The title compound has been examined by single-crystal X-ray crystallography and crystallizes in the space-group P21/c with Z= 2 in a unit cell of dimensions a= 8·555, b= 16·962, c= 7·122 Å and β= 113·15° The structure was solved by conventional Fourier techniques and was refined anisotropically by full-matrix least-squares methods to R 0·039 using 1600 independent reflections measured by counter methods. The cation is regular and normal. The SnCl62– ion is tetragonally distorted with three crystallographically inequivalent Sn–Cl bonds [2·414(4), 2·419(2), and 2·463(3)Å], the source of the distortion being Cl H–N hydrogen bonding between the long Sn–Cl bonds of SnCl62– and the cation. These results account very well for the marked splittings in the 35Cl n.q.r. signals observed for this anion.