Synthesis, structure and magnetic properties of the new mixed-valence vanadate Na2SrV3O9

The new complex oxide Na₂SrV₃O₉ was synthesized and investigated by means of X-ray diffraction, electron microscopy and magnetic susceptibility measurements. This oxide has a monoclinic unit cell with parameters a=5.416(1) Å, b=15.040(3) Å, c=10.051(2) Å, β=97.03(3)°, space group P2₁/c and Z=4. The crystal structure of Na₂SrV₃O₉, as determined from X-ray single-crystal data, is built up from isolated chains formed by square V⁴⁺O₅ pyramids. Neighboring pyramids are linked by two bridging V⁵⁺O₄ tetrahedra sharing a corner with each pyramid. The Na and Sr atoms are situated between the chains. Electron diffraction and HREM investigations confirmed the crystal structure. The temperature dependence of the susceptibility indicates low-dimensional magnetic behavior with a sizeable strength of the magnetic intra-chain exchange J of the order of 80 K, which is very likely due to superexchange through the two VO₄ tetrahedra linking the magnetic V⁴⁺ cations.     

Synthesis and crystal structure of the palladium oxides NaPd3O4, Na2PdO3 and K3Pd2O4

NaPd₃O₄, Na₂PdO₃ and K₃Pd₂O₄ have been prepared by solid-state reaction of Na₂O₂ or KO₂ and PdO in sealed silica tubes. Crystal structures of the synthesized phases were refined by the Rietveld method from X-ray powder diffraction data. NaPd₃O₄ (space group Pm3¯n, a=5.64979(6) Å, Z=2) is isostructural to NaPt₃O₄. It consists of NaO₈ cubes and PdO₄ squares, corner linked into a three-dimensional framework where the planes of neighboring PdO₄ squares are perpendicular to each other. Na₂PdO₃ (space group C2/c, a=5.3857(1) Å, b=9.3297(1) Å, c=10.8136(2) Å, β=99.437(2)°, Z=8) belongs to the Li₂RuO₃-structure type, being the layered variant of the NaCl structure, where the layers of octahedral interstices filled with Na⁺ and Pd⁴⁺ cations alternate with Na₃ layers along the c-axis. Na₂PdO₃ exhibits a stacking disorder, detected by electron diffraction and Rietveld refinement. K₃Pd₂O₄, prepared for the first time, crystallizes in the orthorhombic space group Cmcm (a=6.1751(6) Å, b=9.1772(12) Å, c=11.3402(12) Å, Z=4). Its structure is composed of planar PdO₄ units connected via common edges to form parallel staggered PdO₂ strips, where potassium atoms are located between them. Magnetic susceptibility measurements of K₃Pd₂O₄ reveal a Curie-Weiss behavior in the temperature range above 80 K.     

Synthesis and crystal structure of two tin fluoride materials: NaSnF3 (BING-12) and Sn3F3PO4

A new compound, sodium tin trifluoride (NaSnF₃, which we denote BING-12 for SUNY at Binghamton, Structure No. 12), was synthesized solvothermally from a pyridine-water solvent system. The new compound crystallized in the monoclinic space group C2/c (No. 15), with a=11.7429(12) Å, b=17.0104(18) Å, c=6.8528(7) Å, β=100.6969(2)°, V=1345.1(2) Å³ and Z=16. The layered structure consists of outer pyramidal SnF₃ units, where the fluorides surround a central layer of six- and seven-coordinate sodium atoms. The layers are stabilized by charged Na⁺ galleries that reside in the center of the layers. Tin trifluorophosphate (Sn₃F₃PO₄, Compound 2) was isolated from a related synthetic system, and crystallized in the rhombohedral space group R3 (No. 146), with a=11.8647(11) Å, c=4.6291(6) Å, V=564.34(10) Å³ and Z=3. The framework is made up of helical -Sn-F- chains, which are connected by phosphate groups. The materials were characterized by powder X-ray diffraction (PXRD), variable temperature PXRD (VT-PXRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM).     

The Na2O-SrO-B2O3 diagram in the B-rich part and the crystal structure of NaSrB5O9

The subsolidus phase relations in the B-rich part of the ternary system, Na₂O-SrO-B₂O₃, are investigated by the powder X-ray diffraction method. Four ternary compounds: NaSrBO₃, NaSr₄B₃O₉, Na₃SrB₅O₁₀ and NaSrB₅O₉ were found in it, the two lasts are new. NaSrB₅O₉ crystallizes in the monoclinic space group P2₁/c, with the lattice parameters a=6.4963(1) Å, b=13.9703(2) Å, c=8.0515(1) Å, β=106.900(1)°. Na₃SrB₅O₉ is also monoclinic, space group C2, a=7.290(1) Å, b=13.442(2) Å, c=9.792(1) Å, β=109.60(1). NaSrB₅O₉ is isostructural with another pentaborate NaCaB₅O₉, and its structure was refined by Rietveld method based on the structural model of NaCaB₅O₉. The fundamental building units are [B₅O₉]³⁻ anionic groups, forming complex thick anionic sheets, extending parallel to the ac plane. The Na and Sr atoms are all eight-coordinated with O atoms, forming trigonal dodecahedra. The [NaO₈] polyhedra are distributed between the B-O sheets, while the [SrO₈] polyhedra located in the sheets and connect with each other by edges to form infinite chains along the c-axis.     

Crystal structure of BaMg2Si2O7 and Eu luminescence

Crystal structure of BaMg₂Si₂O₇ was determined and refined by a combined powder X-ray and neutron Rietveld method (monoclinic, C2/c, no. 15, Z=8, a=7.24553(8) Å, b=12.71376(14) Å, c=13.74813(15) Å, β=90.2107(8)°, V=1266.44(2) Å³; R_p/R_wp=3.38%/4.77%). The structure contains a single crystallographic type of Ba atom coordinated to eight O atoms with C₁ (1) site symmetry. Under 325-nm excitation Ba_0.98Eu_0.02Mg₂Si₂O₇ exhibits an asymmetric emission band around 402 nm. The asymmetric shape of the emission band is likely associated with a small electron-phonon coupling in BaMg₂Si₂O₇. The integrated intensity of the emission band was observed to remain constant over the temperature range 4.2-300 K.     

The study of Bi3B5O12: synthesis, crystal structure and thermal expansion of oxoborate Bi3B5O12

The paper presents a new data on the crystal structure, thermal expansion and IR spectra of Bi₃B₅O₁₂. The Bi₃B₅O₁₂ single crystals were grown from the melt of the same stoichiometry by Czochralski technique. The crystal structure of Bi₃B₅O₁₂ was refined in anisotropic approximation using single-crystal X-ray diffraction data. It is orthorhombic, Pnma, a=6.530(4), b=7.726(5), c=18.578(5) Å, V=937.2(5) Å³, Z=4, R=3.45%. Bi³⁺ atoms have irregular coordination polyhedra, Bi(1)O₆ (d(B-O)=2.09-2.75 Å) and Bi(2)O₇ (d(B-O)=2.108-2.804 Å). Taking into account the shortest bonds only, these polyhedra are considered here as trigonal Bi(1)O₃ (2.09-2.20 Å) and tetragonal Bi(2)O₄ (2.108-2.331 Å) irregular pyramids with Bi atoms in the tops of both pyramids. The BiO₄ polyhedra form zigzag chains along b-axis. These chains alternate with isolated anions [B₂^IVB₃^IIIO₁₁]⁷⁻ through the common oxygen atoms to form thick layers extended in ab plane. A perfect cleavage of the compound corresponds to these layers and an imperfect one is parallel to the Bi-O chains. The Bi₃B₅O₁₂ thermal expansion is sharply anisotropic (α₁₁≈α₂₂=12, α₃₃=3×10⁻⁶ °C⁻¹) likely due to a straightening of the flexible zigzag chains along b-axis and decreasing of their zigzag along c-axis. Thus the properties like cleavage and thermal expansion correlate to these chains.     

Crystal growth, structure determination, and optical properties of new potassium-rare-earth silicates K3RESi2O7 (RE=Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu)

Single crystals of K₃RESi₂O₇ (RE=Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were grown from a potassium fluoride flux. Two different structure types were found for this series. Silicates containing the larger rare earths, RE=Gd, Tb, Dy, Ho, Er, Tm, Yb crystallize in a structure K₃RESi₂O₇ that contains the rare-earth cation in both a slightly distorted octahedral and an ideal trigonal prismatic coordination environment, while in K₃LuSi₂O₇, containing the smallest of the rare earths, lutetium is found solely in an octahedral coordination environment. The structure of K₃LuSi₂O₇ crystallizes in space group P6₃/mmc with a=5.71160(10) Å and c=13.8883(6) Å. The structures containing the remaining rare earths crystallize in the space group P6₃/mcm with the lattice parameters of a=9.9359(2) Å, c=14.4295(4) Å, (K₃GdSi₂O₇); a=9.88730(10) Å, c=14.3856(3) Å, (K₃TbSi₂O₇); a=9.8673(2) Å, c=14.3572(4) Å, (K₃DySi₂O₇); a=9.8408(3) Å, c=14.3206(6) Å, (K₃HoSi₂O₇); a=9.82120(10) Å, c=14.2986(2) Å, (K₃ErSi₂O₇); a=9.80200(10) Å, c=14.2863(4) Å, (K₃TmSi₂O₇); a=9.78190(10) Å, c=14.2401(3) Å, (K₃YbSi₂O₇). The optical properties of the silicates were investigated and K₃TbSi₂O₇ was found to fluoresce in the visible.     

Synthesis, crystal structure and magnetic characterization of Na2Cu5(Si2O7)2: An inorganic ferrimagnetic chain

The hydrothermal synthesis, crystal structure and magnetic properties of the new copper silicate Na₂Cu₅(Si₂O₇)₂, are reported. The crystal structure was determined through synchrotron powder diffraction data. The unit cell was indexed to a triclinic cell, space group P-1 (n° 2) with unit cell parameters a=5.71075(2) Å, b=7.68266(3) Å, c=7.96742(3) Å, α=64.2972(2)°, β=88.4860(2)° and γ=70.5958(2)° with Z=1. A structural model was obtained through a combination of a direct-space Monte-Carlo approach and Rietveld refinement. The crystal structure contains parallel chains consisting of zig-zag copper dimers and trimers. All silicon atoms are present as part of a [Si₂O₇]⁶⁻ anion that connects the chains; therefore the compound belongs to the sorosilicate mineral family. The magnetic susceptibility was measured and shows a behavior typical of one-dimensional ferrimagnetism, in agreement with the observed structure.     

A novel three-dimensional inorganic framework: hydrothermal synthesis and crystal structure of CuMo3O10·H2O

A novel three-dimensional inorganic bimetallic compound Cu[Mo₃O₁₀]·H₂O 1 has been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction. Compound 1 crystallizes in the orthorhombic system, space group Pnma, a=8.6085(17) Å, b=7.5822(15) Å, c=13.690(3) Å, V=893.6(3) Å³, Z=4, λ(MoKα) = 0.71073 Å (R(F)=0.0357 for 1101 reflections). The structure of compound 1 is based on [{Mo₃O₁₀}²⁻]_∞ isopolyoxomolybdate chains bonded together with CuO₄ tetrahedra into a three-dimensional inorganic open framework. Three types of Mo-Cu layers and one-dimensional tunnels are observed in the title compound.     

Synthesis and structure of BaKFeO3: a new quaternary oxide with 1-D ferrate chains

Amber-colored single crystals of the quaternary oxide BaKFeO₃ were synthesized from a mixture of Fe₂O₃, KOH and Ba(OH)₂ heated at 750°C for 5 h then cooled slowly. The structure was determined by single-crystal X-ray diffraction (space group Cmca; a=5.804(1) Å, b=11.528(1) Å, c=12.776(1) Å; Z=8, R₁=0.0376, wR₂=0.0996). The structure is comprised of [FeO₃³⁻]^∞ chains of corner-sharing iron-oxo tetrahedra that are isolated from one another by interspersed Ba and K cations. The iron coordination environment is moderately distorted from perfect tetrahedral symmetry and the Fe-O-Fe bond angles are 152.8°. Magnetic susceptibility data show a pronounced zero-field cooling effect that suggests strong coupling from 5 K to above room temperature.     

Ab initio structure determination of new compound Li4CaB2O6

A new compound, Li₄CaB₂O₆, has been synthesized by solid-state reaction and its structure has been determined from powder X-ray diffraction data by direct methods. The refinement was carried out using the Rietveld methods and the final refinement converged with R_p=10.4%, R_wp=14.2%, R_exp=4.97%. This compound belongs to the orthorhombic space group Pnnm, with lattice parameters a=9.24036(9) Å, b=8.09482(7) Å, and c=3.48162(4) Å. Fundamental building units are isolated [BO₃]³⁻ anionic groups, which are all parallel to the a-b plane stacked along the c-axis. The Ca atoms are six-coordinated by the O atoms to form octahedral coordination polyhedra, which are joined together through edges along the c-axis, forming infinitely long three-dimensional chains. The Li atoms have a four-fold and a five-fold coordination with O atoms that lead to complex Li-O-Li chains that also extend along the c-axis. The infrared spectrum of Li₄CaB₂O₆ was also studied, which is consistent with the crystallographic study.     

Ce10[Si10O9N17]Br, Nd10[Si10O9N17]Br and Nd10[Si10O9N17]Cl oxonitridosilicate halides with a new layered structure type

The isotypic oxonitridosilicate halides Ce₁₀[Si₁₀O₉N₁₇]Br, Nd₁₀[Si₁₀O₉N₁₇]Br and Nd₁₀[Si₁₀O₉N₁₇]Cl were obtained by the reaction of the respective lanthanide metals, their oxides and halides with “Si(NH)₂” in a radiofrequency furnace at temperatures around 1800 °C, using CsBr, resp. CsCl, as a flux. The crystal structures were determined by single-crystal X-ray diffraction (Pbam, no. 55, Z=2; Ce/Br: a=10.6117(9) Å, b=11.2319(10) Å, c=11.688(8) Å, R1=0.0356; Nd/Br: a=10.523(2) Å, b=11.101(2) Å, c=11.546(2) Å, R1=0.0239; Nd/Cl: a=10.534(2) Å, b=11.109(2) Å, c=11.543(2) Å, R1=0.0253) and represent a new layered structure type. The structure refinements were performed utilizing an O/N-distribution model according to Paulings rules, i.e. nitrogen was positioned on all bridging sites and mixed O/N-occupation was assumed on the terminal sites resulting in charge neutrality of the compounds. The layers consist of condensed [SiN₂(O/N)₂] and [SiN₃(O/N)] tetrahedra of Q² and Q³ type. The chemical composition of the compounds was derived from chemical analyses for Nd₁₀[Si₁₀O₉N₁₇]Br and electron probe micro analyses (EPMA) for all three compounds. The results of IR spectroscopic investigations are reported.     

Crystal structure and magnetic properties of Na2Ni(HPO3)2

Na₂Ni(HPO₃)₂, obtained as light yellow-green crystals under mild hydrothermal conditions, crystallizes in the orthorhombic Pnma space-group with lattice parameters: a=11.9886(3), b=5.3671(2), c=9.0764(3) Å, V=584.01 Å³, Z=4. The structure consists of zig-zag chains of NiO₆ octahedra bridged by two HPO₃²⁻ and the chains are further connected through HPO₃²⁻ to four nearest chains to form a three dimensional framework, delimiting intersecting tunnels in which the sodium ions are located. The Na cations reside in the irregular Na(1)O₅, Na-O of 2.276-2.745 Å, and Na(2)O₉, Na-O of 2.342-2.376 Å, environments. The presence of the phosphite monoanion has been further confirmed by IR spectroscopy. Due to the 3D framework of Ni connected by O-P-O bridges, the magnetic susceptibility behaves as a paramagnet above 100 K (C=1.49(2) emu K mol⁻¹, μ_eff=3.45 μ_B, Θ=−39(2) K) and below 6 K, it orders antiferromagnetically as confirmed the sharp drop and the non-Brillouin behavior of the isothermal magnetization at 2 K.     

Synthesis and crystal structure of new uranyl tungstates M2(UO2)(W2O8) (M=Na, K), M2(UO2)2(WO5)O (M=K, Rb), and Na10(UO2)8(W5O20)O8

The solid-state reactions of UO₃ and WO₃ with M₂CO₃ (M=Na, K, Rb) at 650°C for 5 days result, accordingly the starting stoichiometry, in the formation of M₂(UO₂)(W₂O₈) (M=Na (1), K (2)), M₂(UO₂)₂(WO₅)O (M=K (3), Rb (4)), and Na₁₀(UO₂)₈(W₅O₂₀)O₈ (5). The crystal structures of compounds 2, 3, 4, and 5 have been determined by single-crystal X-ray diffraction using Mo(Kα) radiation and a charge-coupled device detector. The crystal structures were solved by direct methods and Fourier difference techniques, and refined by a least-squares method on the basis of F² for all unique reflections. For (1), unit-cell parameters were determined from powder X-ray diffraction data. Crystallographic data: 1, monoclinic, a=12.736(4) Å, b=7.531(3) Å, c=8.493(3) Å, β=93.96(2)°, ρ_cal=6.62(2) g/cm³, ρ_mes=6.64(1) g/cm³, Z=4; 2, orthorhombic, space group Pmcn, a=7.5884(16) Å, b=8.6157(18) Å, c=13.946(3) Å, ρ_cal=6.15(2) g/cm³, ρ_mes=6.22(1) g/cm³, Z=8, R1=0.029 for 80 parameters with 1069 independent reflections; 3, monoclinic, space group P2₁/n, a=8.083(4) Å, b=28.724(5) Å, c=9.012(4) Å, β=102.14(1)°, ρ_cal=5.83(2) g/cm³, ρ_mes=5.90(2) g/cm³, Z=8, R1=0.037 for 171 parameters with 1471 reflections; 4, monoclinic, space group P2₁/n, a=8.234(1) Å, b=28.740(3) Å, c=9.378(1) Å, β=104.59(1)°, ρ_cal=6.13(2) g/cm³,  g/cm³, Z=8, R1=0.037 for 171 parameters with 1452 reflections; 5, monoclinic, space group C2/c, a=24.359(5) Å, b=23.506(5) Å, c=6.8068(14) Å, β=94.85(3)°, ρ_cal=6.42(2) g/cm³,  g/cm³, Z=8, R1=0.036 for 306 parameters with 5190 independent reflections. The crystal structure of 2 contains linear one-dimensional chains formed from edge-sharing UO₇ pentagonal bipyramids connected by two octahedra wide (W₂O₈) ribbons formed from two edge-sharing WO₆ octahedra connected together by corners. This arrangement leads to [UW₂O₁₀]²⁻ corrugated layers parallel to (001). Owing to the unit-cell parameters, compound 1 probably contains similar sheets parallel to (100). Compounds 3 and 4 are isostructural and the structure consists of bi-dimensional networks built from the edge- and corner-sharing UO₇ pentagonal bipyramids. This arrangement creates square sites occupied by W atoms, a fifth oxygen atom completes the coordination of W atoms to form WO₅ distorted square pyramids. The interspaces between the resulting [U₂WO₁₀]²⁻ layers parallel to plane are occupied by K or Rb atoms. The crystal structure of compound 5 is particularly original. It is based upon layers formed from UO₇ pentagonal bipyramids and two edge-shared octahedra units, W₂O₁₀, by the sharing of edges and corners. Two successive layers stacked along the [100] direction are pillared by WO₄ tetrahedra resulting in sheets of double layers. The sheets are separated by Na⁺ ions. The other Na⁺ ions occupy the rectangular tunnels created within the sheets. In fact complex anions W₅O₂₀¹⁰⁻ are built by the sharing of the four corners of a WO₄ tetrahedron with two W₂O₁₀ dimmers, so, the formula of compound 5 can be written Na₁₀(UO₂)₈(W₅O₂₀)O₈.     

Icosahedral Li clusters in the structures of Li33.3Ba13.1Ca3 and Li18.9Na8.3Ba15.3

The intermetallic phases Li_33.3Ba_13.1Ca₃ and Li_18.9Na_8.3Ba_15.3 have been prepared and their crystal structures have been determined. According to single-crystal X-ray diffraction data, both compounds crystallize in new structure types with trigonal unit cells (Li_33.3Ba_13.1Ca₃: R3¯c, a=19.9127(4) Å, c=90.213(3) Å, Z=18, V=30,978(1) Å³ and Li_18.9Na_8.3Ba_15.3: P3¯, a=20.420(3) Å, c=92.914(19), Z=18, V=33,550(10) Å³). The first compound can be described as a complicated variant of the arsenic structure. The second has similar packing of the Ba atoms but differs from the Ca-containing phase in the packing of the light elements. Both compounds contain icosahedron-based polytetrahedral clusters, typical for Li-rich phases, e.g. Ba₁₉Li₄₄.     

The crystal structure of the interrupted framework silicate K9.6Ca1.2Si12O30 determined from laboratory X-ray diffraction data

The crystal structure of a potassium calcium silicate with composition K_9.6Ca_1.2Si₁₂O₃₀ (or K₈CaSi₁₀O₂₅) has been solved by direct methods aided by distance least squares optimization from laboratory X-ray powder diffraction data. The trigonal compound adopts the non-centrosymmetric space group R3c with the following basic crystallographic data: a=11.13623(5) Å, c=21.9890(2) Å, V=2361.63(2) Å³, Z=3, D_calc=2.617 g cm⁻³. The crystal structure can be classified as an interrupted framework with exclusively Q³-units. It can be thought of as being built from layers parallel to (001) containing isolated six-membered tetrahedral rings in UDUDUD conformation. Corner sharing of tetrahedra belonging to adjacent sheets results in a tetrahedral framework. The framework density of the structure is 15.2 T-atoms/1000 Å³. The coordination sequences are identical for both silicon atoms in the asymmetric unit: 3-6-11-20-32-46-60-80-102-122. The vertex symbols for the two tetrahedral centers are 10₂·10₂·6₁. Topologically, the structure can be described as an Archimedean three-dimensional 3-connected net. It can be derived from the diamond or cristobalite net by removing 20% of the knots. Charge compensation in the structure is achieved by the incorporation of mono- and divalent M-cations (M: K, Ca). These extra-framework ions are coordinated by six to nine oxygen ligands. Ca/K distributions for the five symmetrically independent M-sites were obtained from a combination of bond distance considerations, site occupancy refinements and the bulk chemical composition. The structural characterization is completed by a detailed Raman spectroscopic study. Furthermore, possible implications of the structural chemistry of interrupted framework silicates for the field of silicate glass research are addressed.     

Synthesis crystal structure and ionic conductivity of Ca0.5Bi3V2O10 and Sr0.5Bi3V2O10

Two new compounds Ca_0.5Bi₃V₂O₁₀ and Sr_0.5Bi₃V₂O₁₀ have been synthesized in the ternary system: MO-Bi₂O₃-V₂O₅ system (M=M²⁺). The crystal structure of Sr_0.5Bi₃V₂O₁₀ has been determined from single crystal X-ray diffraction data, space group and Z=2, with cell parameters a=7.1453(3) Å, b=7.8921(3) Å, c=9.3297(3) Å, α=106.444(2)°, β=94.088(2)°, γ=112.445(2)°, V=456.72(4) Å³. Ca_0.5Bi₃V₂O₁₀ is isostructural with Sr_0.5Bi₃V₂O₁₀, with, a=7.0810(2) Å, b=7.8447(2) Å, c=9.3607(2) Å, α=106.202(1)°, β=94.572(1)°, γ=112.659(1)°, V=450.38(2) Å³ and its structure has been refined by Rietveld method using powder X-ray data. The crystal structure consists of infinite chains of (Bi₂O₂) along c-axis formed by linkage of BiO₈ and BiO₆ polyhedra interconnected by MO₈ polyhedra forming 2D layers in ac plane. The vanadate tetrahedra are sandwiched between these layers. Conductivity measurements give a maximum conductivity value of 4.54×10⁻⁵ and 3.63×10⁻⁵ S cm⁻¹ for Ca_0.5Bi₃V₂O₁₀ and Sr_0.5Bi₃V₂O₁₀, respectively at 725 °C.     

Crystal structures of lazulite-type oxidephosphates TiTi3O3(PO4)3 and M4Ti27O24(PO4)24 (M=Ti, Cr, Fe)

Single crystals of the oxidephosphates Ti^IIITi^IV₃O₃(PO₄)₃ (black), Cr^III₄Ti^IV₂₇O₂₄(PO₄)₂₄ (red-brown, transparent), and Fe^III₄Ti^IV₂₇O₂₄(PO₄)₂₄ (brown) with edge-lengths up to 0.3 mm were grown by chemical vapour transport. The crystal structures of these orthorhombic members (space group F2dd ) of the lazulite/lipscombite structure family were refined from single-crystal data [Ti^IIITi^IV₃O₃(PO₄)₃: Z=24, a=7.3261(9) Å, b=22.166(5) Å, c=39.239(8) Å, R₁=0.029, wR₂=0.084, 6055 independent reflections, 301 variables; Cr^III₄Ti^IV₂₇O₂₄(PO₄)₂₄: Z=1, a=7.419(3) Å, b=21.640(5) Å, c=13.057(4) Å, R₁=0.037, wR₂=0.097, 1524 independent reflections, 111 variables; Fe^III₄Ti^IV₂₇O₂₄(PO₄)₂₄: Z=1, a=7.4001(9) Å, b=21.7503(2) Å, c=12.775(3) Å, R₁=0.049, wR₂=0.140, 1240 independent reflections, 112 variables). For Ti^IIITi^IVO₃(PO₄)₃ a well-ordered structure built from dimers [Ti^III,IV₂O₉] and [Ti^IV,IV₂O₉] and phosphate tetrahedra is found. The metal sites in the crystal structures of Cr₄Ti₂₇O₂₄(PO₄)₂₄ and Fe₄Ti₂₇O₂₄(PO₄)₂₄, consisting of dimers [M^IIITi^IVO₉] and [Ti^IV,IV₂O₉], monomeric [Ti^IVO₆] octahedra, and phosphate tetrahedra, are heavily disordered. Site disorder, leading to partial occupancy of all octahedral voids of the parent lipscombite/lazulite structure, as well as splitting of the metal positions is observed. According to Guinier photographs Ti^III₄Ti^IV₂₇O₂₄(PO₄)₂₄ (a=7.418(2) Å, b=21.933(6) Å, c=12.948(7) Å) is isotypic to the oxidephosphates M^III₄Ti^IV₂₇O₂₄(PO₄)₂₄ (M^III: Cr, Fe). The UV/vis spectrum of Cr₄Ti₂₇O₂₄(PO₄)₂₄ reveals a rather small ligand-field splitting Δ_o=14,370 cm⁻¹ and a very low nephelauxetic ratio β=0.72 for the chromophores [Cr^IIIO₆] within the dimers [Cr^IIITi^IVO₉].     

Synthesis and structure of organically templated lanthanum sulfate [C4N3H16][La(SO4)3]·H2O

The first organically templated one-dimensional lanthanum sulfate [C₄N₃H₁₆][La(SO₄)₃]·H₂O has been prepared employing hydrothermal methods in the presence of diethylenetriamine (DETA). The structure was determined by single-crystal X-ray diffraction (XRD). The title compound crystallizes in the triclinic system, space group P-1 (No.2) with cell parameters M=551.30, a=8.2773(7) Å, b=9.5660(6) Å, c=10.4363(6) Å, α=105.661(2)°, β=102.849(3)°, γ=104.376(3)°, V=732.72(9) Å³, Z=2, R=0.0285, wR=0.0778. The structure consists of infinite linear chains. The chains are held together by hydrogen bond interactions involving the hydrogens of the amine and the framework oxygens. The as-synthesized product is characterized by powder XRD, inductive couple plasma analysis and thermogravimetric analysis.     

Synthesis and structural characterization of novel tin and titanium potassium silicates K4M2Si6O18

The synthesis of a new potassium titanosilicate, K₄Ti₂Si₆O₁₈ (Ti-AV-11), possessing the crystal structure of potassium stannosilicate AV-11, has been reported. The unit cell of this material is trigonal, space group R3 (no. 146), Z=3, a=10.012, c=14.8413 Å, γ=120°, V=1289 Å³. The structure of AV-11 is built up of MO₆ (M=Sn, Ti) octahedra and SiO₄ tetrahedra by sharing corners. The SiO₄ tetrahedra form helix chains, periodically repeating every six tetrahedra. These chains extend along the [001] direction and are linked by isolated MO₆ octahedra, thus producing a mixed octahedral-tetrahedral oxide framework. AV-11 materials have been further characterized by bulk chemical analysis, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), ²⁹Si and ¹¹⁹Sn magic-angle spinning (MAS) NMR spectroscopy.