Solid-State Nonlinear Optical Properties of Mononuclear Copper(II) Complexes with Chiral Tridentate and Tetradentate Schiff Base Ligands.

Salen-type metal complexes have been actively studied for their nonlinear optical (NLO) properties, and push-pull compounds with charge asymmetry generated by electron releasing and withdrawing groups have shown promising results. As a continuation of our research in this field and aiming at solid-state features, herein we report on the synthesis of mononuclear copper(II) derivatives bearing either tridentate NO Schiff bases L and pyridine as the forth ancillary ligand, [Cu(L)(py)](ClO) (-), or unsymmetrically-substituted push-pull tetradentate NO Schiff base ligands, [Cu(5-A-5'-D-saldpen/chxn)] (-), both derived from 5-substituted salicylaldehydes (sal) and the diamines (1,2)-1,2-diphenylethanediamine (dpen) and (1,2)-1,2-diaminocyclohexane (chxn). All compounds were characterized through elemental analysis, infrared and UV/visible spectroscopies, and mass spectrometry in order to guarantee their purity and assess their charge transfer properties. The structures of - were determined via single-crystal X-ray diffraction studies. The geometries of cations of - and of molecules - were optimized through DFT calculations. The solid-state NLO behavior was measured by the Kurtz-Perry powder technique @1.907 µm. All chiral derivatives possess non-zero quadratic electric susceptibility () and an efficiency of about 0.15-0.45 times that of standard urea.