New complexes of nickel and nickel/cobalt with tetrahydrofuran-2,3,4,5-tetracarboxylic acid, THF(COOH) 4. Crystal structures of Ni[THF(COOH) 2(COOH) 2](H 2O) 3 and Ni 0.7Co 0.3[THF(COOH) 2(COO) 2](H 2O) 3·H 2O and their thermal behaviour

Abstract

The reaction of NiCl 2·6H 2O with tetrahydrofuran-2,3,4,5-tetracarboxylic acid, THF(COOH) 4, partially deprotonated by Na 2CO 3 (1 : 1 metal/ligand molar ratio), yielded Ni[THF(COOH) 2(COO) 2](H 2O) 3 ( 1). The molecular structure of 1 was determined by X-ray diffraction on the monocrystal. The structure consists of a mononuclear neutral unit with the nickel atom coordinated by a [THF(COOH) 2(COO) 2] 2− ligand, which acts as a tridentate ligand, and three water molecules. Direct interaction of NiCl 2·6H 2O and CoCl 2·6H 2O (1 : 1 molar ratio) with THF(COOH) 4 previously deprotonated by Na 2CO 3 (1 : 1 metal/ligand molar ratio) gave, by slow evaporation of the solution obtained, green crystals of the non-stoichiometric complex Ni 0.7Co 0.3[THF(COOH) 2(COO) 2](H 2O) 3·H 2O ( 2). Its crystal structure was solved by single-crystal X-ray diffraction methods. The structure is similar to that determined for compound 1, but with 30% of the sites for the metal atom occupied by cobalt and including a water molecule of crystallization. The thermal decomposition of both compounds showed three effects: An endothermic effect, corresponding to the loss of water which occurred at about 150°C and second and third exothermic processes, which overlapped each other at ca 310 and 330°C, corresponding to the decomposition of the complex and subsequent formation of oxides at very low temperatures.