The compounds [SnR 2 X 2 (bmimt)] (R = Me, Et, Bu; X = Cl, Br; bmimt = bis(1-methyl-2-imida-zolylthio)methane) have been prepared and characterized by conductivity measurements and by IR, Raman, mass, Mössbauer and 1 H NMR spectroscopy. The structures of the diethyldibromo-and dibutyldichlorotin(IV) derivatives were determined by X-ray crystallography. The crystals consist of two slightly different types of discrete [SnR 2 X 2 (bmimt)] unit with the metal atom octahedrally coordinated to the two halogen atoms, two alkyl carbons and the two nonmethylated nitrogen atoms of the ligand. This coordination mode, which the spectroscopic data suggest is also present in all the other complexes studied, results in the formation of an eight-membered CS 2 C 2 N 2 Sn ring. The Sn-N distances in [SnEt 2 Br 2 (bmimt)] (2.53 and 2.42 A ˚) and [SnBu 2 Cl 2 (bmimt)] (2.52 and 2.47 A ˚), suggest that these compounds may have antitumour activity.