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.