THE STRUCTURE OF 2 SOLID ZINC DIPICOLINATE COMPLEXES

When equal amounts of dipicolinic (pyridine-2,6-dicarboxylic) acid and zinc sulfate were incubated at 277 K, two different zinc dipicolinate compounds of composition Zn2(C7H3NO4)2 . 7H2O (1) and Zn(C7H4NO4)2 . 3H2O (2) were formed. An X-ray crystallographic investigation revealed that 1 comprises a solid dinuclear complex a-mu-dipicolinatodipicolin atodizinc(II)-water(1/2) where two zinc ions are bridged by a carboxyl ate group. One zinc ion is coordinated by five water molecules and one carboxylate oxygen atom, and the other by four oxygen atoms and two n itrogen atoms from the two dipicolinate ligands. Compound 2 contains t he mononuclear complex bis(hydrogendipicolinato)-zinc(II)-water(1/3), with the same zinc-dipicolinate coordination as in 1. In both 1 and 2 the coordination polyhedra are distorted octahedra with Zn-N = 2.003(4 )-2.016(4) angstrom and Zn-O = 2.078(3)-2.349(3) angstrom. The compoun ds crystallize in the monoclinic space group P2(1)/c with four formula units in the unit cell. The cell parameters are: 1, a = 8.382(2), b = 27.408(6), c = 9.709(3) angstrom and beta = 98.61(3)degrees; 2, a = 1 4.062(4), b = 10.057(5), c = 13.788(2) angstrom and beta = 116.55(3)de grees.