Coordination of a Hemilabile N,N,S Donor Ligand in the Redox System [CuL 2 ] +/2+ , L = 2‐Pyridyl‐ N ‐(2′‐alkylthio­phenyl)methyleneimine

The new copper(I) complexes [Cu(L1)2](BF4), L1 = 2-pyridyl-N-(2′-methylthiophenyl)methyleneimine, and [Cu(L2)2](ClO4), L2 = 2-pyridyl-N-(2′-benzylthiophenyl)methyleneimine, have been prepared and structurally characterized. In contrast to the known [Cu(L1)2](ClO4)2, which exhibits partial thioether S binding to effect five-coordinate Cu2+, the copper(I) compounds reported here contain four-coordinate metal ions with exclusively N-donor binding. Cyclic voltammetry reveals a fully reversible oxidation of the CuI species, which suggests a small barrier for reorganization. The reduction at negative potentials is irreversible for compounds [Cu(L)2](X) and for the structurally characterized new compound [Cu(L1)(PPh3)2](ClO4). UV/Vis spectroelectrochemistry shows the typical low-energy absorption bands of copper(I) (MLCT transition) and copper(II) (ligand-field transition) in the visible region; the CuII form develops an intense band at 350 nm attributed to a S-to-Cu ligand-to-metal charge transfer (LMCT).