Absorption Band in the Near-Ultraviolet Region Observed for Binuclear Copper(II) Complexes

Elucidation of the origin of near-ultraviolet absorption believed to be characteristic of binuclear copper(II) complexes was attempted. The absorption was attributed to charge transfer transitions from nonbonding orbitals of bridging oxygen atoms to the vacant metal d-orbital. Appearance of the band in the near-ultraviolet region was interpreted in terms of the red-shift due to the decreasing s-character of the nonbonding orbitals enforced by the steric requirement of the complex. On this basis, the spectra of dialkoxo- or dihydroxo- bridged complexes and of copper alkanoates can consistently be explained.

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