Crystal structures of CsFe2S3 and RbFe2S3: synthetic analogs of rasvumite KFe2S3

The isostructural alkali thioferrate compounds CsFe₂S₃, RbFe₂S₃ and KFe₂S₃ have been synthesized by reacting Fe and S with their corresponding AFeS₂ (A=K, Rb, Cs) precursors. The crystal structures of these and binary compounds of intermediate composition were determined by Rietveld analysis of laboratory powder X-ray diffraction patterns. All of the synthesized compounds adopt the space group Cmcm (#63), Z=4 with: a=9.5193(8) Å, b=11.5826(10) Å, c=5.4820(4) Å for CsFe₂S₃; a=9.2202(7) Å, b=11.2429(9) Å, c=5.4450(3) Å for RbFe₂S₃; and a=9.0415(13) Å, b=11.0298(17) Å, c=5.4177(6) Å for KFe₂S₃. These mixed valence alkali thioferrates show regular changes in cell dimensions, AS₁₀ (A=K, Rb, Cs) polyhedron volumes, polyhedron distortion parameters, and calculated oxidation state of Fe with respect to increasing size of the alkali element cation. The calculated empirical oxidation state of iron varies from +2.618 (CsFe₂S₃), through +2.666 (RbFe₂S₃) to +2.77 (KFe₂S₃).     

Gallium substitutions as a means to stabilize alkaline-earth and rare-earth metal pnictides with the cubic Th3P4 type: Synthesis and structure of A7Ga2Sb6 (A=Sr, Ba, Eu)

Three new compounds—Sr_7.04(2)Ga_1.94(2)Sb₆, Ba_7.02(3)Ga_1.98(3)Sb₆ and Eu_7.04(3)Ga_1.90(3)Sb₆—have been synthesized from reactions of the corresponding elements using gallium as a metal flux. Their crystal structures (space group I4¯3d (No. 220), Z=2 with unit cell parameters: a=9.9147(9) Å for the Sr-compound; a=10.3190(9) Å for the Ba-compound; and a=9.7866(8) Å for the Eu-compound) have been established by single-crystal X-ray diffraction. The structures are best described as Ga-stabilized derivatives of the hypothetical Sr₄Sb₃, Ba₄Sb₃ and Eu₄Sb₃ phases with the cubic Th₃P₄ type. Such an inclusion of interstitial Ga atoms in this atomic arrangement results in the formation of isolated [Ga₂Sb₆]¹⁴⁻ fragments, isoelectronic and isostructural with the [Sn₂Te₆]⁶⁻ anions in the K₃SnTe₃ type, and allows for the attainment of a charge-balanced electron count. In that sense, the Sr₄Sb₃, Ba₄Sb₃ and Eu₄Sb₃ binaries, which are expected to be electron-deficient and are currently unknown, can be “turned” into Sr₇Ga₂Sb₆, Ba₇Ga₂Sb₆ and Eu₇Ga₂Sb₆, whose structures are readily rationalized following the Zintl concept.     

Dimensional reductions from 2-D Nb4P2S21 to 1-D ANb2PS10 (A=Na, K, Rb, Cs, Tl) and to 0-D Tl5[Nb2S4Cl8]Cl using halide molten salts

We found new synthetic routes to obtain 1-D quaternary thiophosphate compounds and a 0-D molecular complex containing a Nb₂S₄ core from a 2-D ternary thiophosphate, Nb₄P₂S₂₁. When Nb₄P₂S₂₁ was reacted with alkali metal halides (ACl; A=Na, K, Rb, Cs) or TlCl at 500-700 °C, the -S-S-S- bridges in 2-D Nb₂PS₁₀-S-S₁₀PNb₂ were excised to form a 1-D chain, and cations were inserted between the chains to form ANb₂PS₁₀ (A=Na, K, Rb, Cs, Tl). We also found that thallium chloride (TlCl) is an excellent reagent for further excision, and it substitutes chloride ligands for the sulfur ligands of 2-D Nb₄P₂S₂₁ to form the molecular complex Tl₅[Nb₂S₄Cl₈]Cl. Crystal data for TlNb₂PS₁₀: monoclinic, Pn, a=6.9452(11) Å, b=7.3761(12) Å, 12.873(2) Å, β=104.472(3)°, and Z=2. Crystal data for Tl₅[Nb₂S₄Cl₈]Cl: orthorhombic, Immm, a=7.001(5) Å, b=9.509(7) Å, c=15.546(11) Å, and Z=2.     

Quaternary selenostannates Na2−xGa2−xSn1+xSe6 and AGaSnSe4 (A=K, Rb, and Cs) through rapid cooling of melts. Kinetics versus thermodynamics in the polymorphism of AGaSnSe4

The quaternary alkali-metal gallium selenostannates, Na_2−xGa_2−xSn_1+xSe₆ and AGaSnSe₄ (A=K, Rb, and Cs), were synthesized by reacting alkali-metal selenide, Ga, Sn, and Se with a flame melting-rapid cooling method. Na_2−xGa_2−xSn_1+xSe₆ crystallizes in the non-centrosymmetric space group C2 with cell constants a=13.308(3) Å, b=7.594(2) Å, c=13.842(3) Å, β=118.730(4)°, V=1226.7(5) Å³. α-KGaSnSe₄ crystallizes in the tetragonal space group I4/mcm with a=8.186(5) Å and c=6.403(5) Å, V=429.1(5) Å³. β-KGaSnSe₄ crystallizes in the space group P2₁/c with cell constants a=7.490(2) Å, b=12.578(3) Å, c=18.306(5) Å, β=98.653(5)°, V=1705.0(8) Å³. The unit cell of isostructural RbGaSnSe₄ is a=7.567(2) Å, b=12.656(3) Å, c=18.277(4) Å, β=95.924(4)°, V=1741.1(7) Å³. CsGaSnSe₄ crystallizes in the orthorhombic space group Pmcn with a=7.679(2) Å, b=12.655(3) Å, c=18.278(5) Å, V=1776.1(8) Å³. The structure of Na_2−xGa_2−xSn_1+xSe₆ consists of a polar three-dimensional network of trimeric (Sn,Ga)₃Se₉ units with Na atoms located in tunnels. The AGaSnSe₄ possess layered structures. The compounds show nearly the same Raman spectral features, except for Na_2−xGa_2−xSn_1+xSe₆. Optical band gaps, determined from UV-Vis spectroscopy, range from 1.50 eV in Na_2−xGa_2−xSn_1+xSe₆ to 1.97 eV in CsGaSnSe₄. Cooling of the melts of KGaSnSe₄ and RbGaSnSe₄ produces only kinetically stable products. The thermodynamically stable product is accessible under extended annealing, which leads to the so-called γ-form (BaGa₂S₄-type) of these compounds.     

Syntheses and structures of six compounds in the A2LiMS4 (A=K, Rb, Cs; M=V, Nb, Ta) family

Six new compounds in the A₂LiMS₄ (A=K, Rb, Cs; M=V, Nb, Ta) family, namely K₂LiVS₄, Rb₂LiVS₄, Cs₂LiVS₄, Rb₂LiNbS₄, Cs₂LiNbS₄, and Rb₂LiTaS₄, have been synthesized by the reactions of the elements in Li₂S/S/A₂S₃ (A=K, Rb, Cs) fluxes at 773 K. The A and M atoms play a role in the coordination environment of the Li atoms, leading to different crystal structures. Coordination numbers of Li atoms are five in K₂LiVS₄, four in A₂LiVS₄ (A=Rb, Cs) and Cs₂LiNbS₄, and both four and five in Rb₂LiMS₄ (M=Nb, Ta). The A₂LiVS₄ (A=Rb, Cs) structure comprises one-dimensional chains of tetrahedra. The Rb₂LiMS₄ (M=Nb, Ta) structure is composed of two-dimensional layers. The Cs₂LiNbS₄ structure contains one-dimensional chains that are related to the Rb₂LiMS₄ layers. The K₂LiVS₄ structure contains a different kind of layer.     

Syntheses and characterization of zero-dimensional molybdoantimonites, A2(Mo4Sb2O18) (A=Y, La, Nd, Sm, Gd and Dy)

Six new isostructural A₂(Mo₄Sb₂O₁₈) (A=Y, La, Nd, Sm, Gd and Dy) compounds have been synthesized by solid-state reactions and characterized by single crystal X-ray diffraction and spectroscopic techniques. They crystallize in C2/c space group with 4 formula units and contain A³⁺ cations and discrete centrosymmetric anionic (Mo₄Sb₂O₁₈)⁶⁻ aggregates, made of tetrahedral MoO₄ and disphenoidal SbO₄ moieties. They exhibit characteristic Sb³⁺ photoluminescence.     

Yb3Cu6Sn5, Yb5Cu11Sn8 and Yb3Cu8Sn4: crystal structure of three ordered compounds

Yb₃Cu₆Sn₅, Yb₅Cu₁₁Sn₈ and Yb₃Cu₈Sn₄ compounds were prepared in sealed Ta crucibles by induction melting and subsequent annealing. The crystal structures of Yb₃Cu₆Sn₅ and Yb₅Cu₁₁Sn₈ were determined from single crystal diffractometer data: Yb₃Cu₆Sn₅, isotypic with Dy₃Co₆Sn₅, orthorhombic, Immm, oI28, a=4.365(1) Å, b=9.834(3) Å, c=12.827(3) Å, Z=2, R=0.019, 490 independent reflections, 28 parameters; Yb₅Cu₁₁Sn₈ with its own structure, orthorhombic, Pmmn, oP48, a=4.4267(6) Å, b=22.657(8) Å, c=9.321(4) Å, Z=2, R=0.047, 1553 independent reflections, 78 parameters. Both compounds belong to the BaAl₄-derived defective structures, and are closely related to Ce₃Pd₆Sb₅ (oP28, Pmmn). The crystal structure of Yb₃Cu₈Sn₄, isotypic with Nd₃Co₈Sn₄, was refined from powder data by the Rietveld method: hexagonal, P6₃mc, hP30, a=9.080(1) Å, c=7.685(1) Å, Z=2, R_wp=0.040. It is an ordered substitution derivative of the BaLi₄ type (hP30, P6₃/mmc). All compounds show strong Cu-Sn bonds with a length reaching 2.553(3) Å in Yb₅Cu₁₁Sn₈.     

New open-framework in the uranyl vanadates A3(UO2)7(VO4)5O (A=Li, Ag) with intergrowth structure between A(UO2)4(VO4)3 and A2(UO2)3(VO4)2O

New uranyl vanadates A₃(UO₂)₇(VO₄)₅O (M=Li (1), Na (2), Ag (3)) have been synthesized by solid-state reaction and their structures determined from single-crystal X-ray diffraction data for 1 and 3. The tetragonal structure results of an alternation of two types of sheets denoted S for _∞²[UO₂(VO₄)₂]⁴⁻ and D for _∞²[(UO₂)₂(VO₄)₃]⁵⁻ built from UO₆ square bipyramids and connected through VO₄ tetrahedra to _∞¹[U(3)O₅-U(4)O₅]⁸⁻ infinite chains of edge-shared U(3)O₇ and U(4)O₇ pentagonal bipyramids alternatively parallel to a- and b-axis to construct a three-dimensional uranyl vanadate arrangement. It is noticeable that similar _∞[UO₅]⁴⁻ chains are connected only by S-type sheets in A₂(UO₂)₃(VO₄)₂O and by D-type sheets in A(UO₂)₄(VO₄)₃, thus A₃(UO₂)₇(VO₄)₅O appears as an intergrowth structure between the two previously reported series. The mobility of the monovalent ion in the mutually perpendicular channels created in the three-dimensional arrangement is correlated to the occupation rate of the sites and by the geometry of the different sites occupied by either Na, Ag or Li. Crystallographic data: 293 K, Bruker X8-APEX2 X-ray diffractometer equipped with a 4 K CCD detector, MoKα, λ=0.71073 Å, tetragonal symmetry, space group P4¯m2, Z=1, full-matrix least-squares refinement on the basis of F²; 1,a=7.2794(9) Å, c=14.514(4) Å, R1=0.021 and wR2=0.048 for 62 parameters with 782 independent reflections with I?2σ(I); 3, a=7.2373(3) Å, c=14.7973(15) Å, R1=0.041 and wR2=0.085 for 60 parameters with 1066 independent reflections with I?2σ(I).     

Temperature behavior of the protonic conductor K4LiH3(SO4)4

The results of the X-ray structural study for the K₄LiH₃(SO₄)₄ single crystal are presented at a wide temperature range. The thermal expansion of the crystal using the X-ray dilatometry and the capacitance dilatometry from 8 to 500 K was carried out. The crystal structures data collection, solution and refinement at 125, 295, 443 and 480 K were performed. The K₄LiH₃(SO₄)₄ crystal has tetragonal symmetry with the P4₁ space group (Z=4) at room temperature as well as at the considered temperature range. The existence of a low-temperature, para-ferroelastic phase transition at about 120 K is excluded. The layered structure of the crystal reflects a cleavage plane parallel to (001) and an anisotropy of the protonic conductivity. The superionic high-temperature phase transition at T_S=425 K is isostructural. Nevertheless, taking into account an increase of the SO₄ tetrahedra libration above T_S, a mechanism of the Grotthus type could be applied for the proton transport explanation.     

New alkali-metal-molybdenum(VI)-selenium(IV) oxides: syntheses, structures, and characterization of A2SeMoO6 (A=Na, K, or Rb)

Three new quaternary selenites, A₂SeMoO₆ (A=Na⁺, K⁺, or Rb⁺), were synthesized through the solid-state reaction of A₂MoO₄ with SeO₂ at 400°C. Although the reported materials are ‘stoichiometrically equivalent’, the compounds exhibit strikingly different crystal structures. Whereas Na₂SeMoO₆ has a three-dimensional crystal structure, K₂SeMoO₆ and Rb₂SeMoO₆ are molecular and uni-dimensional, respectively. However, all of the new materials have structures containing Mo⁶⁺ octahedra linked to Se⁴⁺ trigonal pyramids. Although the Mo⁶⁺ and Se⁴⁺ cations are in local asymmetric environments in all three materials, only Na₂SeMoO₆ is non-centrosymmetric. Single crystal X-ray data: Na₂SeMoO₆, cubic, space group, P2₁3 (no. 198), a=8.375(5) Å, Z=4, R(F)=0.0143; K₂SeMoO₆, monoclinic, space group, P2₁/c (no. 14), a=6.118(8) Å, b=15.395(2) Å, c=7.580(9) Å, β=112.39(4)°, Z=4, R(F)=0.0281; Rb₂SeMoO₆, orthorhombic, space group, Pnma (no. 62), a=7.805(9) Å, b=6.188(7) Å, c=14.405(4) Å, Z=4, R(F)=0.0443.     

Synthesis, structure, and magnetism of Tb4PdGa12 and Tb4PtGa12

Single crystals of Tb₄MGa₁₂ (M=Pd, Pt) have been synthesized. The isostructural compounds crystallize in the cubic space group , with Z=2 and lattice parameters: a=8.5940(5) and 8.5850(3) Å for Tb₄PdGa₁₂ and Tb₄PtGa₁₂, respectively. The crystal structure consists of corner-sharing MGa₆ octahedra and TbGa₃ cuboctahedra. Magnetic measurements suggest that Tb₄PdGa₁₂ is an antiferromagnetic metamagnet with a Néel temperature of 16 K, while the Pt analog orders at T_N=12 K.     

Structural studies of five layer Aurivillius oxides: A2Bi4Ti5O18 (A=Ca, Sr, Ba and Pb)

The room temperature structures of the five layer Aurivillius phases A₂Bi₄Ti₅O₁₈ (A=Ca, Sr, Ba and Pb) have been refined from powder neutron diffraction data using the Rietveld method. The structures consist of [Bi₂O₂]²⁺ layers interleaved with perovskite-like [A₂Bi₂Ti₅O₁₆]²⁻ blocks. The structures were refined in the orthorhombic space group B2eb (SG. No. 41), Z=4, and the unit cell parameters of the oxides are a=5.4251(2), b=5.4034(1), c=48.486(1); a=5.4650(2), b=5.4625(3), c=48.852(1); a=5.4988(3), b=5.4980(4), c=50.352(1); a=5.4701(2), b=5.4577(2), c=49.643(1) for A=Ca, Sr, Ba and Pb, respectively. The structural features of the compounds were found similar to n=2-4 layers bismuth oxides. The strain caused by mismatch of cell parameter requirements for the [Bi₂O₂]²⁺ layers and perovskite-like [A₂Bi₂Ti₅O₁₆]²⁻ blocks were relieved by tilting of the TiO₆ octahedra. Variable temperature synchrotron X-ray studies for Ca and Pb compounds showed that the orthorhombic structure persisted up to 675 and 475 K, respectively. Raman spectra of the compounds are also presented.     

Long-range magnetic ordering of S=1/2 linear trimers in A3Cu3(PO4)4 (A=Ca, Sr, and Pb)

Magnetic properties of S=1/2 linear trimer cluster compounds A₃Cu₃(PO₄)₄ (A=Ca, Sr, and Pb) were investigated. Magnetic susceptibility data for the three compounds showed that paramagnetic copper spins form trimers with the total spin of 1/2 below about 45 K. Specific heat and magnetization measurements indicated that the trimer clusters undergo ferromagnetic long-range ordering at for A=Ca and antiferromagnetic long-range ordering at for A=Sr and for A=Pb. A₃Cu₃(PO₄)₄ exhibited 1/3-magnetization plateau at least up to magnetic field of 55 T at 1.3 and 4.2 K. A₃Cu₃(PO₄)₄ with A=Sr and Pb showed a spin-flop transition near 0.03 T in the antiferromagnetic state at 0.08 K. Specific heat data at magnetic fields clearly showed broad maxima at low temperatures due to the finite intra-chain interaction in one-dimensional arrays of the trimers.     

New ferromagnets of Sr8ARe3Cu4O24 (A=Sr, Ca) with an ordered perovskite structure

New phases Sr₈ARe₃Cu₄O₂₄ (A=Sr,Ca) were discovered under high-pressure/high-temperature condition. X-ray powder diffraction and electron diffraction studies for these phases indicated that they have an ordered perovskite-type structure with cubic lattices of ∼8 Å. They showed ferromagnetism at room temperature when they were synthesized under high-oxygen-pressure condition. The Ca-containing phase has a very high T_c of 440 K with a spontaneous magnetization of ∼1 μ_B/f.u.     

Syntheses, structure and rare earth metal photoluminescence of new and known isostructural A2Mo4Sb2O18 (A=Ce, Pr, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) compounds

Nine new A₂Mo₄Sb₂O₁₈ (A=Ce, Pr, Eu, Tb, Ho, Er, Tm, Yb, Lu) compounds have been synthesized by solid-state reactions. They are isostructural with six reported analogues of yttrium and other lanthanides and the monoclinic unit cell parameters of all fifteen of them vary linearly with the size of A³⁺ ion. Single crystal X-ray structures of eight A₂Mo₄Sb₂O₁₈ (A=Ce, Pr, Eu, Gd, Tb, Ho, Er, Tm) compounds have been determined. Neat A₂Mo₄Sb₂O₁₈ (A=Pr, Sm, Eu, Tb, Dy, Ho, Er, Tm) compounds exhibit characteristic rare earth metal photoluminescence.     

Yb3CoSn6 and Yb4Mn2Sn5: New polar intermetallics with 3D open-framework structures

Two new ternary ytterbium transition metal stannides, namely, Yb₃CoSn₆ and Yb₄Mn₂Sn₅, have been obtained by solid-state reactions of the corresponding pure elements in welded tantalum tubes at high temperature. Their crystal structures have been established by single-crystal X-ray diffraction studies. Yb₃CoSn₆ crystallizes in the orthorhombic space group Cmcm (no. 63) with cell parameters of a=4.662(2), b=15.964(6), c=13.140(5) Å, V=978.0(6) Å³, and Z=4. Its structure features a three-dimensional (3D) open-framework composed of unusual [CoSn₃] layers interconnected by zigzag Sn chains, forming large tunnels along the c-axis which are occupied by the ytterbium cations. Yb₄Mn₂Sn₅ is monoclinic space group C2/m (no. 12) with cell parameters of a=16.937(2), b=4.5949(3), c=7.6489(7) Å, β=106.176(4)°, V=571.70(8) Å³, and Z=2. It belongs to the Mg₅Si₆ structure type and its anionic substructure is composed of parallel [Mn₂Sn₂] ladders interconnected by unusual zigzag [Sn₃] chains, forming large tunnels along the c-axis, which are filled by the ytterbium cations. Band structure calculations based on density function theory methods were also made for both compounds.     

Synthesis and characterization of the pseudo-hexagonal hollandites ALi2Ru6O12 (A=Na, K)

The crystal structures, synthesis and physical properties of ruthenium hollandites ALi₂Ru₆O₁₂ (A=Na, K) with a new pseudo-hexagonal structure type are described. Analogous to tetragonal hollandites, the framework is made of MO₆ octahedra in double chains that share corner oxygens with each other to create interstitial tunnels. The tunnels are either hexagonal or triangular in cross-section. Magnetic susceptibilities, low temperature specific heat, and electrical resistivities are reported. The data indicate that these materials are normal, low density of states metals. This new structure type can be extended from A=Group I to A=Group II ions with the synthesis of CaLi₂Ru₆O₁₂ and SrLi₂Ru₆O₁₂.     

Hexafluoro-, heptafluoro-, and octafluoro-salts, and [MnF5n+1] (n = 2, 3, 4) polyfluorometallates of singly charged metal cations, Li-Cs, Cu, Ag, In and Tl

The AMF₆, A₂MF₇, A₃MF₈, AM₂F₁₁, AM₃F_l6 and AM₄F₂₁ compounds (A = Li, Na, K, Rb, Cs, Cu, Ag, In, Tl; M = P, As, V, Rh, Ru, Au, Pt, Ir, Os, Re, Sb, Mo, W, Nb, Ta, Bi) are reviewed.Some of the structural data of the AMF₆ compounds are based just on powder diffraction work from the middle of the last century. The crystal structure types of AMF₆ compounds have been re-classified in this review, based mainly on single crystal data. The crystal structure types of AMF₆ compounds can be classified into six main groups: LiSbF₆ type, NaSbF₆ type, structures of cubic APF₆ and AAsF₆ with orientational disorder of the anions, tetragonal KSbF₆ (T) types and similar structures, AgSbF₆ type and similar structures, and KOsF₆ type.Reported crystal structures of A₂MF₇, A₃MF₈, AM₂F₁₁, AM₃F_l6 and AM₄F₂₁ compounds are limited. K₂MF₇ (M = Nb, Ta) crystallizes in the monoclinic and K₂WF₇ in the orthorhombic crystal system. Among the A₃MF₈ compounds the complete crystal structure has been determined only for Na₃TaF₈, which is monoclinic. The only known examples of crystal structures of AM₂F₁₁ compounds are ASb₂F₁₁ (A = Ag, K, Cs). Crystals of KSb₂F₁₁ are orthorhombic and isostructural to AgSb₂F₁₁, while CsSb₂F₁₁ is monoclinic. CsSb₃F₁₆ is the only example of a structurally characterized AM₃F_l6 compound. Its crystals are orthorhombic. For the rest of the known A₂MF₇, A₃MF₈, AM₂F₁₁, AM₃F_l6 and AM₄F₂₁ compounds, only lattice parameters are known.     

Cation disorder and phase transitions in the four-layer ferroelectric Aurivillius phases ABi4Ti4O15 (A=Ca, Sr, Ba, Pb)

Crystal structures of a series of bi-layered compounds ABi₄Ti₄O₁₅ (A=Ca, Sr, Ba, Pb) have been investigated using a combination of synchrotron X-ray and neutron powder diffraction data. All four oxides adopt an orthorhombic structure at room temperature and the structures have been refined in space group A2₁am. This orthorhombic structure is a consequence of a combination of rotation of the TiO₆, resulting from the less than optimal size of the A-type cation, and displacement of the Ti atoms towards the Bi₂O₂ layers. There is partial disorder of the Bi and A-type cations over two of the three available sites, which increases in the order Ca<Sr and Pb<Ba.