Halogen bonding interactions assisted network expansion of a tetrahedral cobalt phosphonate coordination polymer bearing 4,4′-bipyridine ligand

Abstract

A new cobalt phosphonate coordination polymer {[Co2(BrBzPO3)2(bpy)]∙2H2O}n (1) has been synthesized from the reactions of Co(NO3)2, 2-bromobenzyl phosphonic acid (BrBzP(O)(OH)2), and 4,4′-bipyridine (bpy) via reactants slow diffusion in H2O/ethanol solvent media at 60°C. Single-crystal X-ray diffraction analysis reveals that the Co(II) center has a {CoO3N} tetrahedral geometry. The coordinative network of 1 shows a layer structure constructed from Co–BrBzPO3 chains, which contain four-membered rings assembled from vertex-sharing {CoO3N} and {CPO3} tetrahedral units, connected by bpy linkers. It is worthy to note that net-to-net Br–Br halogen bonding interactions play the key supramolecular interactions to significantly dominate network expansion from a two-dimensional (3,4)-connected coordinative layer with a point symbol of (426)(42638) to a three-dimensional (4,4)-connected supramolecular network having a point symbol of (42638)(42638). Further, there are multiple noncovalent supramolecular interactions involving strong O–H∙∙∙O and weak C–H∙∙∙Br and C–H∙∙∙π interactions that provide powerful supports for stabilizing the whole crystal structure. Thermogravimetric (TG) analysis indicates that the coordinative network of 1 is high thermally stable upon heating to 340°C.