Bridging gold: B-Au-B three-center-two-electron bonds in electron-deficient B(2) Au(n) (-/0) (n = 1, 3, 5) and mixed analogues

Abstract

A systematic density functional theory and wave function theory investigation on the geometrical and electronic structures of the electron-deficient diboron aurides B(2) Au n-/0 (n = 1, 3, 5) and their mixed analogues B(2) H(m) Au n- (m + n = 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) B(2) Au(-) ((1) A(1) ), C(2) B(2) Au 3-((1) A), C(2v) B(2) Au(3) ((2) B(1) ), C(2v) B(2) Au 5-((1) A(1) ), and C(s) B(2) Au(5) ((2) A″), which all prove to possess a B-Au-B three-center-two-electron (3c-2e) bond. For B(2) H(m) Au n- (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) B(2) H(2) Au(-) ((1) A(1) ), C(s) B(2) HAu 2- ((1) A'), and C(1) B(2) HAu 4- ((1) A) lie clearly lower than their H-bridged counterparts C(s) B(2) H(2) Au(-) ((1) A'), C(2) B(2) HAu 2- ((1) A), and C(2v) B(2) HAu 4- ((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.