Copper(II) complexes of 8-hydroxyquinoline derivatives: alternative methods for obtaining crystals suitable for X-ray structural analysis

Six new [Cu(XQ) 2 ] complexes (HXQ are derivatives of 8-hydroxyquinoline bearing methyl or aldehyde functional groups) were prepared with an emphasis on their preparation in a crystalline state using liquid-liquid, vapour-liquid and horizontal diffusions. Their composition is [Cu(dClMeQ) 2 ] ( 1 ), [Cu(dBrMeQ) 2 ] n ( 2 ), [Cu(dIMeQ) 2 ] n ( 3 ), [Cu(AQ) 2 ] n ( 4 ), [Cu(dBrAQ) 2 ] n ( 5 ) and [Cu(dIAQ) 2 ] n ( 6 ) (HdClMeQ is 5,7-dichloro-8-hydroxyquinaldine, HdBrMeQ is 5,7-dibromo-8-hydroxyquinaldine, HdIMeQ is 5,7-diiodo-8-hydroxyquinaldine, HAQ is 8-hydroxyquinoline-2-carbaldehyde, HdBrAQ is 5,7-dibromo-8-hydroxyquinoline-2-carbaldehyde and HdIAQ is 5,7-diiodo-8-hydroxyquinoline-2-carbaldehyde). The complexes were characterised by infrared and UV-vis spectroscopy, elemental analysis and X-ray structural analysis (except 1 ). Deprotonated XQ ligands bind as bidentate chelates to the copper atom via the oxygen and nitrogen atoms of 8-hydroxyquinoline rings in all five compounds in the equatorial plane of an elongated tetragonal bipyramid. Oxygen ( 2c , 4c - 6c ) or iodine atoms ( 3c ) of neighbouring [Cu(XQ) 2 ] molecules occupy axial positions and polymeric structures are thus formed, which are stabilised by hydrogen bonds and π-π interactions. This is a probable reason for their insolubility in a wide range of solvents. Crystal packing was further investigated by Hirshfeld surface analysis.