Supramolecular assemblies involving unusual N(nitrile)∙∙∙π(fum) and nitrile-nitrile non-covalent contacts in fumarato and succinato bridged polymers of Co(II) and Ni(II): Experimental and theoretical studies.

• Fumarato and succinato bridged Co(II) and Ni(II) polymers. • Unusual N(nitrile)∙∙∙π(fum) and antiparallel CN⋯CN interactions. • Inclusion of (H 2 O) 2 cores within supramolecular host cavities. • DFT calculations in combination with NCI plot/QTAIM analysis. • Energetically significant structure-guiding non-covalent interactions. Two new Co(II) and Ni(II) coordination polymers viz. [Co(H 2 O) 2 (μ-fum)(3-CNpy) 2 ] n (1) and {[Ni(H 2 O) 2 (μ-succ)(4-CNpy) 2 ]·2H 2 O} n (2) (where, fum= fumarate, CNpy = cyanopyridine, succ = succinate) have been synthesized and characterized using single crystal XRD, elemental analysis, spectroscopic (IR and electronic) techniques and TGA. Compound 1 crystallizes as a fumarato bridged Co(II) polymer; whereas, compound 2 is a succinato bridged Ni(II) polymer. The presence of various non-covalent interactions in the compounds stabilizes the layered assemblies of the compounds. Antiparallel nitrile∙∙∙nitrile interactions are observed in both the crystal structures involving the nitrile moieties of coordinated CNpy which provide rigidity to the compounds. Further analysis reveals that the N-atom of –CN group of 3-CNpy in 1 is involved in unusual N(nitrile)∙∙∙π(fum) interactions with the π-electrons of the C=C bond of fum. Enclathrated (H 2 O) 2 cores within the supramolecular host cavity of compound 2 provides additional reinforcement to the crystal structure. We have also carried out theoretical studies to analyze the π-stacking and H-bonding interactions present in the crystal structure of compound 1 using quantum theory of atoms-in-molecules (QTAIM), non-covalent interaction plot (NCI plot) and molecular electrostatic potential (MEP) surface analysis. The MEP value at the N-atom of the cyano group of 1 is negative and the value is neutral over the double bond of the fum ; indicating the possibilities of formation of N(nitrile)∙∙∙π(fum) interactions. Energetic analysis suggests that antiparallel π-stacking observed between the 3-CNpy moieties in 1 is the most dominating force followed by N(nitrile)∙∙∙π(fum) interaction and finally the H-bonds. [Display omitted] Fumarato and succinato bridged coordination polymers of Co(II) and Ni(II) involving energetically significant structure guiding N(nitrile)∙∙∙π(fum), antiparallel nitrile∙∙∙nitrile and aromatic π-stacking interactions. [ABSTRACT FROM AUTHOR]