Issue 14, 2015

Copper pyromellitates: a complex story


Reaction of copper(II) salts with pyromellitic acid (benzene-1,2,4,5-tetracarboxylic acid) and bases using slow vapour and gel diffusion techniques produces a variety of complexes containing copper and pyromellitate ions and solvent molecules, both coordinated (usually as terminal ligands) and uncoordinated. In some cases molecules of base are also coordinated, and organic or alkali metal cations may be present. Most of the complexes are 2- or 3-dimensional polymeric networks as expected, though there are also some discrete molecular complex ions, which are unusual for pyromellitate complexes of metals. Coordination of copper(II) is most often square pyramidal with a long apical bond, but with some examples also of square-planar coordination supplemented by additional secondary interactions with carboxylates or solvent molecules above and below the plane to give distorted octahedral geometry. Pyromellitate is fully deprotonated in all but one product, and usually coordinates to 2, 4 or 6 copper ions, and additionally to 8 alkali metal ions where these are present. Hydrogen bonding plays a significant role in all the structures, its role ranging from formation of discrete clusters of coordinated and uncoordinated water molecules to extensive 3-dimensional networks. The impressive structural variety arises from the combination of rigidity of the benzene ring and individual carboxylate groups with torsional flexibility in the connections of these groups, together with the availability of different coordination geometries for copper(II). The results illustrate the considerable structural versatility of pyromellitate ligands and the unreliability of structural design in benzenepolycarboxylate coordination chemistry.

Graphical abstract: Copper pyromellitates: a complex story

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Article information

Article type
06 Mar 2015
09 Mar 2015
First published
09 Mar 2015
This article is Open Access
Creative Commons BY license

CrystEngComm, 2015,17, 2857-2871

Author version available

Copper pyromellitates: a complex story

W. Clegg, J. M. Holcroft and N. C. Martin, CrystEngComm, 2015, 17, 2857 DOI: 10.1039/C5CE00470E

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