CRYSTAL-STRUCTURES, DYNAMIC BEHAVIOR AND ELECTROCHEMICAL PROPERTIES OF THE COPPER(I) AND COPPER(II) COMPLEXES OF A NEW N2S2 LIGAND

The complexing properties of the new quadridentate N2S2 ligand N,N'-bis{[2-(phenylmethylthio)phenyl]methylene} ethane-1,2-diamine, L, with Cu(I) and Cu(II) have been investigated. The perchlorate salt of [CuL]+ occurs as orange crystals in which mirror image forms, [(+/-)-(R*,R*,S*)], of the highly distorted tetrahedral cation coexist. The CuN2-CuS2 dihedral angle = 60.0(1)-degrees, bond lengths and angles are Cu-S 2.285(1) and 2.258(1) angstrom, Cu-N 2.029(3) and 2.069(3) angstrom, N-Cu-N 82.7(1)-degrees, S-Cu-S 123.56(4)-degrees. In nitromethane solution, however, variable-temperature C-13 NMR spectroscopy indicates that [CuL]+ exists predominantly as an equilibrium mixture of the two other diastereomers, [(+/-)-(R*,R*,R*)] and [(+/-)R*, S*,S*)] for which the interconversion barrier corresponds to DELTA-G280 = 59.8 +/- 0.6 kJ mol 1. Exposure of an ethanolic solution of [CuL]ClO4 to the atmosphere leads to slow deposition of brown crystals of [CuL(H2O)][ClO4]2. Crystal structure determination revealed the Cu(II) cation to be square-pyramidal with the water molecule occupying the apical position: Cu-S 2.323(6) and 2.318(5) angstrom; Cu-N 1.94(1) and 2.00(2) angstrom; Cu-O (H2O) 2.29(1) angstrom. The crystals are achiral and racemic, arising through coexistence of the [(+/-)-(R*,R*)] enantiomeric forms of the complex. Cyclic voltammetry indicates a quasi-reversible system for which E1/2 = 0.28 V vs. saturated calomel electrode.