Studies of adduct formation between diisopropyl methylphosphonate and various metal salts and complexes

J inorg nucl. ('hem, Vol. 42, pp. 675-682 © Pergamon Press Lld, 1980 Printed in Great Britain

0022[1902[8010501~67s?$020(11(1

STUDIES OF ADDUCT FORMATION BETWEEN DHSOPROPYL METHYLPHOSPHONATE AND VARIOUS METAL SALTS AND COMPLEXES NICHOLAS M. KARAYANNIS Amoco Chemicals Corporation, Naperville. IL 60540. U.S.A. and

LOUIS L. PYTLEWSKI and CLIFFORD OWENS Department of Chemistry. Rutgers University. Camden, NJ 08102, U.S.A. ~Received 17 July 1979: received for publication 10 September 19791

Abstract--The formation of adducts of diisopropyl methylphosphonate (LJ with a variety of metal salts and complexes was studied by means of conductimetric titrations and gas-solid interactions. Conductimetric titration data indicate that L forms I:1 and 2:1 adducts with SnCI4, TiCI4, FeCI3 and MnCI2; in addition, the possibility of existence of 1.5:1, 3:1 and 6:1 adducts with FeEl3 and a 4:1 adduct with MnCI, was suggested by the titration curves. Studies of the interaction of L vapor with solid metal salts and complexes, under a vacuum of 5 × 10 s mm Hg, suggest that adducts involving the following L to metal molar ratios are the most stable and, therefore, easiest to isolate species: 2:1 with MCI2(M--Co,Ni, Cu, Zn) and NiX2 (X=Br, I, NO3); 4:1 with Ni(CIO4)2;and 1:1 with Ni(II) acetylacetonate and nickelocene. Most of these adducts involve normal donor-acceptor interactions between L and metal ion, as shown by sizeable vp_-oshifts to lower wavenumbers; however, the nickelocene adduct seems to involve a weak interaction of L and Ni2+(Aup_oof only 3 cm-'). NiF_,and Ni(CH3COOhdid not uptake any L during gas-solid interaction, while IrCI3uptook only 0.15 tool L/tool, forming an authentic adduct on its surface. Finally, a number of new solid 2:1 adducts of L with metal salts were synthesized and characterized as follows: [MnX,L2] (X=CI, 1), tetrahedral; [VCI3L2] and [VOCI2L2], both trigonal hipyramidal; [M(O2NO).d_,_,](M=Mn, Cd) and [Sn(OzSO2hLz], low-symmetry hexacoordinated; [FeCIEL4][FeCI4],ionic with a hexacoordinated complex cation combined with the tetrahedral [FeCI4] .

INTRODUCTION

Neutral phosphonate and phosphate alkylester adducts with metal salts are generally not easy to isolate in crystalline form [1]. One of the reasons for this is that, at the temperatures favoring the precipitation of the adduct, reactions of the type n(RObR'P:O + MX,

,[(RO)R'POO]. M + nRX (1)

(where R=alkyl: R'=alkyl or alkoxy; X=anionic group) become facile [1-5]. On the other hand, these esters are substantially weaker donors than triorganophosphine oxides, which readily form adducts with all kinds of metal salts[l,6], and, consequently, enter in severe competition with other ligands, such as anionic groups with coordinating ability and neutral ligands (water, polar organic solvents), for the first coordination sphere of the central metal ion [7, 8]. As a result of the preceding trends, relatively few adducts of these ligands with metal salts have been isolated in solid form and characterized. These include: (i) Adducts with metal salts involving anions with little tendency to coordinate, such as the perchlorate group; complexes of this type are relatively easy to isolate [9, 10]. (ii) Adducts with certain metal halides, e.g. SnX2L2, MX4L2 (M=Ti, Zr, Sn; X=CI, Br, I) [11-13], VCI3L2 [ 1 4 ] , Fe~CI6L3[11], [MgL4(OHzh][MCI4] (M = Mn, Co) [8]. In most other cases, semi-solid or viscous liquid products (e.g. CoCIzL~[15]), having the tendency to decompose by

reactions of type (1), are obtained [1--4,8, 15]. (iii) Adducts with lanthanide (III), Ce(IV), Th(IV)[16, 17], UO~+ [8, 18] and Ag(I)[19] nitrates, UO~ + sulfate[20} and thiocyanate [21], Mg(II) and Ni(II) thiocyanates [8] and Ni(CN)2 [22]. In these laboratories, especial interest has attached to the study and, whenever possible,isolation of adducts of diisopropyl methylphosphonate (dimp; I iC~H70)2CH3P=O) with metal compounds [810,13,22,23]. The present paper describes studies of the stoichiometries of a wide variety of dimp adducts, that could not be obtained in a sufficiently pure state for characterization, as well as the isolation and characterization of a number of new solid adducts of metal salts with dimp. EXPERIMENTAL Preparation of new adducts: Method A: VCl~(dimp)2 and

FeC%(dimp)2. l mmol metal chloride was dissolved in 20 ml of a 5: l(v/v) mixture of p-dioxane and ethanol. Then, 3 mmol dimp were added, and the resulting mixture was stirred at 70°C for 2 hr and then allowed to stand at 0°C. Crystals of VCI3(dimp)2(pink1 or FeCl~(dimp)2(yellow; m.p. 129-131°C) were precipitated after 1-2 days; they were separated by filtration, washed with 10 ml ligroin and stored in vacuo over anhydrous CaSO4. For the V ~+ complex, which is unstable in the atmoshpere, it is important that the preparation and all subsequent handling are done in dry N2 atmosphere (dry-box). The Fe3+ complex and the rest of the adducts synthesized during this work can be prepared in the atmosphere; FeC13(dimp)2is stable in the air Method B: VOCI2(dimph. l mmol VOCI2 was dissolved in 675

676

N.M. KARAYANNIS et al.

20 ml ethanol and 20 ml triethyl orthoformate(teof) were added to the resulting solution, which was heated to 50°C for I hr and then mixed with 2mmol dimp. The light blue-green complex was precipitated after !-2 hr of stirring at 50°C. The complex was filtered off, washed and stored as described above. Mechod C: M(NO3h(dimph (M=Mn, Cd). 1 mmol metal nitrate was treated with 30 ml teof at 50"C for I hr, under stirring. Then, 3 mmol dimp were added and the resulting mixture was stirred at 500C for 2 hr. Mn(NO3h(dimph was gradually precipitated in the form of an off-white powder; recrystallization from teof produced white, non-fluorescent, flaky crystals, which were washed with CH2CI: on the filter. Cd(NO3h(dimp)2 was precipitated when the reaction mixture was cooled to &C, in the form of shiny white crystals, which were washed with CCI4 on the filter. Both complexes are stable in the air and were stored as described above. MnI2(dimph. By following the details of method C, MnI2 yielded a copious bright yellow, fluorescent precipitate of MnI2(dimph (m.p. 46--48°C), immediately upon addition of dimp to the teof solution of MnI2. This complex is very deliquescent in the atmosphere and tends to collapse to a viscous liquid even under N2 or upon storage in oacuo at ambient temperature. It was stored at if'C, under N2, after being rapidly washed with teof on the filter. Method D: MnCI2(dimph. This complex was prepared by dissolving I mmol MnCI2 and 2 mmol dimp in tetrahydrofuran(thf), stirring for I-2 hr, and allowing the mixture to stand at ambient temperature for several days. The green solution eventually afforded very pale green, fluorescent crystals of MnClz(dimph in small yield. This product is very deliquescent in the atmosphere; it was quickly washed with ligroin and stored in vacuo as above. Method E: MnC12(dimp)2 and Sn(SO4)2(dimp)2. The preceding complex and Sn(SO4h(dimph were obtained in good yields by mixing dimp and metal salt at a 2:1 molar ratio in CS2(for MnCI2) or CCh (for Sn(SO4)2), and introducing the resulting mixture in the already described H-shaped recrystallization glass cell, which functions by means of a temperature gradient and was previously used for the growth of single crystals of SnX2(dimp)2 (X--CI, Br) and SnX4(dimp)2 (X---CI, Br, I) adducts [9, 13,231. Large crystals of MnClz(dimph were deposited on the warm arm of the cell within one day, by using a temperature gradient of 8°, while white single crystals of Sn(SO4)2(dimph were obtained after six weeks, at a temperature gradient of 24°. Analytical data for the above new adducts are given in Table 1. Table 2 shows results of unsuccessful attempts to precipitate or grow crystals of dimp adducts with various other metal salts.

Interactions of many 3d metal halides with dimp, under the conditions of methods A through E resulted in products consisting of mixtures of the true adduct and complexes involving partial depropylation of dimp and dehalogenation of the metal salt. This was not unexpected, since reactions of type (1) are especially facile when neutral phosphoryl esters react with metal halides [1-4, 8, 23, 24]. Actually, even VCl3(dimp)2, FeCIz(dimph [251, VOCl2(dimph and MnX:(dimph (X=CI, I) [261 can not be obtained in pure form, unless the temperatures specified in preparative methods A, B or D are never exceeded during their syntheses. The fact that some metal nitrates give also reactions of type (1) with dimp was not surprising, since AgNO3 reportedly reacts with triethyl thiophosphate to form [(C2H~OhPOS]Ag and ethyl nitrate [27]. Studies o[ adduct [ormation: Freezing point studies. Freezing point determinations and utilization of liquidus curves have been successfully employed on binary ligand-metal salt mixtures for ascertaining the existence and stoichiometries of adducts of AsCI3, SbC13, SbCI5 and SnCI4 with organophosphoryl ligands [28,29]. Similar studies of adduct formation between dimp and FeCI2, FeCI3, ZnCI2, ZnBr2 (at 1 : 1, 2:1 and 3: I molar ratios) and SnCh (at I:1 and 2:1 molar ratios) were attempted. However, the cooling-warming curves obtained over the range from ambient down to liquid nitrogen temperature showed a steady decrease or increase in temperature, without any indication of equilibrium change, in all cases investigated. Moreover, the formation of glassy solids upon cooling prevented the construction of phase diagrams and subsequent stoichiometry determinations. Conductimetric titrations. Certain metal chlorides (SnCI4, TiCI4, FeCI3, MnCI2) and their interaction products with dimp are soluble in polar solvents with weak donor ability (e.g. nitrobenzerie and thf); whereas other metal halides, such as FeCI2, NiBr2, CuCI~ and ZnCI2, are either insoluble or produce adducts with dimp that are insoluble in such solvents. For the former series of metal chlorides, conductimetric titrations with dimp were performed on a Wheatstone-bridge type circuit. 0.5-2.5 g metal salt were dissolved in 100 ml of nitrobenzene or thf in a tall-form beaker. A 10 ml micro-buret, calibrated in 0.005 ml increments, was used to add pure dimp to the salt solution, which was magnetically stirred throughout the titration. Suitable increments of dimp were added, and the resistance (R) was measured at 25°C, consistently one minute after each addition. Table 3 shows specific conductance (l/R) data for these titrations. Specific conductance maxima or minima were taken as indicative of the stoichiometries and the nature of the possible adducts of each of

Table 1. Analytical data for adducts of dimp with metal salts. Analysis, Found (Calc.)%

Adduct

C

~

P

~tal

Halozen

~ or S

¥C13(dimp) 2

32.60 (32.48)

6.29 (6.62)

12.33 (11.97)

10.25 20.78 (9.84) (20.55)

VOC12(dimp) 2

34.12 (33-75)

7.17 (6.88)

12.16 (12.43)

10.47 13.75 (10.22) (14.23)

l~C12(dimp) 2

34.83 (34.58)

6.72 (7.05)

13.27 (12.76)

11.64 14.69 (11.30) (14.58)

MnI2(dimp) 2

24.68 (25.13)

5.36 (5.12)

9.38 (9.26)

8.03 38.51 (8.21) (37.93)

I~(I~03)2(dimp)2

30.80 (31.18)

6.74 (6.35)

11.51 (11.49)

10.55 (10.19)

FeCl3(dimp) 2

31.76 (32.18)

6.23 (6.56)

11.47 (11.85)

10.40 20.32 (10.69) (20.35)

Cd(NO3)2(dimp) 2

28.37 (28.18)

6.09 (5.74)

9.94 (10.38)

18.65 (18.83)

4.50 (4.69)

Sn(SO4)2(dlmp) 2

24.77 (25.05)

4.84 (5.11)

8.88 (9.23)

17.91 (17.68)

9.13 (9.55)

5.14 (5.19)

Studies of adduct formation

67 7

Table 2. Unsuccessful attempts at the preparation of dimp-metal salt adducts Metal Salt (dimo/M molar ratio)

Preparative Method (a)

CrC13(3:1),MC12 (M= Fe,Co,Ni,Zn) (2:1)

Tacky s o l i d p r e c i p i t a t e s , a n a l y z i n g a s m i x t u r e s of t h e a d d u c t and p r o -

A

ducts of reactions of type (1). A,C,D

ii

,i

II

C,D

II

,I

.

¢ix 4 (X=F,Z) (2:1) (b)

D

Tt

,I

H

H(N03) 2 (M=Co,NL,Cu,

C

I S o l i d ~ r e c i p i t a t e s , a n a l y z i n g as mixtures of the ~dducts with products

FeCI3,~CI 2 (1:1)

E

No crystals grom~ after 6 months in the H-shspcd tube.

FeC13,MC12 (L=Fe,Ni, Cu,Zn),NiBr 2 (2:1)

E

ft

'l

fl

KnCl 2 (4:1)

E

II

,f

M

HEr 2 (H=Mn,Co,Ni)

(2:1)

XI 2 (H-Co,Ni) (2:1)

Zn) (2:I)

of reaction~

of type (1).

(a) See experimental section. (b) TiCl4(dimp) 2 is easily obtained and was previously characterized;

TiBr4(dimp) 2 is also easy to obtain,but it is

very unstable and was not characterized033. Table3. Conductimetrictitrationsof metalchloridesolutions with dimp 8.55 mmol SnCl 4 9.1 mmol TiCl 4 3.5 mmol FeCI 3 in 100 rnl C~H}NO 2 in 100 ml C~HsNC$ in 100 ml C~H~NO 2

6.4 mmol HnCI 2 in 100 ml thf

dimn/Sn a) 0.00 O.16 0.32 0.49 0.65 O.81 0.97 1.1a 1.30 1.46 1.62 1.95 2.60 3.24 3.8~

dimo/Mn a) ]04 L b) 9.00 O.2C 0.43 c.91

lO4L b) o.14 ~].38 ~.61 o.87 1.10 ! .31 1.48 1.55 ! .44 ~.05 ~ .56 i1.34 0.34 @.33 ~ .33

dimo/Ti a) 0.00 O.16 0.32 0.48 0.64 0.80 0.96 1.12 1.28 1.44 1.60 1.76 1.92 2.08 2.24 2.56 2.88 3.20 3.52 3.84 4.48 5,12 5.76 6.40

I04L b) 0.51 0.88 1.20 1.43 1.54 1.57 1.55 1.41 1.35 1.20 0.85 0.58 0.42 0.50 0.65 0.89 1.O8 1.23

dimo/Fe a) 104L b) 0.00 3.11 O.33 3.52! 0.66 2.79 1.00 1.9(; 1.33 2.55 I .50 2.85 1.66 3.02 2.00 3.22 2.33 3.30 2.67 3.35 3.00 3.37 3.33 3.36 4.16 3.36 5.02 3.45 5.83 3.48 6.66 3.50 8.33 3.4~ 9.99 3.45

0.87 1.o6

1.75 1 np

1 .Z0

1.92

1.73

2.17

i .89 1.67

2.60 3.47 4.34 ~.20

1.54 1.25 1.05 o.91

6.~0

0.81

8.67

O.77

1.34 1.43 1.63 1.74 1.86 1.93

a) Holar ratios, b) Conductivities inTl -I. these metal salts with dimp (conductance minima corresponding to the formation of stable adducts [30], and conductance maxima to that of adducts with a tendency to self-dissociate [31]). Gas-solid interaction studies. IR studies of the interaction products of dimp vapors with metal salts have revealed adduct

formation, suggested by shifts of the ~'p--o vibrational mode (occurring at 1241 cm ' in free dimp) to lower wavenumbers [3211, in several cases [8, 33, 34]. During this work, the following technique was used, in order to determine the highest dimp to metal ratio for stable adducts of this ligand with various Ni 2+ salts and

678

N.M. KARAYANNIS et al.

complexes, as well as a few additional metal salts: An amount of solid metal salt or complex is accurately weighed on the pan of a Cahn RG electrobalance and then allowed to interact with dimp vapors, in a vacuum system, under a vacuum of 5 x 10-5 mm Hg. This interaction is allowed to continue for as long as weight increases, indicative of dimp uptake, are observed. In most cases, the product on the pan is a viscous liquid, presumably

consisting of a solution or suspension of an authentic adduct in excess dimp. Subsequently, excess dimp is pumped off, until no appreciable change in weight of the pan contents is observed during five successive weighings, obtained at 1-2 hr intervals. Table 4 shows the results of our studies (final product refers to the stoichiometry of the pan contents, at the point when no more dimp loss could be brought about by continuation of pumping-off

Table 4. Gas-solid interactions between dimp vapor and solid metal salts or complexes (MXD

Final Product dimo/M ilolar Ratio a) Color

~'~

~p=o,cm-1 b)

~iC12

2:1

Deep blue-purple 1218sh,1190s

I~iZr2

2:1

Deep blue

1220sh,1197s

i~ii2

2:1

Dark red-black

1220sh,1200s

Ni(Cl04) 2

4:1

Yellow

1197s

i~i(i~03)2

2:1

Green

1202s

Ni(acac)2C)

1:1

Olive green

1229s

c

Ni(~-Cs}i5) 2

1:1

Reddish brown

1238s

d)

Light green

d)

a]i(CH3COO) 2

d)

Light green

d)

CoC12

2:1

Dark blue

I196s

CuC12

2:1

Red

I167s

ZnC12

2:1

White

1171s

IrCl~

0.15:1

Greenish black

1145mw

NiF 2

a) Approximate ratios, b) ~P=O occurs at 1241 cm -I in free dimp. c) acac = acetylacetonato ligand, d) Iio weight increases occurred during the progress of dimp vapor interaction with NiF 2 or Ni 2+ acetate; the IR spectra of the final products of these interactions were devoid of any bands attributable to ~P=O" Table 5. Pertinent Infrared data (cm-'), magnetic susceptibilities (300°K) and molar conductivities (10-3M nitromethane solutions: 25°C) of the new dimp adducts with metal salts

................. IR data ............................ ~'l~'-o(dimp)~M-Xa) ~N---Q 3 or V$0@ M°desb)

1 0 ~ ° r , c g su ~eff,~ B AMC)

CRm~lex

~=Q

VC13(dimp) 2

1165s,b 385s

406vs

3313

VOC12(dimP)2 ~)

1173s,b 413s

431vs

2.83

4

1221

1.72

7 3

MnC12(dimp) 2

1170vs

404ms

325m, 313 m

14,911

6.01

Mni2(dimp) 2

1165 a

~97ms

177vs e)

13,996

5.82

5

276m,sh 1763w,1722w;1445vs,1303vs; 1016m;739m,703mw;815 m

14,335

5.89

36

15,459

6.12

48 g)

~n(~lO3)2(dimp) 2

1183vs

304ms

FeC13(dimp) 2

1164s,b 331m,b

379vvs, 292m f)

Cd(NO3)2(dii~ip) ~

1186s

297m,b

241w,sh 1775w,1729w;1453vs,1298vs; 1020s;744m,707mw;820m

Diamagnetic

41

Sn(SO4)2(dimp) 2

1152va

328m

2631n

Diamagnetic

34

1244vs.1137vs,sh.1028vs; 987ms;643s,619s,606s;469m

a) X:CI,I,O2NO or 02S(]2. b) 9~:03! (91+V4);V3;~ 1;~4;~2,respectively; 9S04: V3;~ I;~4;~2 ,respectively' ~) In D-Icm2mol -I. d)~V:O occurs at 992 cm-1., e) Determined by using a Perkin-Elmer 181 spectro1~hotometcr. f)93(FeC14 ) at 379; ~Fe-C1 for the [FeC12(dimp)~ + cation at 292 cm -I [35,37,71,72~. g) i]~lculated or~ t!e basis of the formulation of the complex as [FeC12(dimP)4q

FeC1

•

Studies of adduct formation at 5 × I0 ~mm Hg,~in this direction. The final products on the pan were generally solids. Spectral, magnetic and electrolytic conductance studies. IR spectra (4000-500cm-% of the new solid adducts synthesized (Table 5) and of the final products of the gas-solid interaction studies (Table 4) were obtained on Nujol mulls between KRS-5 (TI(Br, I)) windows, in conjunction with a Perkin-EImer 621 spectrophotometer. IR spectra at 700-200cm-~ were also obtained for the new solid complexes of Table I (Nujol mulls between polyethylene windows) (Table 5); the spectra of these new adducts are generally devoid of IR bands attributable to the presence of water. Solid-state electronic spectra of the new 3d metal complexes were obtained on Nujol mulls, as described elsewhere [351. The vanadium complexes show the following d-d transition band maxima, nm: VCI3(dimp)2:492s, 658sh, 730sh; VOCIz(dimp)2: < 350vvs,424s, 522s, 681 sh. In the spectrum of the MnINO3)~ adduct, the d-d transition bands are completely masked by very strong UV ligand and charge-transfer absorption; on the other hand, the MnC12, Mnl2 and FeCI3 adducts exhibit two or three distinct d-d transition maxima, as follows (nm): MnCl~,(dimp)~: 447w, 469sh; Mnl2(dimp)2: 486w, 502sh, 525w; FeCI3(dimp)2:375ms, 450vw, b, 490vw, b. Magnetic susceptibility (300°K) and molar conductivity (10-3M nitromethane solutions at 25°C) determinations (Table 5) were made by methods described elsewhere [91. DISCUSSION Conductimetric titrations

Among the four metal chlorides studied, only the titration of SnC14 provided unambiguous evidence favoring the exclusive formation of 1:1 and 2:1 dimp adducts with this salt (corresponding to a conductance maximum and a minimum, respectively) (Table 3). The 2:1 adduct has been already isolated and studied[13,23], but we have been unable to obtain the 1:1 analog in the solid state. SnCI4L2 complexes are also well characterized for L--(C6Hs)sP=O or ClsP=O [29], while SnCI4(CIsP=O) has been claimed to exist [31], but was never isolated. In the case of TiCI4, the conductimetric titration data also favor the formation of 1:1 and 2:1 adducts. Nevertheless, as the molar ratio of dimp to TiCI4 increased from 2 to ca. 6.5, a continuous increase in conductance was observed. This behavior is most probably due to self-dissociation of the 2:1 adduct and formation of ionic species, such as [TiCl2(dimp)4][TiC16] [29, 36]. Regarding solid adducts of dimp with TiCI4, we have previously isolated and characterized TiCI4(dimp)2 [13], but were again unable to isolate the 1:1 adduct; both TiCL(CI3P=O)2 and TiCI4(CI3P=O) have been obtained in crystalline form and characterized [29]. The titration curve for FeCI3 shows a conductance minimum at the 1:1 dimp to Fe ratio; in the region between I : I and 6.5 : I, the conductance increased continuously: inflection points appeared at the 1.5:1 and 2:1 ratios, and distinct maxima at the 3:1 and 6:1 ratios. It is rather well established that organophosphoryl ligands or C13P=O form 1 : 1, 1.5 : 1 and 2:1 adducts with FeCI3 [37--40]; the 2: I complexes are ionic, of the [FeC12L4][FeCI4] type [37]. FeC13 solutions in CI~P=O or neutral phosphoryl esters undergo autocomplex formation, yielding, in most cases, the tetrahedral [FeCI4] anion and mixed (chloro, phosphoryl) ligand cationic ferric complexes[39,41]; however, in phosphoryl esters with low dielectric constant, such as tri-n-butyl phosphate, the ionic species formed is of the [FeL6]C13 type [42]. The preceding discussion suggests that the pronounced tendency of phosphoryl ligandFeC13 adducts a.t 2:1 or higher molar ratios to selfdissociate makes somewhat questionable our data concerning the possibility of existence of 3:1 and 6:1

67~

adducts of dimp with this salt. Finally, with MnC12, a clearcut conductance maximum was observed at the 1 :]1 dimp to Mn z+ ratio; increases in the amount of titrant beyond this ratio and up to 9:1 dimp to Mn 2+ resulted in very small incremental conductance decreases and an extremely broad titration curve, showing inflection points at the 2:1 and 4:1 molar ratios. Mn(II) halides easily form solid pseudotetrahedral neutral 2:1 [MnL2X~_] complexes with triphenylphosphine oxide(tppo), while 4:1 [MnL4]I: complexes with tppo and triphenylarsine oxide have been also isolated [43]. The formation of [MnCI4] 2 anions in MnCI2 solutions in neutral phosphoryl alkylesters seems to be favored only in the presence of main group metal chlorides, such as LiCI [44] or MgCI2 [8]. The isolation of solid 2:1 adducts of dimp with FeCI3 and MnCI2 during our synthetic experiments confirmed the significance of the inflection points at this ratio in the conductimetric titration curves of these two salts. Gas-solid interaction studies

The data of Table 4 clearly indicate that 2: 1 adducts of dimp with 3d metal chlorides, bromides or iodides are the most easy to obtain. The colors of the COCI2 and NiX2 (X=C1, Br, I) gas-solid interaction products wit]h dimp are suggestive of pseudotetrahedral configurations of the [MX2(dimp)2] type, as is also the case with the corresponding tppo adducts [32, 45]. 2 : 1 phosphine oxide complexes with CuCI2 usually exist in two isomeric pseudotetrahedral forms, viz. a yellow and an orange or red isomer [46--48]. These two forms differ in the degree of distortion of the coordination tetrahedron [48]. With tppo, the yellow isomer is easily precipitated by wet chemical synthetic methods[46,48], while the orange species is obtained by dehydration of CuCI2 (tppo)2 • 2H20 [48]. It is interesting that during gas-solid interaction between dimp and CuCI2, the formation of the red isomer is favored. [ZnCI2(dimp)2] is also presumably tetrahedral[49]. A 2:1 complex is formed between dimp and Ni(NO3)z; phosphine oxides generally form 2:1 adducts with the nitrates of dipositive 3d metal ions [50,51]. Ni(CIO4)2 yielded the previously isolated and characterized [Ni(dimp)4(OC103)](C104) [9,351, whilst Ni(II) acetylacetonate and nickelocene formed 1 : 1 adducts. Trimeric [Ni(acac)2]3 has the tendency to be converted to the monomer in the presence of and form adducts with Lewis bases; for instance, with pyridine(py) the species [Ni(acac)2]2.py and Ni(acac)2.2py have been isolated [52], while with substituted pyridines IZpy) 1:1 adducts of the Ni(acac)2(Z-py) type are formed [53]. On the other hand, no adducts of nickelocene or other metallocenes with neutral organophosphoryl ligands seem to be known.; cationic complexes of the type [(r/5-CsHs)Co((OR)2P?O)((OR)~POH)~]% involving coordination of the phosphonato ligands through phosphorus, and further reacting with M 2~ ions (M=Mg, Ca, Sr, Ba, Pb, Mn, Fe, Co, Ni, Cu, Zn, Cd, Hg) to yield trinuclear sandwich complexes of the 1('0~CsHs)Co((OR)zP--O)3M(O=-P(OR)2)3Co(r/5-C,H~)] type, in which both the phosphorus and oxygen atoms of the P=O group are coordinated (each to a different metal ion, i.e. -Co-(P=O)3-M-(O=-P)~-Co), were reported recently [54]. However, these compounds exhibit sizeable ~'P-o shifts to lower wavenumbers (Aup o of 65:185cm-')[54], whereas the product of nickelocene reported herein shows a very small negative up_c, frequency shift (3cm %. In the IR spectrum of this

680

N. M. KARAYANNISet al.

product, bands corresponding to the cyclopentadienyl ligand [54] and the rest of the dimp bands remain virtually unchanged, relative to their positions in the spectra of free nickelocene and dimp. Adduct formation by weak dimp-Ni 2÷ donor-acceptor interaction is, nevertheless, suggested by the small negative ~,P--o frequency shift (high resolution IR spectra established that this shift is authentic) and by the fact that the solid residue on the pan of the Cahn balance is reddish brown, while nickelocene is dark green. The rest of the adducts formed by gas-solid interaction show sizeable ~'r,=oshifts to lower wavenumbers, ranging from 12 cm-~ for Ni(acac)2 to 96 cm-' for IrCl3 and indicative of normal P=O ligandmetal ion donor-acceptor interaction [32]. Regarding the polyanion vibrational modes in the Ni(NO3)2 and Ni(CIO4): adducts, the former compound shows evidence favoring the presence of exclusively coordinated nitrato tigands (as is also the case with the Mn2÷ and Cd2+ nitrate analogs: see below), while [Ni(dimp)4(OCIO3)](ClO,d shows bands attributable to both ionic CIO4 and coordinated -OCIO3 ligands [35]. Finally, in a number of cases investigated, dimp uptake was either very small (IrCl3) or did not occur at all (NiF2, Ni(CH3COO)2). These results imply that dimp vapor does not have any disruptive effect on the polymeric crystal lattices of these salts. With IrCl3, a true adduct apparently covers the surface of the salt, and dues not allow any further penetration of the ligand, whilst with Ni2÷ fluoride or acetate donor-acceptor interactions do not occur even on the surface of the solid. Characterization of the new metal complexes The IR spectra of the new complexes synthesized show negative ~,o=ofrequency shifts (Table 5), similar to those observed with all previously reported dimp adducts with metal salts (coordination of dimp through the P=O oxygen) [8, 9, 13, 22]. VOCl2(dimp)2 shows the ~,v--o mode at 992cm-', which is suggestive of a pentacoordinated structure for this complex [26, 55]. The IR evidence for the two M(NO3)2 (M=Mn, Cd) complexes favors the exclusive presence of coordinated nitrato ligands: The ~,3and t,4 fundamental vibrational modes are each split into two components, occurring at wavenumbers typical for compounds with coordinated nitrate, while no maxima are observed in the z,3(1380-1350cm -I) and u4(ca. 720 cm-t) regions of ionic NO3- [56:-59]. Single bands are also observed in the ~,2and, the IR-inactive for ionic NO3, ]/i regions [56-59]. Distinction between uni- and bi-dentate coordinated nitrato ligands (both of C2v local site symmetry) can not be made on the basis of the location of the fundamental vibrations of the NO3 group, but the extent of the separation of the two (~,1+ ~'4) combination modes can be used for such a distinction. Compounds with unidentate -ONO2 ligands show relatively small separation (6-26cm-') of these combination bands, whereas complexes with bidentate =O2NO ligands show a larger separation (20--70cm -I) [56-59]. Since the spectra of the new metal nitrate complexes are characterized by (z,l + z,4) separations of over 40 cm-~ (Table 5), it can be concluded that they contain exclusively bidentate chelating nitrato ligands, being hexacoordinated of the [M(O2NO)2(dimph] type (M=Mn, Cd). The two SO$- groups in Sn(SO4)2(dimp)2 appear to be also bidentate chelating: Thus, both v3 and u4(SO4) are triply split (1224, 1137, 1028 and 643,619, 606cm -~, respectively), while both ~,~ (987 cm-~) and z,2 (469 cm-~) are IR-active; moreover, the location of the split u3

bands favors the presence of chelating rather than bridgit~g --O2SO2 ligands (C2,, symmetry) [61)-62]. Tentative metal-ligand band assignments are included in Table 5. These assignments are suggestive of coordination number four (tetrahedral) for the two Mn2+ halide adducts [35, 63, 64]; five for the V3+[24,63,65] and VO2÷ [26, 63, 66, 67] chloride adducts; and six for the M2÷ (M=Mn, Cd) nitrate [35, 58, 59, 68] and Sn(SO4)2 [13, 23, 62, 69, 70] adducts. The FeCI3 complex appears to be of the [FeCI2(dimp)4][FeCl4] type, involving hexacoordinated Fe 3÷ in the complex cation and the tetrahedral tetrachloroferrate(III) anionic complex. In fact, the ~,3(FeCI4)mode appears at 379 cm-~ [37, 71, 72], whilst the vFe--o and ~'Fe~:t assignments at 331 and 292cm-', respectively, are consistent for a hexacoordinated mixed-ligand (dimp-chloro) cationic ferric complex [35, 37, 72]. The d-d transition spectra of the new Mn2÷, V3+, VO2÷ and Fe 3÷ complexes are generally in agreement with the far-IR evidence. Thus, the two tetrahedral Mn2÷ halide complexes exhibit d-d maxima at 440-530 nm, as was also the case with the pseudotetrahedral tppo analogs [43], while in the spectrum of the Mn(NO3)2 complex the d-d transition bands are completely masked by the UV ligand and charge-transfer absorption. Furthermore, both the Mn2÷ halide complexes are fluorescent under UV excitation, and their fluorescence has a pale yellow-green hue, which is typical of tetrahedral Mn2÷ [43]. On the other hand, Mn(NO3)2 (dimp)2 is not fluorescent, while if MnCl2(dimp)2 is exposed to a moist nitrogen atmosphere it is rapidly converted to the white MnCl2(dimp)2(OH2)2, which shows a pink fluorescence. Both the Mn(NO3)2 and the hydrated MnCI2 complexes are obviously not tetrahedral, and most probably are octahedral [43]. VCl3(dimp)2 is similar to its triorganophosphine oxide [73] and triethyl- or triphenylphosphate [14] analogs. The latter two complexes exhibit similar d-d transition spectra to that of the new V3÷ complex. These complexes were characterized as monomeric, pentacoordinated[14]; d-d band assignments for the new VCl3(dimp)2 complex, nm (assuming a trigonal bipyramidal configuration): 3A2--~ , 3A2(P), , 3E"(P) 492; ~3E'(F) 658; ~ E ' 7 3 0 [14,65]. As far as the d-d transition spectra of VO2÷ compounds are concerned, the V=O bond generally dominates the energy level diagram, irrespective of whether vanadium is penta- or hexa-coordinated [74]. Anyway, the d-d band spectrum of VOCl2(dimp)2 is very similar to that observed for the pentacoordinated bis-(isopropylmethylphosphonato) oxovanadium(IV) polymeric complex [26]. Finally, the d-d transition spectrum of the Fe3÷ complex (375, 450, 490nm) confirms the presence of the [FeCI4]anion [75, 76]. The magnetic moments of the new complexes are generally normal for the 3d I configuration or high-spin 3d 2 and 3d 5 compounds [77]. The molar conducitivity values of the Mn2÷, V3÷ and VO2÷ halide complexes (Table 5) are typical for non-electrolytes [78]. The metal nitrate and sulfate complexes exhibitAM values intermediate between those corresponding to 1:1 and nonelectrolytes [78]; this is presumably due to some dissociation of these compounds in solution. The AM value of 481q-Zcm2mo1-1 determined for FeCI3(dimp)2 in nitromethane is rather low for a 1:I electrolyte. A similar behavior was reported for the tppo analog, and attributed to the formation of species other than [FeCI2L4][FeCI4]in solution [37].

Studies of adduct formation

681

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The overall evidence presented for the new solid adducts synthesized is in favor of the following formulations: [MnXz(dimp)2] (X=CI, I), pseudotetrahedral [43]; [VCl4dimp)z] and [VOCl2(dimp)d, most probably trigonal bipyramidal [14, 65, 79, 80]; [M(O2NO)2(dimp)2] (M=Mn, Cd)[51] and [Sn(O2SO2)2(dimp)d, low-symmetry hexacoordinated; and [FeC12(dimp)4][FeCl4], ionic with a low-symmetry hexacoordinated complex cation and the tetrachloroferrate(II1) anionic group [37, 72, 76]. Regarding the arrangement of the dimp ligands in the 2:1 hexacoordinated new metal complexes, it should be mentioned that the crystal structure determination of [Co(O2NO)2(tmpo)d (tmpo=trimethylphosphine oxide) revealed that the two tmpo ligands occupy cis-positions, relative to one another, in the coordination octahedron [51]. However, dimp is a much more sterically hindered ligand than tmpo, since it contains the two i-C3H70 substituents on phosphorus [81], and 'H NMR studies of [SnXn(dimp)2](X=C1, Br, I; n = 2 or 4) complexes established that the two dimp ligands are trans-to each other in these adducts [13], Hence, it is considered as most likely that [M(O2NO)2(dimp)d (M=Mn, Cd) and [Sn(O~SO2)2(dimp)d are also in the trans-form, as far as the relative positions of the two dimp ligands in the coordination octahedra are concerned. Likewise, the two dimp ligands in the trigonal bipyramidal [VCl3(dimp)2] and [VOC12(dimp)2] would be expected to occupy the two apical positions in the bipyramid, with the three chloro ligands of VCI~ or the two chloro groups and the vanadyl oxygen of VOCI2 forming the equatorial plane [79,80,821. Structures of this type have been reported for 2:1 trimethylamine or tetramethylurea adducts with VCI3 [82] and VOCIz [80], as well as the 2:1 adduct of a sterically hindered organophosphoryl ligand, namely hexamethylphosphoramide, with VOC12 [79].

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