The geometries of ZrX62- (X = FCl,Br,I) were optimized at the ab initio Hartree-Fock SCF level using all-electron MIDI and effective core potential valence basis sets of double-zeta quality, supplemented with diffuse functions. In addition, geometries and energies of X2, as well as energies of gaseous Zr were determined in order to predict energies of formation of ZrX(6)2- 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. Standard routines were employed to evaluate entropies, heat capacities, heats of formation and free enthalpies of formation of gaseous ZrX(6)2-. Electrostatic cohesive energies in hexahalogenozirconates were evaluated by the extended Ewald method. It was assumed that each ion gathers a formal charge +1, +2, or -2. Net atomic charges in complex ions were determined either from various population analyses or fitted to the ab initio quantum mechanical electrostatic potential. The Coulombic energies decrease gradually with the increase in volume of the simplest structural unit. A similar tendency is noted as regards distances between interacting centers. Theoretically determined properties are in a good agreement with available data, mostly of experimental origin.