Synthesis and characterization of copper(II)-bis(pyridin-2-carbonyl)amine (pyca)-pseudohalide complexes: 2D superstructure formation through CH⋯O hydrogen bond and π⋯π interaction in [Cu(pyca)Cl(NCO)]

Three copper(II) complexes of type [Cu(pyca)(Cl)(Y)] (1–3) [pyca = bis(pyridin-2-carbonyl)amine; Y = NCO−, N3−, NCS−] have been synthesized and characterized on the basis of microanalytical, spectroscopic, magnetic, electrochemical, and other physicochemical properties. X-ray diffraction study in [Cu(pyca)(Cl)(NCO)] (1) reveals copper(II) center in a distorted trigonal bipyramidal environment through coordination by two pyridine N atoms, and one amine N atom of the tridentate ligand, one Cl−, and N atom of terminal NCO−. The mononuclear units in 1 are engaged in intermolecular CH⋯O hydrogen bonding leading to 1D chain, which are interlocked through face-to-face π⋯π interactions resulting in a 2D sheet. The complexes 1–3 exhibit solvatochromism as evidenced from UV–Vis study in different solvent media. They display high-energy intraligand 1(π–π∗) fluorescence at room temperature and intraligand 3(π–π∗) phosphorescence in glassy solutions (MeOH at 77 K) and solid states. Electrochemical electron transfer study in MeOH solutions shows a reductive response presumably due to copper(II)–copper(I) couple.