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 (H 2 O 3 P-bipy-PO 3 H 2: 1 ) within the interlayer gallery of α and γ zirconium phosphonate structures. A mixed phosphite/phosphonate compound formulated as Zr(HPO 3 ) 0.8 (O 3 P-bipy-PO 3 ) 0.6 ·5.3H 2 O was obtained by reaction of 5,5‘-bis(dihydroxyphosphoryl)-2,2‘-bipyridine and phosphorous acid with ZrOCl 2 ·8H 2 O in the presence of HF. Another compound formulated as Zr(PO 4 )(H 2 PO 4 ) 0.5 (HO 3 P-bipy-PO 3 H) 0.25 ·2H 2 O was prepared by treatment of Zr(PO 4 )(H 2 PO 4 )·2H 2 O (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 31 P NMR spectroscopy, and isothermal N 2 adsorption−desorption. The mixed α-zirconium phosphonate has a mesoporous area of 330 m 2 /g (pore size, 40 Å) and a microporous surface of 90 m 2 /g whereas the pillared γ-ZrP phase is essentially microporous (350 m 2 /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.