Gas Phase Properties of MX2 and MX4 (X = F, Cl) for M = Group 4, Group 14, Cerium, and Thorium.

Abstract

Structures, vibrational frequencies, and heats of formation were predicted for MX4 and both singlet and triplet states of MX2 (M = group 4, group 14, Ce, and Th; X = F and Cl) using the Feller-Peterson-Dixon composite electronic structure approach based on coupled cluster CCSD(T) calculations extrapolated to the complete basis set limit with additional corrections including spin orbit effects. The spin-orbit corrections are not large but need to be included for chemical accuracy of ±1 kcal/mol. The singlet-triplet splittings were calculated for the dihalides and all compounds have singlet ground states except for the dihalides of Ti, Zr, and Ce which have triplet ground states. The calculated heats of formation are in good agreement with the available experimental data. Our predictions suggest that the experimental heats of formation need to be revised for a number of tetrahalides: TiF4, HfF4, PbF4, PbCl4, and ThCl4 as well as a number of dihalides: GeF2, SnF2, PbF2, TiF2, and TiCl2. The calculated heats of formation were used to predict various thermodynamic properties including average M-F and M-Cl bond dissociation energies and the reaction energies for MX2 + X2 → MX4. Edge inversion barriers were predicted. The calculated edge inversion barriers for the tetrafluorides show that the barriers for the group 14 tetrafluorides decrease with increasing atomic number, the group 4 barriers are ∼50 kcal/mol and CeF4 and ThF4 have inversion barriers of ∼25 kcal/mol.