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Mossbauer and infrared studies of triphenyltin carboxylates Ford, Beverly F.E

Abstract

A study was undertaken to investigate the solid-state structure of about 25 triphenyltin carboxylates, Ø₃SnOCOR. The compounds were synthesized and then analyzed by Mössbauer and infrared spectroscopy. The compounds were divided into three series on the basis of the nature of the R group. The first series of compounds had R groups which were "linear" chain hydrocarbons ranging in length from one carbon atom (triphenyltin formate) to eighteen carbon atoms (triphenyltin stearate). In the second series several compounds had methyl branches at various positions along the hydrocarbon chain, some had longer alkyl groups and a few had a methylene group bonded to the a-carbon atom. The third series contained mono-, di-, and tri- substituted haloacetates. These compounds were prepared in order to test the assumption that bulky R groups would prevent (by steric interaction) polymer formation in the solid. The polymeric structure which is commonly found for triorganotin carboxylates consists of pentacoordinate Sn atoms. Each carboxylate group bridges between two different Sn atoms and this occurs indefinitely to form a polymer. Steric interaction of the R group with neighbouring phenyl groups (bonding to Sn) could prevent polymer formation. The resulting structure would be monomeric and have a tetracoordinate Sn atom and a terminal carboxylate group like that for an organic ester. The majority of compounds were found to be polymeric solids. Structural changes (polymeric to monomeric) were observed for a few compounds and this could be attributed to steric interaction. The Mössbauer and infrared data were complimentary and conclusive when used to differentiate between the two possible structural types. In a polymeric structure the Sn atom can be visualized as being in a trigonal bipyramidal environment in which the oxygen atoms are axial and the phenyl groups equatorial. Using the above idealized structural type it was possible to test a point-charge model which had been used to predict quadrupole splitting values, Δ. The model was tested for the triphenyltin haloacetates and found to give fairly good agreement with the observed quadrupole splitting values.

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