Assembly of a helical zinc(II) chain and a two-dimensional cadmium(II) coordination polymer using picolinate and sulfate anions as bridging ligands

The initial use of the picolinate (pic(-))/sulfate "blend" in metal chemistry has yielded two neutral coordination polymers. Complexes [Zn-2(SO4)(pic)(2)(H2O)(3)](n) (1) and [Cd-2(SO4)(pic)(2)(H2O)(3)](n) center dot nH(2)O (2 center dot nH(2)O) were prepared by the reaction of MSO4 center dot xH(2)O [M = Zn, x = 7; M = Cd, x = 8/3] with one equivalent of picolinic acid (picH) in aqueous solution in the absence of external base. The structures of both compounds have been determined by single-crystal X-ray crystallography. Complex I consists of helical chains which interact through hydrogen bonds and stacking interactions to form a 3D, 5-connected network. Complex 2 - nH(2)O consists of ribbons that are crosslinked by the sulfato ligands to give a 2D, 4-connected network. Hydrogen bonds and stacking interactions lead to the formation of a 3D supramolecular architecture. In both coordination complexes, the pic ligand adopts two different bridging coordination modes (2.111 and 2.201 in 1; 2.211 and 2.201 in 2 center dot nH(2)O), while the SO42- behaves as a bidentate bridging 2.1100 (Harris notation) ligand. The Zn(II) complex has 5- and 6-coordinate metal ions, whereas 6- and 7-coordinate Cd-11 atoms are present in 2 - nH(2)O. Characteristic vibrational (IR, Raman) bands are discussed in terms of the known structures, and the coordination modes of the pic(-) and SO42- ligands. The thermal decomposition of the Cd(11) compound has also been studied. (C) 2007 Elsevier Ltd. All rights reserved.