Crystal structure of a new polar borate Na<Subscript>2</Subscript>Ce<Subscript>2</Subscript>[BO<Subscript>2</Subscript>(OH)][BO<Subscript>3</Subscript>]<Subscript>2</Subscript> · H<Subscript>2</Subscript>O with isolated boron triangles

Crystals of a new polar borate Na₂Ce₂[BO₂(OH)][BO₃]₂ · H₂O were prepared by hydrothermal synthesis. The crystals are orthorhombic, a = 7.2295(7) Å, b = 11.2523(8) Å, c = 5.1285(6) Å, Z = 2, sp. gr. C2mm (Amm2), R = 0.0253. The formula of the compound was derived from the structure determination. The Ce and Na atoms are coordinated by nine and six O atoms, respectively. The Ce position is split, and a small amount of Ce is incorporated into the Na1 site with the isomorphous substitution for Na. The anionic moieties exist as isolated BO₃ and BO₂(OH) triangles. The planes of the BO₂(OH) triangles with mm2 symmetry are parallel to the ab plane. The planes of the BO₃ triangles with m symmetry are perpendicular to the ab plane and are rotated in a diagonal way. The splitting of the Ce positions and the polar arrangement of the BO₂(OH) triangles, water molecules, and Na atoms are observed along the polar a axis. The new structure is most similar to the new borate NaCa₄[BO₃]₃ (sp. gr. Ama2), in which triangles of one type are arranged in a polar fashion along the c axis. Weak nonlinear-optical properties of both polar borates are attributed to the quenching of the second-harmonic generation due to the mutually opposite orientation of two-thirds of B triangles in the unit cell.     

Refinement of the crystal structures of synthetic nickel- and cobalt-bearing tourmalines

The crystal structures of synthetic tourmalines with a unique composition containing 3d elements (Ni, Fe, and Co) have been refined: (Ca_0.12?_0.88)(Al_1.69Ni _0.81 ²⁺ Fe _0.50 ²⁺ )(Al_5.40Fe _0.60 ³⁺ )(Si_5.82Al_0.18O₁₈)(BO₃)₃(OH)_3.25O_0.75 I, a = 15.897(5), c = 7.145(2) Å, V = 1564(1) Å; Na_0.91(Ni _1.20 ²⁺ Cr _0.96 ³⁺ Al_0.63Fe _0.18 ²⁺ Mg_0.03)(Al_4.26Ni _1.20 ²⁺ Cr _0.48 ³⁺ Ti_0.06)(Si_5.82Al_0.18)O₁₈(BO₃)₃(OH)_3.73O_0.27 II, a = 15.945(5), c = 7.208(2) Å, V = 1587(1) ų and Na_0.35(Al_1.80Co _1.20 ²⁺ )(Al_5.28Co _0.66 ²⁺ Ti_0.06)(Si_5.64B_0.36)O₁₈(BO₃)₃(OH)_3.81O_0.19 III, a = 15.753(8), c = 7.053(3) Å, V = 1516(2) ų. The reliability factors are R ₁ = 0.038?0.057 and wR ₂ = 0.041–0.060. It is found that 3d elements occupy both Y- and Z positions in all structures. The excess positive charge is compensated for due to the incorporation of divalent oxygen anions into the O3(V)+O1(W) positions.     

Polymorphism of the borophosphate anion in K(Fe,Al)[BP<Subscript>2</Subscript>O<Subscript>8</Subscript>(OH)] and Rb(Al,Fe)[BP<Subscript>2</Subscript>O<Subscript>8</Subscript>(OH)] crystal structures

The crystal structure of two borophosphates, Rb(Al,Fe)[BP₂O₈(OH)] (a = 9.381(6), b = 8.398(5), c = 9.579(6) Å, β = 102.605(10)°, sp. gr. P2₁/c) and K(Fe,Al)[BP₂O₈(OH)] (a = 5.139(2), b = 8.065(4), c = 8.290(4)Å, α = 86.841(8)°, β = 80.346(8)°, γ = 86.622(8)°, sp. gr. P \(\bar 1\)), obtained by hydrothermal synthesis in the AlCl₃: FeCl₃: K₃PO₄(Rb₃PO₄): B₂O₃: H₂O system has been established using X-ray diffraction (Bruker Smart diffractometer, T = 100 K). Hydrogen atoms are located and their coordinates and thermal parameters are refined. It is shown that the polymorphism of the [BP₂O₈(OH)]^4? borophosphate anion has a morphotropic nature and is related to the substitutions both in the cationic part of the structure and in the octahedral position of the anionic mixed framework. The synthesis of new isotypic triclinic compounds under hydrothermal conditions is predicted.     

Crystal structure of the NaCa(Fe<Superscript>2+</Superscript>, Al,Mn)<Subscript>5</Subscript>[Si<Subscript>8</Subscript>O<Subscript>19</Subscript>(OH)](OH)<Subscript>7</Subscript> · 5H<Subscript>2</Subscript>O mineral: A new representative of the palygorskite group

A specimen of a new representative of the palygorskite-sepiolite family from Aris phonolite (Namibia) is studied by single-crystal X-ray diffraction. The parameters of the triclinic (pseudomonoclinic) unit cell are as follows: a = 5.2527(2) Å, b = 17.901(1) Å, c = 13.727(1) Å, α = 90.018(3)°, β = 97.278(4)°, and γ = 89.952(3)°. The structure is solved by the direct methods in space group P \(\bar 1\) and refined to R = 5.5% for 4168 |F| > 7σ(F) with consideration for twinning by the plane perpendicular to y (the ratio of the twin components is 0.52: 0.48). The crystal chemical formula (Z = 1) is (Na_1.6K_0.2Ca_0.2)[Ca₂(Fe _3.6 ²⁺ Al_1.6Mn_0.8)(OH)₉(H₂O)₂][(Fe _3.9 ²⁺ Ti_0.1)(OH)₅(H₂O)₂][Si₁₆O₃₈(OH)₂] · 6H₂O, where the compositions of two ribbons of octahedra and a layer of Si tetrahedra are enclosed in brackets. A number of specific chemical, symmetrical, and structural features distinguish this mineral from other minerals of this family, in particular, from tuperssuatsiaite and kalifersite, which are iron-containing representatives with close unit cell parameters.     

Refinement of the crystal structures of three fluorine-bearing elbaites

The crystal structures of three Li-Al natural tourmalines (elbaites) containing 0.88–1.39 wt % F are refined to R= 0.0294, 0.0308, and 0.0417. It is revealed that the W threefold anion site is split into two sites, namely, the W1 threefold site and W2 ninefold site (W1–W2 ～ 0.4 Å, Y-W₁ ≥ 1.94 Å, Y-W2 ≥ 1.75 Å). The following hypothesis is proposed and justified: the W1 and W2 sites are partially occupied by OH groups and fluorine anions, respectively. The ratio of the [YO₄(OH)₂] octahedra to the [YO₄(OH)F] octahedra depends on the fluorine content and varies from structure to structure. The fact that the W site is more than 50% occupied by fluorine in the structures of two tourmalines under investigation allows the conclusion that fluor-elbaite with the ideal formula Na(Li_1.5A1_1.5)A1₆(Si₆O₁₈)(BO₃)₃(OH)₃F is a new mineral species and that elbaite can be considered a superspecies.     

Refinement of the crystal structure of Zn-containing greifensteinite

The crystal structure of Zn-containing greifensteinite from the Pirineus Mine (Minas Gerais, Brazil) was refined (R = 0.045, 562 reflections with |F| > 2σ(F)). The unit-cell parameters are a = 15.941(3) Å, b = 11.877(3) Å, c = 6.625(2) Å, β = 95.09(2)°; V = 1249.4 ų; sp. gr. C2/c; and Z = 2. The idealized formula is [Mn(Fe²⁺, Zn)₄]Ca₂Be₄(PO₄)₆(OH)₄ · 6H₂O. The mineral is isostructural with the previously studied monoclinic representatives of the roscherite group from different deposits and differs from these representatives in that it contains Zn in one of two octahedral positions.     

Refined structure of afwillite from the northern Baikal region

The crystal structure of the mineral afwillite [Ca₁₂(H₂O)₈][SiO₄]₄[SiO₂(OH)₂]₄ from the northern Baikal region was refined in a triclinic unit cell with the following parameters: a = 16.330(2) Å, b = 5.6389(6) Å, c = 11.685(1) Å, α = 90.08(1)°, β = 126.446(2)°, γ = 89.95(1)°, and sp. gr. P1. The triclinic unit cell is related to the monoclinic unit cell determined earlier (sp. gr. Cc, a = 16.278(1) Å, b = 5.6321(4) Å, c = 13.236(1) Å, and β = 134.898(3)°) by the transformation matrix [?100/010/101]. The structural model was determined using the phase-correction procedure and refined anisotropically to R = 2.8% based on 3270 independent reflections with F > 3σ(F). The crystal-chemical formula of afwillite was revised. The characteristic features of the IR spectrum of afwillite were explained based on the structural data.     

Crystal structure of holtite I

The crystal structure of As-containing holtite I is refined (Ital Structures diffractometer, 939 crystallographically independent reflections, anisotropic approximation, R = 0.047). The parameters of the orthorhombic unit cell are a = 4.695(1) Å, b = 11.906(3) Å, c = 20.38(3) Å, sp. gr. Pnma, Z = 4. On the whole, the structural formula obtained, (Si_2.43Sb_0.36As_0.21)BO₃[(Al_0.62Ta_0.26□)Al₂(Al_0.98□)₂(Al_0.94□)₂O₁₂](O,OH,□)_2.65, corresponds to the electron-probe analysis data. The statistical replacement of (Si,As)O₄ tetrahedra by pyramidal [SbO₃] groups is confirmed. The X-ray diffraction spectra of holtite I are compared with those of holtite II.     

Rare-earth and lead mixed anionic oxoborates

TheNd_4.5Pb_1.7(VO₄)_0.3(BO₃)O_6.42(I), Tb_4.5Pb_1.6(GeO₄)_0.4(BO₃)O_6.02(II), Dy_4.5Pb_1.68(GeO₄)_0.32(BO₃)O_6.28(III), and Ho_8.66(BO₃)₂(B₂O₅)O₈(IV) crystals were grown by spontaneous crystallization from flux and studied by the methods of X-ray diffraction analysis. The unit-cell parameters are a = 21.946, 21.590, 21.478, and 18.207 Å; b = 3.7881, 3.6565, 3.6333, and 3.6685 Å; c = 16.857, 16.618, 16.544, and 14.024 Å; β = 123.70°, 124.64°, 124.49°, and 119.81°; sp. gr. C2/m; and Z = 4, 4, 4, and 2 for I, II, III, and IV, respectively. In I–III compounds, Pb atoms, together with the atoms of group V, and Pb atoms and Ge atoms occupy the mixed positions. In structure IV, all the five independent Ho positions are occupied only partially.     

Crystal structure of (Al,V)<Subscript>4</Subscript>(P<Subscript>4</Subscript>O<Subscript>12</Subscript>)<Subscript>3</Subscript>, archetype of double cubic ring tetraphosphate

The crystal structure of the (Al,V)₄(P₄O₁₂)₃ solid solution, obtained in the single-crystal form by hydrothermal synthesis in the Al(OH)₃-VO₂-NaCl-H₃PO₄-H₂O system, has been solved by X-ray diffraction analysis (Xcalibur-S-CCD diffractometer, R = 0.0257): a = 13.7477(2) Å, sp. gr. I \(\bar 4\)3d, Z = 4, and ρ_calcd = 2.736 g/cm³. It is shown that the crystal structure of the parent cubic Al₄(P₄O₁₂)₃ modification can formally be considered an archetype for the formation of double isosymmetric tetraphosphates on its basis.     

Refinement of the crystal structure of calcium-lithium-aluminum tourmaline from the pegmatite vein in the Sangilen Upland (Tuva Republic)

The crystal structure of a natural calcium-lithium-aluminum tourmaline, which has the unique composition (Ca_0.62Na_0.32□_0.06)(Al_1.08Li_0.99Fe _0.66 ²⁺ Mg_0.24Ti_0.03)Al₆[Si₆O₁₈](BO₃)₃(OH_2.28O_0.72) · (F_0.84O_0.16), is refined (R = 0.019, R _w = 0.022, S = 1.47). It is found that the O(1)(W) site is split into two sites, O(1) and O(11), which are incompletely occupied by fluorine and oxygen anions, respectively, and that the O(3)(V) site contains bivalent oxygen anions. The solid solution studied is close in composition to the liddicoatite mineral species and differs from the latter one by the Li: Al ratio in the Y octahedra and the presence of bivalent oxygen anions in the O(3) site. The tourmaline studied differs from the hypothetical oxyliddicoatite by the population of the O(1)(W) site by fluorine and accommodation of additional oxygen anions in the O(3)(V) site.     

Na(H<Subscript>2</Subscript>O)[Mn(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>(BP<Subscript>2</Subscript>O<Subscript>8</Subscript>)]: Crystal structure refinement

The crystal structure of synthetic manganese sodium borophosphate hydrate Na(H₂O)[Mn(H₂O)₂(BP₂O₈)] was refined based on X-ray diffraction data. The compound was prepared by soft hydrothermal synthesis in the MnCl₂-Na₃PO₄-B₂O₃-H₂O system. The unit-cell parameters are a= 9.602(1) Å, c= 16.037(3) Å, sp. gr. P6₅22, Z= 6, D _x = 2.57 g/cm³. The water molecules were found to be statistically distributed in the channels of the mixed anionic paraframework consisting of (BO₄) and (PO₄) tetrahedra and [MnO₄(H₂O)₂] octahedra. The hydrogen atoms of the water molecules coordinated to the Mn²⁺ cations were located and their positional and thermal parameters were refined. The crystal-chemical features of borophosphates of the general formula A _x M(H₂O)₂(BP₂O₈)(H₂O) are considered.     

New Data on Isomorphism in Eudialyte-Group Minerals. I. Crystal Structure of Titanium-Rich Eudialyte from the Kovdor Alkaline Massif

An abnormally titanium-rich mineral of the eudialyte group was studied by IR spectroscopy and X-ray diffraction. The trigonal unit cell parameters are a = 14.165(1) Å, c = 30.600(5) Å, V = 5317.23(4) ų, sp. gr. R3m. The crystal structure was refined to R = 0.034 with anisotropic displacement parameters using 2530 reflections with F > 3σ(F). The idealized formula of the mineral (Z = 3) is Na₈(H₃O)₅(K,Ce,Sr)₂Ca₆Zr₂Ti_1.2(Fe,Mn)_0.6Si₂₆O₇₂(OH)₂Cl · 4H₂O. At the ratio Zr: Ti ~ 2: 1, titanium atoms lie in four sites and are not predominant in any of them. Another distinguishing feature of the mineral is the structural separation of chemical elements, such that K, Sr, and Ce cations and H₃O groups are randomly distributed between four split sites to form polyhedra with different volumes. The isomorphism of Zr and Ti in eudialyte-group minerals is discussed.     

Synthesis and structure of Cs[UO<Subscript>2</Subscript>(SeO<Subscript>4</Subscript>)(OH)] · <Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O (<Emphasis Type="Italic">n</Emphasis> = 1.5 or 1)

The synthesis and single-crystal X-ray diffraction study of Cs[UO₂(SeO₄)(OH)] · 1.5H₂O (I) and Cs[UO₂(SeO₄)(OH)] · H₂O (II) are performed. Compound I crystallizes in the monoclinic crystal system, a = 7.2142(2) Å, b = 14.4942(4) Å, c = 8.9270(3) Å, β = 112.706(1)°, space group P2₁/m, Z = 4, and R = 0.0222. Compound II is monoclinic, a = 8.4549(2) Å, b = 11.5358(3) Å, c = 9.5565(2) Å, β = 113.273(1)°, space group P2₁/c, Z = 4, and R = 0.0219. The main structural units of crystals I and II are [UO₂(SeO₄)(OH)]^? layers which belong to the AT ³ M ² crystal chemical group of uranyl complexes (A = UO ₂ ²⁺ , T ³ = SeO₄ ^2?, and M ² = OH^?). In structure I, johannite-like layers are found. Structure II is a topological isomer of I. The two structures differ in the number of U(VI) atoms bound to the central atom by all bridging ligands.     

Pyroxenoids of pyroxmangite–pyroxferroite series from xenoliths of Bellerberg paleovolcano (Eifel,Germany): Chemical variations and specific features of cation distribution

The pyroxferroite and pyroxmangite from xenoliths of aluminous gneisses in the alkaline basalts of Bellerberg paleovulcano (Eifel, Germany) have been studied by electron-probe and X-ray diffraction methods and IR spectroscopy. The parameters of the triclinic unit cells are found to be a = 6.662(1) Å, b = 7.525(1) Å, c = 15.895(2) Å, α = 91.548(3)°, β = 96.258(3)°, and γ = 94.498(3)° for pyroxferroite and a = 6.661(3) Å, b = 7.513(3) Å, c = 15.877(7) Å, α = 91.870(7)°, β = 96.369(7)°, and γ = 94.724(7)° for pyroxmangite; sp. gr. \(P\overline 1 \). The crystallochemical formulas (Z = 2) are, respectively, ^M(1–2)(Mn_0.5Ca_0.4Na_0.1)₂^M(3–6)(Fe, Mn)₄^M7[Mg_0.6(Fe, Mn)_0.4][Si₇O₂₁] and ^M(1–3)(Mn, Fe)₃^M(4–6)[(Fe, Mn)_0.7Mg_0.3]₃^M7[Mg_0.5(Fe, Mn)_0.5][Si₇O₂₁]. For these and previously studied representatives of the pyroxmangite structural type, an analysis of the cation distribution over sites indicates wide isomorphism of Mn²⁺, Fe²⁺, and Mg in all cation M(1–7) sites and the preferred incorporation of Сa and Na into large seven-vertex M1O₇ and M2O₇ polyhedra and Mg into the smallest five-vertex M7O₅ polyhedron.     

Crystal chemistry of KCuMn<Subscript>3</Subscript>(VO<Subscript>4</Subscript>)<Subscript>3</Subscript> in the context of detailed systematics of the alluaudite family

The crystal structure of new manganese potassium copper vanadate KCuMn₃(VO₄)₃, which was prepared by the hydrothermal synthesis in the K₂CO₃–CuO–MnCl₂–V₂O₅–H₂O system, was studied by X-ray diffraction (R = 0.0355): a = 12.396(1) Å, b = 12.944(1) Å, c = 6.9786(5) Å, β = 112.723(1)°, sp. gr. C2/c, Z = 4, ρ_calc = 3.938 g/cm³. A comparative analysis of the crystal-chemical features of the new representative of the alluaudite family and related structures of minerals and synthetic phosphates, arsenates, and vanadates of the general formula A(1)A(1)′A(1)″A(2)A(2)′M(1)M(2)₂(TO₄)₃ (where A are sites in the channels of the framework composed of MО₆ octahedra and TО₄ tetrahedra) was performed. A classification of these structures into subgroups according to the occupancy of A sites is suggested.     

Structural characteristics of Na,Fe-decationated eudialyte with the symmetry <Emphasis Type="Italic">R</Emphasis>3

The crystal structure of a new highly decationated representative of the eudialyte group has been established (R = 0.055, 1734 |F|). The mineral is described by the simplified formula (H₃O)₉Na₂(K, Ba,Sr)₂Ca₆Zr₃[Si₂₆O₆₆(OH)₆](OH)₃Cl · H₂O (Z = 3). The unit-cell parameters are a = 14.078(3) Å, c = 31.24(1) Å; V = 5362 ų; sp. gr. R3. Being chemically and structurally related to the hydrated analogues studied previously (in particular, to potassium oxonium eudialyte), the new mineral differs from its analogues in that it has a higher degree of Na-and Fe-cation depletion. The replacement of 3/4 of Na cations by loose and mobile H₃O groups results in structure destabilization, which is seen from the high values of the thermal parameters of the atoms and the loss of the symmetry plane.     

Crystal structure of zinc(II) hydrated trinuclear complex with monoprotonated ethylenediaminetetraacetate anion(3−), [Zn<Subscript>3</Subscript>(H<Emphasis Type="Italic">Edta</Emphasis>)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)<Subscript>6</Subscript>]

The crystal structure of the [Zn₃(HEdta)₂(H₂O)₆] complex (I) is determined by X-ray diffraction analysis. The crystals are orthorhombic, a = 14.780 Å, b = 29.699 Å, c = 7.032 Å, Z = 4, and space group Pna2₁. The structural units of crystals I are trinuclear linear molecules, in which the peripheral atoms Zn(1) and Zn(2) each coordinate two N atoms and three O atoms of the HEdta ^3? ligand and the O(w) atom of the H₂O molecule, whereas the central Zn(3) atom coordinates four O(w) atoms of the H₂O molecules and two terminal O atoms of the two HEdta ^3? ligands. The HEdta ^3? ligand fulfills a hexadentate chelating—bridging function. The bond lengths are as follows: Zn-O(HEdta), 2.006(4)–2.123(4) Å; Zn-N, 2.214(6) and 2.128(5) Å; and Zn-O(w), 2.006(6)–2.225(5) Å. In structure I, there is a specific contact formed by hydrogen bonds, owing to which the distance between the central atoms of individual molecules appears to be shorter than that in covalently bonded complexes.     

X-ray diffraction study of Rb<Subscript>2</Subscript>[(UO<Subscript>2</Subscript>)<Subscript>2</Subscript>(CrO<Subscript>4</Subscript>)<Subscript>3</Subscript>(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>] · 4H<Subscript>2</Subscript>O

The compound Rb₂[(UO₂)₂(CrO₄)₃(H₂O)₂] · 4H₂O was studied by X-ray diffraction. The crystals are monoclinic, a = 10.695(2) Å, b = 14.684(3) Å, c = 14.125(3) Å, β = 108.396(4)°, sp. gr. P2₁/c, Z = 4, V = 2104.9(7) ų, and R = 0.0491. The main structural units are layers consisting of [(UO₂)₂(CrO₄)₃(H₂O)₂]^2? anions belonging to the crystal-chemical group A ₂ T ₂ ³ B ²M ₂ ¹ (A = UL ₂ ²⁺ , T ³ and B ² are CrO ₄ ^2? , and M ¹ is H₂O) of uranyl complexes. The uranium-containing layered groups are held together by electrostatic interactions with rubidium cations, as well as by hydrogen bonds with the participation of inner- and outer-sphere water molecules.     

Crystal Structure of a Nickel(II) Complex with the Macrocyclic Azadibenzo-14-crown-4 Ether Ligand Containing the Embedded Di(α-pyridyl)bispidone Moiety

The crystal structure of the nickel(II) complex with substituted azadibenzo-14-crown-4 ether containing the embedded di(α-pyridyl)bispidone moiety having the formula [L(H₂O)Ni(NO₃) Ni(H₂O)L](ClO₄)₃ · 0.7EtOH was studied by X-ray diffraction (T = 150(2) K, R = 0.0628). In the complex cation two five-coordinate nickel complexes are bridged by the nitrate anion to form a dimer. The distorted octahedral environment of Ni atoms is formed by four nitrogen atoms of the molecule L and the oxygen atoms of the water molecule and the NO ₃ ^- anion. In the nickel complex, like in the cobalt and copper complexes studied previously, the bispidine moiety of the molecule L adopts a chair-chair conformation.