The molecular structures, electronic structures, and vibrational frequencies of dinuclear gold(II) complexes [Au(CH₂)₂PH₂]₂X₂ (X＝F, Cl, Br, I) have been investigated by ab initio HF, MP2 and density functional theory methods. The obtained results from the different methods were compared to the experimental values. HF method was found to be not suitable for the Au-Au system due to the strong correlation effect. The non-local exchange-correlation functional BP86 and hybrid functional B3LYP afforded long Au—Au and Au—X distances. The MP2 and local density functional theory methods provided good geo-metric features. Local density functional vibrational frequencies are in good agreement with available ex-perimental data. The studies of the electronic structure of the complexes have shown that the 5d and 6s electrons of Au atoms can make great contribution to the bonding of Au—Au and Au—X. The time-dependent density functional theory has been employed to calculate the electronic absorption spectra of the dinuclear gold(II) complexes. These calculations and the molecular orbital analysis have explained the behaviors of the complexes possibly.

Key words: dinuclear gold complex, ab initio, density functional theory, vibrational frequency, electronic spectra