A Hexadecanuclear Copper(I)-Copper(II) Mixed-Valence Compound: Structure, Magnetic Properties, Intervalence Charge Transfer, EPR, and NMR
Résumé
Hexadecanuclear copper mixed-valence complex 2 containing 10 CuII centers and 6 CuI centers was isolated with N,O donor ligands. From the X-ray crystal structure, 2 was found to contain a centrosymmetric dimeric cation - each monomeric unit composed of eight copper centers. It displays a very broad and weak intervalence charge-transfer band around 1100 nm at room temperature in the solid state. Variable-temperature magnetic susceptibility measurements indicate an S = 1/2 ground state for half of 2, explicitly, each Cu8 moiety has a g value around 2.26. Complex 2 was examined by NMR spectroscopy at room temperature in solution and by EPR at low temperature; the data indicates that the valence is delocalized in 2 at room temperature but localized at low temperature.