Cu(II) and Co(II) coordination solids involving unconventional parallel nitrile(π)‒nitrile(π) and energetically significant cooperative hydrogen bonding interactions: Experimental and theoretical studies

Abstract Two new Cu(II) and Co(II) coordination complexes viz. [Cu(3‒CNpy)(PDC)(H 2 O) 2 ] ( 1 ) and [Co(3‒Apy) 2 (4–Clbz) 2 (H 2 O) 2 ] ( 2 ) [3‒CNpy = 3‒cyanopyridine, PDC = 2,6‒pyridinedicarboxylate, 4–Clbz = 4-chlorobenzoate, 3‒Apy = 3-Aminopyridine] have been synthesized at room temperature and characterized by single crystal X-ray diffraction, FT-IR spectroscopy, electronic spectroscopy, elemental analyses and thermogravimetric analysis (TGA). The structures reveal weak non-covalent contacts along with hydrogen bonding interactions that forms 2D network architectures in both the complexes. The theoretical study has been devoted to the analysis of the intermolecular π–π and H-bonding interactions that are observed in the solid state of compounds 1 and 2 . Particularly in compound 1 , the unconventional parallel π–π interactions are observed between the π-systems of the nitrile moieties in the coordinated 3–CNpy ligands. Previous reports have shown that the anti-parallel π-stacking is the most favorable arrangement in metal-coordinated pyridine rings due to the maximum dipole-dipole interaction. Theoretical calculations suggest that in compound 1 , the alignment of the nitrile groups are parallel and of attractive nature. Moreover, the coordination of 3–CNpy to the metal center reinforces the dipole … dipole attraction. In compound 2 , the non-planarity of the ‒NH 2 group and the influence of the metal coordination of 3‒Apy result in remarkable and energetically significant cooperative hydrogen bonding interaction. The interactions have been characterized using AIM and the non-covalent interaction plot (NCI plot) index analyses.