The molecular geometric and electronic structures of Pd(0) and Pd(I) dinuclear complexes Pd2L2 and Pd2L2X2 (L＝Me2PCH2PMe2; X＝F, Cl, Br, I, H) have been investigated by means of ab initio HF, MP2 and density functional theory (DFT) methods. It was found that the interaction between Pd atoms of Pd2L2 was mainly due to the electronic correlation, and the interaction between Pd atoms of Pd2L2X2 was mainly due to the bonding interaction of 4d orbitals. The MP2 and local spin density (LSD) Xα methods had good performance in reproducing the experimental geometric features. In Pd2L2, the counteractions of 4d bonding and anti-bonding orbitals largely weaken the strengths of Pd—Pd bond. However, the bonding of X atom with Pd2L2 makes the occupation of electrons in Pd—Pd anti-bonding orbitals reduced and bonding strength increased. There are good linear correlations between the Pd—Pd bond lengths and NAO Pd—Pd bond orders of Pd2L2 and Pd2L2X2 from the natural orbital analysis. The electronic absorption spectra of the Pd dinuclear complexes have been investigated by the TDDFT method. The influence of haloid ligands on the electronic spectra of Pd2L2X2 was also examined and some explanations were given by the changes of orbital energy level.

Key words: dinuclear palladium complex, density functional theory, Pd—Pd interaction, electronic structure, electronic spectra