Bridging Gold: B-Au-B Three-Center-Two-Electron Bonds in Electron-Deficient B2Aun-/0 (n=1, 3, 5) and Mixed Analogues

A systematic density functional theory and wave function theory investigation on the geometrical and electronic structures of the electron-deficient diboron aurides B2Aun-/0 (n = 1, 3, 5) and their mixed analogues B2HmAun- n (m 1 n 5 3, 5) has been performed in this work. Ab initio theoretical evidences strongly suggest that bridging gold atoms exist in the ground states of C-2v B2Au- ((1)A(1)), C-2 B2Au3-((1)A), C-2v B2Au3(B-2(1)), C-2v B2Au5 ((1)A(1)), and Cs B2Au5((2)A ''), which all prove to possess a B-Au- three-center-two-electron (3c-2e) bond. For B2HmAun- (m + n - 3, 5) mixed anions, bridging B-Au-B units appear to be favored in energy over bridging B-H-B, as demonstrated by the fact that the Au-bridged C-2v B2H2Au- ((1)A(1)), C-s B2HAu2- ((1)A'), and C-1 B2HAu4- ((1)A) lie clearly lower than their H-bridged counterparts C-s B2H2Au- ((1)A'), C-2 B2HAu2- ((1)A), and C-2v B2HAu4- ((1)A(1)), respectively. Orbital analyses indicate that Au 6s makes about 92-96% contribution to the Au-based orbitals in these B-Au-B 3c-2e interactions, whereas Au 5d contributes 8-4%. The adiabatic and vertical detachment energies of the concerned anions have been calculated to facilitate their future experimental characterizations. The results obtained in this work establish an interesting 3c-2e bonding model (B-Au-B) for electron-deficient systems in which Au 6s plays a major role with non-negligible contribution from Au 5d. (C) 2010 Wiley Periodicals, Inc. J Comput Chem 32: 218-225, 2011