Studies on Mixed Chelates. XIV. Influences of Solvent Polarity, and of Substituent Groups in β-Diketonate Ligands, on the Electronic Spectra of 5-Coordinated Mixed Copper(II) Chelates in Organic Solutions

Several chelates of copper(II), Cu(tmen)(dike)X, were newly obtained where tmen=N,N,N′,N′-tetramethylethylenediamine, dike= a β-diketonate ion, and X−= a halide or pseudohalide anion. These complexes exist as 5-coordinated species, with axially coordinated X−, in nonpolar solvents. In more polar solvents, they are ionized according to the solvent polarity, and form the following equilibrium mixtures: [Cu(tmen)(dike)X][Cu(tmen)(dike)]++X− 5–coordinated 4–coordinated(solvated, tetragonal) This equilibrium is controlled by (a) the strengths of acceptor and donor properties of the solvent, which can be expressed by its polarity factor (Pf), i.e., a linear combination of the donor number and acceptor number of the solvent, and (b) the changes of the ligand field strength of dike caused by the electron-withdrawing and -releasing properties of its α-substituent groups.