Comparative analysis of the electronic and EPR spectra of copper(II) and nickel(I) complexes; insights into nickel(I) electronic structure

The nickel(I) complex with the ligand 1,2-bis(pyridine-2-carboxamido)benzene (H(2)bphen), generated by reduction with sodium amalgam of the homologous nickel(II) complex, has been studied by EPR and electronic spectroscopy. The electronic, structural and bonding properties of the complex were elucidated based on a comparison of the EPR and UV/VIS data of isoelectronic complexes of (CUII)-C-63 and Ni-61(I) Of H(2)bphen. Analysis of the spectroscopic data revealed that the complex exhibits low covalency in the sigma in-plane bonding and high covalency in the out-of-plane pi bonds, and has enabled the assignment of the electronic bands at approximate to 13500 and 19600 cm(-1) of [Ni-I(bphen)](-) to d(xz), d(yz) <-- d(xy) and d(x2-y2) <-- d(xy) transitions. Implications for the spectral characterization of cofactor F-430 systems are also presented.