Novel MOFs with tetrahedral cavity assembled from 4,4′,4″-s-triazine-2,4,6-triyltribenzoic acid (H3TATB)

Three novel 3D complexes {H2[Zn6(μ4-O)(TATB)4]}n (1), [Cd3(TATB)2]n (2), and [Mn3(TATB)2]n (3) were synthesized from 4,4′,4″-s-triazine-2,4,6-triyltribenzoic acid (H3TATB) and corresponding metal salts under hydrothermal conditions. These complexes were characterized by elemental analyses, IR spectra, luminescent spectra, thermogravimetric analysis (TGA), and single crystal structure. Complex 1 adopted a straight Zn4(μ4-O) linked by TATB3− subunit to form an adamantane structure with a fully empty tetrahedral cavity. Two naked protons floated in the complex. This structure supports the existence of naked protons in nature. In complexes 2–3, the six deprotonated carboxylic oxygen of TATB3− coordinated to eight metal ions to form a 3D close-packed structure. Its density of 1.837 mg m− 3 made complex 2 one of the most closely packed structure based on H3TATB ever determined. Coordination polyhedral linked each other to form a diamondoid metal–oxygen framework in 2 and 3. All the coordination polymers were thermally stable up to 470 °C. These were the most thermally stable coordination polymers. A high-resolution transmission electron microscope indicated that the metal oxide is porous with pore diameters of ~ 2 nm.

Graphical AbstractThree new coordination polymers were assembled from 4,4′,4″-s-triazine-2,4,6-triyltribenzoic acid and corresponding metal salts under hydrothermal conditions. All three have adamantine M–O framework with very higher thermal stability. {H2[Zn6(μ4-O)(TATB)4]}n (1) has nano-size tetrahedron cavity and naked protons.Figure optionsDownload as PowerPoint slideResearch highlights
► {H2[Zn6(μ4-O)(TATB)4]}n, [Cd3(TATB)2]n and [Mn3(TATB)2]n were synthesized.
► {H2[Zn6(μ4-O)(TATB)4]}n has empty tetrahedron cavity with a dimension of ~ 18 Å.
► Two naked protons exist in {H2[Zn6(μ4-O)(TATB)4]}n.
► [Cd3(TATB)2]n and [Mn3(TATB)2]n are both packed tightly with very high thermal stability.
► After removal of the organic ligand, [Mn3(TATB)2]n becomes a porous metal oxide.