The formation of NaSnX3 (X = halogen) influences the sodium concentration in metal halide lamps making the thermodynamics of such reactions critical for technological developments. Theoretical predictions of the structure and vibrational properties of the quasi-binary NaCl-SnCl2 system lead to thermodynamical data determined through the third law evaluation. Ab initio enthalpy and entropy of dissociation of NaSnCl3 also is reported. Additionally, insight into the nature of chemical bonding is provided by electron population analysis and the interaction energy decomposition scheme.