A Hexadecanuclear Copper(I)–Copper(II) Mixed‐Valence Compound: Structure, Magnetic Properties, Intervalence Charge Transfer, EPR, and NMR

Hexadecanuclear copper mixed‐valence complex 2 containing 10 Cu II centers and 6 Cu I 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 Cu 8 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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)