Theoretical study on linear dicyanide and dicarbonyl complexes of the metals Au, Hg, and Tl. On the possible existence of a [Tl(CO)2]3+ cation

Abstract

DFT-BP86, MP2, and CCSD(T) calculations on the cyanide complexes [Au(CN)₂]^–, [Hg(CN)₂], and [Tl(CN)₂]⁺ and the isoelectronic carbonyl complexes [Au(CO)₂]⁺, [Hg(CO)₂]²⁺, and [Tl(CO)₂]³⁺ are presented using effective core potential wavefunctions in conjunction with polarized double- and triple-zeta basis sets. Geometries, vibrational frequencies, infrared intensities, internal force fields, and charge distributions are discussed. For the Au and Hg systems, the calculated data are in very good agreement with experimental data. For the complexes [Tl(CO)₂]³⁺ and [Tl(CN)₂]⁺, the calculations predict metal–C force constants comparable to those in the respective Hg species. The dissociation of these complexes into Tl⁺ and CO⁺ or CN is computed to be endothermic by about 60 kcal mol^–1 for [Tl(CN)₂]⁺ and exothermic by more than 200 kcal mol^–1 for [Tl(CO)₂]³⁺, with a barrier of 15–20 kcal mol^–1 (UBP86) in the latter case.