Spectroscopic and Electronic Structural Studies of Blue Copper Model Complexes. 2. Comparison of Three- and Four-Coordinate Cu(II)−Thiolate Complexes and Fungal Laccase

To evaluate the importance of the axial ligand in blue Cu centers, the electronic structure of a three-coordinate model compound LCuSCPh3 (2, L = β-diketiminate ligand) is defined using low-temperature absorption, magnetic circular dichroism (MCD), X-ray absorption spectroscopy (XAS), and resonance Raman (rR) profiles coupled with density functional calculations. Using these excited-state spectroscopic methods the electronic structure of 2 is compared to that of a four-coordinate blue Cu model compound LCuSCPh3 (1, L = tris(pyrazolyl)hydroborate ligand) and the three-coordinate blue Cu center in fungal laccase. The spectral features of 2 are substantially altered from those of 1 and reflect a trans influence of the β-diketiminate ligand that involves a strong interaction with the Cu dx2-y2 orbital, concomitant with a decreased S pπ interaction with the Cu dx2-y2 orbital. The lack of an axial ligand coupled with the influence of this equatorial donor leads to many of the perturbed spectral features of 2 re...

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