Dialkyltin(IV) and trialkyltin(IV) derivatives of the coenzyme thiaminepyrophosphate (H 2 TPP) have been synthesized with general formula R 2 Sn(HTPP) 2 ÁnH 2 O (Alk = Me, n = 2; Alk = Bu, n = 4) and R 3 SnHTPPÁnH 2 O (R=Me, n = 2; R = Bu, n = 1), respectively. The solid-state structure of the complexes has been investigated through infrared and Mo ¨ssbauer spectroscopy. The infrared data suggest the involvement of only phosphate oxygen atoms in the coordination of both dialkyl-and trialkyl-tin(IV) moieties, with phosphate anions behaving as monoanionic bidentate bridging or chelating groups, with the tin(IV) involved in six-and five-fold coordination geometries, respectively, in R 2 Sn(HTPP) 2 ÁnH 2 O (R = Me, n = 2; R = Bu, n = 4) and R 3 SnHTPPÁnH 2 O (R = Me, n = 2; R = Bu, n = 1). The 119 Sn Mo ¨ssbauer data, and in particular rationalization of the experimental nuclear quadrupole splittings, D, through the point-charge model formalism, suggests the occurrence of an octahedral trans-R 2 structure in R 2 Sn(HTPP) 2 ÁnH 2 O (R = Me, n = 2; R = Bu, n = 4) and a trigonal-bipyramidal structure in R 3 SnHTPPÁnH 2 O (R = Me, n = 2; R = Bu, n = 1). 1 H and 13 C NMR spectra, in D 2 O, suggested that the soluble derivatives, at room temperature, in solution, maintained the solid-state structure. The interactions of dibutyltin(IV)-thiaminepyrophosphate(DBTPP) and tributyltin(IV) -thiaminepyrophosphate (TBTPP) complexes with Bluescript KS() plasmid and immortalized 3T3 fibroblasts were studied. Both compounds have a clear inhibitory effect on the growth of immortalized mouse embryonal fibroblasts (NIH-3T3), TBTPP being the much more active. No evidence was found, however, for DNA cleavage by the compounds at molar ratios as high as 1:10 (DBTPP, TBTPP/DNA base pairs). According to our observations, the cytotoxicity of TBTPP does not seem to be based on direct interaction with DNA, but in the presence of TBTPP (1:10, TBTPP/DNA bp), plasmid DNA seems to be more susceptible to cleavage by UV.