Metal-organic frameworks based on uranyl and phosphonate ligands

Abstract

Three new crystalline metal-organic frameworks have been prepared from the reaction of uranyl nitrate with nitrilotris(methylphosphonic acid) [H(6)nmp, N(CH2PO3H2)(3)], 1,4-phenylenebis(methylene)diphosphonic acid [H(4)pmd, C6H4(PO3H2)(2)], and (benzene-1,3,5-triyltris(methylene))triphosphonic acid [H(6)bmt, C6H3(PO3H2)(3)]. Compound [(UO2)(2)F(H(3)nmp)(H2O)]center dot 4H(2)O (I) crystallizes in space group C2/c, showing two crystallographically independent uranyl centres with pentagonal bipyramidal coordination geometries. While one metal centre is composed of a {(UO2)O-3(mu-F)}(2) dimer, the other comprises an isolated {(UO2)O-5} polyhedron. Compound [(UO2)(H(2)pmd)] (II) crystallizes in space group P2(1)/c, showing a centrosymmetric uranyl centre with an octahedral {(UO2)O-4} coordination geometry. Compound [(UO2)(3)(H(3)bmt)(2)(H2O)(2)]center dot 14H(2)O (III) crystallizes in space group P (1) over bar, showing two crystallographically independent uranyl centres. One uranyl centre is a {(UO2)O-5} pentagonal bipyramid similar to that in (I), while the other is a {(UO2)O-4} centrosymmetric octahedron similar to that in (II). Compounds (I) and (III) contain solvent-accessible volumes accounting for ca 23.6 and 26.9% of their unit-cell volume, respectively. In (I) the cavity has a columnar shape and is occupied by disordered water molecules, while in (III) the cavity is a two-dimensional layer with more ordered water molecules. All compounds have been studied in the solid state using FT-IR spectroscopy. Topological studies show that compounds (I) and (III) are trinodal, with 3,6,6- and 4,4,6-connected networks, respectively. Compound (II) is instead a 4-connected uninodal network of the type cds.