Structural studies in main group chemistry : XI. Tin-119m mössbauer investigations of triorganotin derivatives of substituted pyridines

Abstract

Tin-119m Mössbauer and selected infrared and 1H NMR data are reported for twenty four triorganotin derivatives of substituted pyridines and related ligands, and conclusions concerning structure inferred. Mössbauer quadrupole splittings in the ranges 3.09–3.38 mm sec −1 and 2.92–3.22 mm sec −1, respectively, for the 2- and 3-pyridone derivatives indicate five-coordinate trans-R 3SnX 2 trigonal bipyramidal configurations at tin with planar R 3Sn moieties. In the case of the derivatives of 2-pyridone, the extra coordination to give linear chain structures arises from bridging oxygen atoms, but bridging via either oxygen or the pyridyl nitrogen atom may occur in the derivatives of 3-pyridone. Similar oxygen-bridged chain structures are also postulated for the triorganotin derivatives of 2-pyridylalcohol and 2-pyridylaldehyde oxime, but lower splittings values of 2.63(5)–2.93 mm sec −1 indicate some relaxation from planarity of the R 3Sn group towards tetrahedral. The splittings are observed to decrease in the order Me > Et > Pr, illustrating that the deviation from planarity and the bond distance of the coordinate O⋯Sn bond increase with the steric bulk of R. Much lower splittings of 1.60–2.27 mm sec −1 are observed for the derivatives of 2-thiopyridone and 8-hydroxyquinoline, which, with the presence of three tin—carbon stretching modes in the infrared spectrum for the methyltin compounds, are consistent with the alternative five-coordinate cis-R 3SnX 2 geometry at tin. The very high splitting values, together with the low values of the anti-symmetric OCO stretching vibration of the carboxylate group and the multiple tin—carbon stretching modes observed for the methyltin compounds in the infrared, have been interpreted in terms of the six-coordinate mer-R 3SnX 3 stereochemistry for the triorganotin esters of 2-pyridylcarboxylic and 2,6-pyridyldicarboxylic acids. The low and almost constant value of the two-bond coupling constant 2 J( 1HC 119Sn) for the methyltin derivatives indicate that n solution either four or five-coordinate cis-R 3SnX 2 structures are adopted.