Synthesis, crystal structures, and molecular hyperpolarizabilities of a new Schiff base ligand, and its copper(II), nickel(II), and cobalt(II) metal complexes

A new ligand (HL) obtained from the Schiff base condensation of 4-(diethylamino)salicylaldehyde with 4-nitroaniline is reported, with its nickel(II), copper(II), and cobalt(II) complexes. The crystal structures are reported for the four derivatives. While, (NiL2)-L-II and (CuL2)-L-II are centrosymmetric molecules, (CoL2)-L-II exhibits a pseudo-tetrahedral molecular structure. The quadratic hyperpolarizabilities (beta) of HL and (CoL2)-L-II measured by electric field induced second harmonic (EFISH) technique, are equal to 66 and 110 x 10(-30) cm(5) esu(-1), respectively. Beside a geometric effect (pseudo-T-d symmetry), the coordination of the metal center provides an intrinsic enhancement of the NLO response. In addition, an enhancement of the thermal stability of about 60degrees is found upon metal complexation. (C) 2004 Elsevier B.V. All rights reserved.