Two Hexagonal Series of Lanthanoid(III) Oxide Fluoride Selenides: M6O2F8Se3 (M = La – Nd) and M2OF2Se (M = Nd,Sm, Gd – Ho)

Two hexagonal series of lanthanoid(III) oxide fluoride selenides with similar structure types can be obtained by the reaction of the components MF₃, M₂O₃, M, and Se in sealed niobium tubes at 850 °C using CsI as fluxing agent. The compounds with the lighter and larger representatives (M = La – Nd) occur with the formula M₆O₂F₈Se₃, whereas with the heavier and smaller ones (M = Nd, Sm, Gd – Ho) their composition is M₂OF₂Se. For both systems single‐crystal determinations were used in all cases. The compounds crystallize in the hexagonal crystal system (space group: P6₃/m) with lattice parameters of a = 1394–1331 pm and c = 403–372 pm (Z = 2 for M₆O₂F₈Se₃ and Z = 6 for M₂OF₂Se). The (M1)³⁺ cations show different square antiprismatic coordination spheres with or without an extra capping fluoride anion. All (M2)³⁺ cations exhibit a ninefold coordination environment shaped as tricapped trigonal prism. In both structure types the Se^2– anions are sixfold coordinated as trigonal prisms of M³⁺ cations, being first condensed by edges to generate trimeric units and then via faces to form strands running along [001]. The light anions reside either in threefold triangular or in fourfold tetrahedral cationic coordination. For charge compensation, both structures have to contain a certain amount of oxide besides fluoride anions. Since F^– and O^2– can not be distinguished by X‐ray diffraction, bond‐valence calculations were used to address the problem of their adjunction to the available crystallographic sites.     

Crystal Growth and Structure Determination of Pigment Orange 82

The crystal structure of the important industrial orange pigment PO82, major part of the BASF Colors & Effects^® product Sicopal^® Orange K/L 2430, was solved from combined X‐ray single crystal, X‐ray and neutron powder diffraction, ¹¹⁹Sn Mössbauer spectroscopy, transmission electron microscopy, electron diffraction, and chemical analyses. The structure contains Keggin type clusters composed of four [M₃O₁₃] trimers consisting each of three MO₆ octahedra that share edges and one common oxygen atom connecting the trimers to the central ZnO₄ tetrahedron. The octahedrally coordinated metal atom position is mixed occupied by Ti⁴⁺, Sn⁴⁺, and Zn²⁺. Adjacent Keggin clusters share vertices and are further interconnected to four ZnO₄ tetrahedra. This framework of interconnected MO₆ octahedra and ZnO₄ tetrahedra contains channels along [110], in which the Sn²⁺ cations are located.     

Cd2Cu(PO4)2

During an investigation of the insufficiently known system M1O–M2O–X₂O₅–H₂O (M1 = Cd²⁺, Sr²⁺ and Ba²⁺; M2 = Cu²⁺, Ni²⁺, Co²⁺, Zn²⁺ and Mg²⁺; X = P⁵⁺, As⁵⁺ and V⁵⁺), single crystals of the novel compound dicadmium copper(II) bis[phosphate(V)], Cd₂Cu(PO₄)₂, were obtained. This compound belongs to a small group of compounds adopting a Cu₃(PO₄)₂‐type structure and having the general formula M1₂M2(XO₄)₂ (M1/M2 = Cd²⁺, Cu²⁺, Mg²⁺ and Zn²⁺; X = As⁵⁺, P⁵⁺ and V⁵⁺). The crystal structure is characterized by the interconnection of infinite [Cu(PO₄)₂]_n chains and [Cd₂O₁₀]_n double chains, both extending along the a axis. Exceptional characteristics of this structure are its novel chemical composition and the occurrence of double chains of CdO₆ polyhedra that were not found in related structures. In contrast to the isomorphous compounds, where the M1 cations are coordinated by five O atoms, the Cd atom is coordinated by six. The dissimilarity in the geometry of M1 coordination between Cd₂Cu(PO₄)₂ and the isomorphous compounds is mostly due to the larger ionic radius of the Cd cation in comparison with the Cu, Mg and Zn cations. Sharing a common edge, two CdO₆ polyhedra form Cd₂O₁₀ dimers. Each such dimer is bonded to another dimer sharing common vertices, forming [Cd₂O₁₀]_n double chains in the [100] direction. The Cu atoms, located on an inversion centre (site symmetry ), form isolated CuO₄ squares interconnected by PO₄ tetrahedra, forming [Cu(PO₄)₂]_n chains similar to those found in related structures. Conversely, the [Cd₂O₁₀]_n double chains, which were not found in related structures, are an exclusive feature of this structure.     

Hierarchical Modulation of Optical Anisotropy Driven by Metal Cation Polyhedra in Fluorooxoborates MIIB4O6F2 (MII=Be,Mg, Pb,Zn, Cd)

The enhancement mechanism of birefringence is very important to modulate optical anisotropy and materials design. Herein, the different cations extending from alkaline-earth to alkaline-earth, d¹⁰ electron configuration, and 6s² lone pair cations are highlighted to explore the influence on the birefringence. A flexible fluorooxoborate framework from AEB₄O₆F₂ (AE=Ca, Sr) is adopted for UV/deep-UV birefringent structures, namely, M^IIB₄O₆F₂ (M^II=Be, Mg, Pb, Zn, Cd). The maximal enhancement on birefringence can reach 46.6 % with the cation substitution from Ca, Sr to Be, Mg (route-I), Pb (route-II), and Zn, Cd (route-III). The influence of the cation size, the stereochemically active lone pair, and the binding capability of metal cation polyhedra is investigated for the hierarchical improvement on birefringence. Significantly, the BeB₄O₆F₂ structure features the shortest UV cutoff edge 146 nm among the available anhydrous beryllium borates with birefringence over 0.1 at 1064 nm, and the PbB₄O₆F₂ structure has the shortest UV cutoff edge 194 nm within the reported anhydrous lead borates that hold birefringence larger than 0.1 at 1064 nm. This work sheds light on how metal cation polyhedra modulate birefringence, which suggests a credible design strategy to obtain desirable birefringent structures by cation control.     

Comparaison des champs de force des niobates,tantalates et antimoniates de structure columbite et trirutile

A comparison is made between the force fields calculated for the M^IINb^V₂O₆ and M^IITa^V₂O₆ columbite series and the M^IITa^V₂O₆ and M^IISb^V₂O₆ trirutile series. The trirutile structure is shown to be particularly more rigid than the columbite structure. For this reason, the trirutile structure exists only for divalent cations of small size. The stability of the two structures and their relative modifications are then compared. From a comparison of the vibrational spectra of the rutile FeSbO₄ with those of the trirutile MSb₂O₆ compounds, a short-range order in the rutile structure is proposed.     

Relative stabilities of layered perovskite and pyrochlore structures in transition metal oxides containing trivalent bismuth

In order to investigate the factors determining the relative stabilities of layered perovskite and pyrochlore structures of transition metal oxides containing trivalent bismuth, several ternary and quaternary oxides have been investigated. While d⁰ cations stabilize the layered perovskite structure, cations containing partially-filled d orbitals (which suppress ferroelectric distortion of MO₆ octahedra) seem to favor pyrochlore-related structures. Thus, the vanadium analogue of the layered perovskite Bi₄Ti₃O₁₂ cannot be prepared; instead the composition consists of a mixture of pyrochlore-type Bi_1.33V₂O₆, Bi₂O₃, and Bi metal. The distortion of Bi_1.33V₂O₆ to orthorhombic symmetry is probably due to an ordering of anion vacancies in the pyrochlore structure. None of the other pyrochlores investigated, Bi₂NbCrO₇, Bi₂NbFeO₇, TlBiM₂O₇ (M = Nb, Ta), shows evidence for cation ordering in the X-Ray diffraction patterns, as indeed established by structure refinement of TlBiNb₂O₇.     

Sc2Te5O13 und Sc2TeO6: Die ersten Oxotellurate des Scandiums

Sc₂Te₅O₁₃ and Sc₂TeO₆: The First Oxotellurates of Scandium Sc₂Te₅O₁₃ and Sc₂TeO₆ are the first oxotellurates of scandium that could be structurally elucidated by X‐ray diffraction using single crystals. The scandium(III) oxotellurate(IV) Sc₂Te₅O₁₃ was synthesized by reacting Sc₂O₃ with TeO₂ at 850 °C and crystallizes in the triclinic system with space group (no. 2) and the lattice parameters a = 660.67(5), b = 855.28(7), c = 1041.10(9) pm, α = 86.732(8), β = 86.264(8), and γ = 74.021(8)° (Z = 2). The crystal structure contains chains respectively strands of alternatingly edge‐ and vertex‐sharing [ScO₆]^9? and [ScO₇]^11? polyhedra. These strands are connected by [TeO₃₊₁]^(2+2)? oxotellurate(IV) anions. The coordination spheres of Sc³⁺ appear markedly smaller than those of M³⁺ cations in the other known compounds of the formula type M₂Te₅O₁₃ (M = Y, Dy – Lu), therefore Sc₂Te₅O₁₃ is not really isotypic, but only isopuntal with these compounds. Single crystals of the scandium(III) oxotellurate(VI) Sc₂TeO₆ were obtained through the fusion of a mixture of Sc₂O₃ and TeO₃ at 850 °C. It crystallizes trigonally (a = 874.06(7), c = 479.85(4) pm and c/a = 0.549) with the Na₂SiF₆‐type structure in space group P321 (no. 150) and three formula units per unit cell. Its crystal structure is built up by a hexagonal closest packing (hcp) of oxide anions with the Sc³⁺ cations residing in ¹/₃ and the Te⁶⁺ cations in ¹/₆ of the octahedral interstices in a well‐ordered occupation pattern. Thus one can address the structural situation in Sc₂[TeO₆] as a stuffed β‐WCl₆‐type arrangement.     

M+M3+2As(HAsO4)6 and α‐ and β‐M+M3+(HAsO4)2 (M+M3+ = RbAl or CsFe): six new compounds crystallizing in three closely related structure types

The crystal structures of hydrothermally synthesized (T = 493 K, 7–9 d) rubidium aluminium bis[hydrogen arsenate(V)], RbAl(HAsO₄)₂, caesium iron bis[hydrogen arsenate(V)], CsFe(HAsO₄)₂, rubidium dialuminium arsenic(V) hexakis[hydrogen arsenate(V)], RbAl₂As(HAsO₄)₆, and caesium diiron arsenic(V) hexakis[hydrogen arsenate(V)], CsFe₂As(HAsO₄)₆, were solved by single‐crystal X‐ray diffraction. The four compounds with the general formula M⁺M³⁺(HAsO₄)₂ adopt the RbFe(HPO₄)₂ structure type (Rc) and a closely related new structure type, which is characterized by a different stacking order of the building units, leading to noncentrosymmetric space‐group symmetry R32. The second new structure type, with the general formula M⁺M³⁺₂As(HAsO₄)₆ (Rc), is also a modification of the RbFe(HPO₄)₂ structure type, in which one third of the M³⁺O₆ octahedra are replaced by AsO₆ octahedra, and two thirds of the voids in the structure, which are usually filled by M⁺ cations, remain empty to achieve charge balance.     

Pyroxene‐type compounds NaM3+Ge2O6, with M = Ga,Mn, Sc and In

The four title compounds, namely sodium gallium germanate, NaGaGe₂O₆, sodium manganese vanadate germanate, NaMnV_0.1Ge_1.9O₆, sodium scandium germanate, NaScGe₂O₆, and sodium indium germanate, NaInGe₂O₆, adopt the high‐temperature structure of the pyroxene‐type chain germanates, with monoclinic symmetry and space group C2/c. The lattice parameters, the individual and average bond lengths involving M1, and the distortion parameters scale well with the ionic radius of the M1 cation. NaGaGe₂O₆ has more distorted M1 sites and more extended tetrahedral chains than NaInGe₂O₆, in which a high degree of kinking is required to maintain the connection between the octahedral and tetrahedral building units of the pyroxene structure. An exceptional case is NaMnGe₂O₆, in which the strong Jahn–Teller effect of Mn³⁺ results in more distorted octahedral sites than expected according to linear extrapolation from the other NaM³⁺Ge₂O₆ pyroxenes. In contrast with the literature, minor incorporations of V⁵⁺ in the tetrahedral site and a corresponding reduction of Mn³⁺ to Mn²⁺ in the octahedral sites in the present sample lower the Jahn–Teller distortion and stabilize the Mn‐bearing pyroxene, even allowing its synthesis at ambient pressure.     

An investigation of polyhedral deformation in two mixed‐metal diarsenates: SrZnAs2O7 and BaCuAs2O7

Two isostructural diarsenates, SrZnAs₂O₇ (strontium zinc diarsenate), (I), and BaCuAs₂O₇ [barium copper(II) diarsenate], (II), have been synthesized under hydrothermal conditions and characterized by single‐crystal X‐ray diffraction. The three‐dimensional open‐framework crystal structure consists of corner‐sharing M2O₅ (M2 = Zn or Cu) square pyramids and diarsenate (As₂O₇) groups. Each As₂O₇ group shares its five corners with five different M2O₅ square pyramids. The resulting framework delimits two types of tunnels aligned parallel to the [010] and [100] directions where the large divalent nine‐coordinated M1 (M1 = Sr or Ba) cations are located. The geometrical characteristics of the M1O₉, M2O₅ and As₂O₇ groups of known isostructural diarsenates, adopting the general formula M1^IIM2^IIAs₂O₇ (M1^II = Sr, Ba, Pb; M2^II = Mg, Co, Cu, Zn) and crystallizing in the space group P2₁/n, are presented and discussed.     

Cations in a Molecular Funnel: Vibrational Spectroscopy of Isolated Cyclodextrin Complexes with Alkali Metals

The benchmark inclusion complexes formed by α‐cyclodextrin (αCD) with alkali‐metal cations are investigated under isolated conditions in the gas phase. The relative αCD‐M⁺ (M=Li⁺, Na⁺, K⁺, Cs⁺) binding affinities and the structure of the complexes are determined from a combination of mass spectrometry, infrared action spectroscopy and quantum chemical computations. Solvent‐free laser desorption measurements reveal a trend of decreasing stability of the isolated complexes with increasing size of the cation guest. The experimental infrared spectra are qualitatively similar for the complexes with the four cations investigated, and are consistent with the binding of the cation within the primary face of the cyclodextrin, as predicted by the quantum computations (B3LYP/6‐31+G*). The inclusion of the quantum‐chemical cation disrupts the C₆ symmetry of the free cyclodextrin to provide the optimum coordination of the cations with the ‐CH₂OH groups in C₁, C₂ or C₃ symmetry arrangements that are determined by the size of the cation.     

(H3O)3Sb2Br9: the first member of the M3E2X9 structure family with oxonium cations

(H₃O)₃Sb₂Br₉ [trihydroxonium enneabromidodiantimonate(III)] is the first representative of the M₃E₂X₉ family (M = cation, E = Sb and Bi, and X = Br and I) with oxonium cations. The metastable compound was obtained in trace amounts from a solution of CsBr and SbBr₃ in concentrated aqueous HBr. Single crystals were isolated from the mother liquor and investigated by single‐crystal X‐ray diffraction at 100 K. (H₃O)₃Sb₂Br₉ crystallizes with the Tl₃Bi₂I₉ structure type, which is a distorted defect variant of cubic perovskite. The crystal structure comprises characteristic ²_∞[SbBr₃Br_3/2] double layers of corner‐sharing SbBr₆ octahedra with a [001] stacking direction. Due to the small size of the H₃O⁺ cation and O—H…Br hydrogen bonding, the octahedra are tilted.     

Crystal Growth and Crystal Structures of Gold(V) Compounds: Cu(AuF6)2, Ag(AuF6)2, and O2(CuF)3(AuF6)4 ⋅ HF

Crystal growth from anhydrous hydrogen fluoride solutions of M²⁺ (M=Cu, Ag) and [AuF₆]⁻ gave M(AuF₆)₂ salts (M=Cu, Ag). Similar attempts to prepare single crystals of the corresponding nickel, zinc and magnesium salts failed. The crystal structure of Cu(AuF₆)₂ consists of layers of Cu²⁺ cations connected by [AuF₆]⁻ anions, thus forming slabs. Only van der Waals interactions exist between adjacent slabs. The crystal structure of Ag(AuF₆)₂ consists of a three-dimensional framework in which Ag⁺ cations are linked by [AuF₆]⁻ anions. Both structures are members of the M^II(X^VF₆)₂ family, in which seven different structure types have been observed to date. In the crystal structure of O₂(CuF)₃(AuF₆)₄ ⋅ HF, the bridging AuF₆ units connect [−Cu−F−Cu−F−]_∞ chains to form stacks between which O₂⁺ cations and HF molecules are located.     

AgCo3PO4(HPO4)2

The structure of the hydro­thermally synthesized compound AgCo₃PO₄(HPO₄)₂, silver tricobalt phosphate bis­(hydrogen phosphate), consists of edge‐sharing CoO₆ chains linked together by the phosphate groups and hydrogen bonds. The three‐dimensional framework delimits two types of tunnels which accommodate Ag⁺ cations and OH groups. The title compound is isostructural with the compounds AM₃H₂(XO₄)₃ (A = Na or Ag, M = Co or Mn, and X = P or As) of the alluaudite structure type.     

Intergrowth in tunnel structures: The titanates A2Ti6O13)n·A′Ti4Og

A new structural family, (A₂M₆O₁₃)_n·A′M₄O₉, was isolated and studied by means of X-ray diffraction, electron diffraction, and electron microscopy. The structure consists of an ordered intergrowth of two types of structural units: A₂Ti₆O₁₃ and hypothetical A′M₄O₉, both characterized by zigzag ribbons of, respectively, 2 × 3 and 2 × 2 edge-sharing octahedra, joined by corner sharing to form a series of open tunnels containing A and A′ cations. The monoclinic unit-cell parameters can be deduced, for an “n” term, from those of A₂Ti₆O₁₃.     

The six-layer structure of BaSn0.9Fe5.47O11

The crystal structure of BaSn_0.9Fe_5.47O₁₁ was determined using neutron powder diffraction data and the profile refinement method. The hexagonal compound, space group , has hcc-stacked BaO₃ and O₄ layers. A new building unit for this type of structure is introduced, the Q block with formula Ba₂M₇O₁₄, consisting of two c-stacked BaO₃ layers and two O₄ layers. Between the BaO₃ and O₄ layers one tetrahedral and one octahedral site is occupied; between the BaO₃ layers there are no other cations. BaSn_0.9Fe_5.47O₁₁ shows a magnetic behavior with an ordering temperature T_c of 420 K. Starting models for the structure determination were derived from the known structures of hexagonal ferrites and related compounds. Several isomorphs with formula Ba₂Sn₂M²⁺Fe₁₀O₂₂ could be prepared, in which a partial substitution of Fe by Ga is possible. The nonstoichiometry of BaSn_0.9Fe_5.47O₁₁ can be explained by the surplus of positive charge if the available tetrahedral and octahedral sites of the structure are completely occupied with Sn⁴⁺ and Fe³⁺. To achieve charge compensation either the occupation rates of Sn⁴⁺ and Fe³⁺ have to be lowered or a divalent ion has to be introduced, as is effected in the isomorphs.     

A non‐twinned polymorph of CaTe2O5 from a hydrothermally grown crystal

In contrast with the multiple twinning and/or domain formation found in the mica‐like polymorphs of CaTe₂O₅, calcium pentaoxidoditellurate(IV), that have been prepared by solid‐state reactions and for which complete structure determinations have not been successful up to now, the crystal structure of a hydrothermally grown phase was fully determined from a non‐twinned crystal. The structure is made up of alternating layers of Ca²⁺ cations and of ²_∞[Te₂O₅]²⁻ anions stacked along [100]. The lone‐pair electrons E of the Te^IV atoms are stereochemically active and protrude into channels within the anionic layer. In comparison with analogous M^IITe₂O₅ structures (M = Mg, Mn, Ni or Cu) with ditellurate(IV) anions that are exclusively made up of corner‐sharing TeO_x (x = 3–5) polyhedra resulting in flat ²_∞[Te₂O₅]²⁻ layers, the anionic layers in CaTe₂O₅ are undulating and are built of corner‐ and edge‐sharing [TeO₄] polyhedra.     

Structure and 31P NMR spectroscopy of a new phosphate,Na8Ca1.5Mg12.5(PO4)12

A new phosphate, sodium calcium magnesium tetrakis(phosphate), Na₈Ca_1.5Mg_12.5(PO₄)₁₂, has been synthesized by a flux method. Its novel structure consists of MgO_x (x = 5 and 6) polyhedra and MO₇ (M = Mg or Na) octahedra linked directly through common corners or edges to form a rigid three‐dimensional skeleton, reinforced by corner‐sharing between identical Mg₁₂MO₄₈ units. The connection of these units by the PO₄ tetrahedra induces cavities and crossing tunnels where the Na⁺ and Ca²⁺ cations are located. This structural model was supported by a ³¹P NMR spectroscopy study which confirmed the existence of 12 crystallographically independent sites for the P atoms.     

Über Oxotantalate der Lanthanide des Formeltyps MTaO4 (M = La – Nd,Sm – Lu)

About Lanthanide Oxotantalates with the Formula MTaO₄ (M = La – Nd, Sm – Lu) Besides being a by‐product of solid state syntheses in tantalum ampoules the lanthanide(III) oxotantalates of the formula MTaO₄ can be easily prepared by sintering lanthanide sesquioxide M₂O₃ and tantalum(V) oxide Ta₂O₅ with sodium chloride as flux. Under these conditions two structure types emerge depending upon the M³⁺ cationic radius. For M = La – Pr the MTaO₄‐type tantalates crystallize in the space group P2₁/c with lattice constants of a = 762(±1), b = 553(±4), c = 777(±4) pm, β = 101(±1)° and four formula units per unit cell. With M = Nd, Sm – Lu, the monoclinic cell dimensions (space group P2/c) shrink to the lattice constants like a = 516(±9), b = 551(±9), c = 534(±9) pm, β = 96.5(±0.3)° and there are only two formula units present. Both structures show a coordination sphere of eight oxygen atoms for the lanthanide trications shaped as distorted square antiprism for the structure with the larger lanthanides (in the following referred to as A‐type) and as trigonal dodecahedron for the structure with the smaller ones (called as B‐type in the following). The coordination environment about the Ta⁵⁺ cations can be described as a slightly distorted octahedron (CN = 6) for the A‐type structure of MTaO₄ and a heavily distorted one (CN = 6) for the B‐type. The difference between the two types results from the interconnection of these [TaO₆]^7? octahedra. Whereas they are connected via four vertices to form corrugated layers according to parallel the bc‐plane in the A‐type, the octahedra of the B‐type MTaO₄ structure share edges to built up zig‐zag chains along the c axis.     

K2M(H2P2O7)2·2H2O (M = Ni,Cu, Zn): ortho­rhom­bic forms and Raman spectra

The crystal structures of three isotypic ortho­rhom­bic dihydrogendiphosphates, namely dipotassium copper(II)/nickel(II)/zinc(II) bis­(dihydrogendiphosphate) dihydrate, K₂M(H₂P₂O₇)₂·2H₂O (M = Cu, Ni and Zn), have been refined from single‐crystal data. The M²⁺ and K⁺ cations are located at sites of m symmetry, and the P atoms occupy general positions. These compounds also exist in triclinic forms with very similar structural features. The structures of both forms are compared, as well as the geometry of the MO₆ octa­hedron, which is considerably elongated towards the water mol­ecules for M = Ni and Cu. Such elongation has not been observed among the other representatives of the family. A Raman study of the whole series K₂M(H₂P₂O₇)₂·2H₂O (M = Mn, Co, Ni, Cu, Zn and Mg) is reported.