that temperature Attempts to observe EPR signals m the undiluted compounds were unsuccessful 1g7~1g8 but

Rickards et al lg7 diluted Fe(S,CNMe,)3 with the diamagnetic Co” analogue, and at 4 2°K obtained gl = 2 11 I, g2 = 2 076, and g3 = 2 015 Both the EPR parameters and the small Mossbduer quddrupole splittings (this complex 1s almost entirely low-sprn at 42°K) have

COORDINATION

CHEMISTRY

207

OF IRON(II1)

TABLE 5 Mossbauer

parameters

for low-spm

Iron(II1) complexes

Complex

with Sdonors

6 (mm set’

I-e(.$CPh)s

AE )” (mm SIX?)

Rcf

Temp (“K)

-O_lOb

I 87

ca 300

209

046

1 84

293

213

OS5

190

0 54

196

42

0 59 065

157 1.69

190 77

220

fe(PhCSCHCOPh)3 Fe(hIeCSCHCOMe)3

060 0 52

190 0 24

80 80

234 234

Fc(MeCSCHCOPh)3 Fe(PhCSCHCOMe)3

061

191

80

234

058 042

168 071

80 77

234

Fe(MeCSCHCSMe)3

Fe(S2CNMe2)3

; Relative

83

196

to nitroprusside

Relative

to “Co

m Pt

been taken to imply little deviation from 0, microsymmetry. The weakness of this correlation (and those for other Fe-S complexes of known structure lW) with structural results IS probably a consequence of neglectm, 0 factors such as configuration interaction lW. bearmg

m mmd the proxinuty of the Dq values for many of these systems to the ‘crossover’ region, it 1s easy to see how this may come about For a more complete descrlptlon of the magnetic phenomena

m the dlthlocarbamate

systems.

the reader

IS referred

to a recent

revlew2”

On treatment of the tns(dlalkyldlthlocarbamates) with small quantltles of concentrated hydrohahc acid, complexes of the formula FeX(S2 CiUR)2 (X = Cl. Br, 1) are obtdmcd Crystallographic

study

201 has shown

that the configuration

about

the non atom

1s dls-

torted square-pyramidal, w1t.h the iron atom slightly raised out of the S4 basal plane. The magnetic behavlour m both the sohd state and solution I2 has shown that there are three unpaired electrons (S = 3/Z), whilst bands m the far-IR spectra of FeX(S2CNEt2)2 (X = Cl, Br) at 353,309

and 225 cm-’ are assigned as v(Fe-S), (Fe-Cl) and (Fe-Br) respectively with a S = 3/2 ion with an apEPR results ” V202gwe g,=4, g,, N 2 at X-band, consistent preciable zero-field sphttmg Mossbauer results on solid samples 203 indicate a large quadrupole splitting (A.E N 3 8 mm see-’ ) but a low Q S has been noted 2W m DMF at 77°K a value sumlar to that notea for the tns(dlthlocarbamates), and m terms of salvation and hence hexacoordmatlon. Rapid removal of DMF from

(AE = 0 70 mm set-I),

Interpreted

these solutions partial

gives a product

dimerlsatlon

had taken

It IS clear that whilst Coot-d Chem Rev,

having

a four-line

an S = 3/Z system

8 (1972)

Mossbauer

specrrum,

It was suggested

that

place. 1s not possible

m a regular

octahedral

or tetra-

S A COTTON

10s

hedrdl field lo under the pomt group C + d ground state 4-A* can be obtamed It IS not surpnsmg, therefore, that many workers hdve studied the magnetic and spectroSLO~IC properties of~ron(ill)-sulphur Martin and his co-workers

The

xanthates

ferric Lhlorlde

Fe(ROCS2)3

complexes

m the years followmg

dnd thloxanthates

Fe(RSCS2

the dls.overles

)3 are readily

prepared

of

from

and the sodmm

salt of the hgand All the xanthates, except the ethylxanthdte, Jppear to be examples of ,I spm-equlare vlrtudlly pure low-spm I5 but the thloxdnthates hbrlur? system ‘05 The alhylthlouanthdte Lomplexes readily ehmmate CS2 to form the dlmerlc d1amagnetlL complexes [Fe(SR)(S2CSR)2] 2, where there are two mercaptide and two thloxanthate dnd no evldeme

bridges ‘06 ‘07 Fe(BufSCS2)3 of dlmer formatlon was found.

1s mere stable than the other thloxanthates this IS asLrlbable to sterlc factors The

structure of Fe(S2 COEt), has been de termmed ‘OR hhe Fe(S2 CNBu’*)3. It contams J very dlstorted arr.mgement of SIX sulphurs about the Iron atom (although the distortion 1s less marked) The dlthlobenzoate, Fe(S? CPh)g IS rather more stable than the foregomg systems, and IS prepared from ferric chloride and sodmm dlthlobenzodte, being purified by recrystalhsdtlon from apolar solvents the usual method for such systems Attempts to prepare FeCI(& CPh), analogous to the dlthlocarbamate systems. were unsuccessful ‘Og COUCOUm the v.m~s and Llppard 210 prepared the smnlar (also low-spm) system Fe@-tolCSz)3 Lourse of studying

the reactlons

of ferrtL chlortde

with Zn(p-tolCS& ,

when the complexes

Fe(~mACS3)2 (p-toICY& ) drid Fe(~+tolCS3)(/~-tolCS2 structure mcludmg magnetic

)* were JISO obtained The crystJ of the last-named complex shows that the coordmatlon of the iron IS octahedral, an FedWsL .s/C Imhage All these complexes are low-spun, with room temperature moments of 2 2-2 5 B M

When an aqueous Fe(MeCS.CHCS*Me),

solution Lontammg aLetylJc.etgne Cl4 IS produced “I. The crystal

and F&I; IS treated with Hz!% the violet structure 2’2 shows the complex to

be composed of (MeCSCHCSMe)’ and FeClj- Ions, upon dlthlontte or borohydrtde reduction, the red-brown complex Fe(MeCSCHCSMe)3 IS formed The g v&es ‘I3 of 2 14, 3 09 dnd 2 01 are typical of low-spin Iron(III) complexes “‘, Mossbauer and magnetic results are m accord with this The structure. determined by X-ray methods, shows that the octahedron of SIX sulphurs dround the iron atom IS only shghtly dIstorted *I’. the quadrupole sphttmg of cd 1.90 mm seL_’ IS rather large, however (c,J Dlthoo.ralarcs The dlthlooxalate ion binds to metals vta sulphur, Dwyer and Sargeson first synthewed the [ Fe(S2 C2 O2 )3 ] 3- Ion *I4 and found /.L,~ to be 2 9.5 B M This 1s very high for a low-span d5 ion. and the authors ascrlbe part of this value to the preseme of high-spm lmpur!tles Later workers *15 prepared samples of KBd[Fe(Sz C2 02)3] 6H2 0 having d mdgnetxc moment of 2 28 B.M . by studymg the Con1 and Crlll analogues, they showed that whilst dlthIooxalate does not lead to excepttonal 04 values, It does reduce the separation of the energy levels of the metal Ion by a constderable

amount,

maktng

sulphur

hgdnds appear

to be ‘strong’

hgands

COORDINATION

CHCMISTRY

Ol- IRON(lII1

209

In the spectrochemlcal sense The Ph4As’ salt IS Jso low-spm, but the (Ph3 PI2 M’ salts (M = Cu, Ag) are lugIt-spm ‘16. It was suggested thdt the metal M binds to two C=G groups and reduces& sufficiently for the change in spm state Treatment of [Fe(S, C2 O2 j3 ] 3- wxth I2 leads to the formation

of [Fel(S,

Cz O2 )t ] 3-_ whose

reported

magnetic moment at room temperature IS 4 03 B M . thts IS quite conststent wttli Its bemg an (S = 3/2) system (cf the monohalob~s(d~th~ocarb,unates)) The EPR spectrum has not been reported, we antlclpdte it being of the (gl = -l,g,, = 2) variety at X-bJnd On reiluxmg a CH2C12 solutmn of [Fe(S,C,02)3 ] 3-, [Fe2(S2C,02)5] 4-, ofunbnown structure, IS

formed (d) Dwymw-l There has been [(S2C2(CN)2 )‘-I [V(S,C2(CN)2)3

?d~throIcncs

atldrelated hgarzds

much interest

ln the structures of complexes of LW-dl~yano- I.?-dlthlolene complexes The envn-onment of the vanddmm Ion m (MeJN)2 ] is that of a very distorted oLtdhedron of sulphurs ‘17 (Phs P)3 [Fe(S2 CZ(CN)2 )3 1 IS prepared from FeCI, *6H, 0 dnd exLess Na2 S2 C2(CN)2. 111 the absence of air, as d darh red solid ‘I’. it 1s readily ouldlsed to the dlamomc species m soiutlon (this cdn be reduced ba& to the Iron(lI1) Lomplex with sulphltc, for ex.mlple) but IS quite stable m the solId state This 1s low-spm and the EPR spectrum *I9 1s qurte typlcsl of .m (S = l/2) species It should however. be noted that the separation of the tzs levels orlgmally suggested ‘I9 IS mLorrect 199 The Mossbduer spectrum Y’ “’ shows d IJrge qudin terms of d conslderdble dIstortIon from drupole sphttmg (CJ 1 6 mm see-’ ) interpreted of nieaningtul cubic symmetry In view of the controversy surroundm, n the dsslgqnient

states to the met&l Ion m such complexes, it is worth noting that on reducmg [Fe(S, C2(CN)2 I,] ‘- to the tn-.mlomL spccrcs. the Isomer shift mcredses from 0 50 to

oxldatlon

0 65 mm set-’ . mdlcatmg that the unpaired electron has entered dn orbital of largely metathc (presumably 3d) character “’ Recently 2t’ , the mixed l-l- I,‘-dlthlolene complexes have been prepared by treatmg

the complexes [Fe(S, C2(CN)2)z ] - with 1, I-dlthtolene hgand, followed by sulphlte reductIon_ Thus (Ph, P)3 [Fe {L-L)(S2 C,(CN), j2 ] (where L-L = c g S2 C C(CN)2. S2C N(CN)) were obtained They are low-spm. havmg room temperature moments of ca. 2 5 B-M at room temperature, however, no EPR or MbGbauer ddtahre yet avarlablc The complexes of the type [ Fe(& Ct (CN), )z ] - are m fact dmlertc. m the solId state,

the environment

of the Iron atom being pentacoordmdte

223*224 In solution, however, the

magnetic behavlour IS typical of an (S = 3/Z) spebies so thdt solvated monomers are probably formed_ A number of sohd complexes of the type [FeL( S, C z (CN)2 )* ] -, where L = m both the e g pyndme, have been prepared 225 which exhlblt S = 3/2 mdgnetll. behavlour sohd state and solution. when L = e g PPh,, blpy, phen, the behavtour IS typlcJl of an value m the (S = l/2) species (S = I /2) ton. The shift of gdv away from the free-electron

may be correlated with the declme m Lewis bastclty of the donor 19’ B&h 226 has very recently reported more adducts of the type [Fe(L”-)(S2 C2 X2 j2] Wan)- (X = CN CF3. L = Ph,PO, Ph3As0, py0. py, Cl, Br) which exhlblt 3 90-4 02 B M dt 296” K)

S = 3/Z mag*letlc

bchdvlour

(P,~~ =

210

S A COTTON

Reactlon of (Bun4N) [Fe {S,CZ(CF~)Z~Z J with tnphenylphosphme, m the presence of air, leads to the for-matron of the S = 3/2 complex (Bu n4N) [Fe(Ph,PO)IS*C2(CFJ)2}21 whrch has a square-based pyrarmdal structure, the non atom being 0.43 A above the basal plane 262 The EPR spectra of frozen acetone or dtchloromethane solutrons of [Fe(py)(S1 C2 (CN),)* ] - are consistent wrth the presence of an (S = 3/2) Ion wnh a defimte zero-field sphttmg,g, N 3.8,g,, N 2. In frozen pyrtdme solutron, however, a strongg, = 2 13,g,, = I 99 resonance IS observed, and this has been ascribed to the low-spur [Fe(py)a (S, C, (CN)t )a I-_ The Mossbauer data 220 for [FetPy)& C, (CN), )2 I- (S = 3/Z

6 = 0.59

l/2, mmsec-’ , A = 2 41 mm set-’ at 77°K) and [Fe(phen)(&Ca(CN)&]-(S= 6=057mmsec’-‘,A=1 80mmsec-’ at 77°K) are interesting as they provide evidence for strong dlstortlons of the field about the iron atom We have, so far, been concerned with complexes exhtbrtmg, at least partly, S = 3/2 or l/2 behawour. The trrs-complexes of 1,I-drcyanoethylene-2,2-drthrolene, [S2 C (CN)2 ] *-,

are high-spin (S = 5/2)227Y228 with reported moments of 5 89 - 5 95 B M At X-band, the EPR spectrum of (Pr “4N)3 [Fe(S,C C(CN),),] hasg, N 6 andg,, ~2, mlplymg a nearly octahedral coordmatlon of sulphurs about the ferric ion rgq_This 1s interesting m view of the fact that the metal-chelate ring IS only four-membered, and a greater dtstortlon might have been expected (e) Dithrophospkates The four complexes Fe(S,PR2)3 (R = Et EtO, Ph, PhO) were first prepared by Malatesta and Przzottr ‘*’ who found that they were h&-spur with peff N 5 9 B M , they are rather hygroscoprc black sohds Jorgensen 230 re-exammed Fe(S2 P(OEt),), and found that crystals of the uon(II1) complex doped mto the mdmm(II1) analogue are quote stable More recentiy, the temperature dependence of ,ueff has been exammed ” for a number of complexes Fe(S20Rz)3 (R = MeO, EtO, Pr”0, and Pr’O), over the range 96-300”K, peff values were in the range 5 61 - 5 85 B M , showmg the complexes to be genumely h&-spur.

(f) S,O dorlors ‘Mixed’ donors where one donor atom IS sulphur and the other oxygen wtll now be considered Fe(2-thropyrtdme N-oxrde)3 has been shown by magnettc measurements 231 and EPR lqq to be high-spin The related mono&no-fl-dtketonates Fe(Rr -CS*CHCO-R2)s (R = e g. Ph, OEt, CF3) were prepared by Ho and Lrvmgstone 232*233who studred-the magnetic properties and postulated a ‘sptn-equthbrtum between S = l/2 and S = S/2 specres, with the (S = l/2) form favoured at low temperatures. They showed that peff was field-mdependent, excludmg ferromagnetic specres, and that the analogous FeIr complexes were not obtamable. Room temperature peif values were 2 3 - 5.8 B M. for then choice of Ri, Ra, for Ri =pvaried from 2 11 B M at 83°K to 5 06 B M at 378°K. W’L R2 = -3, peff Fttzstmmons and co-workers 234 studied the Mossbauer spectra and magnetrc moments of the four complexes where Rr or R2 = Ph or Me. They found similar magnetrc behavtour to that found previously 2327233and, moreover, were able to detect the resonances from

COORDINATION

the separate

spm-Isomers

terns. The high-spm AE ~0,

whilst

1.9 mm.sec-’ complexes temperature

211

CHFMISYRY Ol- IRON(W)

m the Mossbauer

spectra,

m contrast

(S = S/3) species are chdracterlsed

the low-spm

to the dlthlocarbamate

SYS-

by S - 0 75 f 0.1 S mm.set-* ,

speLles have 6 - 0 65 + 0.05 mm set-’ , and AE values

up to

_The mdrvrdual spur-Isomers were also observed m the EPR spectra of the m both the soled state and frozen solution over a wide ‘99, which were obtained range, showing

that the ‘spin-equlhbnum

high-spm species were characterlsed S = I/2 species gave spectra closely

IS not just a solid state effect

The observation of separate EPR and Mossbauer resonances phes that the relaxatron trme from one spur-state to another electron spin relaxation tune and to the hfetlme of the “Fe (g) Other conlplexes Berzelms 235 reported

The

by nearly lsotroplc signals with geE N 4 3 whilst the srmllar to those of complexes of bldentate S donors.

the dark brown

for the two spur-isomers nnis long compared to both the exerted state.

Fe2(CS3)3

as the product of reacttcn between on this and Fe(SEt),, the wrth N&E: 236_ The Iatrer complex IS

FeC13 and NatCS3, but more recent work would be welcomed amorphous of especial

red product interest

of the analogous

m that a monodentate

reaction S donor

1s mvolved

The only example of a complex of a Se donor discussed m this work 1s the ted-brown 2FeC13*MeSe(CH2)3*SeMe whose reported 237 magnetic moment is 5.34 B M. Two possible structures are (I) a polymer with antiferromagnetic mteractlon, or (11) a species of the type [FeC12(MeSe(CH2)3SeMe)2]+ (FeC14)- whrch would require peff for the catlon of ca. 4 7 B M Thus it seems the complex 1s probably a polymer G COMPLEXES 01- PHOSPHOROUS

(I) Monoden

AND ARSENIC DONORS

tate

FeCl, .PPh3 and FeCl, *AsPh3 were prepared 238 by refluxmg Fe3(CO),2 m CHC13 with the &and for 12 h, addrtron of hexane to the concentrated mother-lrquors gave an od whrch on further treatment with hexane and ethanol gave yellow solids, recrystallisable from ethanol Far-IR assignments were v(Fe-P) at 525 cm-’ and v(Fe-Cl) at 370 and 320 cm-’ A number complexes complexes

of amine complexes of reportedly similar storchrometry were shown to be lron(II) and arsme by Blrchall 239, who found the Mossbauer spectra of the phosphme quite consistent with a pseudo-tetrahedral structure For FeC13 .PPhJ at 77”K,

6 = 0 54 mm set-’ and AE = 0 _2 1 mm set-’ , whilst FeCl, lAsPh3 gave 6 = 0 57 mm see-’ , AE=OZmmsec ’ On the other hand, Naldmi ?-XI exammed the reactions of rrlphenylphosphme and tnphenylarsme with a number of ferric salts. Ethereal solutions of Ph3P and Ph3As reacted with anhydrous FeC13 to give very dark red crystals of Fe(Ph3 R)2 Cl3 (R = P, As), which gave non-conducting

MeCN solutions.

the red Fe(Ph3P),(NCS)3, gave the yellow Coord Cllem Rev

ethanohc

Fe(Ph3R)2(N0s)3 8 (1972)

A slmdar ferric nitrate

reaction

occurred

on treatment

These were non-electrolytes

with Fe(NCS)3

t? give

with the hgands

m ether

m mtrobenzene.

All of

212

S A COTTON

these complexes were high-splr, 24’ reported complexes

Nyholm

with peff values of 5 75 - 6 14 B M at room temperature of various tertidry arsme$ of two types, FeC13(R’R;As)2

dnd (FeC13)2 (R’R~As)~ When R’ = Me, R” = Ph, both types of complex were isolated, when R’ = o-tolyl. R” = Me, only the former were obtamed, and when R’ and R” = p-tolyl or Me, only the latter were isolated The colour of the Lomplexes varied from yellow brown. Issheb and Bra& 242 Isolated the yellow FeCIJ *P(Cs H,, )3 from ethanol

to

(It) Polytleittate &mot-s

With this class of hgdnd. all those reported involve Arsenic as donor, mostly with the ltgand dears (cl-phenylenebisdimethylarsme) Reaction of dnhydrous FeC13 m ethanol or benzene with dears affords the crnnson FeCIJ ‘didrs whlLh IS m faLt 243 of an acetone [FeC12 (dlars)t ] ‘(FeCL )-, having petI = 4 55 B M per Fe atom Treatment solution of the complex with HCLO, afford< the red [Fe(dlars)2 C12]+C104-, wtth peft- = 3 34 B M 243 ‘4-1 the FeCl; ton IS of course high-spin Addltlon of dears to excess anhydrous FeBr3 m benzene affords the chocolate-brown FeBr3 -dears (&_tf = 4 57 B M per Fe). bemg fFe(dlars)2 Brz]’ (FeBr4)On careful hydrolys~s, the green [Fe(dlars), Br2 ]+Br- IS formed (this can also be prepared from a 1 1 ratlo of reactants tn ethmol) Fdr-IR assignments are v(Fe-Cl) at 376 cm-’ m [ Fe(dlars), Cl2 ]‘BF;, Y(Fe-Br) at 292 cm-’ m [Fe(dlars)2 Brz ]+BF,, and 273 and 306 cm-’ m [Fe(dlars)2 Brl ]‘Br- (refs 245, 246) The I,?-bts(dlmethyldrsnio)ethylene (edas) [Fe(edasJ2 C12]+(FeClJ)have been prepared, analogue. and the latter by direct reactlon of Methyl-bn(3-propane-dlmethylarsme)arsme llgdnd and the deep green complex Fe(NCS)3

B M . has been isolated 24s Reportedly, Further

mvestlgatlon

The analogous FeC13 m ethanol [Fe(TTA)Cl*]’ IL COUPLCXES

Wtthtn tammg

IS merited

tetradent,tte

complexes Fe(edas)3(C104)3 and the former by HN03 oxldatlon of the Fell the hgand with anhydrous FeC13 m ethanol 247 (TAS, MeAs[(CH2)3AsMet] 2) IS a terdentate -TAS, a non-electrolyte havmg &tt = 2 22

other ferric hcllldes form analogous complexes

here &and

TTA (= As[(CH2)3AsMel]

3) reacts with anhydrous

to form [Fe(TTA)C12]+(FeCla)pefl per Fe = 4 45 B M , so that pelt for IS CA 2 2 B M The chlorines are thought 249 to be (IS 01- CARBON

DONORS

this class, we shall discuss

cyclopentadlenyl

two types,

those contammg

cyanide

and those con-

type hgands

(a) Cyamde K3 Fe(CN)6 1s well known, as are pentacyano species of the type [Fe(CN)sX] ‘-, where X= q !+ 0, NO2 : these are all S = l/2 systems The blue sohds formed from reaction of Fe’II with Fe(CN)b4- or FeI* with Fe(CN)63-

are also famlllar, and appear to be bdsed upon d cubic array of iron atoms with CN- ions

COORDINATION

CHChlISTRY

Oi- IRON(II1)

213

contam along cube edges between them 250 Mossbauer spectra show that these complexes discrete ferrous and ferric tons, measurements on Fe(CN)63- have been made by a number of workers

L’8y2s1_ Magnetrc

measurements

over a temperature

range

I46 on KsFe(CN)e

have been mterpreted in terms of an orbital reductton factor k PL 0.8 and an axial field EPR results a’ grve k = 0.57, A = 220 cm-’ , the g values beingg, = 2 35, A = 400 cm-’ gY =2 lO,g, =0915 For K3Fe(CN)b, has been assigned

reportedly

havtng a monochmc

unit cell (CHID-p7_I,c).

2s2 to an IR band near 520 cm-‘,

dnd 6 (Fe-CN)

studtes in solution 253 give results rather stmtlar, although rather lower energy More work might be carried out m the field of cyanide simple

ligdnd affords

studred

complexes

Crystallographtc

where n-bonding

data \/ould

v(Fe-CN)

Raman

has been assrgned

complexes,

and delocahsatron

Y,,(Fe-CN)

near 400 cm-’

dt

ds thts relatively should

be readily

dlso be welcomed

Oxtdatron of ferrocene yrelds the ferrtcmmm ion, [Fe(n-Cs HS)2]+, whrch contams one unpaired electron and may be formally regarded as a ferric complex It seems that [ Fe(rr-Cs HS )2 ] I3 contams a planar ferrrcmmm Ion ‘~4. although the X-ray study was complicated by drsorder There has been controversy concermng the ground state m these systems, which mtght in Dsd symmetry, dnd, unttl recently, no definite g’)4(a1g’)’ be (alp*)2(e2gf)3 or (e2 EPR data were dvatlable Some carborane

systems

have been synthesrsed2s6

[(rr-CSHS)Fe(B9C2H1r)] Crystallographtc both the ‘carbollide’ and cyclopentadtenyl carbon

and three boron

atoms

bonded

2s6 such as [Fe(B9C2

study 2s7 of the latter hgands were n-bonded,

to the Iron atom,

HI1 )* ]- and

complex showed that the former havmg two

the rmgs were eclipsed,

in contrast

to ferrocene

the EPR of a number of rron(III)-carborane systems at Makl and Berry *” exammed 85”K, and found signals that could be descrtbed in terms of an axially symmetrtc g-tensor (see Table 6) and a certam amount of delocahsatron Comparrson wrth theoretrcai predrctrons indicated the ground state to be (alg1)2(e2g’)3 Recent EPR studies on highly purified samples of [Fe(lr-CsHs)2]+ salts gave srmrlar spectra at 77”K, rmplymg a stmrlar ground-state configuratton These workers ascnbe the prevrous

non-observatron

small quantrties

of impurity

of spectra

at 77°K

to the extensive

2sg Prms 260 has also Investigated

lure-broadenmg

effect

the EPR spectra

of

of some

ferrtcmtum systems HIS spectrum from {Fe(rr-CS H,)a}’ 13- IS not ds well resolved as those between the reported of Horsfield and Wasserman 2s9, it may account for some dtfferences g values (see Table 6), but it does appear that amon or solvent perturbations also are rmportant Hn results are m general concordance with other workers. the energy levels are The calculated separatron between the ]MJ I= S/3 and ]MJ I= 3/Z 2 Se2g3 < *elg arg ton, this small sphttmg levels is 800 cm-’ m the ferricinmm the short relaxation tunes above 77OK. Coord

Chem REV., 8 ( 1972)

IS undoubtedly

responsrble

for

S A COTTON

214 TABLE 6 Values ofg for ferrvaruum-type systems

Compound

g1

lFe(%&H1r)21I~e(BgHK2Mez)21-

3 94

1 532

2 79

1711

Glass ( l- 1 DMr CHCI3) Glass (1 1 DMF CHC13)

Medium

gll

j(nCsWre(BgC2Hlt)J

3

58

1 778

Gldss (1 1 DMI- CHC13)

Ire(B9H9C2HPh)2

I-

3 57

1 799

Glass (1 1 DMr CHC13)

I-

3 70

1 725

Powder

3 28

1 87

Smgle crystal

3 26

1 86

3 35

1 85

Pobder Glass (CH2C12)

3 15

1 82

Powder

3 20

190

Glass (H20)

4 35

1 26

Glass (DMF)

4 17

1 47

Glass (DMr)

3 98

1 58

Class ( DMl-)

3 83

167

Glass ( DMr)

3 88

1 68

Gla~.s (DMr)

3 69

1 73

Glass (DMF)

3 63

1 74

Glass (H2SO4)

3 62

1 76

Glass (DMl-)

lre(BgHgC2HPhJ2 l

IFeC~Cs~Js)z

1

(trlchloroxetdte)-

There IS obviously much scope here for work on complexes containing u-bonded carbon. .%I obvious reactlon which could be tried IS that of a benzyl Grlgnard with fernc chloride, m the hope of obtammg 1

Fe(CH2 Ph)3 or a related

compound

CONCLUSION Rather limited X-ray data are avadable (see Appendix)

but it IS clear that most FeII*

complexes mvolve approximately octahedral coordmatlon. Ferric iron readily complexes with oxygen donor hgands and with hahdes (except I-, because of the redox reaction Ee3+ + I- + Fe’+ +* I*) Its affrmty for monodentate nitrogen donors IS hmlted, the most stable ones seem to be those where Cl IS also present in the coordmatlon sphere. Fe-S complexes are also very important, although they often decompose

readily. Very little has been done with other donor atoms, and this remams a major omlssmn The Isolation, and more Important, characterrsatron of further stable phosphme complexes would bz a malor step forward. Much of the work performed

so far has been of a very haphazard nature, complexes

COORDINATION

CHEMISTRY

OF IRON(W)

215

have generally prepared with the sole object of comparison with other Ions, so :hat generai trends are obscured, and there is a need for a systematic approach Since the hrgh-spm d5 ion has no crystal-field stabrhzatron energy, mvestrgatton of unusual coordmation numbers (espectally pentacoordmate species) mrght prove rewarding; investigation \zf mteracttons between ferrtc salts and ammo acrds or nucleotrde bases could be mterestmg from the brological angle Generally speaking, there IS much scope for both experimental and theoretrcal work m the field One example of this hes m the field of electronic spectra, where, m S = S/2 systems, opportunity is afforded for calculatmg the D value from the electronic spectra and comparmg tt with the value obtained from EPR or single crystal susceptrbrhty measurements The D value IS related I9 to the sphttmg of the lowest 4T1 state by the equation

where 5 1s the spin-orbit coupling constant and E,, Ey, Ez the ener@es of the components of the 4Tl state relattve to the 6A1 ground state Lrkewrse, the mterpretatron of the electronic spectra of the low-spur complexes would be an important step towards an a M-0 scheme whtch would account for the bmdmg m these complexes, as well as for the Mossbauer and EPR parameters ACKNOWLEDGEMENTS

The reviewer w&es to thank Dr. Peter Thornton (Queen Mary College, London) for helpful comments upon the manuscript, and Dr. John Gibson (Imperial College, London) who introduced hrm to ferric complexes He is indebted to the Science Research Council for financial support

Coord

Chem

Rev,

8 (1972)

--

2 35-2

----p

4 I(CI)

I e(mc)2CI

K3I e(o’&te)3

We {(NSlh)&

I

~C(~dCl~)CIg(Cli3N02),

’ 1918(N)

2 064- 2 099(N)

I 879-1885(O),

2 238(Cl)

2 09(0112)

2 017-2,092(O), 2 29(N)

2 ~07(0~~2)

1 938-2,128(O), 2 304-2,346(N)

] eH20

LI[ I’e(LDTA)OH2

Cd[l c(DCI ~I)0112 ] 48H2O

2 lO6(Oll2)

I 974-2 085(O), 2 312-2322(N)

1 *l-l20

Rbll c(LDTA)0H2

P3/L

2

2

4

c2/1 Ai21a

8

PlJta

I?/a

N3

02N2CI

N2O5

142

100

125

II9

I20

N2O5

N2O4

25(N)

I’?., Ic

2 19-2

1 93-Z 03(o), 2 07(OH2)

I>IIAH)OH2]

[h(I

82

II3

X8

XI

164

163

I61

50,

35

34

7-r

38

__P-....

II9

06

6 4

RXc

2 008(O)

I_

Rcl

N2O5

06

4

I’?, /c

4

04Cl

4

I’? * /t1

m(0)

I 95(O), 2 213(CI) 2 01-2

Cl4

8

06

Cl4 Cl4

4 4

Cl4

2

04c12

I’lJta

I c( tropolon,~tc)3

31-120

I 986-2,004(O)

I c(mc)3

01

/‘?I 212, P/JClli

2 180-2218(CI) 2 182-2 I87(CI)

l~cl,+I~ccI;

NJ+I &Ii

CCIi

14

(l’h4A\)+I /‘/JC ?,

OCIS

4

4

141/a

t’JJlJl(J

O4Cl2

2

/‘4/ftirw~

14% 04c12

2 2

/‘4/u

--____

l/l ( lmwoplmrc

C?/lll

_-_

S]LILCgou]~

-cI_-P-_-______

2 19(CI)

2 l62(1 cc’&)

2 07(O), ? 37(U)

2 08(O),

(NII4)21l CCI5(Oll2)] [I c(Mc2S0)&t2 J+hCl~

e(0112)4&

1fSbCI~*4H20

2 36(U)

7, 08(O),

(I‘c(Otl~)~Cl~]+CI-.2tl~0

[I

I 94(1 ) 2 3O(CI)

1 94(O), 2 07(O),

31120

p-r

cl-3

__--

dfk-x)

ddtd tor won(lll) complcm

(A) --I_

Crysullogrrpho -_-_

AI’I’CNl)IX

I62

--

_

IJ m

COORDINATION CHEMISTRY OF iRON(II1)

Coard. Chem Rev, 8 (1972)

217

218

S A COTTON

RI-I l-RIINCCS 1 N V

Stdgutck, The Chemtcal EletltCtztS arid Ttznr Compourzds, Vols I and II. Oxford Unrverslty Press, London 1950 2 Gnzelztz’s Ilandhuciz dcr Anorgamschen Chcmre Verldg Chemlc, Wemhctm 1932 3 J W \lellor, Comprelzenszre Treatzse OH lnorgazzzc arzd Tlzeorerzul Chenzzstry Longmans Green. London, 1932 4 P Pascal, Noun razz TraztPde Clzzzzzzehlzneinle Masson, P,Iw, 1959 5 R Colton and J H Cantertord, Halzdes of the Fvst Row Trarzstttott Elements Wtley-Intersctence, Neu York, 1969 6 H A 0 H111and P Ddy, Physzcai Teclzmqzw~ III Advanced Inorgazzzc Chemzstry Wzley-Interxlencc, rrlew York, 1968 7 N N Greenwood, Cizem Brat 3 ( 1967) 56 8 B A Goodman and J B R.zynor, Adian Inorg Clzem Radzoclzem 13 (1970) 135 9 P W Atkms and M C R S> mons, Tlie Strzccrzzrc oj Izzorganzc Radzcals Elsevrcr, Amsterdam, 1967 10 J S Grztfith, J itzorg Nrtcl CXem 2 (1956) 1 11 J S Grzffith,Dlscuss Faraday SOC 26 (1958) 81 12 R L hfartm and A H Wbzte, Itzofg Chem 6 (1967) 7 12 13 B N I‘~ggzs, Irons Faraday Sot 57 (196 1) 199 14 B N I’I~~Is, M Gerlocb .md R Mason, Proc Ro, Sot. Ser A 309 (1969) 91 IS A H fwald, R L hl.xtzn, C Sznn Jnd A II Whzte, horg Clzem 8 (1969) 1837 16 J H Van Vlec?. .md W G PcnncJ , flzrl brag 17 ( 1934) 96 1 17 A Abrngam and hl H L Pry~e, Prop ROY Sot Ser_ A 205 (1951) 135 18 B R N&arvey, rransztzozz Mefal Clzem 3 ( 1966) 89 19 J S Grzflith,Mol P/z~s 8 (1964) 213, 217 20 R D Doxcsmgand J I Czbson J Clzc~z Plz~s SO (1969) 294 21 B Bleancy and hl C hl 0 Brzen, f’ro~ Phys Sot Londozz, Sect B 69 (1956) 1216, J S Griffith, TFze Theory Of Trazzsztzorz-Metal fofzs Cambrzdge Unzverszt> Press, London, 196 1 22 R l-1 Herbcr, R B Kmg and G K Werthclm, frzorg CIzerzz 3 ( 1964) 101 23 S A Cotton and J I‘ Gzbbon, J Chenz Sot A (1971) 1693 24 B Blc.mcy and R S Trenam, Proc Roy Sot Scr A 223 (1953) 1 25 hl D Lmd, J Cizem P~I_IS 47 ( 1967) 990 26 B R Pentold and J A Grrgor, Acta Crystallogr , 12 (1959) 850 27 Y Kerznarrcc, Compt Rend X8 (1964) 5836 28 E R.zbmo\rzt7 and W H Stockm+wr, J Amer Clzem Sot 64 ( 1942) 335 29 H L l‘rzedznan, J Amer C!zem Sot 74 (1952) 5 30 G W Bradv, %I B Robm .md J Varlmbz, Inorg C/zcnz 3 ( 1964) I168 31 S B.dt and A M A Ver\~e~,SpeLtrocl~rtzz Acta Part A 23 (1967) 1069 32 L-Y. Wang, J Chem Plzys 32 ( 1960) 598 33 R I‘ Wemland and C rczgc. Clrefzz Ber 36 ( 1903) 244 34 A Icrrarl, L C.w.11c.z .md XI L f.ml, Gazz Clznn Ital 87 (1957) 22 35 I Lmdqvlst, ,trh Kenzl 24A (1947) 1 36 H P Mug, I: Kummer and L Alexmder,J Avzer Chenz Sot , 70 (1948) 3064 37 I‘ Kr.nzs and T V Heidelberg, J PraXt Cizcnz 121 (1929) 364 38 G Teutcr, Acta Crystallogr 17 (1964) 1480 39 1 \V Breman, A M A Veraey And S Bait Spectroclzzm Arta Part A, 7-4 (1968) 1623 40 R C. Wallace, Z Knstallogr Mzrzeral 49 ( 19 11) 4 17 41 H RCmy and H Busch, Chem Ber 66 (1933) 96 1 42 G A Barbzerz, Attz Accad Naz Lzzzcez Rezzd Ci Scz Fzs Mat ,Vatur 22 (1913) 867 43 S A Cotton and J r Gzbson, J C/zem Sac A. (1971) 1690 44 S. Holt and R Dangle, Acfa Clrem Stand 22 (1968) 1091 45 R B Penland, S Mzzushuna, C Curran and J V Quaglzano, J Anzer Chem Sot 79 (1957) 1575 46 R J Berm, R R Benertto and H B Jonarsen, J Inorg Nucl Cilem 31 (1969) 1023

COORDINATION

CHEMISTRY

219

OF IRON(III)

47 F 4 Cotton and R rrancls, J Amer Chem. Sot 82 (1960) 2986 48 H L Schlafer and H P. Opttz, Z Anorg AIlg Chem , 3 13 (196 1) 178. 49 C H Langford and F M Chung, J Amer Chem Sot 90 (1968) 4485 SO hl J Bennett, f- A Cotton and D L Weaver, Acia CrysruiIogr, 23 (1967) 581 51 B r G Johnson and R-A W.dton, Spectrochn Acta 22 (1966) 1853. 52 C V Berney and J H Weber, Inorg Chem 7 (1968) 283 53 R Frances and F A Cotton, J Chem Sot (1961) 2078 54 C C. Prapakharan and C C Patel, J Inorg Nucl. Chent 32 (1970) 1223 55 J V Quagharto. J fUJIta, G Trzmz, D J Phtlllps, J A W~lmslcy and S Y Tyree

J Imer

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