Density functional theory study on the structures and electronic spectra of quadruply bonded metal compounds M2X4(PMe3)4 (M = Cr, Mo, W; X = F, Cl, Br, I)

The geometric and electronic structures of quadruply bonded metal dinuclear compounds M2Cl4(PMe3)(4) (M=Cr, Mo, W) and Mo2X4(PMe3)(4) (X=F, Cl, Br, I) have been investigated by means of density functional theory method with TZ2P-STO basis sets. It was shown that the title compounds can be accurately predicted by DFT included ZORA relativistic correction. The present calculations show that the ground state configurations of all quadruply bonded dinuclear compounds are sigma(2)pi(4)delta(2), and the energetic ordering of metal-metal orbitals is pi(lig)<pi(d)/sigma(d)<delta(d)<delta(d)*. Although the orbital energy levels changed with different metal atoms and haloid ligands, the energetic ordering of orbitals is not exchanged. The electronic excitation energies Of M2X4(PMe3)(4) have been studied employing the time-dependent density functional theory (TD-DFT). The effects of metal atoms, haloid ligands, and relativistic effect on these compounds were examined. The calculated transition energies are in fairly good agreement with experimental values and the spectral shifts trends predicted by TD-DFT compare well with available experimental data.