Structural diversity from co-crystal to 1D coordination polymers of 2,6-naphthalenedicarboxylic acid with 4,4′-bipyridine as coligand: structural and computational approach

Abstract

The co-crystal 2,6-naphthalenedicarboxylic acid (2,6-NDCA) and 4,4′-bipyridine (4,4′-bipy) I and metal (Li+) complex of 2,6-NDCA with 4,4′-bipy i.e. {[Li(2,6-NDC)0.5.(H2O)2] n .4,4′-bipy} II (2,6-NDC = 2,6-naphthalenedicarboxyle) have been characterized by single crystal X-ray diffraction, IR spectra, elemental, and TGA analyses. The co-crystals are stabilized by strong H-bonding between acid–base units whereas the Li+ ion based mixed complex is stabilized by both coordination and H-bonding interactions. During investigation of strong or weak intermolecular interactions, X-ray diffraction analysis and Hirshfeld surface analysis gave rise to comparable results but in the Hirshfeld surface analysis, two-third times more close contacts were observed. Thermogravimetry shows that the complex is stable up to 200 °C after the removal of coordinated water molecules. To get some insights in the chemical reactivity indices, the HOMO-LUMO gap, chemical potential, chemical hardness, and electrophilicity indices for both systems (in gas phase) have been analyzed on the basis of theoretical investigations along with their molecular electrostatic potential surfaces and the total electron density plots; I has been found to be more stable than II which appears to be because of the strong H-bonding interaction(s). The fingerprint plots demonstrate that these weak nonbonding interactions are important for stabilizing the crystal packing.