Polyhedron Vol. 3, No. 6, pp. 66&%5, 1984

Printed in Great Britain. 0277-5387/84 s3.00 + Ml

0 1984 Pergamon Pm8 Ltd.

12’Sb Mt)SSBAUER SPECTRAL AND RELATED STUDIES ON Sb(III) COMPLEXES

ANIL SAXENAt and JAGDISH P. TANDON Department of Chemistry, University of Rajasthan, Jaipur, India

THOMAS BIRCHALL* Department of Chemistry, McMaster University, Hamilton, Ontario, Canada L85 4Ml

and

BERNARD DUCOURANT and GUY MASCHERPA U.S.T.L., Montpellier, France

(Received 12 July 1983; accepted 23 September 1983)

Abstract-The bonding and structural features of antimony(II1) complexes of the type, (Pr’O)SbL and Sb2L3 are described (where L is the dianion of semicarbazone or

thiosemicarbazone). The Miissbauer spectra are typical of Sb(II1) complexes in which the non-bonding pair of electrons is stereochemically active. The thiosemicarbazone complexes show more negative isomer shifts compared to the semicarbazone complexes.

In recent years, there has been considerable interest in the chemistry of organoantimony (III) and (V) complexes with various nitrogen and sulphur do- nor ligands. ‘9’ Thiosemicarbazone and semi- carbazone can function as either bifunctional or monofunctional ligands depending on the reaction conditions. Complexes of these ligands with many different central metal ions have been extensively studied.3,4 However, little information on the bond- ing and structural properties is available for com- plexes with antimony.5 It was therefore, considered worthwhile to synthesize antimony (III) derivatives by reacting Sb(OPr’), with semicarbazones and thiosemicarbazones of the following type.

Comparative studies have been carried out on these complexes using IR, NMR and “‘Sb Moss- bauer spectroscopies.

EXPERIMENTAL

Chemicals and solvents used were dried and purified by standard methods, and moisture was excluded from the glass apparatus using CaCI, drying tubes. The ligands and antimony iso-

*Author to whom correspondence should be ad- dressed.

TPresent address: School of Molecular Sciences, University of Sussex, Brighton, BNI SQJ, England.

propoxide were prepared by standard literature methods.6*7 All the manipulations were carried out under absolutely dry conditions. The complexes were prepared by mixing antimony tris- isopropoxide and the ligands in 1: 1 and 2: 3 molar ratios. The contents were refluxed on a fraction- ating column with benzene as the solvent. The isopropanol liberated was removed azeotropically and the completion of the reaction was followed by monitoring the isopropanol produced. The excess solvent was removed and the compounds dried in vacua. The details of these reactions together with the physical properties of the products are given in Table 1.

The complexes were analyzed by literature meth- ods. Molecular weights were determined by the Rast camphor method. Infrared spectra, as Nujol mulls or in chloroform solution, were obtained using a Perkin-Elmer 577 grating spec- trophotometer. NMR spectra were recorded on a Perkin-Elmer RB 12 spectrometer in DMSO-d, using TMS as an internal standard.

Antimony- 12 1 Miissbauer spectra were recorded using an Elscint drive system in conjunction with a Promeda multichannel analyzer. The source was a nominally 0.5 mCi. Ba ‘*imSn03, purchased from New England Nuclear and was cooled, together with the sample to 4.2 K in a cryostat designed by

661

662 A. SAXENA et al.

a OH OH

0 C /” -a - 0

CzN-N=

I \NH2

I CHa CH3

Table 1.

Sl. Reactants (g) Analyses X No. molar Yield Product and M.P. PriOH in

Sb(OPri)3 Ligands Ratio % Characteristics "C Azeotrope Sb C H (colour and state) Found Found Found Found

(Calcd.) (Calcd. Calcd. Calcd.)

1. 0.78 0.50 1:l 93 WOPr’ )(C9H9N302) 26oC 0.29 36.59 37.05 4.95

C9H11N302 Yellow solid 0.31 32.52 38.73 4.30

2. 1.01 0.98 2:3 a5 “2(C9%N302)3 198 0.43 31.35 39.68 3.34

CgH11N302 Yellow solid 0.48 29.82 39.06 5.60

3. 1.63 1.14 1:l 92 Sb(OPri)(CgH9N30S) 239 0.59 35.61 38.52 4.90

C9M11%0S Orange solid 0.65 31.39 37.13 4.12

4. 1.76 1.85 2:3 a2 Sb2(CgHgR30S)3 252 0.95 30.59 37.30 3.90

C9Hll IsO5 Brick red solid 1.05 28.16 37.48 3.13

l Decomposition temperature.

B. Ducourant and manufactured by Aire Liquide. The window of the single channel analyzer was set on the escape peak of the 37 KeV y-ray. Samples contained N 15 mg Sb cm - 2 and all isomer shifts were measured with respect to InSb. The velocity range was calibrated periodically using a “Co source and a standard iron foil. About 10’ counts per folded channel were accumulated and the data were computer fitted using the program described by Ruebenbauer and Birchall* which incorporated the full transmission integral procedures which are necessary for the successful refinement of 12’Sb Miissbauer spectra.

RESULTS AND DISCUSSION The reactions of Sb(OPr’), with these bi-

functional tridentate ligands have been carried out in 1 : 1 and 2 : 3 molar ratios in refluxing benzene. The reactions proceed with the liberation of iso- propanol, which was removed azeotropically with benzene until the reaction was complete.

Sb(OPr’), + LH, +Sb(OPf)L + 2Pr’OH (2)

2Sb(OPr’), + 3LH2+Sb2L, + 6Pr’OH (3) [where L = C9H9N30S or C9H9N30J

These reactions are quite facile and are com-

pleted after refluxing for 15-25 hr. The resulting complexes are yellow to brick red coloured solids and their physical properties are recorded in Table 1. Molecular weight measurements show these to be monomeric complexes which are partially solu- ble in most of the common organic solvents; they are susceptible to moisture.

In the IR spectra of these complexes (Table 2) two bands are observed at N 3440 and 3310 cm -I due to the symmetric and antisymmetric modes of the primary amino group.9 These vibrational modes are in the same positions as in the free ligands suggesting that the NH2 group is not involved in chelation to the antimony. The region 3300-2850 cm-’ is that where one would normally expect vou and vNH vibrations to occur but no bands are visible in this region indicating that the O-H and N-H protons have been removed in reactions (2) and (3) making these sites available for coordination to the antimony.” A sharp strong band is observed in all complexes in the region 1595-1580 cm-’ and this is assigned to the VGN

stretching mode. The position of this band is lower than the corresponding band in the free ligand strongly suggesting that the nitrogen of the azome- thine moiety is coordinated to antimony. Similar shifts on coordination to Sb(V) have been observed for the oximate ligand by Mehrotra et al.”

%b Miissbauer spectral and related studies on Sb(II1) complexes

Table 2. ‘*‘Sb Miissbauer (mms- ‘) and IR (cm-‘) spectral data of antimony complexes

Compound 6" e2q121Q; rc v(C=N) v(Sb*N) v(Sb-0) u(Sb-s)

mm 5 -1 cm

-1

663

1. Sb(OPri)(C9H9N302) -3.65 17.31 1.52 1595 410 518 -

2. Sb2(C9HgN302)3 -3.54 17.45 1.42 1580 405 520 -

3. Sb(OPri)(CgH9N30S) -4.42 15.48 1.65 1587 412 510 350

4. Sb2(CgHgN30S)3 -4.56 12.88 1.88 1585 405 517 342 7.20 -- 2.20

InSb -8.73 -- --

a t 0.01 mms -1

b * 0.13 mms-'

-1 c t 0.04 ,nms

In the region N 520 - 350 cm-’ new bands are observed in the complexes which are not present in the free ligands. There have been assigned to vsm,

vSbNandVSM vibrations (Table 2). This is based on the results of Olera and Okawara,i2 who have suggested that bands in the region 380-360 cm-i may be attributed to Sb-S vibrations, and those of Chremos and Zingaro13 who have assigned bands in the 430 cm-’ region to Vs,,_N vibrations. All of our complexes show bands in the 405--412cm-’ region and suggests the presence of Sb-N bands in these compounds. The bands in the range 5 10-520 cm-i indicate the presence of Sb-0 inter- actions.

Proton NMR spectra of the free ligands and of the Sb,L, complexes have been recorded in DMSO-ds using T.M.S. as an internal standard. The free ligands show bands at 6 = 12.10 ppm and 6 = 9.81 ppm which are assigned to the OH and secondary amino protons respectively. These bands are absent in the complexes, confirming the IR evidence that these protons are removed in the complexation process. The CH3 protons on the carbon adjacent to the =N are shifted from 6 = 1.70 ppm and 6 = 1.62 ppm to 6 = 2.48 ppm and 6 = 2.25 ppm in the semicarbazone and thio- semicarbazone complexes respectively. This is fur- ther evidence that the nitrogen of the CH,-C=N- group is coordinated to the antimony. The multi- plet arising from the aromatic protons remains essentially unchanged in the 6 = 6.58-7.75 ppm region. However those peaks due to the NH, protons undergo a downfield shift to 6 = 3.58 ppm and 3.22 ppm in the semicarbazone and thio- semicarbazone respectively. This is consistent with

presence of the =C -NH2 group in the complexes

X

II compared to the predominant -C -NH2 grouping in the free ligand. The downfield shift being the result of the proximity of the N=C group to the primary amino protons.

‘*‘Sb Miissbauer spectra were recorded and these data are summarised in Table 2: typical spectra are shown in Fig. 1. These data are characteristic of antimony(II1) complexes since they show large negative isomer shifts. Since 6R/R is negative for antimony these shifts indicate a high s electron density at the antimony nucleus, typical of Sb(II1). These shifts may be compared with those of the Sb(OR), series. I4 The complexes examined in this study all have isomer shifts that are more negative than the Sb(OR), compounds, indicating that there is a higher s electron density at the antimony in the complexes than in the alkoxy compounds. It is also noted that the thiosemicarbazone complexes have much more negative isomer shifts than their 0x0 analogues. This strongly suggest that the X- (X = 0, S) is bound to the antimony. More nega- tive isomer shifts are found for Sb(III)-S species than for the 0x0 analogues.‘4T’5 We note also that the sulphur containing complexes have smaller quadruple coupling constants than their 0x0 an- ologues. This, taken with the trend in isomer shifts, indicates a less active participation of the antimony 5s electrons in the bonding scheme of the thio complexes than in the 0x0 species.

Based upon the evidence suggested above we propose the following structures, I and II, for those complexes with the semicarbazone behaving as a tridentate ligand. The antimony then has four ligands and a non-bonding electron pair in its immediate environment, an example of the AX,E

664 A. SAXENA et al.

I , ,

-17 7 -8 9 0 8.9 17 7

Velocity (mm/s)

(4

I I I I I I

-16.9 -8 5 0 8.5 16 9

Velocity (mm/s)

@)

Fig. l(a). The ‘*‘Sb Miissbauer spectrum of Sb(OPri)(C9H9N30J at 4.2 K. Miissbauer spectrum of Sb&H9N30S)3 at 4.2 K.

(b) The %b

type. For Pr’OSbL there are two likely arrange- shown as I has the OPr’ group, the N and the ments of the ligands, the first having the non- non-bonding electron pair in the equatorial plane bonding electron pair, the 0 and atom X in the while the 0 and X atoms occupy the axial positions equatorial plane, while the N and the OPr’ group of a virtually strain free idealised trigonal bi- would occupy the axial positions of a trigonal pyramid. This latter is the structure that we favour. bipyramid. This arrangement would have consid- In II the equatorial OPr’ groups in Pr’OSbL have erable strain and would lead to a very distorted been replaced in one case by an 0 and in the other structure. The alternative arrangement which is by an X of a semicarbazone ligand which bridges

I

CH3

iZ’Sb Miissbauer spectral and related studies on Sb(II1) complexes 665

two SbL units. Other structures are possible in which the semicarbazone bridges different anti- mony atoms, but polymeric structures are not likely in view of the solubility of the complexes in common solvents and are ruled out by the molec- ular weight measurements. For the Sb2L, complex when X=S there will actually be two different antimony (III) environments: one [:Sb(O),SN] and the other [:Sb(O)(S),Nj. These should have different ‘*‘Sb Miissbauer parameters. Un- fortunately it is not possible to resolve these two sites but their presence manifests itself in the increased line width for Sb2L3 when X=S (Table 2). It is also noted that the ‘*‘Sb Miissbauer spectrum of this complex shows evidence of the presence of a small amount of an Sb(V) species. Presumably the thio analogue of Sb,L, is much more easily oxidised than the other complexes where no Sb(V) is visible in the Miissbauer spectrum.

Acknowledgements4ne of us (A. S.) is thankful to the C.S.I.R., New Delhi for the award of P.D.F. and (T.B.) is grateful to N.S.E.R.C. of Canada and C.N.R.S. France for the opportunity to participate in the Canada-France Cultural Exchange Scheme.

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