Synthesis, characterization and theoretical investigation of the structure, electronic properties and third-order optical nonlinearity of M(dnpi)2 (M = Cu2+, Co2+ and Pb2+; dnpi=4,5-Diphenyl-2-(4-nitrophenyl)-1H-imidazole)

Three complexes of M(dnpi)(2) (M = Cu2+, Co2+ and Pb2+; dnpi = 4,5-Diphenyl-2-(4-nitrophenyl)-1H-imidazole) were synthesized and characterized by elemental analysis, IR, UV-Vis, X-ray diffraction and the Z-scan technique. The X-ray diffraction results revealed crystal structures with a rare tetrahedral Co(dnpi)(2) and distorted pyramidal Pb(dnpi)(2). The equilibrium geometries and molecular orbitals of the complexes are calculated based on B3LYP using LANL2DZ basis sets. Their nonlinear optical properties were measured by the Z-scan technique, and yielded a nonlinear absorption coefficient, gamma, of 2.1 x 10(-12) m/W for Co(dnpi)(2) and 4.7 x 10(-11) m/W for Pb(dnpi)(2). In the range of the visible spectrum, the maximum absorption wavelengths are at 410.0 nm (epsilon = 4.42 x 10(4) L mol(-1) cm(-1)), 399.8 nm (epsilon = 3.61 x 10(4) L mol(-1) cm(-1)) and 441.7 nm (epsilon = 2.51 x 10(3) L mol(-1) cm(-1)) for Cu(dnpi)(2), Co(dnpi)(2) and Pb(dnpi)(2), respectively. (C) 2013 Elsevier Ltd. All rights reserved.