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

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 pi-pi and H-bonding interactions that are observed in the solid state of compounds 1 and 2. Particularly in compound 1, the unconventional parallel pi-pi interactions are observed between the pi-systems of the nitrile moieties in the coordinated 3-CNpy ligands. Previous reports have shown that the anti-parallel pi-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 center dot center dot center dot 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. (C) 2019 Elsevier B.V. All rights reserved.