Supramolecular association involving nitrile-nitrile interactions in polymeric Mn(II) coordination complexes: A combined experimental and theoretical study

Two new Mn(II) coordination polymers viz. [Mn(p-NBz)(2) (4-CNpy)(2)](n) (1) and [Mn(4-CNpy)(2)(H2BTC)(2)](n) (2) [p-NBz = p-nitrobenzoate, H3BTC = 1,3,5-benzenetricarboxylic acid and 4-CNpy = 4-cyanopyridine] 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 complexes are stabilized by several non-covalent interactions along with a rather uncommon nitrile(pi)-nitrile(pi) interactions resulting in layered structures. The supramolecular association in both the polymers results in 3D network structures involving C-H center dot center dot center dot O interactions in the direction perpendicular to the existing layers. The anti-parallel CN center dot center dot center dot CN interaction observed in the polymeric chains of the complexes are studied using DFT calculations and characterized using the Bader's theory of atoms-in-molecules. The interaction energy of the anti-parallel nitrile-nitrile interactions is similar to hydrogen bonds which are enhanced by the coordination of 4-CNpy to the Mn(II) metal centre.