Syntheses and crystal structures of two new nickel(II) complexes with pyrazine-2,3,5,6-tetracarboxylate

Abstract

Pyrazine-2,3,5,6-tetracarboxylic acid (H4pztc) reacted with Ni(ClO4)2·6H2O and 1,10-phenanthroline (phen) in aqueous solutions to form two different complexes, [Ni(H2pztc)(phen)H2O]·H2O (1), [Ni(phen)3](H2pztc)·10.5H2O (2), under hydrothermal conditions and at room temperature respectively. In 1, Ni(II) ion is coordinated by tridentate chelated H2pztc2−. The carboxyl and carboxylate groups of H2pztc2− are roughly coplanar with the pyrazine ring and form intramolecular hydrogen bonds. While in 2, H2pztc2− remains uncoordinated, the carboxyl and carboxylate groups of H2pztc2− are out of plane of the pyrazine ring and do not form intramolecular hydrogen bonds. H2pztc2− and water molecules form negatively-charged channels and the channels are filled with [Ni(phen)3]2+ in the 3D supramolecular structure of 2. In addition, a novel water tape is present in 2.