Enhanced second harmonic generation on passing from a mono- to a dicopper(II) bis(salicylaldiminato) schiff base complex.

A new ligand (H2LOH) obtained from the Schiff base condensation of 4-(diethylamino)salicylaldehyde with 1,3-diamino-2-propanol is reported, which yields two different copper(II) complexes: CuLOH and Cu2LO(AcO). Crystal data are as follows. CuLOH*EtOH: monoclinic, P2(1)/n, a = 17.810(2) A, b = 8.515(1) A, c = 18.912(2) A, beta = 112.72(1) degrees, Z = 4. Cu2LO(AcO)*1/2H2O: monoclinic, P2(1)/c, a = 21.407(4) A, b = 15.308(2) A, c = 20.156(3) A, beta = 116.83(2) degrees, Z = 4. Cu2LO(AcO)*1/2H2O is antiferromagnetically coupled with J = -207.7 cm(-1) (J being the parameter of the exchange Hamiltonian H = -J S(A).S(B)). CuLOH and Cu2LO(AcO) exhibit good transparencies in the visible frequency range with absorption maxima at 353 and 372 nm, respectively. An enhancement of 83% of the quadratic hyperpolarizability (beta) is observed by the electric field induced second harmonic (EFISH) technique on passing from the mono- to the dinuclear species. Qualitative ZINDO/SCI quantum-chemical predictions give a satisfactory account for this enhancement. The spin dependence of the NLO response of Cu2LO(AcO)*1/2H2O is found to be negligible within the framework of the DFT theory.