Non-linear optically active zinc and cadmium p-pyridinecarboxylate coordination networks

Non-centrosymmetric 1D and 3D coordination networks [Zn(L)(2)(H2O)](2).CH3CN.3H(2)O (1), and [Cd-2.5(L)(5)].EtOH.5H(2)O (2), have been synthesized hydro(solvo)thermally between Zn(II) or Cd(II) ions and methyl 4-[2-(4-pyridyl)ethenyl]cinnamate (L-Me), respectively. X-ray single-crystal diffractions studies show that 1 adopts a caterpillar-shaped I D chain structure, while 2 has a complicated 3D structure formed by linking cadmium-carboxylate chains with the L ligands. Both face-to-face and edge-to-face pi-pi interactions between the L ligands are key to the polar arrangement of the L ligands in 1. The dipole moments of all the L ligands have on the other hand essentially cancelled out in 2, and the polar axis is defined by the cadmium-carboxylate chains. Consistent with their polar structures, powder second harmonic generation measurements indicate that I and 2 exhibit powder SHG intensities of 75 and 20 versus alpha-quartz, respectively. (C) 2004 Elsevier B.V. All rights reserved.