Comparative Crystal-chemical Analysis Research Articles

Non-ambient crystal chemistry of stillwellite-like BaBPO<SUB>5</SUB> from single crystal XRD data

Stillwellite-(Ce) and some its synthetic analogues tend to undergo phase transition from polar (ferroelectric) to nonpolar (paraelectric) modification on heating. However, the reasons for the transition and phase stability remain the subject of scientific debate. Here we present detail studies (scanning electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy and single-crystal X-ray diffraction (SCXRD)) of hydrothermally grown BaBPO5 isostructural with stillwellite-(Ce). Its thermal behavior was studied by an in situ low- (from –173 to +25 °C) and high-temperature (HT; 25–800 °C) SCXRD. Fully ordered crystal structure of BaBPO5 (at T = 25 °C: trigonal, P3221, a = 7.1166(1) Å, c = 7.0011(1) Å, V = 307.07(1) Å3, R1 = 1.42 %) does not exhibit any change of symmetry upon cooling / heating unlike natural stillwellite-(Ce). Thermal expansion of BaBPO5 is almost isotropic (αmin = 8.4, αmax = 8.7⋅10-6 °C-1) despite the chain nature of borophosphate anion. The comparative crystal chemical analysis of HT behavior of cationic polyhedra in the stillwellite-family members is presented.

Sol—Gel Synthesis and Structure Formation of Manganese Zirconium (Titanium) Phosphates

Compounds Mn0.5Ti2(PO4)3 and Mn0.5Zr2(PO4)3 and Mn0.5+2xZr2 – x(PO4)3 (0 < x ≤0.35) solid solution were prepared by two variants of the sol-gel method using inorganic and organic reagents and were characterized using X-ray diffraction and IR spectroscopy. Mn0.5Ti2(PO4)3, a compound with an NaZr2(PO4)3 (NZP) structure, is formed at 600°C and is stable up to 950°C. Mn0.5Zr2(PO4)3 has dimorphism; its low-temperature phase having the Sc2(WO4)3 (SW) structure was prepared at 650°C, and the high-temperature NZP phase, at 1200°C. Mn0.5 + 2xZr2−x(PO4)3 solid solution crystallizes in an SW-type structure; it is thermally unstable at temperatures above 900°C. The thermal stability of samples decays as x rises. p ]The numbers of the stretching and bending vibrations in an $${\rm{PO}}_4^{3 - }$$ ion in the IR spectra of NZP and SW ortho-phosphates agree with factor-group analysis for space group R3 and P21/n. Structure refinement was carried out for the low-temperature Mn0.5Zr2(PO4)3 phase (space group P21/n, a = 8.861(3) A, b = 8.869(2) A, c = 12.561(3) A, β = 89.51(2)°) and for the solid solution. The basis of the structures is a framework built of corner-sharing tetrahedra PO4 and octahedra ZrO6 or (Mn,Zr)O6. The framework interstices are occupied by cations Mn2+ in tetrahedral oxygen coordination. A comparative crystal-chemical analysis of the morpho-tropic series of M0.5Zr2(PO4)3 phosphates (M stands for a metal in the oxidation state +2) elucidated a relationship between structural features.

Jahn–Teller Effect in the [CuEn3]CrO4 Structure

A change in the coordination of the copper atom in the crystal structure of [CuEn3]CrO4 (En is ethylenediamine) in studied in the range 150–300 K. According to the single crystal X-ray diffraction (XRD) data at 150 K, the single crystal has a complicated twining character based on the triclinic cell (a = 9.027(2) A, b = 13.335(3) A, c = 13.339(3) A, α = 71.77(3)°, β = 70.53(3)°, γ = 70.42(3)°) composed of two crystallographically independent [CuEn3]2+ complex cations. The coordination of copper atoms is a distorted square bipyramid; four short Cu–N distances lie in the range 2.049-2.082 A; two long ones are 2.415 A and 2.470 A. According to the differential scanning calorimetry (DSC) data, near 218 K there is a phase transition. The single crystal XRD experiment performed at 250 K (a = 15.6992(19) A, c = 9.7573(13) A, V = 2082.6(6) A3, space group P\(\bar 3\)c1 (No. 165), Z = 6) shows that chromate anions are disordered over three positions about the с axis, and Cu–N distances are 2.120-2.177 A. According to the DSC data, on further heating the structure undergoes yet another two alterations (260 K and 270 K) due to the disordering of oxygen atoms of chromate anions and the subsequent equalization of Cu–N distances. At 300 K in the structure (a = 9.0778(6) A, c = 9.7715(5) A, V = 697.4 A3, space group P\(\bar 3\)c (No. 163), Z = 2) all Cu–N distances are 2.155 A, and chromate anions are disordered over six positions about the с axis. A comparative crystal chemical analysis of the packing of the studied structures is carried out.

Conditions for the formation of a non-autonomous phase at the structural deformation of complex vanadium oxides

A new previously unknown effect of a reversible transition from a single-phase system to a heterophase system containing a non-autonomous phase was observed during thermal and chemical deformations of the Zn2-2xCd2xV2O7 structure.The role of local symmetry in the formation of the non-autonomous phase is shown on the basis of X-ray diffraction studies in situ and a comparative crystal-chemical analysis of the structural deformations of isoform monoclinic solid solutions of zinc and copper pyrovanadates with zero volumetric thermal expansion.

X-ray diffraction study of the monoclinic modification of [Cu(NH3)4](ReO4)2 in the range 100-410 K

The monoclinic modification of [Cu(NH3)4](ReO4)2 complex salt in the range 100-410 K is studied by single crystal X-ray diffraction. The crystallographic data for 300 K are as follows: a = 10.6123(3) A, b = 7.5443(2) A, c = 15.2261(4) A, β = 108.406(1)°, V = 1156.67(5) A3, space group Р21/n, Z = 4, dx = 3.623 g/cm3. The coordination environment of the Cu atom, being a distorted square formed by four nitrogen atoms with Cu–N of 1.997-2.018 A, is completed by the contacts with two oxygen atoms Cu…O of 2.472 A and 2.598 A. The comparative crystal chemical analysis with the triclinic modification of [Cu(NH3)4](ReO4)2 known in the literature is performed.

Synthesis, crystal structure refinement, and nonlinear-optical properties of CaB3O5(OH): Comparative crystal chemistry of calcium triborates

Calcium triborate CaB3O5(OH) obtained by hydrothermal synthesis in the Ca(OH)2–H3BO3–Na2CO3–KCl system is studied by single-crystal X-ray diffraction. The parameters of the orthorhombic unit cell are as follows: a = 13.490(1), b = 6.9576(3), and c = 4.3930(2) A; V = 412.32(3) A3 and space group Pna21. The structure is refined in the anisotropic approximation of the atomic displacement parameters to R = 4.28% using 972 |F| > 4σ(F). It is confirmed that the crystal structure of Ca triborate CaB3O5(OH) is identical to that described earlier. The hydrogen atom is localized. An SHG signal stronger than that of the quartz standard is registered. The phase transition of calcium triborate into calciborite is found on heating. The comparative crystal-chemical analysis of a series of borates with the general chemical formula 2CaО · 3В2О3 · nH2О (n = 0–13) with the constant CaО: В2О3= 2: 3 ratio and variable content of water is performed.

Synthesis and crystal structure of novel complex phosphate Li5Cu2Al(PO4)4

A new complex phosphate Li5Cu2Al(PO4)4 has been obtained by the flux method in the Cs-Li-Cu-V-P-O system. Its crystal structure has been determined by X-ray diffraction (R 1 = 2.74%) to be as follows: sp. gr. \(P\bar 1\), a = 4.860(5) A, b = 7.788(5) A, c = 8.324(5) A, α = 69.542(5)°, β = 90.016(5)°, γ = 75.318(5)°, Z = 1, and V = 284.2(4) A3. The compound under study has a dense structure and a three-dimensional framework build up of [LiO5], [AlO6], [Cu/LiO5], and [CuO4] polyhedra and [PO4] tetrahedra. A comparative crystal-chemical analysis of two isotypic compounds with a general formula Li5Cu2 M(PO4)4 (M = Fe, Al) has been performed. Topological relations between the Na2Mg5(PO4)4 and Li5Cu2 M(PO4)4 crystal structures, which are characterized by different cationic compositions, are revealed.

Structure of the monoclinic modification of Re3B

By powder X-ray diffraction the structure of the monoclinic modification of Re3B is studied. The phase is obtained under high pressure and high temperature (10 GPa, 1800°C) using nanocrystalline rhenium and amorphous boron. The results of the comparative crystal chemical analysis are reported.

Crystal-chemical and structural characterization of fluorapatites in ejecta from Somma-Vesuvius volcanic complex

The mineralogy and crystal chemistry of apatites occurring in 14 ejecta of historical eruptions (1631 and 1872 A.D.) of the Somma-Vesuvius volcanic complex were investigated by a multi-methodological approach including polarized optical microscopy, scanning electron microscope, electron microprobe analysis in wavelength-dispersive mode, laser ablation inductively coupled plasma mass spectroscopy, and single-crystal X‑ray diffraction. Five different groups of apatite, with different mineralogical and crystal-chemical features, were identified. Apatite crystals occur with well-developed hexagonal prismatic habit and, more rarely, with skeletal acicular forms. The crystals are yellow (type 1), transparent and colorless (type 2 and type 3), green (type 4) and aquamarine colored (type 5), with different paragenesis: macro-crystalline aggregates of clinopyroxenes, phlogopite, and apatite (type 1; type 4); clusters of apatite with micro-crystalline clinopyroxene, minerals of the cancrinite group, feldspars, and opaque minerals (type 2); aggregates of apatite, sellaite, wagnerite, gypsum, and phlogopite (type 3); aggregates of davyne, nepheline, mica group minerals, and apatite (type 5). Chemical analyses of apatites show variable amounts of Na, REE, Mg, Sr, and Fe replacing Ca, not negligible amounts of Si and S substituting P, and a significant substitution of Cl and OH instead of F. Five crystals representative of each apatite-type were studied by single-crystal X‑ray diffraction. Their crystal structure was refined in the hexagonal P6 3/m space group. A significant variation of the unit-cell parameters with the composition was observed. A comparative crystal-chemical analysis between apatites from Somma-Vesuvius and those from other localities is carried out.

ChemInform Abstract: Crystal Chemistry of Compounds Containing Mercury in Low Oxidation States

The published data are surveyed and a comparative crystal-chemical analysis is presented for the structures of compounds containing mercury in low oxidation states as cluster Hgn groups with covalent Hg–Hg bonds. The geometry of compounds with Hg–Hg and Hg–X bonds (X = O, S, Se, N or Hal) is analysed and the types of coordination of mercury ions, the packing modes and the relationships between structural units are described. The crystallographic and crystal-chemical data for mercury compounds are given. The bibliography includes 124 references.

Unified formula and volume characteristics in comparative crystal chemistry of natural zeolites

Formulas of natural zeolites are generally cumbersome and not easily comparable because of differences in their written form. A summary of the formulas normalized at n=1 is given for aluminosilicate zeolites with the [(Si,Al)nO2n] frameworks. Novel volume parameters are proposed for the framework instead of the framework density (FD) and a zeolite as a whole, which are calculated as the effective volumes of a mean (Si, Al, O) atom and a mean atom of the compound. We show the efficiency of the comparative crystal chemical analysis of zeolites in a common scale with the use of unified characteristics.

Crystal structure of a new synthetic calcium pentaborate, Ca2[B5O8(OH)]2 · [B(OH)3] · H2O, and modular crystal chemistry of pentaborates with polar boron-oxygen layers

The crystal structure of a new calcium pentaborate, Ca2[B5O8(OH)]2 B(OH)3 · H2O, synthesized by the hydrothermal method, has been determined (a = 6.6620(4) A, b = 6.5990(4) A, c = 10.5830(6) A, α = 103.372(5)°, β = 78.296(5)°, γ = 120.931(7)°, space group P1, Z = 1; R 1 = 0.0712 for 4263 reflections with I > 2σ (I)). This structure is built up of three-layer stacks isolated from each other and consisting of Ca (Sr, Ba) polyhedra joined into columns with boron-oxygen networks located on both sides. Building blocks of the network are the pentaborate groups [B 2 t B 3 Δ O8(OH)]2− formed by two boron tetrahedra and three boron triangles. A comparative crystal chemical analysis has been performed for divalent metal pentaborates that have similar compositions and structures. A common fundamental building block {M[B5O8(OH)]}2 · {[B(OH)3],H2O}2 (M = Ca, Sr, Ba) is determined. The diversity of mineral species in the subgroup of pentaborates under consideration is associated both with the variations in the composition and symmetry of individual blocks and with the types of their joining in the structure.

A novel representative {[Rb1.94(H2O,OH)3.84](H2O)0.1}{Al4(OH)4[PO4]3} in the pharmacosiderite structure type

The crystal structure of a new synthetic aluminophosphate {[Rb1.94(H2O,OH)3.84](H2O)0.1}{Al4(OH)4[PO4]3} synthesized under mild hydrothermal conditions (T = 280°C, P = 100 atm) in the Rb2O-Al2O3-P2O5-H2O system is determined using X-ray diffraction (Stoe IPDS diffractometer, λMoK α, graphite monochromator, 2θmax = 64.33°, R = 0.032 for 312 reflections). The main crystal data are as follows: a = 7.4931(6) A, space group P \( \bar 4 \)3m, Z = 1, and ρcalcd = 2.76 g/cm3. It is shown that the synthesized compound belongs to the pharmacosiderite structure type with a characteristic mixed open microporous framework composed of octahedra and tetrahedra. A comparative crystal chemical analysis of related phases is performed, and the chemical compositions of promising absorbents, i.e., hypothetical compounds potentially possible in the structure type under consideration, are proposed. It is established that pharmacosiderite and rhodizite are homeotypic to each other.

Pyrometamorphic osumilite: occurrence, paragenesis, and crystal structure as compared to cordierite

A detailed mineralogical study and single-crystal X-ray analysis were carried out on K-Mg osumilite from high temperature pyrometamorphic rocks. These rocks were generated during spontaneous combustion of coal-bearing spoil-heaps in the South Urals, Russia. The osumilite-bearing metapelitic rocks – clinkers – contain K-Na- and K-Na-Ca feldspars, tridymite, mullite as main phases and magnesian K-bearing cordierite, corundum, native iron, pyrrhotite, cohenite, graphite, black carbon, and iron phosphide as minor phases. The composition of pyrometamorphic osumilites approaches the synthetic compound KMg 2 Al 3 (Al 2 Si 10 )O 30 . Pyrometamorphic alterations of sedimentary protolith during coal combustion proceeded at atmospheric pressure. The osumilite-bearing parageneses are formed under the conditions of low f O2 and water activity, at temperatures above 900 °C and below the melting point for the osumilite-bearing associations. The crystal structure of osumilite was refined from X-ray single-crystal data. Its crystal-chemical formula is K 0.83 C Na 0.10 B′ (Mg 1.78 Fe 0.16 Mn 0.03 Ti 0.03 ) A (Al 2.88 Fe 0.12 ) T2 (Al 1.91 Si 10.09 ) T1 O 30 . K cations occupy the standard 12-coordinated C site, whereas Na cations populate the B′position, located between three 6-membered double rings above the A position. The comparative crystal-chemical analysis shows that in the structure of osumilite, in contrast to cordierite, potassium not only compensates for the framework charge, but also stabilizes the structure. The role of sodium in cordierite and osumilite is similar and consists in a charge compensating function.

New crystal modification of the di(nitrato)di(aqua)palladium(II) complex β-trans-[Pd(NO3)2(H2O)2

Single crystals of a new modification of the di(nitrato)di(aqua)palladium(II) complex β-trans-[Pd(NO3)2(H2O)2] were obtained. Their crystal structure was determined: monoclinic crystal system, a = 5.7469(4) A, b = 5.3942(6) A, c = 10.0956(10) A, β = 97.401(3)°, P21/c, Z = 2, dcalc = 2.851 g/cm3, Bruker X8 APEX CCD, MoKα, 836 independent reflections, room temperature. The square-plane coordination of the Pd atom is formed by four oxygen atoms (Pd-O(NO3) 2.003(3) A and Pd-O(H2O) 2.021(4) A) and completed to a distorted bipyramid by two intramolecular contacts (Pd…O(NO3) 2.893 A). A comparative crystal-chemical analysis with α-trans-[Pd(NO3)2(H2O)2] was carried out.

Refined crystal structure of parakeldyshite and the genetic crystal chemistry of zirconium minerals with [Si2O7] diorthogroups

The structure of the mineral parakeldyshite Na1.93ZrSi2O6.93(OH)0.07 is refined by X-ray diffraction analysis. The main crystallographic data are as follows: space group P $$\overline 1 $$ , a = 6.617(2) A, b = 8.813(1) A, c = 5.426(1) A, α = 87.26(3)°, β = 85.68(3)°, γ = 71.45(3)°, and R F = 0.0153. The initial structural model of this mineral is confirmed. Within this model, the structure of parakeldyshite is based on the heteropolyhedral framework formed by [Si2O7] diorthogroups, which are linked together through isolated zirconium octahedra. The fundamental difference between the structure under investigation and the initial structural model is associated with the arrangement of the extraframework cations. A comparative crystal chemical analysis of the zirconium silicates with [Si2O7] diorthogroups is performed.

Comparative crystal chemical analysis of borophosphates and borosilicates

A comparative crystal chemical analysis of mixed borophosphate and borosilicate anionic radicals revealed the main difference between them: the condensation of [PO4] tetrahedra does not proceed via common vertices, whereas the sharing of vertices is possible for the [SiO4] tetrahedra. In all the borophosphates considered, phosphorus is found only in the formally isolated tetrahedra. The central part of the heterogeneous radicals is formed by tetrahedra of lower charge ions (B+3), and the tetrahedra that incrust the central part have higher valences (Si+4, P+5). In borosilicates, silicon forms its own constructions up to complex layers and frameworks because its charge (Si+4) is lower than that of phosphorus (P+5). The higher charge of phosphorus impedes two-dimensional and three-dimensional condensation. As a result, borophosphates form a variety of soro and chain radicals and only few layer and framework constructions.

Comparative crystal-chemical analysis of anhydrous salts My(TQ4)z (T = Si, Ge, P, As; Q = S, Se, Te) and binary compounds

Topological analysis and crystal-chemical classification of 67 compounds with tetrahedral anions with the general formula My(TQ4)z (T = Si, Ge, P, As; Q = S, Se, Te) have been carried out. These compounds are classified into 36 topological and 38 structure types. Cases of similarity of ternary anhydrous salts My(TQ4)z to binary compounds AyXz are revealed and discussed with the use of the TOPOS structural topological program package. Analysis of the topology and uniformity of ionic matrices shows that the matrices of chalcogenide ions and tetrahedral TQ4y− anions play, as a rule, a leading structural role in My(TQ4)z compounds.

Comparative crystal-chemical analysis of simple sulfites and selenites and binary compounds

With the use of the TOPOS structural topological program package, comparative crystal-chemical analysis has been performed for anhydrous inorganic salts with pyramidal anions, namely, for 12 simple sulfites and 23 simple selenites. Comparative topological analysis has been carried out for simple sulfites and selenites and 1417 representatives of the topological types of binary compounds. This analysis shows that six sulfites and selenites are topologically similar to NaCl, NiAs, TiO2 (rutile), and ZnTe. The topology and uniformity of the ionic matrices in all the structures are surveyed: in 10 of the 35 salts under consideration, at least one of the matrices has close packing topology.

Comparative crystal-chemical analysis of d-metal sulfides, selenides, and tellurides and binary compounds

The structures of d-metal sulfides, selenides, and tellurides containing a tetrahedral complex anion have been compared to 1573 representatives of the topological types of binary compounds with the use of the TOPOS structural topological program package. The cases of similarity between these classes of compounds are found and discussed. Based on the results of topological analysis of ionic matrices, the rules are formulated that allow one to predict specific features of the structures of salts with complex chalcogen-containing anions.