PMR studies on oxygen-iron complexes

Jouma1ofMokcularStructure,46(1978)18~195 0 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands

189

PMR STUDIES ON OXYGEN-IRON COMPLEXES

A. O?AROmSKt , JE2owsKA : TRZEBIATOWSKA, Institute of Chemistry, Wroc2.a~ University,

B,

II.

LATOS-GRAikNsEI

Wroc%aw, Poland

ABSTRACT

The binuclear owgen bridged iron(II1) complexes containing seven-membered chelate rings have been prepared and investigated by means of the magnetic susceptibility measurements in solid state and by the PMR technique in deuterochloroform solutions. Both the magnetic and PMR data have been interpreted in terns of equations derived from the Hefsenberg Hamiltonian E JS,S2 . The exchange integrals, J, and the contact hyperfine interaction constants, A, have been evaluated.

INTRODUCTION

The iron(II1) ions are able to form the binuclear oxygen bridged complexes of the general formula (Fe,,,0 , where ligands coordinating via nitrogen or via both nitrogen and oxygen atoms are attached to the metal. /ref. I/ Among the binuclear compounds one can distinguish a group of the complexes of Schiff bases as very interesting from the stereochemical point of view. These compounds have been extensively studied in the recent years, mainly by the magnetic susceptibility measurements and IX spectroscopy. /ref. 1-4 / The NMR method which is expected to lead to the information on the electronic states of the metal centers and on the electron delocalisation mechanisms, has also been used in several cases. /ref. 1,5,6 / In this paper we report the results of the magnetic and NMR studies on the binuclear oxygen bridged iron
190

ptrescine /tetramethylenediamine / Par comparative studies the binuclear iron(II1) compounds of salen, salpn and phenen have also been synthesised. The abbreviations used in this paper are elucidated in Fig. 1.

Fig. 7. The general structure of thEdligands: salen: n = 2, salput: n = 4, vanput: n = 4, the 3 proton of benzene ring replaced by -OCH3, phenent n = 2, asomethine proton replaced - instesd of -(5H2)n-* salpn: -CH@H-CH3 The complexes (Fesalput)20 and (Fwanput)20 contain the seven membered chelate rings FeNCCCCX, which are very rarely encountered in the coordination chemistry. / ref. 7,8 / SYNTHESIS The compound (Fesalen)20 was prepared as previously described, / ref. 2 / and recrystallized from chloroform. (Fesalput)20, (Fevanput)20, (Fephenen)20 and (Fesalpn)20 were prepared by hydrolysis of appropriate mononuclear compounds by KOH in methanolic solutions. / ref. I,2 / When using trimethglenediamine to prepare the Schiff base, we were not able to synthesise any binuclear complex by any of the published synthetic methods. /ref. I,2 / On the other hahd, the ligands deriving from penta- and hexamethylenediamine formed the unsoluble, most probably polymeric compounds. Thus, only the Schiff bases deriving from ethylenediamine and tetramethylenediamine are able to form the binuclear oxygen bridged complexes with iron(II1). The complexes (Fesalput) 0 and (Fevanput)20 crystallized from CHC13 form adducts (Fesalpu%)20eCHC13 and (Fevanput)20.CHC13, which are stable for several weeks, while the compounds crystallized from CH2C12 contain only traces of the solvent.

The magnetic susceptibility measurements over the temperature range 77 - 295 K were made by the Gouy method. Hg[Co(SCN)Jwas

191

used

as calibrant,

field The

The

susceptibilities

were

independent

on the

strength, diamagnetic , vanput

following

-162-104

salput

The Nb5R spectra

were

COrreCtiOnS for the ligands-were -199=10?6 t phenen -162~10~6.

as the internal

10.8

ppm was

Calibrated

were

performed

over

the temperature

using glgcol

were

isotropic

The

saturated

sweep

width

technique.

108 and

The measurements

deuterochloroform

solutions

215 0 322 IL Probe temperature was varied and was C8libr8ted with ethylene -3 8ccessory,

VT

and methanol

ligands

reference.

by the sideband

for almost

the JES

on the JEOL PS 100 spectrometer.

recorded

TMS 88s used

used:

used

shifts

range

samples

by standard

as diamagnetic for

procedures.

references

The free

to calculate

the

the complexes.

l?BSULTS AND DISCuSSIC3N The Heisenberg-Dirac-Van of the magnetic equation

Vleck

susceptibility

derived

in this

theory

data.

theory

for

of monomeric

impurities,

lity

affects

strongly

have

written

a computer

squares meric

method

the exchange

impurities,

iron(IIS)compounds, l8t8r and

by Hanson

196 cm 4

t%vsly

were

the formula stat8 PMR

/ref.

J, and the

Zs

some

susceptibi-

integrals,

we

by the le8St contents

of mono-

was

from taken

of 8 high-spin

of J equal

to 200

8nd (Fevanput)20*6hG13,

the fitting

procedures.

8s 2, as expected

iron(III) ion.

for

respecThe g value in

the 6A,(6S)

ground

/ref. l-13/

spectra A theory

been

of the temperature

d8V8lOp8d

/ ref.

5,6/

dependence

for a given

system, using the HDVV model. aW v= H

magnetic

calculates

The values

??/.

@esalput)20~6HCZ13

obtained 0)

integral,

H = JS,S,

always

of exchsnge

which

to account

susceptibility

Such a method, which is very useful for binuclear was used in our previous paper /ref. 10/ 8nd

8t 81.

for

high

used

. The

contain

their

the calculation programme

9/

the Hamiltonian

Where S varies from IS,S2\ to S,+S2. Since the binuclear iron(III)complexes admixture

is usually

/ ref.

g$h 6g&kT

.

of the

proton

contact

@+I)

has

in the binuclear

The calculated expression >-A(S)C2S+1)(S+1)Sexp(-JS(S+'1)/2~) >

shift

for&H/E is <2)

exp(-JScT';+l)K2kT))

192

,

70

I

40 SHIFT

1

,

(0

(ppm)

0

Pig, 2, Left: The low-field pax& of the B&R spectrum for (F8Salput)20, Right: The temperature dependencies of the contact shifts for the gfotons of benzene ring 4HGI>, GHCB), s(C); The solid lines were calculated for the parameters given in Tab18

210

250

?.

300 T(K)

gig. 3. The temperature

dependencies of the contact shifts the protons from the -CHkI?- gPOUp /left/ and from =%C+ fright/ in (Fesalput&O. for

There are opposfng Vf9Ws on the theoretical interpretation of the contact shift data, / ref,l/ Blrurrag /ref. 1,5/, Boyd and Smith /ref. %!/ use on8 A value to describe the Bystem, While La Mar / ref. 61 and Wicholas /ref. 13/ use different A&> values for each spin state, The fitting prOcedur8s allOW to d8t8mLin8 the J and A(S) values using eq. 2. The J values obtained in this way by many authors are sometimes 35 % bigger than those calculat8d from the magnetic SUSC8ptibiliiXy data of solids. /ref., 5,12/

193

This fact was thought to be due to the straightening of the F&Fe bridge in solution../ref. I/ However, our current works do elimiWe have found, that the change of the FeOFe nate this possibilitg. angle from 144' for
=ELCH2- groups

The protons of the methylens group bound to the nitrogen give two lines, their isotropic shifts are equal to 35.9 and 15.2 ppm, respectively.

194

The hyperfine coupling constants for (Fesalput) 0 calculated for both models - with one A value and with differe g t A for various spin states", assuming J = 200 cm-1 L&CHA.lO+Hz -Al A2 A3

11.18

4;.Sf 3145

=NCHo-_; 5.91 5.92 5.97 5.43

2.14 2.11 2.02 3.54

4H 0.86 oo:z1.03

5H -0.82 -0.76 -0.89 -1.00

-6H 0.40 0.36 0.47 0.46

x In this case the summation in eq.2 ran over the spin states with S = O,l,2,3 since the states with S = 4 and 5 contribute nothing to the contact shifts. Considerably smaller splitting of methylene group8 is observed for /22.0 and 17.0 ppm, respectively/ /this paper and ref.6/ (Fesalen]20 This splitting may be due to the angular dependence of the contact shift for a system of6 bandings, like in the nickel complexes /ref. 16,17/ The similar dependence was found in aromatic systems. /ref. 18,19/. The coupling constant A depends on the angle built by the planes FeNC and NCE /ref. 16/ : A = B, + Bcos'@ 01 B. is usually equal to zero. /ref.16/ Us&ng eq.3 the values for both protons in =NCH2- group in@'esalput>20 were calculated: @l=53.30 and.@2=@l+1200= 173.3o, and B =5.98.105Hx. The coupling constants for methylene protons were then calculated for (Fesalen)20 for the values found from the published X - ray data: /ref.31 A axial =0.71=105 Rz,@=69.9', Aequatorial =5.68.105 Hz,@=l92.9'. The paramagnetic shifts calculated for above A and J =I90 cm-'/ref.2/ are in discrepancy with the experimental data /ref. 6/. However, the average arithmetic value of the calculated shifts /20.6 ppm/ is close to that measured /lg.5 ppm/ The same we have found for the monomeric complex (FerCMesale&!H CCC /ref. 6/. Such results 3 suggest the equilibrium between two possible conformations of the. five-membered chelate ring - K and K'in Pesalen complexes. The averaging of the methylene group signals in (Fesalen)20 could be also explained in terns of assumption that the chelate ring in solution was more planar than in the solid phase. The seven-membered chelate ring in @esalput)20, which is made additionally more rigid by the six-membered rings FeNCCCO can not, doubtless become planar in solution, and most probably it is unable to change its conformation.

195

1. II, S. Murray, Coord.- Chem. Rev. 12 /1974/ 1 2. J, Lewis, F. E. Mabds, A. Richards, J. Chem. Sot. /1967/1014 .F. E. i%abbs, V. Ni McBachlan 3. P. Coggon, A. T. &&hail J, Chem. Sot. A /1971/ 1614 4. A. Van den Bergen, K.S. Murray, 3. 0. West, Aust. J. mem 21/?9@31 151'1 5. P.D.W. Bosd, K.S. Murray, 3. Chem. Sec. A /197-J/ 2711 6. G. La Mar, G.R. Eaton, R.H. Holm, F.A. Walker J. Am. Chem. Sot. 95 /1973/ 63 7. P. Naksgama, Shun~ichiro Qoi, E. Kuroga, Bull. Chem. SUC. Japan 49/I/ /1976/ '151 8. Y. Nakayama, K. Matsumoto, Shun'ichiro Oof, H. KuroYa, J, Chem. Sot. Chem. Commun. /1973/ 170 9. J. S. Griffith, Struct. Bonding /Berlin/ 10 /1972/ 87 10. B. Jeaozska-Trzebiatoaska, A. OBarowski, H. Kozkowski, T. Cuk%erda, 5. Hanuza, J. Inorg. Rucl, Chem. 38 /1976/ 1447 11. M. V. Hanson, W. E. Marsh, G. 0, Carlisle, Inorg. Rucl. Chem. setters, 13 /1977/ 277 12, P. D, W. Bogd, T. D. Smith, Inorg. Chem. 10 /I9711 2041 13. M. Wicholas, R. kIustacich, D. Jagne, 5. Am. Chem. Sot. 94 /1972/ 4518 14. J. E. Davies, B.M. Gatehouse, Cryst. Struct. Commun. 1 /1972/ 115 13. To be published 16. J. E, S-arneski, Ch. B. Relllez, Inorg. Chem. 13 /1974/ 977 17. I,. Pratt, 3.13, Smith, Trams. Faraday Sot. 65 119691 915 18. R. Knorr, A. Weis, J. Chem. Sot., Chem. Commun. 11977/ 173 19. R, Knorrc A. WeZs, H. Polzer, E, Bischfer, 5. Am. Chem, Sot. 97 /1975/ 643