Indian Journal of ChemistryVo). 20A, April 1981, pp. 363-365

119SnM~ssbauer Spectroscopic Study of Novels-Carbomethoxyetliylttn/Iv ) Compoundsf

M. v. GARAD, M. P. GUPTA, (Mrs) SARADA GOPINATHAN & C. GOPINATHAN*National Chemical Laboratory, Poona 411 008

Received 19 May 1980; revised and accepted 19 September 1980

The Mossbauer parameters are presented for ~-carbomethoxyethyltrichlorotin and biS-\3-carbomethoxyethyl-dichlorotin, their substitution products of the type RSnCI.L, RSnCIL., RSnLa, R2SnL2 and molecular additioncompounds of the trichloro derivative with neutral donor molecules. The chelating ligands used are'S·hydroxYquinoline,acetylacetone, dibenzoylmethane, 2-hydroxy-4-methoxybenzophenone, salicylaldazine, 1,lO-pbenanthroline, 2,2'-bipyridyl and hexamethylphosphortriamide. On the basis of observed isomer shift and quadrupole splitting data,possible structural assignments have been made for these compounds.

THE Mossbauer spectral studies on ~-carbomethoxyethylchlorotins, their chlorinesubstitution products containing chelating

1igands and their addition compounds with neutraldonor molecules have not been done so far, thoughsimilar studies on several organotin chelates andorganochlorotin chelates-; organotin derivatives ofanionic ligands containing O,N,S atoms in pairs+",adducts of organotin halides; and ketoorganostan-nanes and ketoorganochlorostannanes- have beenmade. The present paper concerns with the structuralstudies by Mossbauer spectroscopy on title com-pounds.

Materials and MethodsReactions were carried out under dry nitrogen

atmosphere. Solvents and chemicals used were ofAR grade.

The Mossbauer spectra were taken using a MBS-35spectrometer (Electronic Corporation of India)operated in the constant acceleration mode coupledto a ND 100 multichannel analyser. The spectro-meter was calibrated with 1 mil natural iron foilusing a 4 mCi 57 Co in a Pd matrix. All the spectrawere recorded with 2 mCi Ba 119SnOamatrix (NewEngland Nuclear Corporation). The absorbers wereprepared by spreading well ground powder of eachsample between two thin Al foils of 1 inch radius,sandwitched between two brass rings. The thicknessof the absorber was so adjusted that it containedabout 40 rug/em 2 of natural tin. In all the cases Wicounts were collected in each channel.

The IR spectra were recorded on a Perkin-Elmermodel 221 or 599 B spectrophotometer using sodiumchloride or caesium iodide optics.

Bis-~-Carbomethoxyethyldichlorotin and ~-carbomethoxyethyltrichlorotin were prepared byknown methods",

tNCL Communication No. 2564.

(

Bis-~-carbomethoxyethy/- bis -8 - hydroxyquinolino-tine/V) - Sodium derivative of 8-hydroxyquinoline(0.64 g; 0.0044 mol) was suspended in benze~e(30 ml) and bis-~-carbomethoxyethyldichlorot1U(0.73 g; 0.002 mol) added to it. The mixture wasrefluxed for 3 hr and filtered. The clear solution wasconcentrated to crystallization to get a pale yellowsolid. It was washed with cold hexane and driedin vacuo at 60°; yield 1.89 g (81 %); m.p. 146°.[Found: Su, 20.61; C, 53.16; H, 4.92. (C9H6NOhSn(C4H702)2 requires Sn, 20.42; C, 53.69; H, 4.47%].

Other compounds listed in Table 1 were preparedsimilarly.

Preparation of an addition compound: ~-carbo-methoxyethyl-trichlorotin-2,2 -bipyridyl - The tworeactants (0.002 mol each) were mixed and refluxedin benzene (50 ml) for 2 hr. The pink crystals obtainedwere washed with hexane and dried; m.p. 196°;yield 92 %. [Found C1, 22.89; Sn, 25.30. (C4H702)

SnCI3,CloHsN2 requires CI, 22.71; Sn 25.35 %].Other addition compounds (Table 1) were preparedsimilarly.

Results and DiscussionThe Mo ssbauer spectrum of bis-s-carbomethoxy-

ethyldichlorotin shows an isomer shift (0) value of1.28 mm/sec and a quadrupole splitting (f':,EQ) of3.46 mm/sec, the magnitude of which indicates transconfiguration of the organic groups as shown instructure (I). For an octahedral complex containingtwo organic groups the point charge treatment pre-dicts a f':,EQ value of 2 mm/sec for cis isomer and4 mm/sec for trans isomert-". The trans-configurationis further supported by the appearance of singleinfrared band at 578 em= attributable to vasSn-C.In all its substitution products with bidentateligands (except in the case of the 8-hydroxyquinolinecomplex), the geometry around tin is trans-octahedralsince the f':,EQ values fall between 3.04 and 3.97rom/sec. The o-values of the above complexes are

363

INDIAN J. CHEM., VOL. 20A, APRIL 1981

C~

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I

TABLE 1- THE MoSSBAUER SPECTROSCOPIC DATA FOR ~-CAR-

DOMETHOXYETHYLTIN COMPOUNDS

No. Compound Colour 8±0.03 f:,EQ p=m.p. (rnm/sec) ±0.06 f:,EQ/8(DC) (mm/sec)

1. R.SnClz White 1.28 3.28 2.5625132

2. R,Sn(dibenzoyl- Orange 1.21 3.97 3.2810methane), 104

3. R.Sn(acetylacetonato)2 White 1.21 3.97 3.2810147

4. R.Sn(2-oxy-4-methoxy- Yellow 1.15 3.04 2.6435_ benzophenone), 150

5. R.Sn(salicylaldazine) Yellow 1.09 2.81 2.5780158

6. R2Sn(8-hydroxyquino- Yellow 0.82 2.08 2.5366linato), ' 146

7. RSnCI3 White 0.95 1.95 2.052667

8. RSnCli8-hydroxy- Yellow 0.92 1.90 2.0652quinolinaio) 170

..9. RSnCl(8-hydroxy- Yellow 0.71 1.53 2.2836quinolinato) 164

10. RSn(8-hydroxyquino- Yellow 0.70 1.50 2.1429linato), 185

11. RSnCI3.1,10-phenan- Pink 0.84 1.45 1.7242throline 186

12. RSnCI e- 2,2'-bipyridyI Pink 0.82 1.26 1.5366196

13. RSnCl a- (hexamethyl- White 0.77 2.19 2.8442phosphortriamide ). 70

R = ~-carbomethoxyethyl group.

between1.l5 and 1.21 mm/sec. This close resemblancebetween the isomer shifts of bis-~-carbomethoxy-ethy1dichlorotin and its chelated complexes suggestsalmost the same s-electron density at tin nucleus.

In contrast to the above findings, bis-p-carbo-methoxyethyltin-bis-8-hydroxyquino1inate has a cis-octahedral arrangement of organic groups as revealedby L:,.EQ= 2.08 mm/sec. This cis-complex, likeother di-organotin bis-chelates", shows a consider-'ably lower ~-value of 0.82 rnm/sec than their trans-analogues due to a decrease in the 5s character inthe Sn-C a-bonds in the cis-position. IIi all the bis-chelates examined, the p values fall between 2.50 and3.28 suggestingtv+' a six-coordinated tin atom.

In the salicylaldazine _complex with bis-Bscarbo-methoxyethy1tin, the possible geometry' around tinis trigonal bipyramidal as it is monomeric in benzene.The non-coordinating nature of the ester carbonyland coordination of C = N group of the ligand areconfirmed from IRand PMRdata12• The quadrupolesplitting observed is 2.81 mm/sec and the ~ value isabove 2.10. The possible arrangements of organic

364

I

(

R R

ct~ '~t'I~'---r- "--N~,...... ~

Trans- (II) ~

groups around tin are shown in structures (II) and(III).

From a study of the five-coordinated organotincomplexes of the type [MeaSnCl. terpyridyl]+[Me2SnC13t it was concluded that L:,.EQ value forequatorial arrangement of ligands in trigonalbipyramida1 structure was not very different fromthat for trans-octahedral R2SnL4 species-e. Anexample for a five-coordinated tin complex withcis-phenyl groups is (C6H5)2 SnNCS(8-hydroxyquino-linate). Mullins and Curran= obtained L:,.EQvaluesfor this compound and similar other compounds inthe range 2.4 - 2.5 mm/sec and concluded that thephenyl groups are in cis-position. Poller and Ruddick!found the corresponding values five-coordinatedcis-complexes of the type EtaSnX (8-hydroxy-quino-linate) to be between 3.10 and 2.85 mm/sec. In thelight of the above findings, the possible arrangementof organic groups in the salicylaldazine compoundwill be a cis disposition of the monodentate estergrouping since L:,.EQ value of 2.81 mm/sec is insame range. The corresponding value for Bu2SnNCS(8-hydroxyquinolinate) with trans butyl groups is3.25 mm/seo (see ref. I).

Mossbauer isomer shift values (Table 1) de-monstrate that bis-~-carbomethoxyethyldichlorotin(~= 1.28 mm/sec) is a weaker Lewis acid than thecorresponding trichlorotin compound (~ = 0.95 mm/see) as expected. This decrease in ~-value of thetrichloro compound suggests greater a-electron with-drawing power of chlorine atom due to inductiveeffect.

A decrease in asymmetry of electron cloud aroundtin atom in ~-carbomethoxyethyltrichlorotin com-pared to the. dichloro derivative is evident fromlower L:,.EQ value. The decrease may also be due tothe small difference in the polarity of Sn-C and Sn-Clbonds. The new molecular addition complexes of~-carbomethoxyethyltrichlorotin of the type RSnC13•

L or RSnCI3.2L, where L is a mono- or bi-dentateligand give a-values in the range 0.77 to 0.84 mm/sec(Fig. 1) which are smaller than the value for the tri-chloro compound itself. This decrease may beinterpreted in terms of change in the hybridizationat tin from sp3d to sp~d2 thereby reducing the s-electron density at the tin nucleus due to the shield-ing effect of occupied 5 d-orbitals. Further the polarityof Sn-O bond in ~-carbomethoxyethyltrichlorotin-hexamethylphosphoramidea dduct is more than thatof Sn-N in nitrogen heterocyclics as seen from lowera-values for the former. The L:,.EQ values for thesecomplexes fall in the range 1.26 to 2.19 rum/sec.

"\

GARAD et al. : MOSSBAUER SPECTROSCOPIC STUDY OF ORGANOTIN(IV) COMPOUNDS

VI

~ '·0=>>-a::~ 9'8'....a;0::

< 9·6>-....inz~ 9'4z

.';.: :...

0·4 0'2- ye vel.el I y

Fig. 1 - Mossbauer spectrum of (3-carbomethoxyethyItin(IV)- Ll Osphenanthroline adduct.

0'4 0·6 0'8+ ve velocity

This is a much wider range when compared to cis-or trans- octahedral complexes of the type R2SnL4and may be due to higher order of distortion fromperfect octahedral symmetryv-".

The stepwise substitution products of ~-carbo-methoxyethyltrichlorotin with one, two and three8-hydroxyquinoline groups contain hexa-coordina-ted tin. In ,B-carbomethoxyethyldichlorotin-8-hyd-roxyquinolinate adduct, the ester group is acting asa bidentate moiety as seen from its IR spectrumwhereas in other two compounds ester cabonyl isnon-coordinating. The a-values decrease graduallyfrom the trichloro derivatives to the chlorine-freecompound (from 0.95 to 0.70 mrn/sec). This decreasemay arise by the replacement of chlorine by bidentateligands or due to extra-nuclear shielding caused byhigher hybridization at tin, sp3d2 or sp3c/3 as in BuSn-(Svhydroxyquinolinate), (ref. 17).

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3. MAY, J. C., PETRIDIS, D. & CURRAN, C., Inorg . chint. Acta,S (1971), 511.

I

""..;:

0·0 0'2mm/sflc

"0

4. NAIK, D. V. & CURRAN, C., J. coord. Chem., 2 (1973),309.

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