Oxygen Vertices Research Articles

Synthesis, structure, and thermal expansion of BiCr<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub>, SbCr<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub> and Bi<sub><sub>1-</sub><sub><i>x</i></sub></sub>Sb<sub><i>х</i></sub>Cr<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub> solid solutions

The manifestations of the Bi1- x Sb x Cr2(PO4)3 system with the α-CaMg2(SO4)3 structure were obtained and characterized by the evaporation of salt solutions with heat treatment. Refinement of the Rietveld method for the structure of BiCr2(PO4)3 ( x = 0) and SbCr2(PO4)3 ( x = 1) showed that the [Cr2(PO4)3]3∞ framework is formed by CrO6 octahedra doubled by faces, PO4 tetrahedra are between the dependences, attached to the octahedrons by oxygen vertices, the voids of the framework are populated by six-coordinated bismuth or antimony atoms. By varying the composition of the Bi1- x Sb x Cr2(PO4)3 solid solution everywhere, it is possible to obtain materials with low thermal expansion coefficients: 0.5×10-6 ≤ α av ≤ 1.9×10-6 °C-1.

Paratobermorite, Ca4(Al0.5Si0.5)2Si4O16(OH)·2H2O·(Ca·3H2O), a new tobermorite-supergroup mineral with a novel topological type of the microporous crystal structure

Abstract A new mineral paratobermorite with the ideal crystal-chemical formula Ca4(Al0.5Si0.5)2Si4O16 (OH)·2H2O·(Ca·3H2O) is a member of the tobermorite group within the tobermorite supergroup. It was found at the Bazhenovskoe chrysotile asbestos deposit, Central Urals, Russia, in cavities of grossular rodingite in association with prehnite, pectolite, thomsonite-Ca, and calcite. Paratobermorite occurs as well-shaped prismatic to acicular crystals up to 1 × 1.5 × 8 mm3 typically assembled in spray- or bush-like radial clusters or open-work aggregates up to 1.5 cm across, which form interrupted crusts up to 3 × 5 cm2. Paratobermorite is transparent, colorless, pale yellowish, pale beige, or pinkish, with a vitreous luster. The mineral is brittle, with the (001) perfect cleavage. The Mohs hardness is ca. 3½. Dmeas = 2.51 (2) and Dcalc = 2.533 g/cm3. Paratobermorite is optically biaxial (+), α = 1.565 (2), β = 1.566 (2), γ = 1.578 (2), 2 Vmeas = 25 (10)° and 2 Vcalc = 32° (589 nm). Optical orientation is: X = c, Y = b, Z = a. The chemical composition of paratobermorite (electron microprobe, H2O by selective sorption from gaseous products of heating) is Na2O 0.40, K2O 0.28, CaO 36.60, MnO 0.04, BaO 0.07, Al2O3 6.46, SiO2 42.32, H2O 14.10, total 100.27 wt%. The empirical formula calculated on the basis of 22 O atoms per formula unit and (O,OH)17·5H2O is Na0.09K0.04Ca4.72Al0.92Si5.09O15.69(OH)1.31·5H2O. Like other members of the tobermorite supergroup, paratobermorite displays OD character, with two MDO (maximum degree of order) structures: one (MDO1), with non-standard space group F2/d11 and the second (MDO2), just corresponding to the structure-type of the new mineral, with non-standard space group C1121/m; its unit-cell parameters obtained from single-crystal X-ray diffraction data are: a = 11.2220(4), b = 7.3777(2), c = 22.9425(8) Å, γ = 89.990(3)°, V = 1899.46(10) Å3, and Z = 4; polytype 2M. The structure of paratobermorite is solved on a single crystal, R = 8.36%. Like structures of other “tobermorites 11 Å,” it is based on the complex layer built of a sheet of sevenfold Ca-centered polyhedra with wollastonite-type chains of T tetrahedra attached to the Ca-sheet from both sides. The tetrahedral (T) sites T1 and T2 are fully occupied by Si, while alternating T3 and T4 sites are filled by Al and Si in the ratio 1:1. The chains of tetrahedra belonging to neighboring complex layers share common oxygen vertices of the bridging T3,4 tetrahedra to form xonotlite-type ribbons [Si6O17]∞. The heteropolyhedral Ca-T-O scaffolding appears as a microporous quasi-framework with wide channels, which contain additional Ca atoms and H2O molecules. The complex Ca-T-O layers in paratobermorite (so-called “complex modules of type A”) significantly differ in topology (mutual arrangement of T tetrahedra and Ca polyhedra) from the complex Ca-T-O layers in tobermorite (“complex modules of type B”). IR spectrum confirms the presence of nonequivalent H2O molecules and nonequivalent T-O-T angles involving T atoms of two neighboring wollastonite-type chains. Due to the original topological type of the structure and the presence of significant amount of Al, which substitutes Si, paratobermorite can be considered as a novel microporous material, a perspective cation-exchanger.

Double molybdates of silver and monovalent metals

The Ag2MoO4–Cs2MoO4 system was studied by powder X-ray diffraction, the formation of a new double molybdate CsAg3(MoO4)2 was established, its single crystals were obtained, and its structure was determined. CsAg3(MoO4)2 (sp. gr. P3¯, Z = 1, a = 5.9718(5), c = 7.6451(3) Å, R = 0.0149) was found to have the structure type of Ag2BaMn(VO4)2. The structure is based on glaserite-like layers of alternating MoO4 tetrahedra and Ag1O6 octahedra linked by oxygen vertices, which are connected into a whole 3D framework by Ag2O4 tetrahedra. An unusual feature of the Ag2 atom environment is its location almost in the centre of an oxygen face of the Ag2O4 tetrahedron. Caesium atoms are in cuboctahedral coordination (CN = 12).We determined the structures of the double molybdate of rubidium and silver obtained by us previously and a crystal from the solid solution based on the hexagonal modification of Tl2MoO4, which both are isostructural to glaserite K3Na(SO4)2 (sp. gr. P3¯m1). According to X-ray structural analysis data, both crystals have nonstoichiometric compositions Rb2.81Ag1.19(MoO4)2 (a = 6.1541(2), c = 7.9267(5) Å, R = 0.0263) and Tl3.14Ag0.86(MoO4)2 (a = 6.0977(3), c = 7.8600(7) Å, R = 0.0174). In the case of the rubidium compound, the splitting of the Rb/Ag position was revealed for the first time am ong molybdates. Both structures are based on layers of alternating MoO4 tetrahedra and AgO6 or (Ag, Tl)O6 octahedra linked by oxygen vertices. The coordination numbers of rubidium and thallium are 12 and 10

La4Te7O20: A new ternary rare-earth metal(III) oxotellurate(IV) with isolated [TeO3]2– and [Te3O8]4– anions

The new rare-earth metal(III) oxotellurate(IV) La4Te7O20 was obtained as a single-crystalline by-product of the La2Te3O9 synthesis through a solid-state reaction of the corresponding binary oxides La2O3 and TeO2. The colorless, lath-shaped crystals of La4Te7O20 crystallize in the monoclinic space group C2/c with the lattice parameters a ​= ​2740.63(16) pm, b ​= ​580.92(3) pm, c ​= ​1326.71(8) pm and β ​= ​106.849(3)° for Z ​= ​4. The structure consists of two crystallographically distinct lanthanum-oxygen polyhedra with the coordination numbers of seven plus one and eight (d(La3+–O2–) ​= ​241 – 262 pm plus 310 pm). These lanthanum-oxygen polyhedra are attached to one ψeq1-trigonal [TeO4]4– bipyramid (d(Te4+–O2–) ​= ​186 – 214 pm, ​2× each) and three different ψ1-[TeO3]2– tetrahedra (d(Te4+–O2–) ​= ​184 – 189 pm) with twice the frequency of occurrence. So the central [TeO4]4– core is linked with two [TeO3]2– groups via common oxygen vertices to form an isolated [Te3O8]4– anion, leading to the structural formula La4[Te3O8][TeO3]4. The presence of all these different oxotellurate(IV) units is confirmed by a single-crystal Raman spectrum.

Novel aluminophosphate Na6[Al3P5O20] with the original microporous crystal structure established in the study of a pseudomerohedric microtwin.

The synthesis and characterization of a new aluminophosphate, Na6[Al3P5O20], obtained as single crystals in the same experiment together with Cl-sodalite, Na8[Al6Si6O24]Cl2, is reported. Na6[Al3P5O20], with a strongly pseudo-orthorhombic lattice, is described by the monoclinic crystal structure established in the study of a pseudomerohedric microtwin. The design of Na6[Al3P5O20] can be interpreted as an alternative to sodalite, with a monoclinic (pseudo-orthorhombic) 2×4×1 super-structure and unit-cell parameters multiples of those of sodalite: a ≃ 2as, b ≃ 4bs and c ≃ cs. The triperiodic framework is built by AlO6, AlO4 and PO4 polyhedra having vertex-bridging contacts. While all the oxygen vertices of the Al-centred octahedra and tetrahedra are shared with phosphate groups, some of the PO4 tetrahedra remain `pendant', e.g. containing vertices not shared with other polyhedra of the aluminophosphate construction. Na atoms occupy framework channels and cavities surrounded by eight-, six- and four-membered windows with maximal effective pore widths of 4.86× 3.24 and 4.31× 3.18 Å. The generalized framework density is equal to 19.8, which means that the compound may be classified as a microporous zeolite. The Na6[Al3P5O20] crystal structure is discussed as being formed from octahedral rods arranged in two perpendicular directions, similar to the rods elongated in one direction in the NASICON-type compounds, which have been intensively investigated as promising materials for batteries. Analogous properties can be expected for phases with a modified composition of the Na6Al3P5O20 topology, where the Al atoms at the centres of octahedra are replaced by Fe, V or Cr.

Synthesis and Structure of Two Phosphate Representatives Formed by Metal Cations in Oxidation State III, α-CaMg2(SO4)3 Analogues

Polycrystals of the BiFe2(PO4)3 compound and Bi1 – xSbхCr2(PO4)3 solid solution, which form a family isostructural to α-CaMg2(SO4)3 (sp. gr. P63/m), have been synthesized from an aqueous solution by the salt co-precipitation method. The samples are characterized by X-ray diffraction, IR spectroscopy, differential thermal analysis, and thermogravimetry, microprobe analysis. The BiFe2(PO4)3 single crystals have been grown by the flux method. The structure consists of polyhedra of three types: PO4 tetrahedra, two face-sharing FeO6 octahedra, and BiO6 octahedra. Isolated PO4 tetrahedra, which share oxygen vertices with doubled FeO6 octahedra, form a three-dimensional [Fe2(PO4)3]3∞ framework, whose voids are occupied by bismuth atoms. Structures of the BiFe2(PO4)3 and NASICON types are compared.

Long-range and local crystal structures of the Sr1−xCaxRuO3 perovskites

The crystal structures of the Sr1-xCaxRuO3 perovskites are investigated using both long range and local structural probes. High resolution synchrotron powder X-ray diffraction characterization at ambient temperature shows that the materials are orthorhombic to high precision, and we support previous work showing that Ca2+ substitution for Sr2+ primarily changes the tilting of rigid corner-sharing RuO6 octahedra at their shared oxygen vertices. X-ray pair distribution function analysis for SrRuO3, CaRuO3 and one intermediate composition show them to be locally monoclinic, and no long range or local phase transitions are observed between 80 and 300 K for materials with intermediate compositions. High-resolution transmission electron microscopy shows that the Sr/Ca distribution is random at the nanoscale. We plot magnetic characteristics such as the ferromagnetic Tc, Curie-Weiss theta, effective moment, and ambient temperature susceptibility vs. the octahedral tilt and unit cell volume.

Synthesis, structural feature and properties of rosiait structure compound BiGeSbO6

The layered oxide BiGeSbO6 has been synthesized for the first time via solid state reaction. Rietveld refinement showed that BiGeSbO6 belongs to PbSb2O6 structural type (P-31m space group) with unit cell parameters a = 5.1314(9), c = 4.9974(1) Å, α = 90°, γ = 120°, Z = 1. Using the EXAFS and XANES methods, it was shown that a structural feature of this compound is a strong disordering of the Bi–O octahedron caused by the stereochemical activity of the 6s2 lone pair of Bi3+ electrons. A model according to which one oxygen vertex in the oxygen coordinated Bi3+ octahedron is absent, and the lone pair of electrons builds this polyhedron to the octahedron, was proposed. A particularity of the structure of BiGeSbO6 is that the existing oxygen vacancy does not have a specific position. It was established that BiGeSbO6 does not exhibit any polymorphic transition up until its incongruent melting point Тm = 985°С. Isobaric heat capacity was measured and thermodynamic functions (entropy, enthalpy increment and Gibbs free energy) were calculated for BiGeSbO6 in the 10–1200 K temperature range. We found that the band gap of BiGeSbO6 is due to the allowed direct interband transition with the energy of 3.16 eV. It was shown that BiGeSbO6 has a wide transmission region in the visible and near-IR ranges. BiGeSbO6 is a self-activated phosphor, but its luminescence spectrum is atypical for Bi3+-containing oxides. The luminescent properties of Bi1-xEuxGeSbO6 solid solutions (x = 0.3, 0.5) were also studied.

Partial Substitution of Potassium with Sodium in the K2Ti2(PO4)3 Langbeinite-Type Framework: Synthesis and Crystalline Structure of K1.75Na0.25Ti2(PO4)3.

The interaction of TiN with Na2O–K2O–P2O5 melts was investigated at (Na+K)/P molar ratios of 0.9, 1.0, and 1.2 and at Na/K molar ratios of 1.0 and 2.0. Interactions in the system led to the loss of nitrogen and the partial loss of phosphorus and resulted in the formation of KTiP2O7 and langbeinite‐type K2−xNaxTi2(PO4)3 (x=0.22–0.26) solid solutions over the temperature range of 1173 to 1053 K. The phase compositions of the obtained samples were determined by using X‐ray diffraction (including Rietveld refinement), scanning electron microscopy (using energy‐dispersive X‐ray spectroscopy and element mapping), FTIR spectroscopy, and thermogravimetric analysis/differential thermal analysis. K1.75Na0.25Ti2(PO4)3 was characterized by single‐crystal X‐ray diffraction [P213 space group, a=9.851(5) Å]. The 3D framework is built up by TiO6 octahedra and PO4 tetrahedra sharing all the oxygen vertices with the formation of cavities occupied by K(Na) cations. Only one of the two crystallographically inequivalent potassium sites is partially substituted by sodium, and this was confirmed by calculating the bond‐valence sum. The thermodynamic stability of K1.75Na0.25Ti2(PO4)3 crystals and the preferable occupation sites of NaK cationic substitutions were investigated by DFT‐based electronic structure calculations performed by the plane‐wave pseudopotential method.

Synthesis, physico-chemical studies and Hirshfeld surface analysis of a first 0-D Chlorozincophosphate, (H2N(CH2)4NH(CH2)2NH3Cl)ZnCl2(HPO4)

An original zero-dimensional chloro-substituted zincophosphate monomer, (H2N(CH2)4NH(CH2)2NH3Cl)Zn(HPO4)Cl2, was isolated by the reaction of zinc chloride (Zn2+, 2Cl−) with the amine, 1-(2-aminoethyl)piperazine, H3PO4 and HCl under ambient conditions. This phase crystallizes in the triclinic space group P-1 (No. 2) with the lattice parameters a = 8.834(2), b = 8.539(3), c = 11.163(2) A, α = 93.58(2)°, β = 108.62(2)°, γ = 62.96(2)°, V = 707.3(4) A3, Z = 2, R = 0.027 and Rw = 0.037. The tri-protonited organic cations are linked to the isolated chloride ions Cl− through N–H⋯Cl and C–H⋯Cl hydrogen bonds, forming corrugated cationic layers extending parallel to (a b) plane. The inorganic framework of the title compound consists of a network of ZnO3Cl and HPO4 tetrahedral units linked by their oxygen vertices, forming isolated 4-membered rings. These anionic monomers, (Zn2P2O8Cl4H2)4−, which are held by O–H⋯O hydrogen-bonding interactions, lie between the cationic layers to maximize the electrostatic interactions and are linked to (H2N(CH2)4NH(CH2)2NH3Cl)2+cations via N–H⋯O or N–H⋯Cl hydrogen bonds, forming a 3-D supra molecular structure. Hirshfeld surface analysis, Solid state NMR, Infrared spectroscopies and DTA/TGA analysis were also performed to characterize the title compound. Solid state31P and13C MAS NMR spectroscopy results were found to be in full agreement with the XRD results.

Water-Soluble and Ultrastable Ti4L6 Tetrahedron with Coordination Assembly Function.

We have successfully constructed a tetrahedral Ti4L6 cage with calixarene-like coordination-active vertices. It further features high solubility and stability in H2O and DMF/H2O solution, affording an interesting stepwise assembly function with other metal ions. Through trapping of different amounts of Co or Ln ions, the Ti4L6 tetrahedra can be organized into various dimensional architectures, including a Ti4L6-Co3 cage, a Ti4L6-Ln2 cage, a Ti4L6-Ln2 chain, and a three-dimensional Ti4L6-Ln framework. An unusual mixed-valence phenomenon was observed in the Ti4L6 cage, whose Ti3+/4+ compositions were adequately identified by electron spin resonance and X-ray photoelectron spectroscopy analyses. More remarkably, the calixarene-like oxygen vertices of the Ti4L6 cage can also be used for the recognition of C3-symmetric dye molecules through N-H···O hydrogen bonding. Accordingly, driven by visible light, selective and efficient homogeneous photodecomposition of acid blue 93 and alkali blue 4B were successfully achieved. Therefore, this work not only represents a milestone in constructing symmetric Ti-based cages with interesting coordination assembly function but also provides a new method for preparing technologically important soluble photoactive cages.

Crystal structure and spin-trimer magnetism of Rb2.3(H2O)0.8Mn3[B4P6O24(O,OH)2

The novel borophosphate Rb2.3(H2O)0.8Mn3[B4P6O24(O,OH)2] was prepared under hydrothermal conditions at 553 K. Its crystal structure was determined using single-crystal X-ray diffraction data obtained from a non-merohedral twin and refined against F2 to R = 0.057. The compound crystallizes in the orthorhombic space group Pbcn, with unit-cell parameters a = 20.076(2) Å, b = 9.151(1) Å, c = 12.257(1) Å, V = 2251.8(2) Å3, and Z = 4. The title compound is the first example of a borophosphate with manganese ions adopting both octahedral and tetrahedral coordinations. Its unique crystal structure is formed by borophosphate slabs and chains of Mn2+-centered polyhedra sharing edges and vertices. These 2D and 1D fragments interconnect into a framework with open channels that accommodate Rb+ cations and water molecules. Topological relationships between borophosphates built from three-membered rings of two borate and one phosphate tetrahedra sharing oxygen vertices, amended by additional PO4 and HPO4 tetrahedra, are discussed. The temperature dependence of the magnetic susceptibility of Rb2.3(H2O)0.8Mn3[B4P6O24(O,OH)2] reveals predominant antiferromagnetic exchange interactions and the high-temperature effective magnetic moment corresponding to the high-spin S = 5/2 state of Mn2+ ions. At 12.5 K, a magnetic transition is evidenced by ac-susceptibility and specific heat measurements. A spin-trimer model with the leading exchange interaction J ∼ 3.2 K is derived from density-functional band-structure calculations and accounts for all experimental observations.

Li3V2(PO4)3 Particles Anchored in Carbon Nanofiber As a Cathode Material for High-Power Lithium Rechargeable Battery

Lithium rechargeable battery has been rapidly developed for the applications in portable devices, electric vehicles (EV), and hybrid electric vehicles (HEV) due to their high energy density and durable cycle life. From the viewpoint of electrode, fast lithium ion and electron transport are essential to enhance its electrochemical performance. However, it is quite challenging to improve both properties at the same time, especially for cathode materials. Thus, no matter what we develop for new cathode materials, there have been severe limitations in terms of lithium ion diffusivity and electronic conductivity. Phosphate (PO4)3--based materials have been attracting tremendous interests due to their competitive energy density and remarkable thermal stability. Among these phosphates, monoclinic Li3V2(PO4)3 (LVP) was proposed as a highly promising cathode material, owing to its high operating voltage and very high theoretical capacity of 197 mAh g-1 when all three lithium ions are extracted/inserted between 3.0 and 4.8 V. In particular, its three-dimensional structure framework consisting of slightly distorted VO6 octahedral and PO4 tetrahedral sharing oxygen vertex provides large interstitial space that makes lithium ions capable of moving fast inside the structure. However, just like the other metal phosphates, it shows a limited electron conductivity (10-8 - 10-9 S cm-1), which makes LVP to be difficult for practical applications. Herein, we present a sagacious design of LVP/carbon nanofiber with a distinctive morphology where LVP nanoparticles are anchored in the surface of carbon nanofiber. In general carbon-coated LVP 1D materials, there has been a problem that the carbon coating layer additionally interferes with lithium ion diffusion into LVP bulk. However, in our structure, LVP particles can directly contact with electrolytes leading to an improved lithium ion conductivity. Furthermore, carbon nanofiber can provide fast electron transport along its 1D pathway. As a result, it was demonstrated that this unique structure is favorable for simultaneously maximizing Li ion conductivity and electronic conductivity for great electrochemical improvement of LVP materials. Figure 1

Two-dimensional zeolite-like network in the new caesium copper aluminate Cs2CuAl4O8.

Monoclinic dicaesium copper tetraaluminate, Cs2CuAl4O8, space group P2(1)/c, a = 8.4551 (7), b = 10.012 (1), c = 17.073 (2) Å, β = 101.643 (9)°, Z = 6, was obtained by high-temperature crystallization from a phosphate flux. Its microporous crystal structure presents the first example of double layers built from [AlO4] tetrahedra combined in 4-, 6- and 8-rings, topologically similar to those found in the ATT-type zeolites and isostructural minerals armstrongite, davanite and dalyite. These layers show a rare arrangement of three [AlO4] tetrahedra sharing one oxygen vertex. The aluminate slabs are further linked by chains of edge-sharing [CuO4] square planes to form a mixed anionic three-dimensional framework with Cs(+) cations in channels and cavities. An unusually short Cu···Cs distance of 3.166 Å is ascribed to the strong Jahn-Teller effect of Cu(2+). The magnetic subsystem demonstrates properties of an alternating antiferromagnetic chain with a gap in the spectrum of magnetic excitations.

Crystal structure interconnections in a family of hydrated phosphate-sulfates

The phosphate-sulfate family incorporates several water-containing hypergene minerals with various structures. We determined the crystal structure of lately discovered [1] fibrous mineral arangasite, [Al2F(H2O)6(PO4)(SO4)]·3(H2O) using single-crystal synchrotron diffraction at 100 K (a =7.073(1), b=9.634(2), c=10.827(2) Å, β=79.60(1)0, P2/a, Z=2). Its crystal chemical interpretation has allowed us to reveal some interesting features in a title group of compounds. The arangasite crystal structure is dominated by chains extending in the [100] direction and built of pairs of corner-shared Al octahedra joined through bridging F atoms and P tetrahedra. They alternate in the [001] with S tetrahedra forming layers parallel to the ac plane through a system of hydrogen bonds. Along [010] the complex layers are separated by layers of H2O molecules. Hydrogen bonding serves here as the only mechanism providing linkage between the main structural fragments. The Al/ P chains are topologically identical to the chains built from Fe octahedra and P tetrahedra in the triclinic structure of destinezite, Fe2(OH)(PO4)(SO4)(H2O)6[2]. The repeating subunit of both chains consists of two octahedra and one tetrahedron sharing vertices. A main difference among the chains arises from their chemistry; Al octahedra in arangasite form pairs by sharing the F vertex of neighboring polyhedra, whereas pairs of Fe octahedra in destinezite are linked together through the oxygen vertex of an OH group. As a result, the larger size of the Fe octahedra compared to Al octahedra causes a larger c = 7.31 Å along the chain in destinezite. Additional SO4tetrahedra here are attached to these chains along their periphery through an oxygen vertex bridge with Fe octahedra. The monoclinic sanjuanite, Al2(PO4)(SO4)(OH)(H2O)9structure [3] is composed of Al/P chains, parallel to a = 6.11 Å. These chains are also built from three-member units that include corner-sharing pairs of octahedra connected by PO4tetrahedron, but they are not topologically equivalent to the chains in the arangasite and destinezite structures. Similar to arangasite, sulfate groups and H2O molecules reside between chains in the sanjuanite structure with hydrogen bonding. Thus, similar the crystal chemical formulae of sanjuanite and arangasite differ with respect to the (OH) → F substitution, which results in contrasting unit cell parameters. Note, that the unit cell volume of sanjuanite, is twice as large as arangasite.

Thortveitite-type Tm2Si2O7.

Single crystals of dithulium disilicate, Tm2Si2O7, were obtained in flux synthesis experiments in the system SiO2–Tm2O3–LiF at ambient pressure. The compound belongs to the group of sorosilicates, i.e. it is based on [Si2O7]-units and crystallizes in the thortveitite (Sc2Si2O7) structure type. The Tm3+ cation (site symmetry .2.) occupies a distorted octa­hedral site, with Tm—O bond lengths in the range 2.217 (4)–2.289 (4) Å. Each of the octa­hedra shares three of its edges with adjacent [TmO6] groups, resulting in the formation of layers parallel to (001). The individual [SiO4] tetra­hedra are more regular, i.e. the differences between the bond lengths between Si and the bridging and non-bridging O atoms are not very pronounced. The layers containing the octa­hedra and the sheets containing the [Si2O7] groups (point group symmetry 2/m) form an alternating sequence. Linkage is provided by sharing common oxygen vertices.

KNi0.93FeII0.07FeIII(PO4)2: a new type of structure for a compound of compositionMIMIIMIII(PO4)2

The solid solution KNi(0.93)Fe(II)(0.07)Fe(III)(PO4)2 {potassium [nickel(II)/iron(II)] iron(III) bis(orthophosphate)} has been prepared by the flux method. The compound shows a new type of structure for a phosphate with the general composition M(I)M(II)M(III)(PO4)2. The framework is formed by [(Ni/Fe)O6] polyhedra [Fe site occupancy = 0.069 (14)] linked via shared oxygen vertices forming a cis-like parallel chain stretching along a and [FeO5] polyhedra (located on alternate sides of the chains) connected via two types of PO4 groups into a three-dimensional structure. The K atoms are disordered between two sites, denoted K1A and K1B, with occupancies of 0.930 (9) and 0.070 (9), respectively, and reside inside channels along the a axis. Calculations of the Voronoi-Dirichlet polyhedra of the K atoms give a coordination scheme for K1A of [9 + 3] and for K1B of [10 + 2]. The most remarkable feature of the structure is the splitting of the K-atom site and the population of the K1A and K1B positions due to substitution of Ni by Fe in the (Ni/Fe) position.

The First Vanadate–Carbonate, K2Mn3(VO4)2(CO3): Crystal Structure and Physical Properties

Mixed potassium-manganese vanadate-carbonate, K(2)Mn(3)(VO(4))(2)(CO(3)), represents a novel structure type; it has been synthesized hydrothermally from the system MnCl(2)-K(2)CO(3)-V(2)O(5)-H(2)O. Its hexagonal crystal structure was determined by single-crystal X-ray diffraction with a = 5.201(1) Å, c = 22.406(3) Å, space group P6(3)/m, Z = 2, ρ(c) = 3.371 g/cm(3), and R = 0.022. The layered structure of the compound can be described as a combination of honeycomb-type modules of [MnO(6)] octahedra and [VO(4)] tetrahedra, alternating in the [001] direction with layers of [MnCO(3)] built by [MnO(5)] trigonal bipyramids and [CO(3)] planar triangles, sharing oxygen vertices. The K(+) ions are placed along channels of the framework, elongated in the [100], [010], and [110] directions. The title compound exhibits rich physical properties reflected in a phase transition of presumably Jahn-Teller origin at T(3) = 80-100 K as well as two successive magnetic phase transitions at T(2) = 3 K and T(1) = 2 K into a weakly ferromagnetic ground state, as evidenced in magnetization, specific heat, and X-band electron spin resonance measurements. A negative Weiss temperature Θ = -114 K and strongly reduced effective magnetic moment μ(eff)(2) ~ 70 μ(B)(2) per formula unit suggest that antiferromagnetic exchange interactions dominate in the system. Divalent manganese is present in a high-spin state, S = 5/2, in the octahedral environment and a low-spin state, S = ½, in the trigonal-bipyramidal coordination.

Synthesis and Crystal Structure of the Fluoride‐Rich Rubidium Scandium Fluoride Oxosilicate Rb3Sc2F5Si4O10

AbstractThe new quinary fluoride‐rich rubidium scandium oxosilicate Rb3Sc2F5Si4O10 was obtained from mixtures of RbF, ScF3, Sc2O3 and SiO2 in sealed platinum ampoules after seventeen days at 700 °C. The colourless compound crystallises orthorhombically in space group Pnma with a = 962.13(5), b = 825.28(4), c = 1838.76(9) pm and Z = 4. For the oxosilicate partial structure, [SiO4]4– tetrahedra are connected in (001) by vertex‐sharing to form corrugated unbranched vierer single layers ${2}\atop{{\infty}}${[Si4O10]4–} (d(Si–O) = 158–165 pm, ∠(O–Si–O) = 103–114°, ∠(Si–O–Si) = 125–145°) containing six‐membered rings. Similar oxosilicate layers with 63‐net topology are well‐known for the mineral group of micas or in sanbornite Ba2Si4O10. Regarding other systems, identical tetrahedral layers can be found in the synthetic borophosphate Mg(H2O)2[B2P2O8(OH)2]·H2O. The Sc3+ cations are coordinated octahedrally by four F– and two O2– anions. These cis‐[ScF4O2]5– octahedra (d(Sc–F) = 200–208 pm, d(Sc–O) = 202–205 pm) share one equatorial and two apical F– anions with others to build up slightly corrugated ${1}\atop{{\infty}}${[Sc2F${t}\atop{2/1}$F${v}\atop{6/2}$O${t}\atop{4/1}$]7–} double chains along [010]. These are linked with the oxosilicate layers via two oxygen vertices to construct a three‐dimensional framework with cavities apt to host the three crystallographically independent Rb+ cations with coordination numbers of eleven, twelve and thirteen.

Synthesis and crystal structure of phosphate Ba1.5Fe2(PO4)3

Double phosphate Ba1.5Fe2(PO4)3 was synthesized and structurally studied. Single crystals were synthesized by the fusion method. Cubic crystals, Z = 4, space group P213, a = 9.866(1) A. This structure is built of polyhedrons of four types: PO4 tetrahedrons, two virtually regular FeO6 octahedrons, BaO12 twelve-vertex polyhedrons, and BaO9 nine-vertex polyhedrons. These polyhedrons share common oxygen vertices to form three-dimensional [Fe2(PO4)3]3∞ framework containing barium atoms in cavities.