Structural Study of Bromo-Bridged One-Dimensional NiII–NiIVMixed Valence Complexes by Means of Exafs

Abstract

Nickel K-edge and Bromine K-edge EXAFS spectra have been measured for Br-bridged one-dimensional NiII-NiIV mixed valence compounds and their reference NiII and NiIV complexes. Fourier transforms of the Br K- and Ni K-edge EXAFS data of the mixed valence compounds show one and two sharp peaks, respectively, assigned to the Br-Ni distance, and the Ni-N and Ni-Br distances. By applying least-squares curve-fitting analyses for the Fourier back-transformed first peaks, a mean NiIV-Br distance for the mixed valence compounds has been determined to be 2.64 A, which is comparable to 2.63 A for the discrete NiIII complex. This suggests a significant elongation of the NiIV-Br bond owing to the charge transfer interaction between the NiII and NiIV atoms, resulting in the high electrical conductivities of NiII–NiIV compounds as compared with those of the Pd and Pt analogues. Mean Ni-N distances were accurately determined and were found to increase in the order, octahedral high-spin NiII > octahedral NiIII ≃ octahedra...