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, NiIIL2 and CuIIL2 are centrosymmetric molecules, CoIIL2 exhibits a pseudo-tetrahedral molecular structure. The quadratic hyperpolarizabilities (β) of HL and CoIIL2, measured by electric field induced second harmonic (EFISH) technique, are equal to 66 and 110 × 10−30 cm5 esu−1, respectively. Beside a geometric effect (pseudo-Td 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 60° is found upon metal complexation.