Untersuchungen zu Bismutseltenerdoxidhalogeniden der Zusammensetzung Bi2SEO4X (X = Cl,Br, I)

Investigations on the Bismuth Rare‐Earth Oxyhalides Bi₂REO₄X (X = Cl, Br, I) Compounds of the composition of Bi₂REO₄X (RE = Y, La–Lu; X = Cl, Br, I) have been prepared by solid state reaction of stoichiometric mixtures of BiOX, Bi₂O₃, and RE₂O₃. They were characterized by X‐ray powder diffraction, IR spectroscopy, mass spectrometry and DTA/TG measurements as well. The crystal structure (tetragonal, P4/mmm, a ≈ 3.9 Å, c ≈ 9 Å) was determined by the Rietveld method. In the structure [M₃O₄]⁺ layers are interleaved by single halogen layers. Rare‐earth and bismuth atoms in Bi₂REO₄X are 8‐coordinated. The structure can be derived from the LiBi₃O₄Cl₂ type structure. The enthalpies of formation are derived from heats of solution. The standard entropies were calculated from low‐temperature measurements of the specific heat capacities.     

Synthesis,Structures, and Properties of Layered Quaternary Chalcogenides of the General Formula ALnEQ4 (A = K,Rb; Ln = Ce,Pr, Eu; E = Si,Ge; Q = S,Se)

Four related quaternary compounds containing rare‐earth metals have been synthesized employing the molten flux method and metathesis. The reactions of Eu and Rb₂S₅ with Si and Ge in evacuated fused silica ampoules at 725 °C for 150 h yielded RbEuSiS₄ ( I ) and RbEuGeS₄ ( II ), respectively. On the other hand, a reaction between CeCl₃ and K₄Ge₄Se₁₀ at 650 °C for 148 h has yielded KCeGeSe₄ ( III ) and KPrSiSe₄( IV ) was obtained by the reaction of elemental Pr, Si and Se in KCl flux at 850 °C for 168 h. Crystal data for these compounds are as follows: I , orthorhombic, space group P2₁2₁2₁ (#19), a = 6.392(1), b = 6.634(2), c = 17.001(3) Å, α = β = γ = 90°, Z = 4; II , monoclinic, space group P2₁/m (#11), a = 6.498(2), b = 6.689(3), c = 8.964(3) Å, β = 108.647(6)°, Z = 2; III , monoclinic, space group P2₁ (#4), a = 6.852(2), b = 7.025(2), c = 9.017(3) Å, β = 108.116(2)°, Z = 2; IV , monoclinic, space group P2₁ (#4), a = 6.736(2), b = 6.943(2), c = 8.990(1) Å, β = 108.262(2)°, Z = 2. The crystal structures of I ‐ IV contain two‐dimensional corrugated anionic layers of the general formula, [LnEQ₄]^? (Ln = Ce, Pr, Eu; E = Si, Ge and Q = S, Se) alternately piled upon layers of alkali cations. In addition to structural elucidation, Raman and UV‐visible spectroscopy, and magnetic measurements for compound III (KCeGeSe₄) are also discussed.     

Two New Quaternary Thiophosphates with Pseudo One‐dimensional Structures: Syntheses and Crystal Structures of Cs3Sm[PS4]2 and Rb3Sm[PS4]2

The new thiophosphates Rb₃Sm[PS₄]₂ and Cs₃Sm[PS₄]₂ were obtained as pale yellow needles using an in‐situ formed thiophosphate flux. Rb₃Sm[PS₄]₂ crystallizes in the space group P2₁ with a = 9.7061(19) Å, b = 6.7517(14) Å, c = 11.395(2) Å, β = 90.63(3)°, (Z = 2); Cs₃Sm[PS₄]₂ in space group P2₁/n with a = 15.311(3) Å, b = 6.8762(14) Å, c = 15.352(3) Å, β = 99.49(3)°, (Z = 4). The crystal structures are characterized by the formation of complex anionic chains, which run along the [010] direction in both structures. One of the two independent thiophosphate groups connects three Sm³⁺ cations to form an infinite zigzag like arrangement, while the other acts as a terminal ligand to one Sm³⁺ions. Such a μ₃ or face‐grafting coordination mode of a [PS₄]³⁻ anion is not very common. The Sm³⁺ ions are in bicapped trigonal prismatic chalcogen coordination. The average Sm–S distances within the trigonal prisms are close to 2.88Å, while the bonds to the capping atoms are distinctly longer. The chains are chiral yet their symmetry is close to 2₁/m. In contrast to the rubidium compound, Cs₃Sm[PS₄]₂ contains both enantiomorphs. In both structures the chains are arranged as a distorted hexagonal rod packing.     

CeAgAs2 — a New Derivative of the HfCuSi2 Type of Structure: Synthesis,Crystal Structure and Magnetic Properties

Single crystals of CeAgAs₂ have been obtained by chemical transport reactions starting from a pre‐reacted powder sample. The crystal structure was solved using X‐ray diffraction (space group Pmca, No. 57, a = 5.7586(4) Å, b = 5.7852(4) Å, c = 21.066(3) Å, Z = 8) and refined to a residual of R(F) = 0.029 for 46 refined parameters and 1020 reflections. The structure of CeAgAs₂ represents a new distorted and ordered variant of the HfCuSi₂ type. The characteristic feature of this structure are infinite cis‐trans chains of As atoms with As—As distances of 2.563(1) Å and 2.601(1) Å. CeAgAs₂ is paramagnetic (μ_eff = 2.37 μ_B, θ = —10.5(2) K), with antiferromagnetic ordering at 5.5(2) K and exhibits a metamagnetic transition starting at 4.6 kOe and T = 1.8 K.     

Beiträge zur Kristallchemie und zum thermischen Verhalten von wasserfreien Phosphaten. XXXIII [1] In2P2O7, ein Indium(I)‐diphosphato‐indat(III) und In4(P2O7)3 — Darstellung,Kristallisation und Kristallstrukturen

Contributions on Crystal Chemistry and Thermal Behaviour of Anhydrous Phosphates. XXXIII [1] In₂P₂O₇ an Indium(I)‐diphosphatoindate(III), and In₄(P₂O₇)₃ — Synthesis, Crystallization, and Crystal Structure Solid state reactions via the gas phase lead to the new mixed‐valence indium(I, III)‐diphosphate In₂P₂O₇. Colourless single crystals of In₂P₂O₇ have been grown by isothermal heating of stoichiometric amounts of InPO₄ and InP (800 °C; 7d) using iodine as mineralizer. The structure of In₂P₂O₇ [P2₁/c, a = 7.550(1) Å, b = 10.412(1) Å, c = 8.461(2) Å, b = 105.82(1)°, 2813 independent reflections, 101 parameter, R1 = 0.031, wR2 = 0.078] is the first example for an In⁺ cation in pure oxygen coordination. Observed distances d(In^I‐O) are exceptionally long (d_min(In^I‐O) = 2.82 Å) and support assumption of mainly s‐character for the lone‐pair at the In⁺ ion. Single crystals of In₄(P₂O₇)₃ were grown by chemical vapour transport experiments in a temperature gradient (1000 → 900 °C) using P/I mixtures as transport agent. In contrast to the isostructural diphosphates M₄(P₂O₇)₃ (M = V, Cr, Fe) monoclinic instead of orthorhombic symmetry has been found for In₄(P₂O₇)₃ [P2₁/a, a = 13.248(3) Å, b = 9.758(1) Å, c = 13.442(2) Å, b = 108.94(1)°, 7221 independent reflexes, 281 parameter, R1 = 0.027, wR2 = 0.067].     

Crystal Structure of a New Cation-ordered Fluorite-related Phase: Bi2Te2WO10

Bi₂Te₂WO₁₀ crystallises in the monoclinic system (space group C2/c, Z = 4) with a = 12.4972(7) Å, b = 5.6414(3) Å, c = 12.2705(6) Å and β = 91.38(3)°. The structure has been solved by means of single crystal X-ray diffraction data analysis. The reliability factors are R1 = 0.030 and wR2 = 0.065 for 1258 structure factors and 70 parameters. The Bi₂Te₂WO₁₀ crystal structure can be described as a regular stacking along the Ox axis of polyhedral layers with the stereochemically active lone pairs E of the Bi^III and Te^IV atoms all located between these layers. The cohesion of the three-dimensional network is therefore only ensured between succesive layers by weak Bi? O(5) bonds.     

Darstellung und Kristallstrukturen von Ln2Al3Si2 und Ln2AlSi2 (Ln: Y,Tb–Lu)

Synthesis and Crystal Structures of Ln ₂Al₃Si₂ and Ln ₂AlSi₂ ( Ln : Y, Tb–Lu) Eight new ternary aluminium silicides were prepared by heating mixtures of the elements and investigated by means of single‐crystal X‐ray methods. Tb₂Al₃Si₂ (a = 10.197(2), b = 4.045(1), c = 6.614(2) Å, β = 101.11(2)°) and Dy₂Al₃Si₂ (a = 10.144(6), b = 4.028(3), c = 6.580(6) Å, β = 101.04(6)°) crystallize in the Y₂Al₃Si₂ type structure, which contains wavy layers of Al and Si atoms linked together by additional Al atoms and linear Si–Al–Si bonds. Through this there are channels along [010], which are filled by Tb and Dy atoms respectively. The silicides Ln₂AlSi₂ with Ln = Y (a = 8.663(2), b = 5.748(1), c = 4.050(1) Å), Ho (a = 8.578(2), b = 5.732(1), c = 4.022(1) Å), Er (a = 8.529(2), b = 5.719(2), c = 4.011(1) Å), Tm (a = 8.454(5), b = 5.737(2), c = 3.984(2) Å) and Lu (a = 8.416(2), b = 5.662(2), c = 4.001(1) Å) crystallize in the W₂CoB₂ type structure (Immm; Z = 2), whereas the structure of Yb₂AlSi₂ (a = 6.765(2), c = 4.226(1) Å; P4/mbm; Z = 2) corresponds to a ternary variant of the U₃Si₂ type structure. In all compounds the Si atoms are coordinated by trigonal prisms of metal atoms, which are connected by common faces so that Si₂ pairs (d_Si–Si: 2.37–2.42 Å) are formed.     

Gasphasengleichgewichte quaternärer Bismut‐Selen‐Oxidchloride

Gas‐Phase Equilibria of Quaternary Bismuth Selenium Oxidechlorides The existence of new compounds Bi₄O₄SeCl₂, Bi₁₀O₁₂SeCl₄, and Bi₂₂O₂₈SeCl₈ in the pseudoternary area Bi₂O₃/Bi₂Se₃/BiCl₃ has been established by solid state and chemical vapour transport reactions. Furthermore, heterogeneous equilibria between solid state and vapour phase have been studied by mass‐spectrometric measurements. The novel gas‐molecule BiSeCl has been detected. The results of ab initio calculations for structure and refining of thermochemistry of this molecule are given: (Bi–Se) = 2,44 Å; (Bi–Cl) = 2,49 Å; (Se–Bi–Cl) = 106,0°; Thermodynamics: δH°_B,298 (BiSeCl_g) = 6,0 kcal/mol; S°₂₉₈ (BiSeCl_g) = 75,8 cal/mol K; Cp (BiSeCl_g) = 13,583 + 0,64 · 10^–3 · T – 0,41 · 10⁵ · T^–2 – 0,35 · 10^–6 · T² cal/mol K. Finally, the composition of the gaseous phase has been calculated and estimations about chemical vapour transport were carried out by thermodynamic modelling.     

Yb2+3—xPd12—3+xP7 (x = 0.40): Different Ytterbium Species in a Substituted Structural Motif of the Zr2Fe12P7 Type

The new compound Yb_2+3—xPd_12—3+xP₇ x = 0.40(4)) was synthesized by sintering of a mixture of elemental components at 1100 °C with subsequent annealing at 800 °C. The crystal structure of Yb_2+3—xPd_12—3+xP₇ was solved and refined from X‐ray single‐crystal diffraction data: space group P6¯, a = 10.0094(4)Å, c = 3.9543(2)Å, Z = 1; R(F) = 0.022 for 814 observed unique reflections and 38 refined parameters. The atomic arrangement reproduces a structure motif of the hexagonal Zr₂Fe₁₂P₇ type in which one of the transition metal positions is substituted predominantly by ytterbium (Yb : Pd = 0.86(1) : 0.14). The ytterbium atoms are embedded in the 3D polyanion formed by palladium and phosphorus atoms. Two different environments for ytterbium atoms are present in the structure. Magnetic susceptibility measurements and XAS spectroscopy at the Yb L_III edge show the presence of ytterbium in two electronic configurations, 4?¹³ and 4?¹⁴. The following model was derived. Ytterbium atoms in the 3k site are in the 4?¹³ state, the two remaining positions contain ytterbium in intermediate‐valence states, giving totally 79 % ytterbium in the 4?¹³ electronic configuration.     

Electronic Structures of Highly Symmetrical Compounds of f Elements. 34 [1] Synthesis and Spectroscopic Characterization of Biscyclohexylisocyanide Adducts derived from the Tris(bis(trimethylsilyl)amido)lanthanide(III) Moiety as well as Crystal,Molecular, and Electronic Structure of the Corresponding Neodymium Compound

The reaction of tris(bis(trimethylsilyl)amido)lanthanide(III) (Ln(btmsa)₃) with two equiv. of cyclohexylisocyanide gives good yields of complexes of composition Ln(btmsa)₃(CNC₆H₁₁)₂ (Ln = Y( 1 ), La( 2 ), Ce( 3 ), Pr( 4 ), Nd( 5 ), Sm( 6 ), Eu( 7 ), Tb( 8 ), Dy( 9 ), Ho( 10 ), Tm( 11 ) and Yb( 12 )). Complex 5 crystallizes in the monoclinic space group C2/c with a = 25.689(8) Å, b = 12.165(2) Å, c = 17.895(15) Å, β = 122.47 (2)°, V = 4718.07 ų, Z = 4 and R = 0.0342. The structure of compound 5 shows the five‐coordinate Nd³⁺ ion in a nearly exact trigonal bipyramidal environment with two CNC₆H₁₁ molecules in the axial and the three btmsa ligands in the equatorial positions. The linear dichroism spectrum of a single crystal of complex 5 was measured at room temperature, and the absorption spectrum of powdered material at low temperatures. From the spectra obtained a truncated crystal field (CF) splitting pattern is derived, and simulated by fitting the parameters of a phenomenological Hamiltonian. For 80 assignments a reduced r.m.s. deviation of 20.7 cm^—1 is achieved. Making use of the calculated wavefunctions and eigenvalues the experimentally determined temperature dependence of μ²_eff could be reproduced by adopting an orbital reduction factor k = 0.991, and on the basis of the CF parameters used the experimentally oriented non‐relativistic molecular orbital scheme of compound 5 is set up.     

[{Er(NC5H4COOH)(H2O)2}2(H5O2)(HgCl5)(HgCl4)2(H2O)2]n – Synthesis,Crystal Structure and Properties

The first heterometallic 4f‐5d inorganic‐organic metal‐isonicotinic acid hybrid [{Er(NC₅H₄COOH)(H₂O)₂}₂(H₅O₂)(HgCl₅)(HgCl₄)₂(H₂O)₂]_n ( 1 ) has been synthesized via hydrothermal reaction and structurally characterized. Complex 1 crystallizes in the space group C2/c of the monoclinic system with four formula units per unit cell: a = 24.194(3), b = 20.792(3), c = 15.289(4) Å, β = 128.39(2)°, V = 6028(2) ų, C₃₆H₄₇Cl₁₃Er₂Hg₃N₆O₂₀, M_r = 2280.94, D_c = 2.513 g/cm³, S = 0.929, μ(MoKα) = 11.017 mm^?1, F(000) = 4248, R = 0.0425 and wR = 0.0739. The crystal structure analysis reveals that the title complex is characteristic of a one‐dimensional chain‐like structure. Photoluminescent investigation reveals that the title complex displays interesting emissions. Optical absorption spectra of 1 reveal the presence of an optical gap of 3.45 eV. The magnetic properties show that complex 1 exhibits antiferromagnetic interactions.     

The First Rare Earth Metal Thioborate: Synthesis and Crystal Structure of EuB2S4

Systematic studies on thio‐ and selenoborates containing heavier metal cations led to the new crystalline phase EuB₂S₄. The crystal structure of the europium metathioborate reveals polymeric [(B₂S₄)^2—]_n anions and divalent Eu‐cations which are connected via ionic interactions. The building blocks of the anions consist of BS₄‐tetrahedra. Condensation of these BS₄‐tetrahedra leads to corner‐ and edge‐sharing 2D‐networks running parallel to (1 0 0). Evacuated carbon coated silica tubes were used as reaction vessels since temperatures up to 990 K were applied. EuB₂S₄ crystallizes in the monoclinic space group P2₁/c (no. 14) with a = 6.4331(6)Å, b = 14.099(1)Å, c = 6.0731(6)Å, β = 110.55(8)° and Z = 4.     

Sm2O2I – A New Mixed‐Valence Samarium(II,III) Oxide Halide

Dark red single crystals of Sm₂O₂I were obtained from a reaction of SmI₂ (in the presence of SmOI) and Na in a sealed tantalum ampoule at 650 °C. The title compound crystallizes in the monoclinic system (C2/m, Z = 4, a = 12.639(2), b = 4.100(1), c = 9.762(3) Å, β = 117.97(2)°). The structure consists of corrugated [Sm²⁺Sm³⁺(O^2?)₂]⁺ layers of edge and vertex‐connected Sm₄O tetrahedral units with I^? anions separating the layers.     

Gd2AlGe2: An “Almost‐Zintl Phase” and a New Stacking Variant of the W2CoB2 Type

The synthesis, structure determination and calculated electronic structure of the new phase, Gd₂AlGe₂, are reported. The compound crystallizes in a new structure type with space group C2/c, a = 10.126(2) Å, b = 5.6837(12) Å, c = 7.7683(16) Å, and β = 104.729(3)s. Tight‐binding linear‐muffin‐tin orbital (TB‐LMTO‐ASA) calculations show a distinct minimum in the total density of states for this structure at 18 valence electrons per formula unit (Gd₂AlGe₂ has 17 valence electrons in its formula unit), which arises from polar covalent bonding within the three‐dimensional [AlGe₂] net, Gd‐Ge interactions and three‐center, two‐electron bonding between Al and Gd. The structure is a new stacking variant of the W₂CoB₂ structure type, which is observed for numerous ternary rare‐earth silicides and germanides.     

SrNi10P6, EuNi10P6 und BaCo10As6: Phasenumwandlungen und Kristallstrukturen

SrNi₁₀P₆, EuNi₁₀P₆, and BaCo₁₀As₆: Phase Transitions and Crystal Structures SrNi₁₀P₆, EuNi₁₀P₆ and BaCo₁₀As₆ were prepared by heating mixtures of the elements in the range of 800°–1000 °C and were investigated by means of single‐crystal X‐ray methods. At higher temperatures the isotypic Ni phosphides (HT‐SrNi₁₀P₆: a = 6.481(2), b = 16.080(4), c = 8.763(2) Å (350 °C); HT‐EuNi₁₀P₆: a = 6.509(2), b = 16.063(4), c = 8.766(4) Å (500 °C)) crystallize in the BaNi₁₀P₆ type structure (Cmca; Z = 4), which can be described as an arrangement of Ni₁₄P₁₂ cages with Sr or Eu atoms in the centres. The cages are linked to layers separated by additional Ni atoms, which are coordinated tetrahedrally by P atoms of different cages. Cooling down both compounds undergo from about 270 °C (SrNi₁₀P₆) and 410 °C (EuNi₁₀P₆) respectively a second‐order phase transition involved with a change to an orthorhombic P lattice. In the structure of the NT phases (Pnma; Z = 4; NT‐SrNi₁₀P₆: a = 15.993(1), b = 6.473(1), c = 8.735(1) Å; NT‐EuNi₁₀P₆: a = 15.925(1), b = 6.478(1), c = 8.720(1) Å (25 °C)) the Ni₁₄P₁₂ cages are slightly distorted in comparison with the high temperature modifications. BaCo₁₂As₆ (a = 16.405(9), b = 6.858(4), c = 8.955(7) Å) crystallizes in the same structure (Pnma), but doesn't exhibit a comparable phase transition up to 600 °C. Measurements of the suszeptibiliy of EuNi₁₀P₆ between 4 K and 850 K showed divalent Europium and no magnetic order down to 4 K.     

A Three‐Dimensional Lead 2,6‐Dihydroxybenzoate with Channels

A lead 2,6‐dihydroxybenzoate of the formula Pb(C₁₄H₁₀O₈) ( I ) has been synthesized and characterized by X‐ray crystallography and spectroscopic techniques. (crystal data: monoclinic, space group = Cc (no. 9), a = 11.2155(2), b = 9.2942(2), c = 13.5112(3) Å, β = 96.510(1)°, V = 1399.31(5) ų, Z = 4). This is the first three‐dimensional metal dihydroxybenzoate structure, comprising 3,6‐connected periodic net and having channels with the dimensions 3.8 × 3.8Å and 10.8 × 3.8Å. The coordination of the PbO₈ polyhedron is holodirected and the electron lone pair of the lead is, therefore, not manifested in I . It exhibits photoluminescence in the violet, green and red when excited at 240, 390 and 525 nm, respectively.     

Hydroxo Bridged Dinuclear Rare Earth Complexes: Syntheses and Crystal Structures of [Ln2(phen)4(H2O)4(OH)2](NO3)4(phen)2 with Ln = Er,Lu

Reactions of phenanthroline (phen) and Er(NO₃)₃ · 5 H₂O or Lu(NO₃)₃ · H₂O in CH₃OH/H₂O yield [Ln₂(phen)₄(H₂O)₄(OH)₂](NO₃)₄(phen)₂ with Ln = Er ( 1 ), Lu ( 2 ). Both isostructural complex compounds crystallize in the triclinic space group P 1 (no. 2) with the cell dimensions: a = 11.257(2) Å, b = 11.467(2) Å, c = 14.069(2) Å, α = 93.93(2)°, β = 98.18(1)°, γ = 108.14(1)°, V = 1696.0(6) ų, Z = 1 for ( 1 ) and a = 11.251(1) Å, b = 11.476(1) Å, c = 14.019(1) Å, α = 93.83(1)°, β = 98.27(1)°, γ = 108.27(1)°, V = 1689.0(3) ų, Z = 1 for ( 2 ). The crystal structures consist of the hydroxo bridged dinuclear [Ln₂(phen)₄(H₂O)₄(OH)₂]⁴⁺ complex cations, hydrogen bonded NO₃^– anions and π‐π stacking (phen)₂ dimers. The rare earth metal atoms are coordinated by four N atoms of two phen ligands and four O atoms of two H₂O molecules and two μ‐OH groups to complete tetragonal antiprisms. Via two common μ‐OH groups, two neighboring tetragonal antiprisms are condensed to a centrosymmetric dinuclear [Ln₂(phen)₄(H₂O)₄(OH)₂]⁴⁺ complex cation. Based on π‐π stacking interactions and hydrogen bonding, the complex cations and (phen)₂ dimers form 2 D layers parallel to (1 0 1), between which the hydrogen bonded NO₃^– anions are sandwiched. The structures can be simplified into a distorted CsCl structure when {[Ln₂(phen)₄(H₂O)₄(OH)₂](NO₃)₄} and (phen)₂ are viewed as building units.     

Polymorphism and photoluminescence properties of K3ErSi2O7

Two polymorphs of tripotassium erbium disilicate, K₃ErSi₂O₇, were synthesized by high‐temperature flux crystal growth during the exploration of the flux technique for growing new alkali rare‐earth elements (REE) containing silicates. Their crystal structures were determined by single‐crystal X‐ray diffraction analysis. One of them (denoted 1 ) crystallizes in the space group P6₃/mmc and is isostructural with disilicates K₃LuSi₂O₇, K₃ScSi₂O₇ and K₃YSi₂O₇, while the other (denoted 2 ) crystallizes in the space group P6₃/mcm and is isostructural with disilicates K₃NdSi₂O₇, K₃REESi₂O₇ (REE = Gd–Yb), K₃YSi₂O₇, K₃(Y_0.9Dy_0.1)Si₂O₇ and K₃SmSi₂O₇. In the crystal structure of polymorph 1 , the Er cations are in an almost perfect octahedral coordination, while in the crystal structure of polymorph 2 , part of the Er cations are in a slightly distorted octahedral coordination and the other part are in an ideal trigonal prismatic coordination environment. Sharing six corners, disilicate Si₂O₇ groups in the crystal structure of polymorph 1 link six ErO₆ octahedra, forming a three‐dimensional network and nine‐coordinated potassium cations are located in its holes. In the crystal structure of polymorph 2 , the disilicate Si₂O₇ groups connect four ErO₆ octahedra, as well as one ErO₆ trigonal prism. Three differently coordinated potassium cations are situated between them. Different site symmetries of the erbium cations in the crystal structures of polymorphs 1 and 2 affect their photoluminescence properties. Only polymorph 2 exhibits luminescence. Intense narrow lines in the emission spectrum are a result of the 4f–4f transition. The green emission line at 560 nm is the result of the Er³⁺ transition ⁴S_3/2→⁴I_15/2, and the luminescence line at 690 nm is the result of a ⁴F_9/2→⁴I_15/2 transition. The crystal morphologies of the two polymorphs are similar. Crystals of polymorph 1 are in the form of a hexagonal prism in combination with a hexagonal base, while crystals of polymorph 2 contain a dihexagonal prism in combination with a hexagonal base, although poorly developed faces of the dihexagonal pyramid can also be noticed.     

Syntheses and Crystal Structures of Hydrated Ternary Cerium Sulfates: Mixed‐valence K5Ce2(SO4)6·H2O and K2Ce(SO4)3·H2O

A new chemical and structural interpretation of K₅Ce₂(SO₄)₆·H₂O ( I ) and a redetermination of the structure of K₂Ce(SO₄)₃·H₂O ( II ) is presented. The mixed‐valent compound I crystallizes in the space group C2/c with a = 17.7321(3), b = 7.0599(1), c = 19.4628(4) Å, β = 112.373(1)° and Z = 4. Compound I has been discussed earlier with space group Cc. In the structure of I , there are pairs of edge sharing cerium polyhedra connected by sulfate oxygen atoms in the μ₃ bonding mode. These cerium dimers are linked through edge and corner sharing sulfate bridges, forming layers. The layers are joined by potassium ions which together with the water molecules are placed between the layers. No irregularity in the distribution of the Ce^III and Ce^IV to cause the lost of a crystallographic center of symmetry was detected. We suggest that the charge exerted by the extra f¹ electron for every cerium dimer is delocalized over the Ce1–O₂–Ce2 moiety in a non‐bonding mode. As a result, the oxidations state of each cerium ion is a mean value between III and IV at each atomic position. Compound II crystallizes in the space group C2 with a = 20.6149(2), b = 7.0742(1), c = 17.8570(1) Å, β = 122.720(1)° and Z = 8. The hydrogen atoms have been located and the absolute structure has been established. Neither hydrogen atom positions nor anisotropic displacement parameters were given in the previous reports. In compound II , the cerium polyhedra are connected by edge and corner sharing sulfate groups forming a three‐dimensional network. This network contains Z‐shaped channels hosting the charge compensating potassium ions.     

Synthesis and crystal structure of KBi(C6H4O7) · 3.5H2O

A novel compound, KBi(C₆H₄O₇) · 3.5H₂O (I), has been synthesized in the Bi(NO₃)₂-K₃(HCit) system (HCit^3? is an anion of citric acid C₆H₈O₇) at a component ratio (n) of 8 in a water-glycerol mixture, and its crystal structure has been determined. The crystals are unstable in air. The crystals are triclinic: a = 7.462 Å, b = 10.064 Å, c = 17.582 Å, α = 100.27°, β = 99.31°, γ = 105.48°, V = 1221.2 ų, Z = 2, space group $P\bar 1$ . In the structure of I, asymmetric binuclear fragments [Bi₂(Cit^4?)₂(H₂O)₂]^2? are linked through inversion centers into polymeric chain anions. Ions K⁺ and crystal water molecules are arranged in channels between the chains. The Bi(1)...Bi(2) distances in the binuclear fragment are 4.62 Å, and the Bi(1)...Bi(1) and Bi(2)...Bi(2) distances between bismuth atoms in the chain are 5.83 and 5.95 Å, respectively. The chains are linked through bridging oxygen atoms of the ligands Cit to form layers. In the centrosymmetric four-membered chelate ring Bi₂O₂ formed through Bi-O(Cit) bonds, the distances Bi(1)-Bi(1) are equal to 4.55 Å, and Bi(1)-O are 2.66 and 2.84 Å. The Bi-O bond lengths in I are in the range 2.12–3.16 Å. The Cit ligands act as hexadentate chelating/bridging ligands.