The molecular structures of SnCl2 and Sn2Cl4 have been calculated by high-level quantum chemical methods. The global minimum structure found for the tin dichloride dimer is of C, symmetry and has two halogen bridges. This structure is very different from the one suggested earlier by Fields et al. based on their gas-phase Raman spectroscopic measurements. Thermodynamic functions for gaseous SnCl2 and Sn2Cl4 have also been calculated. The minimum-energy geometry of the trimeric molecule, Sn3Cl6, has a six-membered ring with alternating Sn and Cl atoms in the highly puckered ring. The possible structural changes during evaporation are discussed in some detail.