Crystal structure of a chloride-bridged copper(II) dimer: piperazine-1,4-dium bis(di-μ-chlorido-bis[(4-carboxypyridine-2-carboxylato-κ2N,O2)chloridocuprate(II)]

Abstract

Crystals of a new dimeric chloride-bridged cuprate(II) derived from pyridine-2,4-dicarboxylic acid were obtained solvothermally in the presence of piperazine and hydrochloric acid. The crystal structure determination of the title salt, (C4H12N2)[Cu2(C7H4NO4)2Cl4], revealed one of the carboxyl groups of the original pyridine-2,4-dicarboxylic acid ligand to be protonated, whereas the other is deprotonated and binds together with the pyridine N atom to the CuII atom. The coordination environment of the CuII atom is distorted square-pyramidal. One of the chloride ligands bridges two metal cations to form a centrosymmetric dimer with two different Cu—Cl distances of 2.2632 (8) and 2.7853 (8) Å, whereby the longer distance is associated with the apical ligand. The remaining chloride ligand is terminal at one of the basal positions, with a distance of 2.2272 (9) Å. In the crystal, the dimers are linked by intermolecular O—H...O hydrogen bonds, together with N—H...O and N—H...Cl interactions involving the centrosymmetric organic cation, into a three-dimensional supramolecular network. Further but weaker C—H...O and C—H...Cl interactions consolidate the packing.

Keywords

• crystal structure
• solvothermal synthesis
• coordination polymer
• centrosymmetric dimer