Structural diversity and optical properties in the M-X-isonicotinic (M = Zn, Cd; X = Cl, Br, I) system: New zero-, one-, two- and three-dimensional inorganic-organic hybrids

Assembly of isonicotinic acid ligand (HL) with metal halide, five new hybrid complexes [CdI2(C5H4NCOOH)(C5H4NHCOO)] center dot H2O (1), Na-n[ZnCl2(C5H4NCOO)](n) center dot 2nH(2)O (2), [CdX(C5H4NCOO)](n) (X = Br (3), I (4)) and [Cd3Cl2(OH)(2)(C5H4NCOO)(2)](n) (5) were obtained, which display a variety of structural motifs, ranging from zero-dimensional to complicated three-dimensional networks. Complex I possesses an isolated unit MX2 that is further connected into 3D networks through hydrogen bonding and n-T1 stacking interactions. Complex 2 is characterized by an infinite one-dimensional chain of zinc atoms bridged by L- ligands. While complexes 3 and 4 possess X-bridging (infinity)(1) [CdX2/2] inorganic chains connected by L- ligands to form a 2D hybrid network structure. In the case of 5, the cadmium(II) cation is bridged by mu(3)-Cl atom and mu(3)-OH- group to form a 2-D (infinity)(2)[Cd6/2Cl6/3(mu(3)-OH)2] inorganic layer which is further extended into 3-D framework by bridging L- ligand via Cd-N and Cd-O bonds. The optical properties of 1, 4, and 5 in the solid state are investigated at room temperature and time-dependent DFT (TDDFT) calculation using the B3LYP functional has been performed on 1. The result indicated that the emission band of 1 is attributed to an admixture of MLCT (metal-to-ligand charge-transfer) and LLCT (ligand-to-ligand charge-transfer). (c) 2006 Elsevier B.V. All rights reserved.