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

Non-centrosymmetric 1D and 3D coordination networks [Zn(L)2(H2O)]2 · CH3CN · 3H2O (1), and [Cd2.5(L)5] · EtOH · 5H2O (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 1D 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 π–π 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 1 and 2 exhibit powder SHG intensities of 75 and 20 versus α-quartz, respectively.