POLYMORPHISM AND PHASE-TRANSITION IN NANOTUBULAR URANYL PHENYLPHOSPHONATE - (UO2)(3)(HO3PC6H5)(2)(O3PC6H5)(2)CENTER-DOT-H2O

The synthesis and crystal structure of a new nanotubular phenylphospho nate, epsilon-(UO2)(3)(HO3PC6H5)(2)(O-3- PC6H5)(2) . H2O, is reported. The compound crystallizes in the orthorhombic system, space group P2( 1)2(1)2(1) with a = 16.8268(7) Angstrom, b = 7.1673(8) Angstrom, c = 2 8.8228(12) Angstrom, and Z = 4. The structure has been refined by the Rietveld method, and the final agreement factors were R(w)p = 13.1% an d R-F = 10.1%. The structure of the epsilon-phase is very similar to t hat reported earlier for the delta-phase, and it consists of closed pa cked nanotubes. The main difference between delta- and epsilon-polymor phs is a slightly different interactions through the phenyl rings. The inside walls of these nanotubes are hydrophilic and the organic group s are projected outward, which results in hydrophobic regions between nanotubes. These nanotubes are held together only by van der Waals for ces. The topotactic reversible phase transition between the two phases has been characterized by powder thermodiffractometry. P-31 MAS NMR d ata are also shown to display the structural relationship between both polymorphs.