Neutron diffraction experiments on CsCrI3 at 300, 77, and 1.2 K

CsCrI₃ has been investigated by neutron powder diffraction at room temperature and 77 and 1.2 K. It undergoes a phase transition at 150 K due to the cooperative Jahn-Teller effect. The high-temperature form, α-CsCrI₃ (hexagonal, space group $\text{P6}{}_3\text{mmc}\text{, a = 8.127(1)}$Å, c = 6.944(1)Å, Z = 2), adopts the BaNiO₃ structure with a local Jahn-Teller distortion. The low-temperature form, β-CsCrI₃ (orthorhombic, space group Pbcn, a = 8.102(1)Å, b = 13.792(1)Å, c = 6.900(1)Å, Z = 4), has a structure not yet been reported for a Jahn-Teller distorted BaNiO₃ structure. It is shown that the low-temperature form can be derived from the BaNiO₃ structure by means of a canting of triangles, formed by the three common I^? ions of two adjacent CrI₆^4? octahedra. The magnetic structure of β-CsCrI₃ at 1.2 K is found to consist of an antiparallel sequence of ferromagnetic (0 0 1) planes with a magnetic moment in the ∥1 0 0∥ direction of 3.16 μ_B.     

Neutron powder diffraction on RbCrl3 and magnetic measurements on RbCrl3 and CsCrl3

β-RbCrI₃ (a = 13.772(3), b = 8.000(2), c = 7.069(2) Å β = 95.85(1)°, $\text{Z = 4,}\text{C2}\text{m}$ at 293 K) and γ-RbCrI₃ (a = 13.586(2), b = 7.923(2), c = 14.094(3) Å, β = 96.88(1)°, Z = 8, C2 at 1.2 K) are isostructural to β-RbCrCl₃ and γ-RbCrCl₃ and are both Jahn-Teller distorted BaNiO₃ structures. In both compounds elongated octahedra occur. γ-RbCrI₃ most probably has a magnetic spiral structure at 4.2 and 1.2 K. Theoretically, a spiral propagating along the b axis is expected. A model with k = 9/19b1 yielded the best result. However, no good fit was obtained possibly because of a misfit in k and canting of the magnetic moments due to anisotropy. χ vs T single-crystal measurements on β-CsCrI₃ are in accordance with its magnetic structure. The three-dimensional magnetic ordering temperature T_c is estimated as 27(1) K. From the χ vs T curves of γ-RbCrI₃, T_c could not be determined. From fits to χ vs T powder data $\text{J}\text{k}$ of CsCrI₃ and RbCrI₃ are estimated to be ?14(2) and ?11(1) K, respectively.     

Neutron powder diffraction on α-Tl4CrI6 and β-Tl4CrI6

α-Tl₄CrI₆ (a = 9.132(1), c = 9.667(1) Å, $\text{Z = 2,}\text{P4}\text{mnc}$ at 293 K) adopts a distorted Tl₄HgBr₆ structure. In α-Tl₄CrI₆ there occurs a random distribution of Jahn-Teller distorted octahedra which are elongated perpendicular to the c axis. Between 77 and 4.2 K a phase transition occurs. In β-Tl₄CrI₆ (a = 12.941(3), b = 12.596(3), c = 9.602(2) Å, Z = 4, Cccm at 4.2 K) the directions of elongation of the octahedra are ordered. The structure is very much related to that of α-Tl₄CrI₆. A three-dimensional magnetic ordering takes place at 2.7(2) K. The magnetic space group at 1.2 K is C_I22′2′. The magnetic moments (3.48(6) μ_B) are parallel to (0 0 1) and have an angle of 41(9)° with the a axis. Four magnetic sublattices are present, forming two independent magnetic lattices which have no interaction due to the antiparallel ordering.     

Synthesis and structure determination of a new layered compound: V2P4S13

V₂P₄S₁₃ was prepared from the elements taken in stoichiometric proportions and heated in an evacuated Pyrex tube for 10 days at 450°C. The crystal symmetry is triclinic, space group P1¯ with the parameters: a = 9.112(1) Å, b = 9.680(1) Å, c = 11.620(1) Å, α = 72.15(1)°, β = 110.82(1)°, γ = 110.13(1)°, V = 879.5(1) ų, and Z = 2. The structure was solved from 3052 independent reflections and 173 parameters, the least-squares refinement yielding R = 0.033. The building units of the structure are made up of two distorted (VS₆) octahedra and four distorted (PS₄) tetrahedra sharing edges to form (V₂P₄S₁₆) groups. These share sulfur atoms through their four (PS₄) tetrahedra with the same neighbor groups. Infinite (V₂P₄S₁₃) planes parallel to (101) are thus obtained, with no bonds other than van der Waals' ones between them. Within the slabs, the layered phase presents the following average distances: d_V-S = 2.471(1) Å, d_P-S = 2.050(1) Å, d_V-V = 3.715(2) Å. From the various oxydation states of the atoms, the developed formula can be written V^III₂P^V₄S^?II₁₃. The phase is semiconducting and magnetic susceptibility measurements show a Curie behavior with the occurrence of high spin d² vanadium. Antiferromagnetic ordering is observed below 10 K.     

High-pressure syntheses of TaS3, NbS3, TaSe3, and NbSe3 with NbSe3-type crystal structure

Transition metal trichalcogenides TaSe₃, TaS₃, NbSe₃ and NbS₃ were prepared under the reaction conditions of 2 GPa, 700°C, 30 min. NbSe₃ is exactly the same as that obtained in the usual sealed-tube method. The other products are modifications of each usual phase. They have crystal structures very similar to that of NbSe₃. The lattice parameters are a = 10.02Å, b = 3.48 Å, c = 15.56 Å, β = 109.6° for TaSe₃, a = 9.52 Å, b = 3.35 Å, c = 14.92 Å, β = 110.0° for TaS₃, and a = 9.68 Å, b = 3.37 Å, c = 14.83 Å, β = 109.9° for NbS₃. In spite of the similarity in their crystal structures, these high-pressure phases show a variety of electrical transport properties. TaSe₃ is a superconductor having T_c at 1.9 K. TaS₃ is a semiconductor with two transitions at 200 and 250 K. NbS₃ is a semiconductor with E_a = 180 MeV.     

Synthesis and crystal chemistry of NH3(MoO3)3

NH₃(MoO₃)₃ crystallizes with hexagonal symmetry, space group $\text{P6}{}_3\text{m}$, lattice constants a = 10.568 Å, c = 3.726 Å, and Z = 2. The crystal structure has been determined by Patterson synthesis and refined assuming isotropic temperature factors to a final conventional R value of 0.085. The structure shows a three-dimensional arrangement built up of double chains of distorted MoO₆ octahedra, parallel to the [001] direction. The octahedral double chains are linked among each other through common oxygen atoms. In addition to the shared oxygen atoms, each molybdenum is coordinated to one terminal oxygen. MoO distances range from 1.645 to 2.378 Å and OMoO angles from 74.3 to 114.3°. These results are consistent with the fact that molybdenum in high-valence states shows octahedral coordination with terminal oxygens.     

Crystal structures of the fluorite-related phases CaHf4O9 and Ca6Hf19O44

Crystal structures for the fluorite-related phases CaHf₄O₉$\text{ф}{}_1$) and Ca₆Hf₁₉O₄₄ ($\text{ф}{}_2$) have been determined from X-ray powder diffraction data. qf₁ is monoclinic, $\text{C2}\text{c}$, with a = 17.698 Å, b = 14.500Å, c = 12.021 Å, β = 119.47° and Z = 16. qf₂ is rhombohedral, $\text{R}\text{3}\text{c}$, with a = 12.058 Å, α = 98.31° and Z = 2.Both phases are superstructures derived from the defect fluorite structure by ordering of the cations and of the anion vacancies. The ordering is such that the calcium ions are always 8-coordinated by oxygen ions, while the hafnium ions may be 6-, 7-, or 8-coordinated. The closest approach of anion vacancies is a $\text{1}\text{2}\text{〈111〉}$ fluorite subcell vector, and in each structure vacancies with this separation form strings.     

X-ray and mössbauer studies of tricyclohexyltin(IV) halides. The crystal structures of (cyclo-C6H11)3SnX (X = F,Br and I)

The structures of tricyclohexyltin fluoride (I), bromide (II) and iodide (III) have been determined by X-ray analysis. Compound I crystallizes in the space group P2₁/m with a = 10.422(6), b = 17.238(9), c = 5.769(3) Å, β = 104.6(1)° and Z = 2. Compounds II and III crystallize in the space group Pcmn with a = 10.427(6), b = 16.914(9), c = 11.366(6) Å, Z = 4; and a = 10.400(6), b = 16.900(10), c = 11.400(4) Å, Z = 4, respectively. All three structures consist of discrete tetrahedral (cyclo-C₆H₁₁)₃SnX units.The temperature dependence of the Mössbauer resonance areas has been examined in order to obtain information about the relationship between chemical structure and lattice dynamics.     

Structure types and phase transformations in KMnCl3 and TlMnCl3

KMnCl₃ and TlMnCl₃ are known to crystallize in tetragonal and cubic perovskite structures, respectively. Room temperature X-ray diffraction data obtained in our laboratory proved that the perovskite structure of KmnCl₃ is orthorhombic. The space group is Pnma and Z = 4. Unit cell parameters are a = 7.08(1), b = 9.97(1), and c = 6.98(1) Å. Experimental data showed that the perovskite structures of KMnCl₃ and TlMnCl₃ are not stable, and that both materials transform slowly into another orthorhombic, nonperovskite KCdCl₃ structure with space group Pnma and Z = 4. Cell parameters of these structures are a = 8.769(7), b = 3.883(9), and c = 14.42(1) Å for KMnCl₃ and a = 8.926(8), b = 3.839(9), and c = 14.77(1) Å for TlMnCl₃. The nonperovskite structures of KMnCl₃ and TlMnCl₃ transform on heating to the perovskite structures and these phase transitions are not immediately reversed. No correlation could be found between the KCdCl₃ structure and water incorporation in the crystal lattice as has been previously suggested. An analysis of the factors that cause the K structure to be exhibited in chloride and to be absent in the fluoride compounds is also presented.     

Cristallochimie de TlIII6TeVIO12 et TlI6TeVIO6E6: un exemple original de l'activite´ste´re´ochimique de la pairee´lectronique 6s2(E) du thallium(I)

Both crystal structures of Tl₆TeO₁₂ and Tl₆TeO₆E₆ compounds have been determined, the former by X-ray single crystal techniques, the latter by powder neutron diffraction techniques. They crystallize in the trigonal system, space groupR3¯ the corresponding hexagonal cell parameters area = 9.645(2) Å,c = 9.421(2) Å, anda = 9.5722(3) Å,c = 9.3494(4) Å, respectively, withZ = 3. In both compounds tellurium(VI) is octahedrally coordinated to oxygen atoms with TeO distances of 1.936Åfor the Tl(III)-containing compound, i.e., Tl₆TeO₁₂, and 1.946Åfor Tl₆TeO₆ (Tl(I)). Tl(III) is surrounded by seven oxygen atoms sitting at the summits of a distorted monocapped trigonal prism. Tl(I) is linked to three oxygen atoms, forming a distorted TlO₃ pyramid. The lone pairs brought by Tl(I) are in the positions precedingly occupied by oxygen atoms in the crystal structure of Tl₆TeO₁₂. This is an outstanding example of the crystallochemical role of the lone pairsE which act like oxygen atoms, making Tl^I₆Te^VIO₆E₆ isostructural with Tl^IIITe^VIO₁₂. Structural relationships with fluorite type network are discussed.     

Etude des equilibres solide-liquide des systems MIPO3Sm(PO3)3 (MI = Li,Na, Ag)

The M^IPO₃Sm(PO₃)₃(M^I = Li, Na, Ag) systems were studied. Differential thermal analysis and X-ray diffraction were used to investigate the liquidus and solidus relations. Three compounds LiSm(PO₃)₄, NaSm(PO₃)₄, and AgSm(PO₃)₄ were obtained which melt incongruently at 1248, 1143, and 1078 K, respectively. These compounds are isomorphous with their homologs LiLn(PO₃)₄, NaLn(PO₃)₄, AgLn(PO₃)₄ (Ln = Ce, La, Nd). They belong to the monoclinic system. The LiSm(PO₃)₄ unit cell parameters refined by least squares method are a = 16.43(3) Å, b = 7.16(1) Å, c = 9.65(3) Å, β = 125,9°(1), with the space group $\text{C2}\text{c}$ and Z = 4. NaSm(PO₃)₄ and AgSm(PO₃)₄ are isotypic; they cristallize in the $\text{P2}{}_1\text{c}$ space group, Z = 4; their unit cell parameters are, respectively, a = 12.18(1) Å, b = 13.05(1) Å, c = 7.25(5) Å, β = 126,53°(4), $\text{a = 12.25(1)}\text{A}\text{?}$, b = 13.06(1) Å, c = 7.201(9) Å, β = 126,57°(7). The ir spectra of the last two compounds indicate that these phosphates are chain phosphates.     

Kristall- und molekülstruktur vonzwei metallcarbonyl-derivaten des PH3: (CO)3Cr(PH3)3 und (CO)5Cr(PH3)

The structures of two carbonylphosphine complexes of chromium were determined by X-ray analysis. cis-Tricarbonyltriphosphinechromium(0), [(CO)₃(PH₃)₃Cr], crystallizes in space group P2₁/m with a = 6.90± 0.01, b = 11.29±0.02, c = 6.41±0.01 Å, β = 93.80±0.08°, Z=2. The structure was solved by conventional methods and refined by least squares (R₁ = 0.056). The idealized octahedral molecule shows approximate C_3v, symmetry. The mean CrP-distance is 2.346±40.003 Å. Pentacarbonylphosphinechromium, [(CO)₅(PH₃)Cr], crystallizes in spacegroup Pnma with a = 12.23±0.02, b = 11.33±0.02, c = 6.61 ±0.01 Å, Z = 4. Cell dimensions and structural parameters are very similar to those of hexacarbonylchromium(0). In the crystal the PH₃ group is disordered over three mutually cis-positions of the coordination octahedron.     

The crystal structure and some properties of Eu2Sb3

The Mooser-Pearson phase Eu₂Sb₃ crystallizes in a new monoclinic structure type, space group $\text{P2}{}_1\text{c}$ (No. 14) with a = 6.570(1) Å, b = 12.760(2) Å, c = 15.028(2) Å, β = 90.04(1)°; Z = 8. The Sb atoms form six-membered twisted chain fragments oriented along the b-axis. The Eu atoms are eight- and nine-coordinated by Sb. The Eu₂Sb₃ structure is closely related to the structure of Ca₂As₃. The relations between their space-group symmetries are derived and hypothetical higher-symmetry structures are discussed. The semiconducting Eu₂Sb₃ is antiferromagnetic below T_N = 14.4°K. An Eu₂Sb₃-type structure was found also for Sr₂Sb₃.     

Synthesis and characterisation of HRuRh3(CO)12. Crystal structures of HRuRh3(CO)12, HRuRh3(CO)10(PPh3)2 and HRuCo3(CO)10(PPh3)2

A new ruthenium-rhodium mixed-metal cluster HRuRh₃(CO)₁₂ and its derivatives HRuRh₃(CO)₁₀(PPh₃)₂ and HRuCo₃(CO)₁₀(PPh₃)₂ have been synthesized and characterized. The following crystal and molecular structures are reported: HRuRh₃(CO)₁₂: monoclinic, space group P2₁/c, a 9.230(4), b 11.790(5), c 17.124(9) Å, β 91.29(4)°, Z = 4; HRuRh₃(CO)₁₀(PPh₃)₂·C₆H₁₄: triclinic, space group P$\text{1}$, a 11.777(2), b 14.079(2), c 17.010(2) Å, α 86.99(1), β 76.91(1), γ 72.49(1)°, Z = 2; HRuCo₃(CO)₁₀(PPh₃)₂·CH₂Cl₂: triclinic, space group P$\text{1}$, a 11.577(7), b 13.729(7), c 16.777(10) Å, α 81.39(4), β 77.84(5), γ 65.56°, Z = 2. The reaction between Rh(CO)₄^? and (Ru(CO)₃Cl₂)₂ tetrahydrofuran followed by acid treatment yields HRuRh₃(CO)₁₂ in high yield. Its structural analysis was complicated by a 80–20% packing disorder. More detailed structural data were obtained from the fully ordered structure of HRuRh₃(CO)₁₀(PPh₃)₂, which is closely related to HRuCo₃(CO)₁₀(PPh₃)₂ and HFeCo₃(CO)₁₀(PPh₃)₂. The phosphines are axially coordinated.     

Structural chemistry of Sr3Cr2WO9, Ca3Cr2WO9, and Ba3Cr2WO9

We have studied the preparation and crystallographic structure of three perovskite-type compounds: Sr₃Cr₂WO₉, cubic, the lattice parameter of which is a = 7.812Å; Ca₃Cr₂WO₉, tetragonal, the lattice parameters of which are a = 5.408 Å and c = 7.635Å; and Ba₃Cr₂WO₉, hexagonal, the lattice parameters of which are a = 5.691 Å and c = 13.957Å. We have compared these three structures and shown the relationship between the dimensions of the alkaline-earth metal and the existence of the different structures.     

Low-temperature structural determination of anhydrous Li2SeO4

Anhydrous Li₂SeO₄ crystallizes in the trigonal space group $\text{R}\text{3}$ with a = 13.931(2), c = 9.304(3) Å, V = 1563.7 ų, Z = 18, D_c = 2.988 g cm^?3. The unit cell transforms to the rhombohedral coordinate system as a = 8.620 Å, α = 107.81(2)°, V = 521.2 ų, Z = 6. The structure contains selenate anions bridged by Li in the phenacite structural type. Data collection was performed at low temperature for precise placement of the Li cations which are tetrahedrally surrounded by oxygen atoms. Some problems with secondary extinction were apparent and a correction was made. The structure refined to an R value of 0.034.     

Crystal structure of cerium(III) diammonium polyphosphate (NH4)2Ce(PO3)5

Cerium(III) diammonium polyphosphate, (NH₄)₂Ce(PO₃)₅, is triclinic P1 with the following unit cell dimensions: a = 7.241(5) Å, b = 13.314(8) Å, c = 7.241(5)Å, α = 90.35(5)°, β′ = 107.50(5)°, γ = 90.28(5)°, and Z = 2, V = 665.7 ų, D_x = 2.85 g/cm³. The crystal structure of this new type of polyphosphate has been solved and refined from 4130 independent reflections to a final R value 0.029. The most interesting feature of this salt is the existence of two infinite crystallographically nonequivalent (PO₃)^?_∞ chains, one running parallel to the a axis, the other along the c axis, both with a period of five tetrahedra. This compound seems to be the first example of a long chain polyphosphate with crystallographic independent chains.     

The structure of the metallated iridium complex [(C8H12)Ir{P(OC6H3Me)(OC6H4Me)2} {P(OCH2)3CMe}]

The crystal structure of [(C₈H₁₂)$\text{Ir{P(OC}$₆H₃Me)(OC₆H₄Me)₂} {P(OCH₂)₃CMe}] has been determined. a 18.32, b 18.98, c 9.35 Å, U 3251 ų, Pn2_1^a, Z = 4, R = 0.048, 2541 observed data.The coordination about the iridium atom is distorted trigonal bipyramidal; the two phosphorus atoms are equatorial, the σ-bonded carbon is axial, and the bidentate cyclooctadiene is bonded axialequatorial. The IrC(axial) bonds are longer than the IrC(equatorial) bonds: 2.22, 2.26; 2.17, 2.19 Å. The IrC(σ) bond length is 2.19 Å, not significantly different from the formally π-bonded C to Ir distances. The IrP lengths of 2.201 and 2.240 Å and the PIrP angle of 108.7° are normal. The longer IrP bond is in the five-membered chelate ring. The inertness to substitution is discussed.     

Crystal structure of Na3PCr3O13·3H2O: A new type of chromophosphoric anion

We describe the chemical preparation and crystal structure of a new sodium phosphochromate: Na₃PCr₃O₁₃·3H₂O. This salt is orthorhombic with a = 11.72(3) Å, b = 14.89(3) Å, c = 16.59(3) Å, and Z = 8, space group Pbc2₁. The final R value is 0.063 for 2133 independent reflections. The main feature of this atomic arrangement is the existence of a new type of chromophosphoric anion: PCr₃O₁₃. Infinite chains of NaO₆ run along the a direction. A survey of some phosphochromates previously described by the authors is given.     

Phase equilibrium relations in the binary systems LiPO3CeP3O9 and NaPO3CeP3O9

The LiPO₃CeP₃O₉ and NaPO₃CeP₃O₉ systems have been investigated for the first time by DTA, X-ray diffraction, and infrared spectroscopy. Each system forms a single 1:1 compound. LiCe(PO₃)₄ melts in a peritectic reaction at 980°C. NaCe(PO₃)₄ melts incongruently, too, at 865°C. These compounds have a monoclinic unit cell with the parameters: a = 16.415(6), b = 7,042(6), c = 9.772(7)Å; β = 126.03(5)°; Z = 4; space group $\text{C}{}_2\text{c}$ for LiCe (PO₃)₄; and a = 9.981(4), b = 13.129(6), c = 7.226(5) Å, β = 89.93(4)°, Z = 4, space group $\text{P2}{}_1\text{n}$ for NaCe(PO₃)₄. It is established that both compounds are mixed polyphosphates with chain structure of the type |M^I_IM^III_II (PO₃)₄|_∞M^I_I: alkali metal, M^III_II: rare earth.