Abstract: The ab initio MP2 method was employed to fully optimize the structures of C（AuPH₃）₄[1a（C_4v ）;1b（T_d）],[C（AuPH₃）₅]⁺[2a（C_3h ）;2b（C_s）] and [C（AuPH₃）₆]²⁺[3a（C_2h ）;3b（C_2v）]. The calculated geometry parameters agreed with the experimental values. The natural bond orbitals （NBO） analysis at the second-order perturbation approximation level shows that the Au atom possesses d（sp） hybrid character,in which the （sp） means the mixed orbital character with the s and p orbitals. The interplay between the radial C—Au σ bonding and the tangential Au-Au weak interaction stabilizes the title compounds. Compounds 1a,2 and 3 possess 2 or 3 three-center two-electron bondings,suggesting that it is necessary to adopt a delocalized molecular orbital bonding description to account for their electronic and stereochemical requirements.

Key words: Carbon-centered gold cluster, Natural bond orbitals, Three-center two-electron bonding