A theoretical study on the formation of EX4+ and E2X5+ (E = P, As; X = Br, I) from Ag+ and EX3/X2

Abstract

The mechanism and the thermodynamics of the formation of EX₂⁺, EX₄⁺ and E₂X₅⁺ (E = As, P; X = Br, I) was carefully analyzed with MP2/TZVPP calculations and inclusion of entropy and solvation effects (COSMO model approximating CH₂Cl₂). Thus, as likely intermediates the complexes of Ag⁺ and one or two EX₃ as well as EX₃/X₂ were optimized. The global minimum isomers of the Ag(EX₃)₂⁺ intermediates were found to be P-coordinated Ag(PI₃)₂⁺ and (BrPBr₂)Ag(PBr₃)⁺ but exclusively halogen coordinated Ag(X₂AsX)₂⁺ complexes. Similarly complicated is the situation for the Ag(EX₃)(X₂)⁺ intermediates: (I₃E)Ag(I₂)⁺, (BrAsBr₂)Ag(Br₂)⁺ and (Br₃P)(Br–Br)Ag⁺ complexes were found to be the global minima. Based on all available results likely mechanisms for the formation of the known PX₄⁺, AsBr₄⁺, P₂X₅⁺ salts (X = Br, I) from these intermediates were proposed. An explanation for the failure to prepare an AsI₄⁺ salt is also given.