RAMAN SPECTROELECTROCHEMICAL STUDIES AND CRYSTAL-STRUCTURE OF A BINUCLEAR COPPER(I) COMPLEX WITH A BRIDGING DIIMINE LIGAND

Raman spectroelectrochemical and X-ray crystallographic studies have b een made for the binuclear copper(I) complex, [(Ph(3)P)(2)Cu(dpq)Cu(PP h(3))(2)][BF4](2), where dpq is the bridging ligand 2,3-di(2-pyridyl)q uinoxaline. The X-ray data show that the pyridine rings are twisted ou t of plane with respect to the quinoxaline ring which is itself non-pl anar. The UV/VIS spectra of the metal-to-ligand charge-transfer excite d state and those of the electrochemically reduced complex are similar . The resonance-Raman spectrum of the latter species exhibits little c hange in the frequency of the pyridinylquinoxaline inter-ring C-C bond stretching mode, compared to the ground electronic state. This sugges ts minimum change in the inter-ring C-C bond order in the electrochemi cally or charge-transfer generated radical anion. Semiempirical molecu lar-orbital calculations on both the neutral dpq and radical anion sho w two near-degenerate lowest unoccupied orbitals in the neutral specie s. One is strongly bonding across the inter-ring C-C bond while the ot her is almost nun-bonding. The Raman data suggest that it is this latt er orbital which is populated in the transient and electrochemical exp eriments.