Sheets Of Polyhedra Research Articles

The crystal structure of cesbronite, Cu3TeO4(OH)4: a novel sheet tellurate topology

The crystal structure of cesbronite has been determined using single-crystal X-ray diffraction and supported by electron-microprobe analysis, powder diffraction and Raman spectroscopy. Cesbronite is orthorhombic, space group Cmcm, with a = 2.93172 (16), b = 11.8414 (6), c = 8.6047 (4) Å and V = 298.72 (3) Å3. The chemical formula of cesbronite has been revised to CuII 3TeVIO4(OH)4 from CuII 5(TeIVO3)2(OH)6·2H2O. This change has been accepted by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association, Proposal 17-C. The previously reported oxidation state of tellurium has been shown to be incorrect; the crystal structure, bond valence studies and charge balance clearly show tellurium to be hexavalent. The crystal structure of cesbronite is formed from corrugated sheets of edge-sharing CuO6 and (Cu0.5Te0.5)O6 octahedra. The structure determined here is an average structure that has underlying ordering of Cu and Te at one of the two metal sites, designated as M, which has an occupancy Cu0.5Te0.5. This averaging probably arises from an absence of correlation between adjacent polyhedral sheets, as there are two different hydrogen-bonding configurations linking sheets that are related by a ½a offset. Randomised stacking of these two configurations results in the superposition of Cu and Te and leads to the Cu0.5Te0.5 occupancy of the M site in the average structure. Bond-valence analysis is used to choose the most probable Cu/Te ordering scheme and also to identify protonation sites (OH). The chosen ordering scheme and its associated OH sites are shown to be consistent with the revised chemical formula.

Crystal structure of a silver-, cobalt- and iron-based phosphate with an alluaudite-like structure: Ag1.655Co1.64Fe1.36(PO4)3.

The new silver-, cobalt- and iron-based phosphate, silver cobalt iron tris(ortho-phosphate), Ag1.655Co1.64Fe1.36(PO4)3, was synthesized by solid-state reactions. Its structure is isotypic to that of Na2Co2Fe(PO4)3, and belongs to the alluaudite family, with a partial cationic disorder, the AgI atoms being located on an inversion centre and twofold rotation axis sites (Wyckoff positions 4a and 4e), with partial occupancies of 0.885 (2) and 0.7688 (19), respectively. One of the two P atoms in the asymmetric unit completely fills one 4e site while the Co and Fe atoms fill another 4e site, with partial occupancies of 0.86 (5) and 0.14 (5), respectively. The remaining Co2+ and Fe3+ cations are distributed on a general position, 8f, in a 0.39 (4):0.61 (4) ratio. All O atoms and the other P atoms are in general positions. The structure is built up from zigzag chains of edge-sharing [MO6] (M = Fe/Co) octa-hedra stacked parallel to [101]. These chains are linked together through PO4 tetra-hedra, forming polyhedral sheets perpendicular to [010]. The resulting framework displays two types of channels running along [001], in which the AgI atoms (coordination number eight) are located.

The alluaudite-type crystal structures of Na2(Fe/Co)2Co(VO4)3 and Ag2(Fe/Co)2Co(VO4)3.

Single crystals of the title compounds, disodium di(cobalt/iron) cobalt tris-(orthovanadate), Na2(Fe/Co)2Co(VO4)3, and disilver di(cobalt/iron) cobalt tris-(orthovanadate), Ag2(Fe/Co)2Co(VO4)3, were grown from a melt consisting of stoichiometric mixtures of three metallic cation precursors and vanadium pentoxide. The difficulty to distinguish between cobalt and iron by using X-ray diffraction alone forced us to explore several models, assuming an oxidation state of +II for Co and +III for Fe and a partial cationic disorder in the Wyckoff site 8f containing a mixture of Co and Fe with a statistical distribution for the Na compound and an occupancy ratio of 0.4875:0.5125 (Co:Fe) for the Ag compound. The alluaudite-type structure is made up from [10-1] chains of [(Co,Fe)2O10] double octa-hedra linked by highly distorted [CoO6] octa-hedra via a common edge. The chains are linked through VO4 tetra-hedra, forming polyhedral sheets perpendicular to [010]. The stacking of the sheets defines two types of channels parallel to [001] where the Na(+) cations (both with full occupancy) or Ag(+) cations (one with occupancy 0.97) are located.

Crystal structure of (Na0.70)(Na0.70,Mn0.30)(Fe(3+),Fe(2+))2Fe(2+)(VO4)3, a sodium-, iron- and manganese-based vanadate with the alluaudite-type structure.

The title compound, sodium (sodium,manganese) triiron(II,III) tris[vana-date(V)], (Na0.70)(Na0.70,Mn0.30)(Fe(3+),Fe(2+))2Fe(2+)(VO4)3, was prepared by solid-state reactions. It crystallizes in an alluaudite-like structure, characterized by a partial cationic disorder. In the structure, four of the 12 sites in the asymmetric unit are located on special positions, three on a twofold rotation axis (Wyckoff position 4e) and one on an inversion centre (4b). Two sites on the twofold rotation axis are entirely filled by Fe(2+) and V(5+), whereas the third site has a partial occupancy of 70% by Na(+). The site on the inversion centre is occupied by Na(+) and Mn(2+) cations in a 0.7:0.3 ratio. The remaining Fe(2+) and Fe(3+) atoms are statistically distributed on a general position. The three-dimensional framework of this structure is made up of kinked chains of edge-sharing [FeO6] octa-hedra stacked parallel to [10-1]. These chains are held together by VO4 tetra-hedral groups, forming polyhedral sheets perpendicular to [010]. Within this framework, two types of channels extending along [001] are present. One is occupied by (Na(+)/Mn(2+)) while the second is partially occupied by Na(+). The mixed site containing (Na(+)/Mn(2+)) has an octa-hedral coordination sphere, while the Na(+) cations in the second channel are coordinated by eight O atoms.

Crystal structure of a sodium, zinc and iron(III)-based non-stoichiometric phosphate with an alluaudite-like structure: Na1.67Zn1.67Fe1.33(PO4)3.

The new title compound, disodium dizinc iron(III) tris-(phosphate), Na1.67Zn1.67Fe1.33(PO4)3, which belongs to the alluaudite family, has been synthesized by solid-state reactions. In this structure, all atoms are in general positions except for four, which are located on special positions of the C2/c space group. This structure is characterized by cation substitutional disorder at two sites, one situated on the special position 4e (2) and the other on the general position 8f. The 4e site is partially occupied by Na(+) [0.332 (3)], whereas the 8f site is entirely filled by a mixture of Fe and Zn. The full-occupancy sodium and zinc atoms are located at the Wyckoff positions on the inversion center 4a (-1) and on the twofold rotation axis 4e, respectively. Refinement of the occupancy ratios, bond-valence analysis and the electrical neutrality requirement of the structure lead to the given composition for the title compound. The three-dimensional framework of this structure consists of kinked chains of edge-sharing octa-hedra stacked parallel to [10-1]. The chains are formed by a succession of trimers based on [ZnO6] octa-hedra and the mixed-cation Fe(III)/Zn(II) [(Fe/Zn)O6] octa-hedra [Fe(III):Zn(III) ratio 0.668 (3)/0.332 (3)]. Continuous chains are held together by PO4 phosphate groups, forming polyhedral sheets perpendicular to [010]. The stacked sheets delimit two types of tunnels parallel to the c axis in which the sodium cations are located. Each Na(+) cation is coordinated by eight O atoms. The disorder of Na in the tunnel might presage ionic mobility for this material.

SERENDIBITE, A COMPLEX BOROSILICATE MINERAL FROM PONTIAC, QUEBEC: DESCRIPTION, CHEMICAL COMPOSITION, AND CRYSTALLOGRAPHIC DATA

Serendibite has been recently discovered in the Portage-du-Fort area, Pontiac Regional County Municipality, Quebec. Dark blue, often polysynthetic twinned on {011} and with no cleavage, serendibite crystals occur exclusively in a calc-silicate rock. Fine-grained anhedral serendibite, sometimes poikiloblastic, occurs with aluminous diopside. Less commonly, serendibite may form decussate masses in the same rock type. Serendibite is biaxial negative, with indices of refraction α 1.685(2), β 1.700(2), and γ 1.712(2); 2 V meas. = 93.6(4)°, 2 V calc. = 91°. Orientation matrix is X ^ c = +20.5°, Y ^ b = −42.6°, and Z ^ a = −24.6°. Dispersion is strong, r with cell parameters refined from an X-ray powder-diffraction pattern: a 10.035(2), b 10.423(3), c 8.648 (2) A, α 106.47(3)°, β 95.91(2)°, γ 124.46(2)°, V 674.3(2) A3. The seven strongest lines of the X-ray powder diffraction pattern [ d in A( I )( hkl )] are: 3.328(45)( ![Formula][2] 230), 3.029 (96)(012, 021, ![Formula][3] ![Formula][4] 2), 2.854(96)(0 ![Formula][5] 3, 0 ![Formula][6] 1, 120), 2.689(29)(3 ![Formula][7] 1), 2.604(95)(030), 2.469(100)( ![Formula][8] ![Formula][9] 3, 0 ![Formula][10] 3), and 2.357(28)(2 ![Formula][11] 3, 23 ![Formula][12] ). The crystal structure determination refined to R = 2.1% for 3877 unique reflections. The borosilicate structure, a member of the aenigmatite-rhonite group, is composed of layers parallel to (011). Layers of tetrahedral chains cross-linked by octahedral polyhedra alternate with layers of octahedral chains cross-linked by square antiprism polyhedral sheets. Tetrahedral and octahedral polyhedra are partially ordered and site assignments were determined. All cation sites are disordered to some degree. [1]: /embed/mml-math-1.gif [2]: /embed/mml-math-2.gif [3]: /embed/mml-math-3.gif [4]: /embed/mml-math-4.gif [5]: /embed/mml-math-5.gif [6]: /embed/mml-math-6.gif [7]: /embed/mml-math-7.gif [8]: /embed/mml-math-8.gif [9]: /embed/mml-math-9.gif [10]: /embed/mml-math-10.gif [11]: /embed/mml-math-11.gif [12]: /embed/mml-math-12.gif

Lead-tellurium oxysalts from Otto Mountain near Baker, California: X. Bairdite, Pb2Cu42+Te26+O10(OH)2(SO4)(H2O), a new mineral with thick HCP layers

Bairdite, Pb2Cu42+Te26+O10(OH)2(SO4)(H2O), is a new tellurate-sulfate from Otto Mountain near Baker, California, U.S.A. It occurs in vugs in quartz associated with khinite, cerussite, goethite, and hematite. It is interpreted as having formed from the partial oxidation of primary sulfides and tellurides during or following brecciation of quartz veins. Bairdite is monoclinic, space group P21/c, with unit-cell dimensions a = 14.3126(10), b = 5.2267(3), c = 9.4878(5) Å, b = 106.815(7)°, V = 679.41(7) Å3, and Z = 2. Bairdite occurs as diamond-shaped tabular crystals up to about 250 mm long and 5 mm thick, in subparallel and fan-shaped aggregates. The color is lime green, the streak is pale lime green, and the luster is adamantine. The Mohs hardness is estimated at between 2 and 3. Bairdite is brittle with an irregular fracture and one perfect cleavage on {100}. The calculated density based on the empirical formula is 6.062 g/cm3. Bairdite is biaxial (+), with calculated indices of refraction of a = 1.953, b = 1.966, and g = 2.039. The measured 2V is 47(2)°, dispersion is r < v, strong and the optical orientation is Y = b; Z ^ a = 34° in obtuse angle b. The pleochroism is strong: Z (pale green) <<< X (green) < Y (green). Electron microprobe analyses (average of 4) provided: PbO 34.22, CaO 0.06, CuO 23.80, TeO3 26.34, SO3 5.74, H2O 2.81 (structure), total 92.97 wt%. The empirical formula (based on 17 O atoms pfu) is: Pb2.05Ca0.01Cu2+3.99Te6+2.00S0.96O17.00H4.16. The eight strongest powder X-ray diffraction lines are [dobs in Å (hkl) I]: 4.77 (110,102) 50, 4.522 (002,011,111) 66, 3.48 (multiple) 62, 2.999 (311,411) 97, 2.701 (502,113,213) 79, 2.614 (013,020) 100, 1.727 (multiple) 65, and 1.509 (911,033,324) 83. The crystal structure of bairdite (R1 = 0.072 for 1406 reflections with Fo > 4σF) contains edge-sharing chains of Te6+O6 and Cu2+O6 octahedra parallel to b that are joined by corner-sharing in the a direction, forming thick stair-step-like hexagonal close packed layers parallel to {100}. The polyhedral sheet has similarities to those in the structures of timroseite and paratimroseite. The thick interlayer region contains PbO10 polyhedra and half-occupied SO4 groups. Raman and infrared spectral data are presented

Lead-tellurium oxysalts from Otto Mountain near Baker, California: IX. Agaite, Pb3Cu2+Te6+O5(OH)2(CO3), a new mineral with CuO5-TeO6 polyhedral sheets

Agaite, Pb3Cu2+Te6+O5(OH)2(CO3), is a new tellurate from the Aga mine on Otto Mountain near Baker, California, U.S.A. The new mineral is known from only one specimen. It occurs on quartz in association with cerussite, Br-rich chlorargyrite, chrysocolla, goethite, khinite, markcooperite, muscovite, phosphohedyphane, timroseite, and wulfenite. It is interpreted as having formed from the partial oxidation of primary sulfides and tellurides during or following brecciation of quartz veins. Agaite is orthorhombic, space group Pca21, with unit-cell dimensions a = 10.6522(7), b = 9.1630(5), c = 9.6011(7) Å, V = 937.12(11) Å3, and Z = 4. Agaite crystals form as blades flattened on {010} and probably elongated on [001], and are up to about 20 μm thick and 200 μm in length. The color is blue, the streak is pale blue, and the luster is adamantine. The Mohs hardness is estimated at between 2 and 3. Agaite is brittle with an irregular fracture and one perfect cleavage on {010}. The calculated density based on the empirical formula is 6.987 g/cm3. Agaite is biaxial (-), with calculated indices of refraction of α = 2.015, β = 2.065, and γ = 2.070°. The measured 2V is 34(5)° and the optical orientation is X = b, Y = c, and Z = a. It is pleochroic: X = pale blue, Y and Z = blue; X < Y = Z. Electron microprobe analyses (average of 4) provided: PbO 65.91, CuO 7.75, TeO3 17.41, CO2 4.33 (structure), H2O 1.78 (structure), total 97.18 wt%. The empirical formula (based on 10 O apfu) is: Pb3.00Cu2+0.99Te6+ 1.01O5(OH)2(CO3). The eight strongest powder X-ray diffraction lines are [dobs in Å (hkl) I]: 4.26 (012) 28, 4.165 (211) 14, 3.303 (022, 310, 221) 100, 2.7472 (131, 203, 312) 68, 2.571 (032, 401, 231) 14, 2.0814 (332, 422) 21, 2.0306 (511) 17, and 1.7468 (multiple) 40. The crystal structure of agaite (R1 = 0.033 for 1913 reflections with Fo > 4σF) contains edge-sharing chains of Cu2+O5 square pyramids and Te6+O6 octahedra parallel to a that are joined by corner-sharing in the c direction, forming a polyhedral sheet parallel to {010}. The polyhedral sheet is very similar to those in the structures of timroseite and paratimroseite. The thick interlayer region contains 8- and 9-coordinated Pb2+, as well as CO3 and OH groups. The Pb coordinations have lopsided distributions of bond lengths attributable to the localization of the Pb2+ 6s2 lone-pair electrons.

The crystal structure of metanatroautunite, Na[(UO2)(PO4)](H2O)3, from the Lake Boga Granite, Victoria, Australia

Metanatroautunite, Na[(UO 2 )(PO 4 )](H 2 O) 3 , from the Lake Boga granite, Victoria, Australia, has tetragonal symmetry, space group P4/ncc, with the unit-cell parameters: a = 6.9935(7), c = 17.5101(12) Å, V = 856.40(13) Å 3 , and Z = 4. The crystal structure has been solved and refined to R 1 = 0.0398 for 368 unique reflections [F &gt; 4σ(F)] and 0.0456 for all 496 unique reflections. Metanatroautunite has an almost identical corrugated polyhedral sheet to meta-autunite-group minerals, consisting of corner-sharing uranyl square pyramids and phosphate tetrahedra. Hydrogen bonds (and cation-oxygen bonds) link the water molecules in the interlayer into square-planar sets, which are connected together creating 8-membered arrays. Metanatroautunite is identical to synthetic Na[(UO 2 )(PO 4 )](H 2 O) 3 .

Disilver(I) trinickel(II) hydrogenphos-phate bis-(phosphate), Ag(2)Ni(3)(HPO(4))(PO(4))(2).

The title compound, Ag2Ni3(HPO4)(PO4)2, has been synthesized by the hydro­thermal method. Its structure is formed by two types of chains running along the b axis. The first chain results from a linear and continuous succession of NiO6 octa­hedra linked to PO4 tetra­hedra by a common vertex. The second chain is built up from two adjacent edge-sharing octa­hedra (dimers) whose ends are linked to two PO4 tetra­hedra by a common edge. Those two types of chains are linked together by the phosphate groups to form polyhedral sheets parallel to the (001) plane. The three-dimensional framework delimits two types of hexa­gonal tunnels parallel to the a-axis direction, at (x, 1/2, 0) and (x, 0, 1/2), where the Ag atoms are located. Each silver cation is surrounded by eight O atoms. The same Ag+ coordination is found in other phosphates with the alluaudite structure, for example, AgMn3(PO4)(HPO4)2. Moreover, O—H⋯O hydrogen bonds link three PO4 tetra­hedra so as to build a three-dimensional network.

Two new frameworks of potassium saccharate obtained from acidic and alkaline solution

Two chiral K(I) complexes based on d-saccharic acid (H 2sac), [K(Hsac)] n ( 1) and [K 2(sac)] n ( 2) were obtained from acidic and alkaline solution. The 3D framework of 1 includes K(I) polyhedral rods and typical pairwise coaxial right- and left-handed helical chains, and displays binodal 6-connected pcu topology. 2 contains 2D polyhedral sheets consisting of left-handed helical chains, and generates 3D network with an unprecedented (7,11)-connected net. Cyclic voltammetry tests and charge–discharge tests indicate that the addition of complex 2 to the electrolyte could improve the electrochemical properties of the nickel hydroxide electrode.

NEPTUNYL COMPOUNDS: POLYHEDRON GEOMETRIES, BOND-VALENCE PARAMETERS, AND STRUCTURAL HIERARCHY

The structures of 59 inorganic Np 5+ and Np 6+ neptunyl compounds are examined and placed within a structural hierarchy, with special attention to the relationships of these structures with U 6+ uranyl compounds. Forty-three Np 5+ neptunyl compounds containing square, pentagonal and hexagonal bipyramids have structural units consisting of isolated polyhedra (2), finite clusters of polyhedra (1), chains of polyhedra (12), sheets of polyhedra (16), and frameworks of polyhedra (12). Cation–cation interactions occur in 18 of these, resulting in a dramatic departure of their topologies from those of U 6+ uranyl compounds. Compounds with cation–cation interactions have structural units consisting of chains (4), sheets (4) and frameworks (10) of polyhedra. Those Np 5+ compounds that lack cation–cation interactions exhibit topologies that are similar or identical to those of U 6+ compounds. Sixteen Np 6+ neptunyl compounds have structural units consisting of isolated polyhedra (1), finite clusters of polyhedra (3), chains of polyhedra (4), and sheets (8) of polyhedra. None of these structures exhibit cation–cation interactions, and their topologies are similar to U 6+ uranyl compounds. Geometries of Np 5+ and Np 6+ polyhedra are examined, and updated bond-valence parameters, R o = 2.035 and b = 0.422, are provided for Np 5+ .

Cation—Cation Interactions in Sr5(UO2)20 (UO6)2O16(OH)6 (H2O)6 and Cs(UO2)9U3O16(OH)5.

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Synthesis, Structure, and Magnetism of Np2O5

The binary oxide Np2O5 has been synthesized by mild hydrothermal reaction and its crystal structure has been determined. It is monoclinic, P2/c, Z = 4, a = 8.168(2), b = 6.584(1), c = 9.313(1) A, β = 116.09(1)°, V = 449.8(2) A3. The structure contains neptunyl square and pentagonal bipyramids that are linked into sheets by edge-sharing. Cation−cation interactions occur within the sheet of polyhedra and provide linkages of the sheets into a three-dimensional structure. Np2O5 undergoes antiferromagnetic ordering at 22(3) K, the highest magnetic ordering temperature observed for any neptunyl compound, and is only the second neptunyl compound found to order antiferromagnetically.

Cation−Cation Interactions in Sr5(UO2)20(UO6)2O16(OH)6(H2O)6 and Cs(UO2)9U3O16(OH)5

Two novel U6+ compounds, Sr5(UO2)20(UO6)2O16(OH)6(H2O)6 (SrFm) and Cs(UO2)9U3O16(OH)5 (CsFm), have been synthesized by mild hydrothermal reactions. The structures of SrFm (orthorhombic, C2221, a = 11.668(1), b = 21.065 (3), c = 13.273 A, V = 3532.5(1) A3, Z = 2) and CsFm (trigonal, R3c, a = 11.395(2), c = 43.722(7) A, V = 4916.7(1) A3, Z = 6) are rare examples of uranyl compounds that contain cation-cation interactions where an O atom of one uranyl ion is directly linked to another uranyl ion. Both structures are complex frameworks. SrFm contains sheets of polyhedra that are linked through cation-cation interactions with uranyl ions located between the sheets. CsFm possesses an unusually complex framework of vertex- and edge-sharing U6+ polyhedra that incorporates cation-cation interactions.

Halogen-mediated supramolecular chemistry in the solid state

Some of exciting recent developments in the field of mineralogical crystallography are considered. The crystal chemical phenomena (e.g. ionic ordering, polyhedral stacking variations, microtwinning etc.) which accompany the formation of real structures, are discussed on the basis of structural studies of a large group of minerals. The new approaches used for their investigation allowed extending the scientific ideas connected with: status of new and questionable minerals, structural classification of minerals, forms of concentration of chemical elements in the Earth’s crust, further development of modular theory and other problems of modern structural mineralogy. The advantage of using of synchrotron radiation opens the gate to a new branch of microgeochemistry (about 20% of known minerals lack a structure determination, mainly because crystals are too small or imperfect for laboratory X-ray sources). As an example the structures of three arsenates are considered. Two of them are Cu-arsenates, namely zdenekite, NaPbCu5(AsO4)4Cl(5H2O and mahnertite, (Na,Ca)Cu3[AsO4]2(Cl(5H2O, contain the new type of mixed polyhedral sheets which are characterized by the different mode of their stacking. The specific feature of these layers are the clusters, formed by four Cu(5 pyramids (φ=O, Cl, H2O) with shared edges. Tillmannsite, (Ag3Hg)(V,As)O4, was found in the old copper mines of Roua (Alpes-Maritimes, France) and its structure is characterised by the presence of two types of tetrahedra: metallic clusters formed by Ag and Hg atoms and As,V-tetrahedra. Similar metallic clusters were revealed in the crystal structures of synthetic Ag,Hg-vanadates and arsenate [1]. The chemical composition of biraite-(Ce), Ce2Fe 2+ (CO3)(Si2O7), which is a new mineral from Siberia with a new structural arrangement, was established as a result of its XRD study, IR-spectroscopy and thermal analysis. The crystal structures of armstrongite, CaZr[Si6O15]x3H2O, which was discovered in a granite pegmatite and alkaline granites of Mongolia, and of two forms of holtite were refined using the Rietveld method. As a result the chemical composition of these minerals was determined. Apparently the new discoveries of minerals will be in the focus of new XRD studies with the use of new methods in the nearest future and will open the new era in physics and chemistry of minerals.

Elegant and mysterious structures of minerals

Some of exciting recent developments in the field of mineralogical crystallography are considered. The crystal chemical phenomena (e.g. ionic ordering, polyhedral stacking variations, microtwinning etc.) which accompany the formation of real structures, are discussed on the basis of structural studies of a large group of minerals. The new approaches used for their investigation allowed extending the scientific ideas connected with: status of new and questionable minerals, structural classification ofminerals, forms of concentration of chemical elements in the Earth’s crust, further development of modular theory and other problems of modern structural mineralogy. The advantage of using of synchrotron radiation opens the gate to a new branch of microgeochemistry (about 20% of known minerals lack a structure determination, mainly because crystals are too small or imperfect for laboratory X-ray sources). As an example the structures of three arsenates are considered. Two of them are Cu-arsenates, namely zdenekite, NaPbCu5(AsO4)4Cl(5H2O and mahnertite, (Na,Ca)Cu3[AsO4]2(Cl(5H2O, contain the new type of mixed polyhedral sheets which are characterized by the differentmode of their stacking. The specific feature of these layers are the clusters, formed by four Cu(5 pyramids (φ=O, Cl, H2O) with shared edges. Tillmannsite, (Ag3Hg)(V,As)O4, was found in the old copper mines of Roua (Alpes-Maritimes, France) and its structure is characterised by the presence of two types of tetrahedra:metallic clusters formed by Ag and Hg atoms and As,V-tetrahedra. Similar metallic clusters were revealed in the crystal structures of synthetic Ag,Hg-vanadates and arsenate [1]. The chemical composition of biraite-(Ce), Ce2Fe (CO3)(Si2O7), which is a newmineral from Siberia with a new structural arrangement, was established as a result of its XRD study, IR-spectroscopy and thermal analysis. The crystal structures of armstrongite, CaZr[Si6O15]x3H2O, which was discovered in a granite pegmatite and alkaline granites of Mongolia, and of two forms of holtite were refined using the Rietveld method. As a result the chemical composition of these minerals was determined. Apparently the new discoveries of minerals will be in the focus of newXRD studies with the use of newmethods in the nearest future and will open the new era in physics and chemistry of minerals.

Biraite-(Ce), Ce2Fe2+(CO3)(Si2O7), a new mineral from Siberia with a novel structure type

Biraite-(Ce), ideally Ce 2 Fe 2+ (CO 3 )(Si 2 O 7 ), has been found in the Biraia deposit (Irkutsk district, Russia), associated with cordylite-(Ce) and -(La), aragonite, strontianite, Sr,Fe- bearing dolomite, ancylite-(Ce) and -(La), hydroxy 1 -bastnasite-(Ce), daqingshanite-(Ce) and -(La), tremolite, winchite, ferriallanite-(Ce), tornebohmite-(Ce), cerite, chevkinite-(Ce), belkovite, humite, fergusonite-(Ce) and -(Nd), pyrochlore, barite, monazite-(Ce) and other unknown minerals. Biraite-(Ce) occurs as irregular to well-shaped grains from 0.1 to 3 mm in length, has brown colour with a white streak, is semi-transparent with a vitreous luster and brittle.The hardness (Mohs) is 5, and the calculated density is 4.76 g/cm 3 . Optically, biraite-(Ce) is biaxial (-), with α 1.785(1),β 1.810(2),γ 1.820(1), 2V 66°(1). Electron microprobe and wet chemical analyses gave the following empirical formula based on 10 O+F:(Ce 1.01 La 0.57 Nd 0.25 Pr 0.09 Sm 0.02 Ca 0.07 Na 0.02 Ba 0.01 )Σ= 2.04 (Fe 0.60 Mg 0.25 Mn 0.11 Ti 0.01 )Σ=0.97 (CO 3 ) 0.99 [Si 1.97 (O 6.87 F 0.17 )Σ=7.04].The simplified formula is Ce 2 Fe 2+ (CO 3 )(Si 2 O 7 ). The IR spectrum confirmed the presence of [CO 3 ] groups. The strongest lines of the X-ray powder pattern [ d in A ( I ) ( hkl )] are: 3.30 (5) (021), 2.92 (10) (006, 21–2), 2.65 (5) (202, 12–4), 2.23 (5) (116, 031). Biraite-(Ce) is monoclinic, space group P 2 1 / c , with a 6.505(7), b 6.744(2), c 18.561(4) A,β 108.75(2)°. Its crystal structure was refined from single-crystal X-ray diffraction data to R(F) = 0.033. Biraite-(Ce) displays a new structure type, based on polyhedral (001) sheets composed of pairs of edge-sharing [FeO 6 ] octahedra, [Si 2 O 7 ] groups, and [CO 3 ] triangles. Ce 3+ cations in ten-fold coordination provide the linkage between neighbour polyhedral sheets. Both the mineral and its name have been approved by the IMA Commission on New Minerals and Mineral Names.

A high-pressure polytypic transformation in type-I chlorite

The compressional behavior of a natural chromian-clinochlore-I a polytype has been studied by synchrotron powder X-ray diffraction to 8 GPa at 298 K under hydrostatic conditions. A reversible polytypic transformation occurs at 6 GPa from the I a -4 to a I b polytype in which all a -type interlayers are converted to b -type by sheet translation across the interlayer, thus removing the high degree of cation superposition between the brucite-like sheet and the adjacent 2:1 layer that is associated with a -type interlayers. The isothermal bulk modulus for the I a polytype to 5.9 GPa was determined by fitting pressure-volume data to a second-order Birch-Murnaghan equation of state: K = 78.7 ± 1.4 GPa. This value is close to that of clinochlore-II b ( K = 81 GPa). Elastic moduli for a , b , and d 001 obtained from second-order fits to a Birch-Murnaghan equation of state are: K a 0 = 113(5) GPa, K b 0 = 91(2) GPa, and K 001,0 = 54(1) GPa. A possible relationship is discussed between the 6 GPa polytypic transformation observed in chromian-clinochlore and the non-polytypic transformation at 9 GPa in clinochlore-II b reported recently. Both transformations are dominated by contraction of the interlayer, with negligible in-plane compression of the polyhedral sheets. Both may also involve an increase in oxygen close-packing across the interlayer. However, in chromian-clinochlore, the destabilization of a -type interlayers is a further significant structural factor that may cause the transformation to occur at a lower pressure. Both transformations also involve an increase in the compressibility of chlorite. Although the transformation in chromian-clinochlore is influenced by the vertical superpositions of cations across the a -type interlayer, the hydrogen bonding is robust and does not reorganize until a considerable pressure (6 GPa) is reached.

Two zincophosphite frameworks templated by 1,4-diaminobenzene: syntheses and structures of C 6N 2H 10·Zn(HPO 3) 2 and (C 6N 2H 8) 0.5·ZnHPO 3

The solution-mediated syntheses and single crystal structures of C 6N 2H 10·Zn(HPO 3) 2 ( I) and (C 6N 2H 8) 0.5·ZnHPO 3 ( II) are reported. Slight variation of the synthesis conditions led to two quite different phases. I contains infinite chains of ZnO 4 and HPO 3 groups with the protonated organic moiety acting as a template and interacting with the chains by NH⋯O hydrogen bonds and possible CH⋯O interactions. In II, the neutral 1,4-diamino benzene molecule bonds to Zn (as a ligand) and an unusual composite, “pillared”, structure results, with the organic species bridging 6 3 polyhedral sheets, although NH⋯O bonds are also present. Similarities and differences to other zinc phosphites and phosphates are briefly discussed for I and II. Crystal data: C 6N 2H 10·Zn(HPO 3) 2, M r=335.48, monoclinic, C2/ c (No. 15), a=17.2471 (14) Å, b=9.0720 (8) Å, c=7.6529 (6) Å, β=103.752 (2)°, V=1163.09 (7) Å 3, Z=4, R( F)=0.038, wR( F 2)=0.084. (C 6N 2H 8) 0.5·ZnHPO 3, M r=199.42, orthorhombic, Pbca (No. 61), a=8.0314 (16) Å, b=8.1299 (16) Å, c=18.830 (4) Å, V=1229.5 (4) Å 3, Z=8, R( F)=0.026, wR( F 2)=0.055.