Bond lengths in octahedral HfX(6)(2-) (X = F, Cl, Br, I) were optimized at the ab initio Hartree-Fock SCF level using all-electron MIDI (X = Cl) and effective core potential valence basis sets of double-g quality, supplemented with diffuse functions. Energies resulting from these calculations were combined with energies of X(2) (at optimal geometries) and Hf in order to obtain energies of formation of HfX(6)(2-). The effects of electron correlation were taken into account at the second-order Moller-Plesset level of theory. Vibrational frequencies were determined in the harmonic approximation and compared with available experimental data. Common routines were employed to evaluate entropies, heat capacities, heats of formation, and free enthalpies of formation of gaseous HfX(6)(2-) in the standard state. Electrostatic cohesive energies for hexahalogenohafnates were evaluated by the Ewald method adapted to complex ions. It was assumed for this purpose that the formal charge of each ion is a whole multiple of e. Net atomic charges in complex anions were found either from various population analyses or by fits to the ab initio quantum mechanical electrostatic potential. The Coulombic energies are inversely dependent on the volume of the simplest structural unit and distance between interacting centers (Hf-cation). Theoretically determined properties are in good agreement with available data, mostly of experimental origin.