Synthesis and Structure of NaZnSiO(3)OH, a New Chiral Zincosilicate Framework Material.

The structure of NaZnSiO(3)OH, synthesized hydrothermally by reaction of Na(2)ZnSiO(4) and NaOH, has been determined from single-crystal X-ray and powder neutron diffraction data (orthorhombic, space group P2(1)2(1)2(1,) a = 7.6872(2) Å, b = 9.3899(2) Å, c = 5.155(1) Å, Z = 4). The structure has a framework constructed from ZnO(4) and SiO(3)OH tetrahedra with bridging and trigonal oxygen atoms. Channels formed from eight-membered rings of tetrahedra house the sodium ions and are also partially blocked by moderately strongly hydrogen bonded OH groups.

New sodalite frameworks; synthetic tugtupite and a beryllosilicate framework with a 3:1 Si:Be ratio.

Compounds of the formula Na8[Si(6 +y)Be(y)Al(6 - 2y)O24]X2, with X = Cl and Br, and y = 1, 2 and 3 have been synthesised and structurally characterised by combined powder X-ray and neutron diffraction profile analysis. These materials adopt the sodalite framework (SOD) with the tetrahedral species, BeO4, AlO4 and SiO4, disordered across the framework positions. Na8[Si8Be2Al2O24]Cl2, (y = 2), is a synthetic analogue of the naturally occurring semi-precious gemstone tugtupite, while Na8[Si9Be3O24]X2, X = Cl and Br represents a new tetrahedral framework stoichiometry with a Si ratio Be ratio of 3 ratio 1. Additional characterisation using 29Si MASNMR, IR spectroscopy and high-temperature, neutron diffraction show that the observed structure-property trends found when modelling sodalite materials can be extended to these new framework compositions.

Correlations between 9Be magic-angle spinning nuclear magnetic resonance spectra and the geometry of beryllium containing framework structures.

A range of sodalite framework structures containing beryllium with general formula M8[BeZO4]6X2; M = Cd, Zn, Z = Si, Ge and X = S, Se or Te have been synthesised. The structures of these materials, which contain a single beryllium environment, have been refined from powder neutron diffraction or powder X-ray diffraction data and the compounds further characterised using 9Be magic-angle spinning nuclear magnetic resonance (MASNMR). Spectra show a single sharp resonance for 9Be(OSi)4 in the chemical shift range +/- 1 ppm from 0.1 M BeCl2. Correlations between the Be-O-Z bond angles and the 9Be chemical shift are reported and show upfield shifts for larger angles as seen previously in MASNMR spectra for 29Si and 27Al.

Structure of uranium(VI) oxide dihydrate, UO3.2H2O; synthetic meta-schoepite (UO2)4O(OH)6.5H2O.

Structure of uranium(VI) oxide dihydrate, P03.2H20; synthetic meta-schoepite (UO2)40(OH)6.5H20 f The structure of uranium oxide dihydrate, also known as meta-schoepite (UO2)4O(OH)6.5H2O, has been determined from a synthetic single crystal. The structure, at 150 K, space group Pbcn, lattice constants a = 14.6861 (4), b = 13.9799 (3) and c = 16.7063 (5) A, consists of layers of stoichiometry (UO2)4O(OH)6, formed from edge-sharing UO7 pentagonal bipyramids, interleaved with hydrogen-bonded water molecules. Three of the layer hydroxyl groups are linked through hydrogen bonding to single water molecules and the three remaining OH units form interactions with water molecules that each act as acceptors in two hydrogen bonds. One of the water molecules in the inter-layer region is disordered over two symmetry-related sites and forms hydrogen-bonded interactions only within the layer and with the uranyl O atoms. The relationship of the structure of meta-schoepite to that of schoepite is discussed in detail.

Correlations between 27Al magic-angle spinning nuclear magnetic resonance spectra and the coordination geometry of framework aluminates.

A range of aluminate sodalites of general formula M8(AlO2)12.X2, where M and X are a divalent cation and anion, respectively, has been synthesised. The structures of these materials, which contain a single aluminum environment, have been refined from powder X-ray or neutron diffraction data and the compounds further characterised using 27Al magic-angle spinning nuclear magnetic resonance (MAS NMR). Correlations between (i) the Al-O-Al bond angles and the 27Al chemical shift and (ii) the quadrupolar coupling constant and the distorted AlO4 tetrahedral geometry have been determined.

Applications of combined EXAFS and powder diffraction analysis in solid state chemistry.

Recent applications of combined EXAFS/powder neutron and X-diffraction analysis are reviewed and provisional results for three additional compounds are presented. Criteria for successful refinements are suggested. The new results relate to the materials: CoAl2O4, La(6.4)Ca(1.6)Cu6Ni2O20 and Pr(0.5)Sr(0.5)FeO(2.75).