Study of the aqueous reactions of metallic ions with benzenetetracarboxylate ions: Part 1. Crystal structures of compounds of the types [M(H2O)6][C6H2(COO)2(COOH)2] (M=Mn, Co and Ni) and Ni(H2O)5(μ-C6H2(COO)4)Ni(H2O)5·6H2O

The reactions of several divalent transition metals with 1,2,4,5-benzenetetracarboxylate ions were studied in aqueous solution. Mn(II), Co(II) and Ni(II) produced ionic products of formula [M(H2O)6][C6H2(COO)2(COOH)2]. The three compounds were characterized by crystallographic methods. The results have shown that the three crystals are isostructural and that they belong to the monoclinic C2/c space group. The metal atom and two O atoms (from two aqua ligands) are located on a two-fold axis, while the other four aqua ligands are located in general positions. The anions contain an inversion center. The two hydrogens on the carboxylic functions form intramolecular H bonds with the carboxylate groups. The average MOH2 bond distances are 2.181(1) Å for Mn(II), 2.092(1) Å for Co(II) and 2.056(1) Å for Ni(II). The ions are linked together by extensive H bonds. With the Ni salt, a dinuclear species, containing a bridging benzenetetracarboxylato ligand was synthesized and characterized by X-ray diffraction. The compound Ni(H2O)5(μ-C6H2(COO)4)Ni(H2O)5·6H2O contains an inversion center in the center of the phenyl ring. The average NiOH2 distance is 2.0710(8) Å and the sixth NiO bond is 2.0356(7) Å. The Ni⋯Ni distance is 11.360(2) Å. The crystal is stabilized by a very elaborate H-bonding system forming a H-bonded three-dimensional network.