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 pentaaqua-mu-dipicolinatodipicolinatodizinc(II)-water(1/2) where two zinc ions are bridged by a carboxylate group. One zinc ion is coordinated by five water molecules and one carboxylate oxygen atom, and the other by four oxygen atoms and two nitrogen atoms from the two dipicolinate ligands. Compound 2 contains the 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 compounds 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 = 14.062(4), b = 10.057(5), c = 13.788(2) angstrom and beta = 116.55(3)degrees.