Stacking of metal chelating rings with π-systems in mononuclear complexes of copper(II) with 3,6-dichloro-2,5-dihydroxy-1,4-benzoquinone (chloranilic acid) and 2,2'-bipyridine ligands.

A series of four novel mononuclear complexes of copper(II) with chloranilic acid and 2,2'-bipyridine were prepared and structurally characterised by X-ray structure analysis and IR spectroscopy. The complexes exhibit square-planar, square-pyramidal and octahedral coordination. The chloranilate dianion coordinates the Cu(II) atom in a terminal bidentate o-quinone-like mode forming a mononuclear complex species. The crystal packing of the aqua complex and the complexes with crystal water molecules are defined by hydrogen bonds. However, significant contributions are from interactions involving five-membered chelate rings with both types of ligands and intermolecular π-systems (bipyridine and chloranilate rings). The crystal packing of the complex with square planar Cu(II) coordination is dominated by interactions of the chelate rings with π-delocalised bonds and intermolecular π-systems. The occurrence of dimorphism could be related to the different types of these interactions in the stacks. The crystal packing of the octahedral complexes of the mono- and dihydrate solvates reveal 3D-networks with pores occupied by non-coordinated bipyridine molecules.