On the Importance of H-Bonding Interactions in the Enclathration of Boric Acids in Na(I) Polymers: Experimental and Theoretical Studies

Abstract

Two Na(I) coordination polymers, namely, {Na(BA)2(μ-H2O)2}n{adp}n (1) and {[Na2(μ-BA)(μ-fum)(μ-H2O)4](BA)}n (2) (where, BA = boric acid, adp = adipic acid, fum = fumarate),were prepared and characterized using elemental analysis, TGA, FT-IR, and single-crystal X-ray diffraction techniques. Various unconventional supramolecular interactions, i.e., CH∙∙∙HC and parallel CO∙∙∙CO interactions, stabilize the layered assembly of compound 1. Interesting dual enclathration of BA molecules within the supramolecular host cavities formed by O-H∙∙∙O and C-H∙∙∙C interactions stabilizes the crystal structure of compound 2. The H-bonding interactions in 1 and 2 were further studied theoretically using the quantum theory of atoms in molecules (QTAIM) and the noncovalent interaction plot (NCI Plot) computational tools. The energy of the H-bonds was estimated using the potential energy density at the bond critical points. Theoretical calculations confirmed the presence of O-H∙∙∙O H-bonding interactions in both compounds, forming structure-guiding R22(8) synthons relevant for the stability of the compounds.