Relativistic effects in gold chemistry. 3. Gold(I) complexes

Abstract

Geometry-optimized Hartree-Fock (HF) calculations have been carried out for the ground-state properties of linear two-coordinated gold(1) complexes, AuLC (L = H, F, CI, Br, I, CN, SCN, CH3, and PH3+), and for AuCH3, AuPH3, AuPH3+, AuCN, and AuSCN by us ing multielectron adjusted nonrelativistic and relativistic pseudopotentials for the gold atom. Configuration interaction calculations have been performed for the gold(]) halide complexes. The relativistic effects in the Au-L bond are analyzed, and the differences from the corresponding Cu-L and Ag-L bonds are explained. The preference of coordination number 2 in Au(1) is strengthened by relativistic effects. I n contrast to singly bonded AuL species ( J . C h e m . P h y s . 1989, 91, 1762), 5d and 6p contributions to t h e Au-L bond are important in Au(1) complexes. The magnitude of these effects is dependent on the elec- tronegativity of the ligand. Relativistic effects increase gold Sd contributions in the Au-L bond, as expected from the relativistic expansion of the A u Sd orbital and the relativistic contraction of the Au 6 s orbital. I n contrast to the diatomics, no significant relativistic bond destabilization was found for the complex halides. Large relativistic bond stabilizations were obtained for A u ( P H ~ ) ~ + and for Au(CN); ( 8 7 and 39 kJ mol-' per Au-L bond at the H F level, respectively), which account for their high stability compared to the analogous copper or silver compounds. The unusually large negative "CI nuclear quadrupole coupling constant in AuCIY compared with CuCIY and AgCI2- is caused by relativistic effects. Relativistic difference density plots are shown for AuH2-, AuFT, and Au(CN)<. AuSCN and Au(SCN)Y are predicted to have a bent Au-S-C conformation. Since structural data on Au(SCN)Y were not available, we have synthesized [ A s P ~ ~ ] A u ( S C N ) ~ and analyzed this compound by infrared and Raman spectroscopy and have determined its structure by single-crystal X-ray diffraction. These studies confirm the calculated nonlinear Au-S-C arrangement of t h e Au(SCN)Y ion.