A Highly Stable Framework of Crystalline Zinc Phosphite with Selective Removal, Recovery, and Turn-On Sensing Abilities for Mercury Cations in Aqueous Solutions

A highly stable framework of organic-inorganic hybrid zinc phosphite (NTOU-4) and its cobalt analogue (NTOU-4a) were synthesized under the hydro(solvo)thermal conditions and structurally characterized by single-crystal X-ray diffraction. Their frameworks consisted of inorganic metallophosphite chains, in which the metal atoms were interlinked through 1H-1,2,4-triazole-3,5-diamine and 1,4-benzenedicarboxylate linkers to form new crystalline materials. It is extremely difficult to achieve the consolidation of three distinct coordinations of metal-carboxylate, metal-triazolate, and metal-phosphite bonds into one crystal, resulting in the synthesis of the first mixed-ligand terephthalate-metallophosphite solids in the absence of organic molecules as templates or space-filling counters in their structures. Interestingly, the zinc compound not only exhibits high thermal stability (up to 400 degrees C in air) and chemical resistance to seawater, aqueous solutions (pH3-11), and organic solvents at boiling conditions, but also shows selective removal, recovery, and turn-on sensing abilities of toxic mercury ions in aqueous solutions. Furthermore, the synthesis, characterization, and the difference of the framework stabilities between isostructural zinc and cobalt compounds are also reported.