Zirconium Phosphonate Frameworks Covalently Pillared with a Bipyridine Moiety

This paper describes for the first time the covalent immobilization of 5,5‘-bis(dihydroxyphosphoryl)-2,2‘-bipyridine (H2O3P-bipy-PO3H2: 1) within the interlayer gallery of α and γ zirconium phosphonate structures. A mixed phosphite/phosphonate compound formulated as Zr(HPO3)0.8(O3P-bipy-PO3)0.6·5.3H2O was obtained by reaction of 5,5‘-bis(dihydroxyphosphoryl)-2,2‘-bipyridine and phosphorous acid with ZrOCl2·8H2O in the presence of HF. Another compound formulated as Zr(PO4)(H2PO4)0.5(HO3P-bipy-PO3H)0.25·2H2O was prepared by treatment of Zr(PO4)(H2PO4)·2H2O (γ-ZrP) with 5,5‘-bis(dihydroxyphosphoryl)-2,2‘-bipyridine. These new materials have been characterized by X-ray powder diffraction, IR spectroscopy, thermogravimetry, one- and two-dimensional MAS 31P NMR spectroscopy, and isothermal N2 adsorption−desorption. The mixed α-zirconium phosphonate has a mesoporous area of 330 m2/g (pore size, 40 Å) and a microporous surface of 90 m2/g whereas the pillared γ-ZrP phase is essentially microporous (350 m2/g). Both materials display a narrow distribution of micropore size centered around 5 Å. The metal binding of the bipyridine moieties remains intact after immobilization as shown by complexation experiments performed by contacting the solids with Cu(I) or Fe(II) methanolic solutions.