摘要:
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) Angstrom for Mn(II), 2.092(1) Angstrom for Co(II) and 2.056(1) Angstrom 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)(mu-C6H2(COO)(4))Ni(H2O)(5). 6H(2)O contains an inversion center in the center of the phenyl ring. The average Ni-OH2 distance is 2.0710(8) Angstrom and the sixth Ni-O bond is 2.0356(7) Angstrom. The Ni ... Ni distance is 11.360(2) Angstrom. The crystal is stabilized by a very elaborate H-bonding system forming a H-bonded three-dimensional network. (C) 2000 Elsevier Science S.A. All rights reserved.