Hypervalent halogen hydrides HalHn (Hal = Cl, Br, I; n = 3, 5, 7): DFT and ab initio stability prediction

Abstract

Stability—both kinetic and thermodynamic—and structure of hypervalent halogen hydrides and respective ionic species were investigated using B3LYP, B3PW91 and MPW1PW91 DFT functionals and second-order Moller-Plesset perturbation theory (MP2) with Def2-TZVPPD basis set (for I atoms) and aug-cc-pVTZ basis set (for Br, Cl and H atoms). Various dissociation pathways were considered: respective reaction enthalpies and H2 elimination activation enthalpies were calculated. At these levels of theory, all of the HalHn species (Hal = Cl, Br, I; n = 3, 5, 7) have covalently bound local minima (except for ClH7) and have a relatively significant kinetic stability with respect to H2 elimination, which indicates the possibility of them being, at the very least, spectroscopically observable, if not isolable. The first candidates for isolation/observation appear to be IH3 and IH5. To aid future identification of hypervalent halogen hydrides, harmonic frequencies for these compounds were calculated. Also, NBO analyses were performed and natural electron configurations, Wiberg bond indices and HOMO–LUMO gaps for these species were determined.