A series of R 3 SnO 2 CR′ compounds, where R) Me (1), Et (2), n Bu (3), Ph (4), and cHex (5) and R′CO 2 is the carboxylate residue of 2-[(E)-2-(2-hydroxy-5-methylphenyl)-1-diazenyl]benzoic acid, has been shown by multinuclear magnetic resonance studies to be monomeric in solution. Crystallography shows that monomeric four-coordinate species are found in the solid state for 4 and 5 but polymeric structures with five-coordinate tin atoms are found for 1-3. The different behavior is ascribed to the steric demands of the tin-bound substituents. A fair correlation is found between the difference in 117 Sn chemical shift between the solution and solid states and the carbonyl oxygen-tin distance of the compounds 1-5, only when the data of 4, R) Ph, are omitted. This indicates that the mesomeric effect of the phenyl group does not express its influence to the same extent in the solid and solution states, unlike the inductive effects. By contrast, a good correlation including 4 is found between the Mössbauer quadrupole splitting and the difference in 117 Sn chemical shift between the solution and solid states. This shows that the nature of the organic group on the tin atom contributes to similar extents to the values of the 117 Sn chemical shifts in solution and solid state, independently of the existence or not of mesomeric effects, and that the parallel behavior of QS and 117 Sn chemical shifts is geometry independent.

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An overview is given of the research performed by the authors at the Université Libre de Bruxelles and Vrije Universiteit Brussel, including the kinetics, stereochemistry and mechanism of S E 2 reactions at a saturated carbon atom, the synthesis of chiral organotin compounds and their configurational and optical stability, the fluxionality of trigonal bipyramidal metal atoms and the stereochemistry of S N 2 reactions at tetrahedrally substituted P, Si, Ge, Sn atoms, the cytotoxicity of many series of organotin compounds and the structure and reactivity of organotin salicylaldoximate clusters.