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

Abstract

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.

From mononuclear to linear one-dimensional coordination species of copper(ii)–chloranilate: design and characterization

“…midpoints of chloranilate rings. 26,27 So far, only a few compounds are known that comprise two different coordination modes of chloranilic acid, 15,17,24,[38][39][40] which could be easily distinguished by IR spectra. The chain B is centrosymmetric, with Cu atoms and chloranilate rings having a crystallographic symmetry C i .…”

“…Generally, the use of nitrogen-and oxygen-donor ligands prevails in the construction of coordination polymers. 26,27 Actually, 2,5-DHQs can be regarded as "extended" (i.e. Also, a good combination of metal(s) and ligand(s) may lead to a coordination polymer which undergoes a reversible magnetic transition under appropriate external stimulus (temperature, pressure, irradiation by a specic wavelength).…”

“…Therefore, Cu 2+ complexes with CA and bidentate N-donor ligands are almost exclusively mononuclear, 26,27 while larger cations can accommodate zig-zag 1D polymers. The use of bridging mode of CA ligand should be in favour of formation of linear Cu(II) polymeric chains due to its ability to mediate electronic effects between paramagnetic metal ions, even at large Cu/Cu separation distance (exceeding 7Å).…”

Double Oxidative Dehalogenation of 2,5‐Bis(diisopropylphosphoryl)‐3,6‐difluoro‐1,4‐hydroquinone leading to Formation of New Copper Quinonoid Complexes

“…[27][28][29] Both apical positions in 5·2H 2 O are occupied by water molecules. These coordination bonds are rather long [O(4W)-Cu 2.358(4) Å, O(1W)-Cu 2.717 Å], which is most likely due to packing effects.…”

Alkali Salts of Nitranilic and Cyanochloranilic Acids

“…[2] They can bind to transition metal ions as terminal or bridging ligands, [2] and are able to form a wide variety of topologies, ranging from discrete complexes, [3][4][5][6][7][8] 1D and 2D coordination polymers [9][10][11][12][13][14] to porous 3D metal-organic frameworks. [15,16] A unique property of 2,5-dihydroxyquinones is their capability for face-to-face π-stacking.…”