Molecular structures of [(Ph3Sn)(2)O3Se] (1) and [(Ph3Sn)(2)O4Cr](CH3OH) (2) have been determined using spectroscopic techniques and X-ray analysis. Each structure consists of polymers containing two types of tin centres: one of them is bridged by two oxygen atoms of the trifunctional oxyanion into a helical chain while the other is pendant to this chain. In the case of the chromato derivative the pendant tin is also bonded to the oxygen atom of the solvent (methanol); hydrogen bonds between the methanol and the non-coordinated oxygen of the chromate generate a three-dimensional structure containing tin atoms in a trigonal bipyramidal environment. In contrast, the two tin centres in the non-solvated selenito derivative have distinct geometries (tetrahedral and trigonal bipyramidal). Variable temperature Mossbauer spectroscopy data are consistent with the polymeric structure of the selenito derivative while NMR spectroscopy shows the presence of monomeric species in solution. (c) 2007 Elsevier B.V. All rights reserved.