Synthesis and crystal structures of the flexible Schiff base complex bis(N-1,2-diphenylethyl-salicydenaminato-κ2N,O)copper(II) (methanol): A rare case of solvent-induced distortion

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-[CuN2O2] 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.

Graphical abstractWe report a new mononuclear Schiff base copper(II) complex, bis(N-1,2-diphenylethyl-salicydenaminato-κ2N,O)copper(II) (green form, 1) and its co-crystal containing methanol solvent molecules (brown form, 2), which take different conformations in the solid state. We also discuss their absorption spectra in various solvents in view of dipole moment and transitions.Figure optionsDownload full-size imageDownload as PowerPoint slide