RELATIVISTIC EFFECTS IN GOLD CHEMISTRY .4. GOLD(III) AND GOLD(V) COMPOUNDS

Hartree-Fock (HF) calculations of the electronic structure and bonding in gold(III) and gold(V) compounds (AuH3, AuF3, AuCl3, AuH4-, AuF4-, AuCl4-, AuBr4-, AuI4-, AuF6-, Au2H6, Au2F6, Au2Cl6) have been carried out. Non-relativistic and relativistic pseudopotentials were applied using a [Xe4f14]-core definition for the gold atom, however, including the 5s and 5p electrons in the valence space. All bond distances and angles were optimized. Moller-Plesset (MP2-4) calculations on the stability of gold(III) halide complexes were carried out to study the effects of electron correlation at the nonrelativistic and relativistic level of the theory. The relativistic effects in the Au-L bond are analyzed. Relativistic changes in Au(III)-ligand bond distances are calculated to be small compared to those in Au(I) compounds. However, relativistic changes in Au(III)-ligand stretching force constants are very large and of comparable magnitude to that in Au(I) compounds. The preference of the oxidation state III in gold is found to be influenced considerably by relativistic effects and is dependent on the electronegativity of the ligand. The conclusions drawn from previously published HF results (J. Am. Chem. Soc. 1989, 111, 7261) on the stability of AuL4- (L = F, Cl, Br, I) are confirmed by MP2-4 calculations; i.e., the decomposition AuL4- --> AuL2- + L2 occurs less easily relativistically than nonrelativistically. Relativistic effects also contribute to the facile decomposition of AuF into Au and AuF3. All calculated AuL3 CoMpounds (L = H, F, Cl) show T-shaped structures as a result of a first-order Jahn-Teller symmetry breaking of the D3h trigonal planar structure into the C2v arrangement. A rationalization for the polymeric helix structure of AuF3 is provided. The stability and structure of gold(III) hydride is examined in detail. Multiple scattering X-alpha calculations were carried out on AuF4-, AuCl4-, AuBr4-, and AuI4- to determine relativistic effects in the nuclear quadrupole coupling constant for Au-197. Au2Cl6 was prepared, and a single-crystal X-ray analysis was carried out to compare with data obtained by the MP2 method (monoclinic, space group P2(1)/c with a = 6.5906 (9) angstrom, b = 11.007 (2) angstrom, c = 6.442 (3) angstrom, Z = 4, 873 reflections, and R = 0.0561).