Ancillary ligand-assisted assembly of C3-symmetric 4,4′,4″-nitrilotribenzoic acid with divalent Zn2+ ions: Syntheses, topological structures, and photoluminescence properties

Abstract

4,4′,4″-nitrilotribenzoic acid (H3L), a C3-symmetric ligand, was found to self-assemble into two polymorphs driven by intermolecular hydrogen-bonding interactions. Reactions of this ligand with Zn2+ under solvothermal conditions resulted in four new coordination polymers bearing interesting structural motifs: [Zn2(L)2(py)2]·2(H2NMe2)+·DMF·2H2O (1), [Zn2(L)(H2L)(bipy)]·1.5H2O·Guest (2), [Zn2(L)2(bipy)]·2(H2NMe2)+·2DMF (3), and [Zn3(L)2(bpa)]·2H2O·Guest (4) (H3L=4,4′,4′′-nitrilotribenzoic acid, DMF=dimethylformamide, py=pyridine, bipy=4,4′-bipyridine, bpa=1,2-bis(4-pyridyl)diazene). Single-crystal structural analysis revealed that compound 1 exhibits a rare example of twofold interpenetrating anionic 3D (3,3)-net framework containing helical channels, whereas in 2, the 3D pillar-layer structure generated from bipy-pillared Zn2(L)(H2L) layer is further reinforced by intermolecular hydrogen bonding among pairs of free –COOH units. Compound 3 shows an interesting entangled architecture of 2D→3D parallel polycatenation consisting five-coordinated Zn2+ ions. Compound 4 displays a 3D pillar-layer framework with trimeric Zn3(CO2)6 serving as secondary building unit (SBU). The syntheses, structures, thermal stabilities, powder X-ray diffractions and solid-state photoluminescence properties for these crystalline materials have been carried out. In addition, supramolecular assembly of H3L under solvothermal conditions will also be addressed.