The complexing properties of the new quadridentate N2S2 ligand N,N′-bis{[2-(phenylmethylthio)phenyl]-methylene}ethane-1,2-diamine, L, with CuI and CuII 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)°, bond lengths and angles are Cu–S 2.285(1) and 2.258(1)Å, Cu–N 2.029(3) and 2.069(3)Å, N–Cu–N 82.7(1)°, S–Cu–S 123.56(4)°. In nitromethane solution, however, variable-temperature 13C 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 ΔG280‡= 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 CuII cation to be square-pyramidal with the water molecule occupying the apical position: Cu–S 2.323(6) and 2.318(5)Å; Cu–N 1.94(1) and 2.00(2)Å; Cu–O (H2O) 2.29(1)Å. 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 E½= 0.28 V vs. saturated calomel electrode.