Synthesis and characterization of the Zintl phase Na4Ba3As6 with isolated As3 anions

The title compound was prepared by direct fusion of the corresponding elements at 800°C followed by slow cooling to room temperature. It crystallizes in the orthorhombic space group Pbcm (No. 57) with a=11.340(2), b=8.745(2), and c=14.920(2) Å, V=1479.8(5) ų, and Z=4. The structure is made of isolated V-shaped trimers As₃⁵⁻ and sodium and barium countercations. According to magnetic and resistivity measurements, Na₄Ba₃As₆ is a narrow-gap semiconductor, i.e. a closed-shell compound that fulfills the Zintl concept.     

Synthesis and crystal structure of LiBa2N and identification of LiBa3N

The metal-rich part of the LiBaN system was investigated using powder and single-crystal X-ray diffraction analysis. The crystal structures of two new ternary subnitrides, LiBa₂N and of LiBa₃N, were determined from single-crystal and powder X-ray diffraction data, respectively. LiBa₂N has a tetragonal structure (space group, P4₂/nmc, Z=8, a=7.980(1), c=14.263(2) Å). The structure contains infinite mutually perpendicular rows of edge-sharing LiBa₅N octahedra. LiBa₃N is isostructural with NaBa₃N (P6₃/mmc, Z=2, a=8.182(1), c=6.922(4) Å).     

High-pressure synthesis and structures of novel chromium sulfides, Ba3CrS5 and Ba3Cr2S6 with one-dimensional chain structures

Two new ternary chromium sulfides, Ba₃CrS₅, and Ba₃Cr₂S₆ were synthesized by the reaction of sulfur, barium sulfide, and chromium metal under a high pressure of 5 GPa at 1200°C. Ba₃CrS₅ crystallized in the hexagonal space group P6₃cm (No. 185) with a=9.1208(3) Å, c=6.1930(3) Å, V=446.17(3) Å³, and Z=6. It had a column structure with one-dimensional chains of [CrS₃]_∞ composed of face-sharing CrS₆ octahedra surrounded with Ba²⁺ ions. Additional S columns surrounded with Ba ions were running along with the CrS₆ columns. Ba₃Cr₂S₆ crystallized in the trigonal space group R-3c (No. 167) with a=11.8179(7) Å, c=12.796(1) Å, V=1547.7(2) Å³, and Z=6. The structure of Ba₃Cr₂S₆ also contains [CrS₃]_∞ chains but the chains are composed of octahedral and trigonal prismatic CrS₆ units, which are alternately stacked in a face-sharing manner. The formal charges of Cr ions in Ba₃CrS₅ and Ba₃Cr₂S₆ are 4+ and 3+, respectively.     

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.     

High-temperature synthesis, single-crystal X-ray structure determination and solid-state NMR investigations of Ba7[SiO4][BO3]3CN and Sr7[SiO4][BO3]3CN

The novel alkaline earth silicate borate cyanides Ba₇[SiO₄][BO₃]₃CN and Sr₇[SiO₄][BO₃]₃CN have been obtained by the reaction of the respective alkaline earth metals M=Sr, Ba, the carbonates M^IICO₃, BN, and SiO₂ using a radiofrequency furnace at a maximum reaction temperature of 1350°C and 1450°C, respectively. The crystal structures of the isotypic compounds M^II₇[SiO₄][BO₃]₃CN have been determined by single-crystal X-ray crystallography (P6₃mc (no. 186), Z=2, a=1129.9(1) pm, c=733.4(2) pm, R₁=0.0336, wR₂=0.0743 for M^II=Ba and a=1081.3(1) pm, c=695.2(1) pm, R₁=0.0457, wR₂=0.0838 for M^II=Sr). Both ionic compounds represent a new structure type, and they are the first examples of silicate borate cyanides. The cyanide ions are disordered and they are surrounded by Ba²⁺/Sr²⁺ octahedra, respectively. These octahedra share common faces building chains along [001]. The [BO₃]³⁻ ions are arranged around these chains. The [SiO₄]⁴⁻ units are surrounded by Ba²⁺/Sr²⁺ tetrahedra, respectively. The title compounds additionally have been investigated by ¹¹B, ¹³C, ²⁹Si, and ¹H MAS-NMR as well as IR and Raman spectroscopy confirming the presence of [SiO₄]⁴⁻, [BO₃]³⁻, and CN⁻ ions.     

Syntheses, crystal structures, and properties of three new metal selenites Na2Co2(SeO3)3, Na2Co1.67Ni0.33(SeO3)3, and Na2Ni2(SeO3)3

Three new sodium cobalt (nickel) selenite compounds, namely, Na₂Co₂(SeO₃)₃, Na₂Co_1.67Ni_0.33(SeO₃)₃, and Na₂Ni₂(SeO₃)₃ have been hydro-/solvothermally synthesized in the mixed solvents of acetonitrile and water. Single-crystal X-ray diffraction analyses reveal that these isostructural compounds belong to the orthorhombic Cmcm space group and their structures feature three-dimensional open frameworks constructed by the two-dimensional layers of [MSeO₃] pillared by the [SeO₃]²⁻ groups. The two different types of Na⁺ ions reside in the intersecting two-dimensional channels parallel to the a- and c-axes, respectively. Their thermal properties have been investigated via TGA-DSC. The magnetic measurements indicate the existence of the antiferromagnetic interactions in these compounds.     

Structure and basic magnetic properties of the honeycomb lattice compounds Na2Co2TeO6 and Na3Co2SbO6

The synthesis, structure, and basic magnetic properties of Na₂Co₂TeO₆ and Na₃Co₂SbO₆ are reported. The crystal structures were determined by neutron powder diffraction. Na₂Co₂TeO₆ has a two-layer hexagonal structure (space group P6₃22) while Na₃Co₂SbO₆ has a single-layer monoclinic structure (space group C2/m). The Co, Te, and Sb ions are in octahedral coordination, and the edge sharing octahedra form planes interleaved by sodium ions. Both compounds have full ordering of the Co²⁺ and Te⁶⁺/Sb⁵⁺ ions in the ab plane such that the Co²⁺ ions form a honeycomb array. The stacking of the honeycomb arrays differ in the two compounds. Both Na₂Co₂TeO₆ and Na₃Co₂SbO₆ display magnetic ordering at low temperatures, with what appears to be a spin-flop transition found in Na₃Co₂SbO₆.     

Contrasting oxide crystal chemistry of Nb and Ta:: The structures of the hexagonal bronzes BaTa2O6 and Ba0.93Nb2.03O6

The high-temperature hexagonal forms of BaTa₂O₆ and Ba_0.93Nb_2.03O₆ have P6/mmm symmetry with unit-cell parameters a=21.116(1) Å, c=3.9157(2) Å and a=21.0174(3) Å, c=3.9732(1) Å, respectively. Single crystal X-ray structure refinements for both phases are generally consistent with a previously proposed model, except for displacements of some Ba atoms from high-symmetry positions. The structures are based on a framework of corner- and edge-connected Nb/Ta-centred octahedra, with barium atoms occupying sites in four different types of [0 0 1] channels with hexagonal, triangular, rectangular and pentagonal cross-sections. The refinements showed that the non-stoichiometry in the niobate phase is due to barium atom vacancies in the pentagonal channels and to extra niobium atoms occupying interstitial sites with tri-capped trigonal prismatic coordination. The origin of the non-stoichiometry is attributed to minimisation of non-bonded Ba-Ba repulsions. The hexagonal structure is related to the structures of the low-temperature forms of BaNb₂O₆ and BaTa₂O₆, through a 30° rotation of the hexagonal rings of octahedra centred at the origin.     

Ba14Cu2In4N7, a new subnitride with isolated nitridocuprate groups and indium clusters

Single crystals of Ba₁₄Cu₂In₄N₇, tetradecabarium dicopper tetraindium heptanitride, were synthesized by slow cooling from 1023 K at 7 MPa of N₂ using an Na flux. The compound crystallizes in the monoclinic space group P2/m with Z = 2, and contains ⁰[CuN₂] nitrido­cuprate units and distorted ⁰[In₄] clusters. One Ba atom, not connected to any N atoms, is surrounded by 12 other Ba atoms in a barium cuboctahedron. The structural formula is expressed as (Ba)Ba₂₇N₆[CuN₂]₄[In₄]₂.     

The structure of a barium niobium silicon oxide with the probable composition Ba6+xNb14Si4O47 (x ⋍ 0.23)

Reaction of BaO, Nb₂O₅, and Nb in mole ratios of 2.4:1.6:1 in an evacuated silica capsule at 1250°C produces a mixture of at least two products, one of which has the probable composition $\text{Ba}{}_{\mathrm{6+x}}\text{Nb}{}_{14}\text{Si}{}_4\text{O}{}_{47}\text{(x ? 0.23)}$. This compound has an hexagonal unit cell of dimensions a = 9,034 ± 0.004 Å, c = 27.81 ± 0.02 Å, probable space group $\text{P6}{}_3\text{mcm}\text{, Z = 2}$. Its structure has been determined from 942 independent reflections collected by a counter technique and refined by least squares methods to a conventional R value of 0.062. The basic structure consists of strings of four NbO₆ octahedra sharing opposite corners, each string joined to the next by edge sharing of the end octahedra, so that the c axis corresponds to the length of a strand of seven corner-linked octahedra. Chains of three such strands are formed by corner sharing between the strands. The chains in turn are joined by NbO₆ octahedra and Si₂O₇ groups in which the SiOSi linkage is linear. Barium atoms are in sites between the chains coordinated by 13 oxygen atoms. A second site, 15 coordinated, probably has a small amount of barium as well; the fractional occupancy for barium in this site is 0.076.     

Synthesis and characterization of Na11[CuO4][SO4]3

Na₁₁[CuO₄][SO₄]₃ was obtained from a redox reaction of CuO with Na₂O₂ in the presence of Na₂O and Na₂SO₄ in sealed Ag containers under Ar atmosphere at 600°C. The crystal structure has been determined from X-ray single crystal data at 293 and 170 K (Pnma, Z=4). The lattice parameters have been refined from X-ray powder data at 293 K as well: a=1597.06(6) pm, b=703.26(3) pm, c=1481.95(6) pm. The structure contains isolated distorted square-planar [CuO₄]⁵⁻ anions and non-coordinating sulfate groups. Furthermore, we report calculations of the Madelung Part of the Lattice Energy (MAPLE) and some of the physical properties of Na₁₁[CuO₄][SO₄]₃.     

Pb2.85Ba2.15Fe4SnO13: A new member of the AnBnO3n−2 anion-deficient perovskite-based homologous series

Pb_2.85Ba_2.15Fe₄SnO₁₃, a new n=5 member of the anion-deficient perovskite based A_nB_nO_3n−2 (A=Pb, Ba, B=Fe, Sn) homologous series, was synthesized by the solid state method. The crystal structure of Pb_2.85Ba_2.15Fe₄SnO₁₃ was investigated using a combination of neutron powder diffraction, electron diffraction, high angle annular dark field scanning transmission electron microscopy and Mössbauer spectroscopy. It crystallizes in the Ammm space group with unit cell parameters a=5.7990(1) Å, b=4.04293(7) Å and c=26.9561(5) Å. The Pb_2.85Ba_2.15Fe₄SnO₁₃ structure consists of quasi two-dimensional perovskite blocks separated by 1/2[110](1?01)_p crystallographic shear (CS) planes. The corner-sharing FeO₆ octahedra at the CS planes are transformed into edge-sharing FeO₅ distorted tetragonal pyramids. The octahedral positions in the perovskite blocks between the CS planes are jointly taken up by Fe and Sn, with a preference of Sn towards the position at the center of the perovskite block. The chains of FeO₅ pyramids and (Fe,Sn)O₆ octahedra of the perovskite blocks delimit six-sided tunnels at the CS planes occupied by double chains of Pb atoms. The compound is antiferromagnetically ordered below T_N=368±15 K.     

Luminescence and vibrational spectra of Ba5Li2W3O15

The infrared and Raman spectra of Ba₅Li₂W₃O₁₅ are reported down to 200 cm^?1. From the internal stretching modes of the tungstate octahedra the crystallographic order between lithium and tungsten in the face-sharing octahedra can be derived. The green tungstate luminescence shows a low quenching temperature that is described with the Dexter-Klick-Russell model. The U⁶⁺ ion shows a yellow emission in Ba₅Li₂W₃O₁₅. There is ample evidence for two different U⁶⁺ centers with different decay times (10 and 80 μsec) and different emission and excitation spectra. One of these is located in a single layer of tungstate octahedra, the other in a double layer of octahedra.     

Substitution in barium-fluoride apatite: The crystal structures of Ba10(PO4)6F2, Ba6La2Na2(PO4)6F2 and Ba4Nd3Na3(PO4)6F2

The crystal structures of the apatites Ba₁₀(PO₄)₆F₂(I), Ba₆La₂Na₂(PO₄)₆F₂(II) and Ba₄Nd₃Na₃(PO₄)₆F₂ (III) have been determined by single-crystal X-ray diffraction. All three compounds crystallize in a hexagonal apatite-like structure. The unit cells and space groups are: I, a = 10.153(2), c = 7.733(1)Å, $\text{P6}{}_3\text{m}\text{; a = 9.9392(4), c = 7.4419(5)}$Å, $\text{P}\text{6}$; III, a = 9.786(2), c = 7.281(1)Å, $\text{P}\text{3}$. The structures were refined by normal full-matrix crystallographic least squares techniques. The final values of the refinement indicators R_w and R are: I, R_w = 0.026, R = 0.027, 613 observed reflections; II, R_w = 0.081, R = 0.074, 579 observed reflections; III, R_w = 0.062, R = 0.044, 1262 observed reflections.In I, the Ba(1) atoms located in columns on threefold axes, are coordinated to nine oxygen atoms; the Ba(2) sites form triangles about the F site and are coordinated to six oxygen atoms and one fluoride ion. The fluoride ions are statistically displaced ～0.25 Å from the Ba(2) triangles. This displacement of the F ions is analogous to the displacement of OH ion in Ca₁₀(PO₄)₆(OH)₂.The structures of II and III contain disordered cations. In II there is disorder between La and Na in the column cation sites as well as triangle sites. In III, Nd and Na ions are ordered in the column sites, but there is disorder among Ba and the remaining Nd and Na ions in the triangle sites to give an average site population of $\text{2}\text{3}\text{Ba}\text{,}\text{1}\text{6}\text{Nd}\text{,}\text{1}\text{6}\text{Na}$. The coordination of the rare earth ions and Na ions in the ordered column sites are nine and six oxygens, respectively, in accord with the greater charge of the rare earth ions as compared with Na. The F ions in both II and III suffer from considerable disorder in position, and their locations are not precisely known.     

The crystal structure of a sodium molybdenum oxide,Na6Mo10O33, containing cross-linked chains of octahedra and square pyramids

Na₆Mo₁₀O₃₃ crystallizes in the triclinic system with unit-cell dimensions a = 8.049(4), b = 12.180(6), c = 7.576(4) Å, α = 99.96(9), β = 100.74(1), γ = 109.88(10)°, and space group $\text{P}\text{1}$ with z = 1. The structure was solved using Patterson and Fourier methods. Of the 3045 unique reflections measured by counter techniques 2758 with I ≥ 3σ(I) were used in the least-squares refinement of the model to a conventional R of 0.030 (R_w = 0.034). The structure of Na₆Mo₁₀O₃₃ consists of two different types of chains of molybdenum-oxygen polyhedra linked to one another approximately at right angles. One chain of edge- and corner-shared distorted MoO₆ octahedra is approximately parallel to [001] and the second chain, consisting of corner-shared pairs of octahedra edge-shared to pairs of edge-shared MoO₅ square pyramids (inverted with respect to one another), is approximately parallel to [100]. These linked chains form an infinite three-dimensional network in the interstices of which the sodium atoms are located. One of the chains of the Na₆Mo₁₀O₃₃ structure is the same as that found in Ag₆Mo₁₀O₃₃; the second chain, however, does not occur in Ag₆Mo₁₀O₃₃.     

Syntheses, crystal structures and Raman spectra of Ba(BF4)(PF6), Ba(BF4)(AsF6) and Ba2(BF4)2(AsF6)(H3F4); the first examples of metal salts containing simultaneously tetrahedral BF4 and octahedral AF6 anions

In the system BaF₂/BF₃/PF₅/anhydrous hydrogen fluoride (aHF) a compound Ba(BF₄)(PF₆) was isolated and characterized by Raman spectroscopy and X-ray diffraction on the single crystal. Ba(BF₄)(PF₆) crystallizes in a hexagonal space group with a=10.2251(4) Å, c=6.1535(4) Å, V=557.17(5) Å³ at 200 K, and Z=3. Both crystallographically independent Ba atoms possess coordination polyhedra in the shape of tri-capped trigonal prisms, which include F atoms from BF₄⁻ and PF₆⁻ anions. In the analogous system with AsF₅ instead of PF₅ the compound Ba(BF₄)(AsF₆) was isolated and characterized. It crystallizes in an orthorhombic Pnma space group with a=10.415(2) Å, b=6.325(3) Å, c=11.8297(17) Å, V=779.3(4) Å³ at 200 K, and Z=4. The coordination around Ba atom is in the shape of slightly distorted tri-capped trigonal prism which includes five F atoms from AsF₆⁻ and four F atoms from BF₄⁻ anions. When the system BaF₂/BF₃/AsF₅/aHF is made basic with an extra addition of BaF₂, the compound Ba₂(BF₄)₂(AsF₆)(H₃F₄) was obtained. It crystallizes in a hexagonal P6₃/mmc space group with a=6.8709(9) Å, c=17.327(8) Å, V=708.4(4) Å³ at 200 K, and Z=2. The barium environment in the shape of tetra-capped distorted trigonal prism involves 10 F atoms from four BF₄⁻, three AsF₆⁻ and three H₃F₄⁻ anions. All F atoms, except the central atom in H₃F₄ moiety, act as μ₂-bridges yielding a complex 3-D structural network.     

Isolated spin 3/2 plaquettes in Na3RuO4

The crystal structure of Na₃RuO₄ determined by powder neutron diffraction is reported. The structure consists of isolated tetramers of edge sharing RuO₆ octahedra in the ab plane, creating isolated four-member plaquettes of Ru atoms comprised of two equilateral triangles sharing an edge. Magnetic susceptibility measurements reveal an antiferromagnetic transition at ∼29 K, with . Neutron diffraction data indicate the onset of three-dimensional magnetic ordering at 29 K.     

Structure of ten-layer orthorhombic Ba5Fe5O14 (BaFeO2.8) determined from single crystal X-ray diffraction

The structure of the mixed-valent Ba₅Fe₅O₁₄ (BaFeO_2.8), prepared using a molten KOH-Ba(OH)₂ flux, has been determined using single crystal X-ray diffraction. Ba₅Fe₅O₁₄ forms twinned crystals with the orthorhombic space group Cmcm, a=5.7615(8), b=9.9792(14) and c=24.347(3) Å, Z=4. The structure, which is closely related to the 10H BaFeO_2.65 perovskite, is composed of two oxygen-deficient BaO₂ layers and eight BaO₃ layers with a (hchhc)₂ stacking sequence, where h and c denote hexagonal or cubic layers. A displacement of barium and oxygen atoms in the BaO₂ layers from hexagonal special positions lowers the symmetry from hexagonal to orthorhombic. This combination of stacking and vacancies creates trimers of face-sharing FeO₆ octahedra pillared by dimers of corner-sharing FeO₄ tetrahedra. The Fe⁴⁺ atoms are located in the center of the trimer and in the tetrahedral sites. The magnetism of Ba₅Fe₅O₁₄, investigated using SQUID magnetometry, is characteristic of a strongly coupled antiferromagnet.     

Ab initio structure determination of new compound Ba3(BO3)(PO4)

The crystal structure of new compound Ba₃BPO₇ was determined by ab initio method from high-resolution conventional X-ray powder diffraction data. The Rietveld refinement converged to R_p=5.92%, R_wp=8.87%, R_exp=5.00% with the following details: Hexagonal, space group P6₃mc, a=5.4898 (1) Å, c=14.7551(1) Å, Z=2. The basic unit of the structure is the [BaO₁₀]-[BO₃]-[PO₄] polar polyhedra-chain composed of Ba1-B-P-O cluster. These chains, running along c-axis, stack in a HCP mode to build the whole structure with triangular prism channels. The channels are parallel to c-axis too, in which Ba2 and Ba3 are located.     

Na6B13O22.5, a new noncentrosymmetric sodium borate

Na₆B₁₃O_22.5 (B/Na=2.17) single crystals were obtained by heating, melting and appropriately cooling borax, Na₂[B₄O₅(OH)₄]·8H₂O. Its formula has been determined by the resolution of the structure from single-crystal X-ray diffraction data. The compound crystallizes in the noncentrosymmetric orthorhombic Iba2 space group, with the following unit cell parameters: a=33.359(11) Å, b=9.554(3) Å, c=10.644(4) Å; V=3392.4(19) Å³; Z=8. The crystal structure was solved from 3226 reflections until R₁=0.0385. It exhibits a three-dimensional framework built up from BO₃ triangles (Δ) and BO₄ tetrahedra (T). Two kinds of borate groups can be considered forming two different double B₃O₃ rings: two B₄O₉ (linkage by two boron atoms) and one B₅O₁₁ (linkage by one boron atom); the shorthand notation of the new fundamental building block (FBB) existing in this compound is: 13: ∞³ [(5: 3Δ+2T)+2(4: 2Δ+2T)]. The discovery of this new borate questions the real number of Na₂B₄O₇ varieties. The existence of Na₆B₁₃O_22.5 (B/Na=2.17) and of another recently discovered borate, Na₃B₇O₁₂ (B/Na=2.33; FBB 7: ∞³ [(3: 2Δ+T)+(3: Δ+2T)+(1: Δ)], with a composition close to the long-known borate α-Na₂B₄O₇ (B/Na=2; FBB 8: ∞³ [(5: 3Δ+2T)+(3: 2Δ+T)], may explain the very complex equilibria reported in the Na₂O-B₂O₃ phase diagram, especially in this range of composition.