A new mononuclear copper(II) complex incorporating a bulky Schiff base ligand, bis(N-1,2-diphenylethyl-salicydenaminato-κ2N,O) copper(II) (green form) and its co-crystal containing methanol solvent molecules (brown form) have been synthesized and characterized by X-ray crystallography, XRD, IR and diffuse reflectance spectra in the solid state. This is a rare case in that both solvent free and containing crystals can be isolated and characterized. Both forms adopt a compressed tetrahedral trans-[CuN 2O2] coordination geometry with coordination bond angles of trans-N-Cu-N = 157.0(4)° and trans-O-Cu-O = 151.1(3)° for the brown form and trans-N-Cu-N = 141.3(3)° and trans-O-Cu-O = 139.9(2)° for the green form. The methanol solvent molecules force the complex of the brown form to adopt a more planar coordination environment in the solid state. Semi-empirical calculations (ZINDO) revealed the magnitude of the dipole moment of both molecules and that the energy of the green form is 5.7 kJ mol -1 higher than that of the brown form. In addition, absorption spectra in various organic solvents were measured and a relationship between absorption spectra and polarity of the solvents is discussed.
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