Calculations of structures and reaction energy profiles of As₂O₃ and As₄O₆ species by quantum chemical methods

Abstract

Abstract Principal component analysis was used in the selection of the B3PW91/6‐311+G(3df) method for calculations of As 2 O 3 molecular species. This multivariate analysis compared experimental properties (structure and ionization energy) of As 4 O 6 molecule with several computational methods (Hartree–Fock, second‐order Møller–Plesset perturbation theory, and density functional theory) and basis sets. At the selected level of theory, we were able to calculate nine structures of As 2 O 3 with three of them being stable ones (no negative force constants) in the following stability order: D3H (0.0), DIAMOND OUT (32.77 kJ mol −1 ), and GAUCHE (43.81 kJ mol −1 ). Several intramolecular conversions were studied with the GAUCHE → DIAMOND OUT transformation being barrierless, whereas the DIAMOND OUT structure is converted into the D3H isomer through a Gibbs free‐energy barrier of 40.83 kJ mol −1 . Starting from the GAUCHE structure of As 2 O 3 and its enantiomeric form, it was possible to obtain directly (barrierless) the As 4 O 6 species in a spontaneous process (Δ r G = −399.92 kJ mol −1 at 298 K and 1 atm) in gas phase. Thus, the As 4 O 6 species is probably the precursor of arsenic hydroxide through hydrolysis reactions. © 2012 Wiley Periodicals, Inc.