Crystal Structures of Three Framework Alkali Metal Uranyl Phosphate Hydrates

• Published in: Journal of solid state chemistry Vol. 167; no. 1; pp. 226 - 236
• Main Authors: Locock, Andrew J., Burns, Peter C.
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 01.08.2002; Elsevier
• Subjects: Chemistry; Colloidal state and disperse state; Condensed matter: structure, mechanical and thermal properties; crystal structure refinement; Exact sciences and technology; General and physical chemistry; hydrothermal synthesis; Inorganic compounds; Metal complexes; Physics; Porous materials; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; uranyl phosphate; hydrothermal synthesis; uranyl phosphate; crystal structure refinement; Inorganic compounds; Potassium compounds; Molecular structure; Uranium compounds; Porous materials; Actinide compounds; Uranyl compounds; Anionic complex; XRD; Rubidium compounds; Experimental study; Open framework; Hydrothermal synthesis; Uranyl Complexes; Cesium compounds; Chemical preparation; Phosphato complex; Actinide complexes; Hydrates; Crystal structure
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1006/jssc.2002.9646

Three homeotypic hydrated alkali metal uranyl phosphates, A 2(UO 2)[(UO 2)(PO 4)] 4(H 2O) 2, A=Cs ( CsUP), Rb ( RbUP), K ( KUP), were synthesized by hydrothermal methods. Intensity data were collected at room temperature using Mo Kα radiation and a CCD-based area detector. Their crystal structures were solved by Patterson ( CsUP) and direct ( RbUP, KUP) methods and refined by full-matrix least-squares techniques to agreement indices ( CsUP, RbUP, KUP) w R 2=0.048, 0.230, 0.072 for all data, and R1=0.023, 0.078, 0.038 calculated for 5338, 4738, 4514 unique observed reflections (∣ F o∣≥4 σ F), respectively. The compound CsUP is orthorhombic, space group Cmc2 1, Z=4, a=14.854(1), b=13.879(1), c=12.987(1) Å, V=2677.5(3) Å 3. Both RbUP and KUP are monoclinic, space group Cm, but are presented in the unconventional pseudo-orthorhombic space group Fm11 to facilitate comparison with CsUP and to allow a model for RbUP that includes the effects of pseudo-merohedral twinning. RbUP is monoclinic, space group Fm11, Z=4, a=15.72(2), b=13.84(1), c=13.05(1) Å, α=90.39°(2), V=2839(5) Å 3; KUP is monoclinic, space group Fm11, Z=4, a=15.257(1), b=13.831(1), c=13.007(1) Å, α=91.760°(1), V=2743.4(3) Å 3. The structures consist of sheets of phosphate tetrahedra and uranyl pentagonal bipyramids, with composition [(UO 2)(PO 4)] −, that are topologically identical to the uranyl silicate sheets in uranophane-beta. These sheets are connected by a uranyl pentagonal bipyramid in the interlayer that shares corners with two phosphate tetrahedra on each of two adjacent sheets and whose fifth equatorial vertex is an H 2O group, resulting in an open framework with alkali metal cations in the larger cavities of the structures. Where CsUP and RbUP have two alkali metal positions and a H 2O group in these cavities, KUP has four K atoms and two H 2O groups, all of which are partially occupied, in the interstitial sites.