Mixed ligand Co(II), Ni(II) and Cu(II) complexes containing terephthalato ligands. Crystal structures of diaqua(2,2 '-dipyridylamine)(terephthalato)metal(II) trihydrates (metal = cobalt or nickel)

Abstract

A series of nine ternary Co(II), Ni(II) and Cu(II) complexes with some aromatic diamines and dianion of terephthalic acid (tpht) have been synthesized and characterized by elemental analysis, magnetic susceptibility measurements, IR and diffuse-reflectance spectroscopy. All compounds were obtained as microcrystalline solids, stable in air and insoluble in common solvents. Two of them, [M(tpht)(dipya)(H2O)(2)]. 3H(2)O [M = Co(II), Ni(II); dipya = 2,2'-dipyridylamine], were obtained as single crystals and their crystal structures have been determined by X-ray structure analysis. Both structures consist of discrete [M(tpht)(dipya)(H2O)(2)](2+) complex units with two H2O molecules in the trans position. Three additional H2O molecules together with coordinated H2O and O atoms from COO groups make a three-dimensional network of hydrogen bonds. Terephthalato ligands are coordinated by only one COO group, which acts as a chelating ligand. Central metal ions are in a distorted octahedral environment. Based on the above-mentioned analysis and known crystal structures, the possible structures and geometry of the complexes are discussed. All Co(II) and Ni(II) complexes are pseudooctahedral and mononuclear, with only one of the tpht COO groups coordinated in a chelate mode. Cu(II) complexes have probably distorted octahedral geometry with bridging role of tpht ions and monodentate or strongly asymmetric coordination of COO groups.