The use of solvatochromic mixed copper(II) chelates with N,N,N′,N′-tetramethylethylenediamine and tropolonato or hinokitiolato ligands, [Cu(trop/hino)(tmen)]B(C6H5)4, as indicator for Lewis basicity of solvents and low-coordinating anions

Mixed copper(II) chelates, [Cu(trop/hino)(tmen)]B(C6H5)4, were prepared with a tropolonato or hinokitiolato ligands (trop/hino) and N,N,N′,N′-tetramethylethylenediamine (tmen). These chelates turned out to be excellent Lewis basicity indicators in solution because their d-d bands continuously shift to red in wider ranges with increasing DN (donor number) of solvent, visualizing the competition between solvent molecule and anion for coordination to metal center.