Diorganotin derivatives of 2-mercapto-5-methyl-1,3,4 -thiadiazole, $$(\hbox{C}_3\hbox{H}_3\hbox{S}_2\hbox{N}_2)[(\hbox{R})_6\hbox {Sn}_3\hbox{O}\hbox{(OH)}_2](\hbox{C}_3\hbox{H}_3\hbox{S}_2 \hbox{N}_2)$$ (R = Me 1, n-Bu 2, Ph 3, PhCH2 4), have been synthesized and characterized by IR, 1H, 13C and 119Sn NMR spectroscopy. Among them, polymer 2 was also characterized by X-ray crystallography diffraction analysis. This revealed that 2 showed a unique tricyclic structure consisting of a fused five-membered Sn2ON2 ring and a four-membered Sn2O2 ring. These formed a planar N2Sn3O2 skeleton, with distorted trigonal bipyramidal coordination at the two tin centers and a distorted octahedral coordination at the other tin center. The supramolecular structure of polymer 2 was a 1D zig-zag polymeric chain stabilized by intermolecular O–H...S hydrogen bonds.