Thermodynamic Stability, Electronic Properties, and Vibrational Spectra of Cr(VI), Mo(VI), and W(VI) Halides and Oxohalides: a Comparative Density Functional Theory Study

A comparative quantum chemical study of the thermodynamic stability, electronic structure, and vibrational spectra of chromium(VI), molybdenum(VI), and tungsten(VI) halides and oxohalides are presented. The calculations are performed by the density functional theory methods using PBE, B3LYP, and r2SCAN density functionals in combination with def2-SVP, def2-TZVP, and def2-QZVP basis sets. The influence of the functional choice and the basis set size on the accuracy of describing geometric parameters and vibrational frequencies is analyzed against experimental data. The thermodynamic stability of the studied compounds is shown to decrease in the F → Cl → Br → I series, as well as with increasing coordination number of the central metal atom. At the same time, the polarizability and dipole moments of molecules increase, especially for structures with reduced symmetry. Analysis of frontier molecular orbitals (HOMO–LUMO) allows the identification of more reactive compounds that can be possibly used as precursors for atomic layer deposition and for identifying thermally stable products in atomic layer etching processes.