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)(H2O)2] (1) and [Co(3‒Apy)2(4–Clbz)2(H2O)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 ‒NH2 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.