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Mixed lead chloride oxalate, Pb2Cl2(C2O4), has been obtained in a polycrystalline form in the course of a study on precursors of nanocrystalline PZT-type oxides. Its crystal structure has been solvedab initiofrom powder diffraction data collected using a monochromatic radiation from a conventional X-ray source. The symmetry is monoclinic, space groupC2/m, the cell dimensions area=5.9411(3) Å,b=5.8714(4) Å,c=9.4212(4) Å, β=95.232(4)° and Z=2. The structure consists of a stacking of complex double sheets, built from lead polyhedra, parallel to (001) and connected together through oxalate groups. The lead atom is nine-fold coordinated by four O atoms from one bidentate and two monodentate oxalate groups and five Cl atoms. The polyhedron can be described as a highly distorted square antiprism mono-capped by a Cl atom. The thermal behavior of lead chloride oxalate, in vacuum and in air, is carefully described from temperature-dependent powder diffraction and thermogravimetric measurements. It is shown that reaction pathways are complicated by the identification of various oxide chloride phases.

Precise powder diffraction data collected with a monochromatic radiation from a conventional X-ray source have revealed the presence of two varieties of Pb2Zr(C2O4)(4).nH(2)O. The powder diffraction patterns have been indexed with a monoclinic and an orthorhombic unfit cells, respectively. The crystal structure of one polymorph has been determined ab initio from powder diffraction data. The changes of the cell dimensions as a function of the water vapour pressure is reported, The framework of the crystal structure is preserved over an extended range of the water content. The thermal behaviour of these phases is described and zeolitic properties of water molecules are pointed out.

The crystal structure of the layered cadmium hydroxide sulfate Cd4SO4(OH)6.1.5H2O has been solved from X-ray powder diffraction data. The compound crystallizes with hexagonal symmetry,a=9.145(1) Å,c=15.099(3) Å,V=1093.5 Å3,Z=4, space groupP63. Due to the unusual environment of one cadmium atom and to the fact that a suitable thin tabular crystal could be found later, a single-crystal X-ray diffraction experiment was also carried out. In both cases the structure was solved applying direct-methods. The refinements converged to the residual factorsRwp=0.152 andRF=0.059 from the powder data andR1=0.058 andwR=0.165 for the single crystal data case. The structure is built from brucite-type layers based on CdO6octahedra, in which one-seventh of the octahedral sites are empty. Directly above and below these empty sites, two additional octahedrically coordinated Cd atoms are located. The crystal chemistry of the cadmium hydroxide sulfate family is discussed.

The crystal structure of the mineral tinticite has been solved by direct methods from integrated intensities of X-ray powder diffraction data and subsequently refined with the Rietveld technique. The sample used for the structure solution comes from the Gava-Bruguers area (20 km SW of Barcelona), which contains a large variety of phosphates, some of which were exploited in gallery mines during the ancient neolithic. Tinticite crystallizes in the triclinic space group P 1 with unit cell parameters a = 7.965(2) A, b = 9.999(2) A, c = 7.644(2) A, α = 103.94(2)°, β = 115.91(2)°, ω = 67.86(2)° and cell content Fe 3+ 5.34 (PO 4 ) 3.62 (VO 4 ) 0.38 (OH) 4 ·6.7 H 2 O; ρ exp = 2.94 g/cm 3 ; ρ cale = 2.88 g/cm 3 . The Rietveld refinement of the data set converged to R wp = 13.1 % and χ 2 = 3.3. Due to the complexity of the disorder in this structure, the refined structure model could only account for part of it. The octahedrally coordinated Fe 3+ ions form dreier single chains of general formula ∞ 1 [Fe 3 O 14 ] at y = 0 and trimers of type cis-[Fe 3 O 14 placed at y = 1/2. While the dreier single chains are linked to each other by fully occupied PO 4 groups yielding in this way predominantly ordered layers, the trimers arc partially disordered and connected to each other and to the ordered layers both by PO 4 groups and through H-bonds. The higher stability of the ordered layers is consistent with the observed platy nature of the microcrystals of tinticite.

A new mixed lead zirconium oxalate, Pb2Zr(C2O4)(4). nH(2)O (3 < n < 9), has been prepared from precipitation of a nitric solution of lead and zirconium cations by an oxalic solution at 345 K. The crystal structure of Pb2Zr(C2O4)(4). 6H(2)O has been determined ab initio from powder diffraction data collected with conventional monochromatic X-rays. The symmetry is monoclinic, space group C2/c (No. 15), cell dimensions a = 9.537(1) Angstrom, b = 29.622(3) Angstrom, c = 8.9398(9) Angstrom, beta = 121.19(4)degrees, and Z = 4. The complex three-dimensional structure is built from 8-fold-coordinated zirconium atoms and 9-fold- and 8-fold-coordinated lead atoms linked by oxalate groups, Only one water molecule has been found free in the structure. The dehydration is reversible, and the cell parameters vary between the composition limits without a major change of the crystal structure framework. A thermodynamical study has demonstrated the zeolitic nature of the water molecules. The enthalpy, Delta(r)H, and entropy, Delta(r)S, of the dehydration reaction have been determined as a function of the number of zeolitic water molecules. The complete decomposition scheme of the anhydrous phase Pb2Zr(C2O4)(4) into PbZrO3 and finally ZrO2, studied from temperature-dependent X-ray powder diffraction and thermogravimetric analysis, is carefully described.

The crystal structure of La(H2O)2K(C2O4)2·H2O has been solved ab initio from powder diffraction data collected with conventional monochromatic X-rays. The symmetry is monoclinic, space group C2/m, cell dimensions a=22.033(1) Å, b=7.6003(5) Å, c=6.6418(4) Å, β=103.814(6)°, V=1080.05(8) Å3, Z=4. Since a disorder of one oxalate group is observed with all possible monoclinic space groups, it has been found convenient to describe the crystal structure in a triclinic subcell. The disorder problem is thoroughly discussed with respect to the powder diffraction data available for this material. From this description the compound exhibits a layered-type structure, which could explain reported cation-exchange properties. The layers are formed by four-membered rings [La(C2O4)]4. The potassium atom and two of the three water molecules are located between the layers. The third water molecule lies on the layer in tunnels with a diamond-shaped cross section. The lanthanum atom is tenfold-coordinated in a distorted bicapped square antiprism and the potassium atom is eightfold-coordinated in a dodecahedron. The crystal structure of La(H2O)2(NH4)(C2O4)2·H2O is isostructural with that of La(H2O)2K(C2O4)2·H2O [a=22.130(4) Å, b=7.774(1) Å, c=6.655(2) Å, β=105.28(2)°, V=1104.4(3) Å3]. The thermal decomposition of these two precursors has been carried out by means of temperature-dependent X-ray diffraction and TG-DSC. The dehydration leads to anhydrous phases, which are amorphous and poorly crystalline for the potassium and ammonium compounds, respectively. Amorphous LaK(C2O4)2 crystallizes at 260°C. Its symmetry is monoclinic with the cell dimensions a=5.687(3) Å, b=15.241(5) Å, c=9.017(4) Å, β=92.82(3)°. At higher temperature, the decomposition of LaK(C2O4)2 yields La2O2CO3 (Type-Ia), La2O2CO3 (Type-II), and pure La2O3, successively. La(NH4)(C2O4)2 leads to La2O2CO3 (Type-II) and, finally, La2O3.

A new hydrated iron(iii) vanadate was synthesized by an aqueous route from a V2O5 suspension in boiling water and iron(iii) nitrate. The crystal structure of this well-crystallized yellow solid was solved ab initio from conventional X-ray powder diffraction data. The unit cell is orthorhombic with a = 11.990(3), b = 9.496(2), c = 8.339(1) Angstrom, Z = 4, space group P2(1)2(1)2(1). The refinement of 70 parameters by the Rietveld method, based on 1413 reflections, converged to the R-factors R-F = 0.044 and R-wp = 0.097. The structure of Fe-2(H2O)[V2O7. VO3(OH)] consists of a three-dimensional framework built from corner-sharing bi-tetrahedral V2O7 and independent tetrahedral VO3(OH) units interconnected with edge-sharing bi-octahedral Fe2O9(H2O) groups. A thermal study of this compound confirmed its water content and showed the existence of the corresponding anhydrous vanadate Fe2V3O10.5, which provides, upon heating, a mixture of the two known iron(iii) vanadates, namely the triclinic FeVO4 and the Fe2V4O13 phases.

The structure of basic iron nitrate has been solved ab initio from X-ray powder diffraction data collected with a conventional X-ray source. The symmetry is monoclinic (Pc) with the cell parameters a = 3.0844(6) Angstrom, b 9.508(2) Angstrom, c = 9.993(3) Angstrom, beta 91.01(2)degrees. The atom positions have been determined by the direct methods and the structure refined by the Rietveld method (R-F = 0.05). The final structure model is consistent with an oxide hydroxide nitrate chemical formula, Fe2O(OH)(3)NO3. H2O. The structure consists of corrugated layers built from six-fold coordinated iron polyhedra sharing alternately edges and corners. The nitrate groups are intercalated between the layers. These groups can be exchanged by anions such as Cl, Br, MnO4 and OCOCH3. Exchange properties and thermal behaviour of exchanged products are discussed.

This paper deals with the synthesis and structure refinements of two orthophosphates of vanadium (III) prepared under hydrothermal conditions. The magnetic properties are discussed in terms of order-disorder phenomena.

A new mixed lead thorium phosphate, Pb0.5Th2(PO4)3, has been isolated in the system PbO–ThO2–P2O5. Its crystal structure (monoclinic symmetry, a=17.459(1) Å, b=6.8451(4) Å, c=8.1438(5) Å, β=101.247(5)°, space group C2/c) has been determined from conventional monochromatic X-ray powder diffraction data. The structure is related to the MITh2(PO4)3 structure type. Lead atoms are located in the channels parallel to the c axis, out of the twofold axis for 0.97 Å, and are statistically distributed on a quarter of crystallographic positions. The thermal stability of this material is greater than that of the monazite-type compound PbTh(PO4)2.

The structure of the two isostructural uranium halogenide phosphates UClPO4·2H2O and UBrPO4·2H2O was determined from conventional monochromatic X-ray powder diffraction data. The crystal symmetry is tetragonal (space groupI4/m,Z=8) with lattice constantsa=14.631(2) andc=6.662(1) Å for the chloride phase anda=14.7480(7) andc=6.6810(4) Å for the bromide compound. The structure solution was found from Patterson and Fourier syntheses and refinements by the Rietveld method (38 parameters, 760 reflections) converged toRF=0.03 for both examples. The configuration around uranium(IV) is derived from the typical pentagonal bipyramid formed by two water oxygen atoms, four phosphate oxygen atoms, and one halide atom. Due to steric considerations, the halide atom deviates from the pentagonal base, leading to a repulsion of the two apical oxygen atoms. The interatomic distances and angles are usual and agree with the values found from neutron diffraction in related compounds. The discrete UX1O6(X=Cl, Br) polyhedra are linked together by phosphate tetrahedra which are viewed as the unique bonding units in the structure. This arrangement results in a 3D network based on two kinds of tunnels along [001]. The widest tunnel contains theXatoms, while half of the water molecules lie in the smallest tunnel.

The new vanadium(III) diphosphate H3OVP2O7, has been prepared under hydrothermal conditions and characterized by means of X-ray powder diffraction, thermogravimetric analysis and magnetic susceptibility measurements. The title compound is isostructural with KAIP(2)O(7). It is indexed on the monoclinic symmetry with the lattice parameters a=7.519(2) Angstrom, b = 10.054(3) Angstrom, c = 8.244(3) Angstrom, beta = 105.86(3)degrees and the figures of merit M(20) = 19.9; F-30 = 25.3(0.014, 85). The structure has been refined from 365 unique reflections and 3401 intensity points by the Rietveld method down to the final R(F) = 0.024 and R(B) = 0.033. Staggered P2O7 groups from corner-sharing PO4 tetrahedra form sheets in the ab-plane. The P-O bonds within the pyrophosphate groups are between 1.60 Angstrom and 1.44 Angstrom and the value of the P-O-P angle is 124 degrees. The P2O7 groups generate octahedral sites filled up by vanadium ions with typical V-O bonds between 1.88 Angstrom and 2.06 Angstrom. Strong H-bonding between the inter-layer water and the surrounding pyrophosphate groups have been evidenced by thermogravimetric studies and X-ray structure refinement. The magnetic susceptibility measurements indicate weak antiferromagnetic interactions (theta = - 6 K) with a magnetic moment of 2.62 mu(B) consistent with V3+ ions.

The thermal decomposition of nonaaquabismuth(III) triflate has been studied by thermogravimetric analysis, from which lower hydrates have been identified. The crystal structure of the tetraaquabismuth(III) triflate, Bi(H2O)(4)(OSO2CF3)(3), has been solved ab initio from powder data collected with conventional monochromatic X-rays even though the asymmetric unit cell contains 29 atoms and 93 atomic coordinates to refine. The structure is built from discrete dimers in which the Bi atoms are 8-fold coordinated to four water molecules and four oxygen atoms belonging to three triflate groups. The structure differences with respect to that of the precursor are discussed.

Cd0.5Zr2(PO4)3(CdZP) and the partially substituted phase Cd0.25Sr0.25Zr2(PO4)3, prepared by the sol-gel route, belong to the NZP family. The structure of CdZP (S.G.R3̄) has been established by the Rietveld method. The thermal behavior of CdZP, investigated by X-ray powder diffraction, is anisotropic, i.e., the structure expands along c axis and contracts along a axis. Dilatometric measurements and SEM micrographs of ceramics, sintered with 5% ZnO, show that CdSrZP presents the advantage to decrease microcracking, and then anisotropy, occurring during the heating cycle. The thermal expansion coefficient abulk of the ceramic CdSrZP is very small (0.6 × 10−6 °C−1).

The structure of CeIIIRb2(NO3)5 · 4H2O was determined from single crystal diffraction. The symmetry is monoclinic (space group Cc): a = 11.050(1) Å, b = 8.977(1) Å, c = 17.859(2) Å, β = 100.877(9) °, Z = 4. The structure consists of icosahedra [Ce(NO3)5(H2O)2]2− linked by hydrogen bonds. The Rb atoms and two water molecules are located between these polyhedra and ranged in an alternating sequence along [010]. From temperature-dependent X-ray diffraction and thermogravimetry measurements, the occurrence of CeRb2(NO3)5 · 3H2O, CeRb2(NO3)5 · 2H2O, α- or β-CeRb2(NO3)5 in crystalline or amorphous forms, and the mixture of Ce2Rb3(NO3)9 and CeRb(NO3)4, have been shown during the thermal decomposition. The transformations are atmosphere and particle-size dependent, and the dehydration mechanisms are discussed.

Temperature-dependent X-ray diffraction has been used to demonstrate that two successive changes of cerium oxidation state occur when the mixed eerie salts CeM(2)(I)(NO3)(6) (M(I) = K, NH4, Rb) are heated. The thermal decomposition of the three compounds proceeds through the formation of the intermediate cerous phase Ce(2)M(3)(I)(NO3)(9). For the rubidium salt, the decomposition scheme is more complicated because another cerous phase, with the suggested formula CeRb(NO3)(4), is also formed. In all cases, the final product of the decomposition is eerie oxide CeO2. The processes of reduction of Ce(IV), induced by thermal decomposition, and the subsequent oxidation of Ce(III) are discussed.

The compounds [(CH3)4N]2MGe4S10(M= Fe, Cd, Mn, (Co, Mn)) have been synthesized under hydrothermal conditions in glass ampoules at 393 K for two days. They have been investigated by means of thermogravimetry, ionic chromatography, X-ray methods, and IR spectroscopy. They crystallize in the tetragonal symmetry, space groupI4. They are isostructural with [(CH3)4N]2MnGe4S10and their structures were refined from X-ray powder diffraction intensity data down to the final reliability factorsRF= 0.07 (RBragg= 0.08) andRF= 0.05 (RBragg= 0.05) for the Fe and Cd compounds, respectively. The structure consists of tetrahedra sharing apices with a space filling of the covalent (Ge,M)–S framework as small as 45%. The anionic framework generates tunnels with a diameter of about 7 Å, determined from structural results, running along the [100], [010], and [112] directions in which theTMAcations are located.

The structure of two polymorphic phases of lanthanum nitrate tetrahydrate, prepared from the thermal decomposition of the hexahydrate compound, have been determined from conventional monochromatic X-ray powder diffraction data. The α phase has a monoclinic unit cell with the parametersa= 6.7778(9) Å,b= 11.3673(1) Å,c= 6.5843(1) Å, β = 90.644(5)°, space groupP21/m. The β phase is orthorhombic with the unit cell parametersa= 11.834(1) Å,b= 12.973(1) Å,c= 13.531(1) Å, space groupPbca. For the α phase, atomic coordinates were found by interpretation of one Patterson and three difference Fourier maps, while for the β phase the starting model was the crystal structure of the related cerium compound. The structure models were refined by the Rietveld method. The structures consist of infinite chains along [001], built from 11-fold coordinated and 10-fold coordinated La atoms in the α and β phases, respectively, and linked by bridging nitrate groups. The cohesion of the structures is ensured by hydrogen bonds.