Synthesis and X-ray structural investigation of K8[(UO2)2(C2O4)2(SeO4)4] · 2H2O

Single crystals of the compound K₈[(UO₂)₂(C₂O₄)₂(SeO₄)4] · 2H₂O (I) are synthesized, and their structure is investigated using X-ray diffraction. Compound I crystallizes in the monoclinic system with the unit cell parameters a = 14.9290(4) ?, b = 7.2800(2) ?, c = 15.3165(4) ?, β = 109.188(1)°, V = 1572.17(7) ?³, space group P2₁/n, Z = 2, and R = 0.0297. The uranium-containing structural units of crystals I are dimers of the composition [(UO ₂)₂(C₂O₄)₂(SeO₄)₄]⁸⁻, which belong to the crystal-chemical group AB ⁰¹ B ² M ¹ (A = UO₂²⁺, B ⁰¹ = C₂O₄²⁻, B ² = SeO₄²⁻, M ¹ = SeO₄²⁻) of the uranyl complexes. The [(UO₂)₂(C₂O₄)₂(SeO₄)₄]⁸⁻ dimers are joined into a three-dimensional framework through electrostatic interactions with the outer-sphere potassium cations. Original Russian Text ? L.B. Serezhkina, E.V. Peresypkina, A.V. Virovets, A.G. Verevkin, D.V. Pushkin, 2009, published in Kristallografiya, 2009, Vol. 54, No. 1, pp. 68–71.     

Nuclear magnetic resonance studies of the glasses in the system Na2OB2O3SiO2

The ¹¹B NMR spectra have been used to study the structure of glasses in the system Na₂OB₂O₃SiO₂. The fraction of BO₄ units, and the fraction of BO₃ units with one or two nonbridging oxygens, are measured and analyzed according to a structural model. The results indicate that: (1) for a sodium oxide to boron oxide ratio of 0.5 or less, the Na⁺¹ ions are attracted primarily by the borate network; therefore, the ternary glasses can be viewed as binary sodium borate glasses diluted by SiO₂; (2) when the sodium oxide to boron oxide ratio exceeds 0.5, the additional Na₂O results in the formation of [BSi₄O₁₀]^?1 units at the expense of diborate and SiO₄ units. In this process, Na⁺¹ ions are still taken up only by the borate network. After all the available SiO₄ units are consumed to form [BSi₄O₁₀]^?1 units, additional Na⁺¹ ions are proportionally shared between the borate and silicate networks.     

Synthesis and structure of K2[(UO2)4(O)2(OH)2(C2O4)(CH3COO)2(H2O)2]·2H2O

Single crystals of the compound K₂[(UO₂)₄(O)₂(OH)₂(C₂O₄)(CH₃COO)₂(H₂O)₂]·2H₂O (I) are synthesized, and their structure is investigated using X-ray diffraction. Crystals of compound I belong to the triclinic system with the unit cell parameters a = 7.6777(6) ?, b = 7.9149(7) ?, c = 10.8729(9) ?, α = 72.379(2)°, β = 86.430(3)°, γ = 87.635(2)°, V = 628.33(9) ?³, space group P , Z = 1, and R ₁ = 0.0323. The main structural units of the crystals are [(UO₂)₄(O)₂(OH)₂(C₂O₄)(CH₃COO)₂(H₂O)₂]²⁻ chains, which belong to the crystal-chemical group A ₄ M ₂³ M ₂² K ⁰² B ₂⁰¹ M ₂¹ (A = UO₂²⁺, M ³ = O²⁻, M ² = OH⁻, K ⁰² = C₂O₄²⁻, B ⁰¹ = CH₃COO⁻, M ¹ = H₂O) of the uranyl complexes. The chains are formed by linking the centrosymmetric tetramers of the composition (UO₂)₄(O)₂(OH)₂(CH₃COO)₂(H₂O)₂ via tetradentate bridging oxalate ions. The uranium-containing groups are joined into a three-dimensional framework through the electrostatic interaction with potassium cations and a system of hydrogen bonds, which are formed with the participation of atoms involved in the composition of the water molecules, hydroxide ions, and uranyl ions. Original Russian Text ? L.B. Serezhkina, A.V. Vologzhanina, N.A. Neklyudova, V.N. Serezhkin, 2009, published in Kristallografiya, 2009, Vol. 54, No. 3, pp. 483–487.     

Glass formation and structure of Na2SSiO2 and Na2SB2O3 glasses

Glass-forming regions of the systems Na₂SSiO₂ and Na₂SB₂O₃ have been investigated in order to clarify whether Na₂S could be substituted for Na₂O in sodium silicate or borate glasses, and the results were interpreted in terms of the structures of silicate and borate glasses. No difference was found in the glass-forming range of SiO₂ content between the Na₂SSiO₂ and Na₂OSiO₂ systems, and the red color of Na₂SSiO₂ glasses suggests that the formation of polysulfides in the glass structure is probably due to the entrance of sulfur ions in the non-bridging sites of the glass network. On the other hand, not all of the sulfur added to the glass batches could be retained in the Na₂SB₂O₃ glasses and the amount remaining in the glass products changed depending upon the amount of sodium ions in the glasses. Only a trace of sulfur was observed in the glasses containing less than 13 mol% of Na₂S in the batches, but the sulfur content in the glasses increased steeply with sodium content up to 35 mol%, reached the maximum and then decreased slowly with sodium content. The insolubility of sulfur in the glasses with low sodium content was interpreted based on the compositional dependence of basicity of alkali-borate glasses, and the change in solubility of sulfur with sodium concentration was explained based on the well-known boron anomaly caused by the change in the coordination state of boron and on the formation of non-bridging oxygens or sulfurs in the glass structure.     

11B and 27Al NMR studies of glasses in the system Na2OB2O3Al2O3 (“NABAL”)

¹¹B and ²⁷Al nuclear magnetic resonances (NMR) in glasses of the NABAL system Na₂OB₂O₃Al₂O₃ have been studied as a function of composition. From the boron data, the fraction of four-coordinated BO₄ units has been determined via computer analysis of the NMR spectra; the method is similar to that employed previously for binary and other ternary borate glasses. The ²⁷Al NMR indicates no abrupt change in the average aluminum environment. Certain linear relationships have been found which yield detailed information on the competing processes of BO₃, BO₄ and AlO₄ formation, and the formation of triclusters consisting of three tetrahedra having one oxygen in common. Furthermore, it is concluded that the oxygen available for the formation of various aluminum-containing species is a function of the soda concentration only and that the conversion to AlO₄ is favored as compared with BO₄.     

Small polaron conduction in V2O5P2O5 glasses

Dc conductivity measurements have been made between 90 and 520 K on three bulk samples of V₂O₅P₂O₅ glass. Heat treatment is found to result in a reduction of the activation energy at a given temperature and this is most noticeable at low temperatures. The behaviour at low temperatures can be described using Mott's variable range hopping arguments, and at high temperatures by non-adiabatic small polaron hopping between nearest neighbours. At intermediate temperatures a simple model is used in which excitations by optical and acoustic phonons are considered to make independent contributions to the jump frequency. Mott's theory is extended to the polaron case for $\text{T>}\text{1}\text{4}\text{?}$ and is shown to be in good agreement with results. Values for $\text{r}{}_{\mathrm{<mtext>p</mtext>}}\text{(～2.8}\text{A}\text{?}\text{)}$ the polaron radius and $\text{α(～3.5}\text{A}\text{?}{}^{\mathrm{?1}}\text{)}$ the electron decay constant are shown to be consistent with the model for small polarons. A method is suggested for obtaining α and N(E_F) from the ac conductivity and the slope of 1nσ versus $\text{1}\text{T}{}^{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}$ at low temperatures. Values of N(E) are obtained which correlate with those obtained by the previous analysis. This implies that the disorder energy separating adjacent sites Δ₀ is large (～0.4 eV) in these materials.     

Glass formation in the systems (K or Cs)2O(Nb or Ta)2O5Al2O3

The glass-forming ability of melts in the systems K₂O(Nb and/or Ta)₂O₅Al₂O₃ as well as those in which K₂O was replaced with Li₂O, Na₂O, Cs₂O, BaO or PbO was investigated. Some melts in the systems (K or Cs)₂O(Nb and/or Ta)₂O₅Al₂O₃ could be made into glasses by cooling, yielding practically useful amounts. The structures of these glasses were discussed on the basis of their infrared spectroscopic and X-ray emission spectroscopic analyses.     

Semiconducting TiO2SiO2 glasses (I): Electronic conductivity

Semiconducting glasses, 70% TiO₂-30% SiO₂, with a Ti³⁺ content varying from zero to 7.8%, have been prepared by rf sputtering in argon/oxygen/hydrogen gas mixtures. Conduction in the Ti³⁺-containing glasses is by small polarons hopping adiabatically. The disorder energy is small (0.05 eV) compared to the hopping energy (0.37–0.51 eV). The variation of the hopping energy with Ti³⁺ content and temperature is ascribed to a polaron overlap effect and to effects arising from the random glass structure, respectively. At low temperatures conduction is a percolation process. The conduction in Ti³⁺-free glasses is not due to polarons; at low temperature these glasses exhibit variable-range hopping.     

ESR and optical absorption of Cu2+ in Na2OSiO2 glasses

ESR and optical absorption spectra of Cu²⁺ in xNa₂O(100?x)SiO₂ glasses were measured, where x ranges from 12 to 70 mol% Na₂O. This glass system was divided into three composition regions, 12 ? x ? 37, 37 ? x ? 55 and 55 ? x, from the composition dependence of the ligand field transition energy and spin hamiltonian parameters of Cu²⁺. Two boundary compositions (37 and 55 mol%) between the two adjacent regions agreed with the eutectics in the equilibrium phase diagram. Two types of Cu²⁺-complexes, with less basic ligands (HFS-1) and much more basic ones (HFS-2), were detected in ESR for ultra-high soda glasses (x ? 55). The distribution of the ESR parameters due to the fluctuation of ligand fields was negligible for HFS-2 compared with that for other glasses. The Cu²⁺ ion responsible for HFS-2 was considered to distribute in the microphase of orthosilicate. Imagawa's basicity, the covalency of the bondings between Cu²⁺ and ligands, was calculated by using Maki and McGarvey's analysis. The basicity of σ-type symmetry remained constant, irrespective of the glass composition, and the value was identical with those for other oxyanionic glasses. The π-type basicity was also constant for the glasses of x ? 55. Two different basicities, each corresponding to HFS-1 or 2, were obtained for the glasses of x ? 55. The value derived from HFS-1 was identical with those for x < 55 glasses, whereas that derived from HFS-2 suggested the formation of much more basic ligands.     

EPR study of crystalline and vitreous forms of the Li2OAl2O3SiO2 system

The epr spectra of V⁴⁺ and radiation centres have been studied in β-eucryptite (LiAlSiO₄), β-, γ-spodumene (LiAlSi₂O₆) and in glasses prepared by the fusion of the single crystals. It is shown that the electronic structures of the vitreous state in the Li₂OAl₂O₃SiO₂ system and that of the crystalline forms differ considerably. The change of the electronic structure on crystallization is not direct, but is realized through the intermediate state whose electronic structure differs from that of glasses and crystals.     

Infrared transmission of (R2O OR R’O)–(TiO2, Nb2O5 OR Ta2O5)-Al2O3 glasses

The new families of aluminate glasses obtained by the present authors from their melts in the systems K₂O–Ta₂O₅–Al₂O₃, Na₂O–K₂O–Ta₂O₅–Al₂O₃, K₂O –Cs₂O– Ta₂O₅–Al₂O₃, K₂O–Nb₂O₅–Al₂O₃, Na₂Oz.sbnd;K₂O–TiO₂–Al₂O₃, BaO–TiO₂–Al₂O₃, BaO–ZrO₂–TiO₂–Al₂O₃ and Na₂O–K₂O–BaO–ZrO₂–Ta₂O₅–TiO₂ –Al₂O₃ showed high transmissions of visible and infrared (IR) radiation ranging from 0.4 to about 6 μm, as well as high refractive indices up to 2.0. Their physical and chemical properties such as glass-forming ability, softening temperature, hardness and hygroscopicity were comparable to conventional silicate glasses. These properties are useful for IR applications. The cause of the high IR transmission of the aluminate glasses was interpreted in terms of the masses of the constituent cations and the single bond strengths of the cations with oxygen ions.     

Infrared spectra and structure of superionic conducting glasses in the system AgIAg2OMoO3

Thin blown films of glasses with the mole ratio Ag₂O/MoO₃ = 1 in the system AgIAg₂OMoO₃ (or the pseudobinary system AgIAg₂MoO₄) show three absorption bands in the range 4000-200 cm^?1; 875 cm^?1 (w), 780 cm^?1 (s), and 320 cm^?1 (m, b), which are characteristic of tetrahedral MoO₄^2? ions. The glasses with the ratio Ag₂O/MoO₃ < 1 have two additional bands at 600 cm^?1 (w) and 450 cm^?1 (vw), which are characteristic of condensed ions of MoO₄ tetrahedra, probably Mo₂ O₇^2? ions. These glasses are thus composed of Ag⁺, I^?, MoO₄^2?, and probably Mo₂O₇^2? ions, and classified as “ionic” glasses containing one type of cations. The presence of partial covalency in the Ag⁺… ^?OMo link and the influence of ion exchange of Ag⁺ with K⁺ on IR spectra are discussed. The molar volume of the glasses with the ratio Ag₂O/MoO₃ = 1 is primarily determined by a fairly dense packing of the constituent anions, I^? and MoO₄^2?.     

Glasses and glass-ceramics from naturally occurring CaOMgOAl2O3SiO2 materials (I) glass formation and properties

Once oil is extracted from oil shales, the inorganic solid which remains is from the CaOMgOAl₂O₃SiO₂ system. The material is easily melted and forms a glass upon cooling. Its viscosity in the forming region is actually less than that of commercial soda-lime glass. Shale glasses exhibit excellent dielectric behavior, while their other properties are generally comparable to commercial glasses. These glasses appear to be promising materials for future applications.     

Brillouin scattering measurements of attenuation and velocity of hypersounds in SiO2B2O3 glasses

Measurements of hypersound wave velocity and attenuation (20–30 GHz) were made at room temperature by Brillouin scattering in SiO₂O₂O₃ glasses. The attenuation shows a maximum with composition. An explanation of this maximum is given in relation to the glass structure. It is thought that this maximum may be due to a coupling effect of hypersounds with structural relaxational process involving SiSi and SiOB bonds.     

A study of the mechanisms of defect formation in K2Ni(SO4)2 · 6H2O/K2Co(SO4)2 · 6H2O bicrystals grown from aqueous solutions

The K₂Co(SO₄)₂ · 6H₂O-K₂Ni(SO₄)₂ · 6H₂O system has been studied, and a series of K₂Ni(SO₄)₂ · 6H₂O/K₂Co(SO₄)₂ · 6H₂O bicrystals have been grown. The processes of defect formation at the substrate/layer interface K₂Co(SO₄)₂ · 6H₂O/K₂Ni(SO₄)₂ · 6H₂O are studied by probe microanalysis, X-ray topography, and optical microscopy. It is found that inclusions and threading dislocations are formed at the interface, due to which elastic stresses relax in the crystal. Nickel is nonuniformly distributed in the layer; its concentration decreases with an increase in the layer thickness, which is indicative of substrate dissolution in the initial stage of interaction. A way for the elastic mismatch stresses to relax in heterostructures of brittle crystals obtained from solutions at low temperatures is proposed which implies the formation of inclusions at the substrate/layer interface. Original Russian Text ? M.S. Grigor’eva, A.é. Voloshin, E.B. Rudneva, V.L. Manomenova, S.N. Khakhanov, V.Ya. Shklover, 2009, published in Kristallografiya, 2009, Vol. 54, No. 4, pp. 679–687.     

Crystal Structures of Two Aromatic Zinc(II) Carboxylates: [Zn(4-Chlorosalicylato)2(H2O)4]·2theophylline·(H2O)2 and Unique [Zn(5-Chlorosalicylato)2(isonicotinamide)2(H2O)]

Abstract  

The crystal structures of two zinc(II) 4-chloro- and 5-chlorosalicylate complexes, [Zn(4-ClC₆H₃-2-(OH)COO)₂(H₂O)₄]·2tph·(H₂O)₂ (I) and [Zn(5-ClC₆H₃-2-(OH)COO)₂(ina)₂(H₂O)] (II), where tph is theophylline and ina is isonicotinamide, have been determined using X-ray diffraction methods. Crystals of both (I) and (II) are triclinic, space group P-1, with Z = 1 in a cell with a = 7.2220(3), b = 8.59700(10), c = 16.0210(5) ?, α = 75.990(2), β = 83.959(2), γ = 68.455(2)°, V = 897.54(5) ?³ (I) and with Z = 2 in a cell with a = 11.4148(11), b = 11.5327(10), c = 12.0685(13) ?, α = 63.458(6), β = 87.547(8), γ = 89.387(7)°, V = 1419.9(2) ?³ (II). The coordination environment of the zinc(II) atom of compound (I) consists of two unidentate carboxylate oxygen atoms and four oxygen atoms of aqua ligands, forming a distorted octahedral configuration. Two theophylline molecules and the remaining water molecules are bound only by hydrogen bonds. The Zn atom of compound (II) is pentacoordinated with two unidentate carboxylate oxygen atoms, two pyridine nitrogen atoms of isonicotinamide ligands, and the oxygen atom of the aqua ligand, forming a distorted configuration between square pyramid and trigonal bipyramid. In both complexes intramolecular O–H···O hydrogen-bonding interactions are present. In the crystal structures, molecules are linked by intermolecular O–H···O and N–H···O hydrogen bonds. The structures are analyzed and compared to the similar Zn(II) complexes, with the chromophores ZnO₆ and ZnO₃N₂.     

Crystallization and phase-separation of Li2OSiO2 glass

The crystallization and phase-separation phenomena in the Li₂OSiO₂ glass are studied by positron lifetime and annihilation lineshape measurements. Analysis of the kinetic data shows three-dimensional morphology of growing crystals. Phase-separation is seen to increase the density of crystal nuclei and the rate of volume crystallization, but it does not affect the morphology. In addition, surface crystallization is detected in glasses with small degrees of phase-separation. The results are consistent with scanning electron and optical micrographs.     

Synthesis and X-ray structural investigation of (C3N6H7)4(CN3H6)2[UO2(CrO4)4] · 4H2O and (H3O)6[UO2(CrO4)4]

Single crystals of the compounds (C₃N₆ H₇)₄(CN₃H₆)₂[UO₂(CrO₄)₄] · 4H₂O (I) and (H₃O)₆[UO₂(CrO₄)₄] (II) are synthesized, and their structures are investigated using X-ray diffraction. Compound I crystallizes in the triclinic system with the unit cell parameters a = 6.3951(8) ?, b = 10.8187(16) ?, c = 16.9709(18) ?, α = 93.674(4)°, β = 97.127(4)°, γ = 92.020(4)°, space group, P Z = 1, V = 1161.6(3) ?³, and R = 0.0470. Crystals of compound II belong to the monoclinic system with the unit cell parameters a = 14.3158(4) ?, b = 11.7477(3) ?, c = 13.1351(4) ?, β= 105.836(1)°, space group C2/c, Z = 4, V = 2125.2(1) ?³, and R = 0.0213. The uranium-containing structural units of crystals I and II are mononuclear anionic complexes of the composition [UO₂(CrO₄)₄]⁶⁻ with an island structure, which belong to the crystal-chemical group Am ₁⁴ (A = UO₂₊², M ¹ = CrO₂₋⁴) of the uranyl complexes. The [UO₂(CrO₄)₄]⁶⁻ anionic complexes are joined into a three-dimensional framework through the electrostatic interactions with outer-sphere cations and a system of hydrogen bonds. Original Russian Text ? L.B. Serezhkina, E.V. Peresypkina, A.V. Virovets, A.G. Verevkin, D.V. Pushkin, 2009, published in Kristallografiya, 2009, Vol. 54, No. 2, pp. 284–290.     

Crystal Structures and Thermal Properties of Two Transition-Metal Compounds {[Ni(DNI)2(H2O)3][Ni(DNI)2 (H2O)4]}·6H2O and Pb(DNI)2(H2O)4 (DNI?=?2,4-Dinitroimidazolate)

Abstract  

Two transition-metal compounds derived from 2,4-dinitroimidazole, {[Ni(DNI)₂(H₂O)₃][Ni(DNI)₂(H₂O)₄]}·6H₂O, 1, and Pb(DNI)₂(H₂O)₄, 2, were characterized by elemental analysis, FT-IR, TG-DSC and X-ray single-crystal diffraction analysis. Crystal data for 1: monoclinic, space group C2/c, a = 26.826(3), b = 7.7199(10), c = 18.579(2) ?, β = 111.241(2)° and Z = 4; 2: monoclinic, space group C2/c, a = 6.5347(6), b = 17.1727(17), c = 14.1011(14) ?, β = 97.7248(10) and Z = 4. Compound 1 contains two isolated nickel centers in its structure, one being six-coordinate and another five-coordinate. The structure of 2 contains a lead (II) center surrounded by two chelating DNI ligands and four water molecules in distorted square-antiprism geometry. The abundant hydrogen bonds in two compounds link the molecules into three-dimensional network and stabilize the molecules. The TG-DSC analysis reveals that the first step is the loss of water molecules and the final residue is the corresponding metal oxides and carbon.     

Phase separation in GeGeO2 glasses

De Neufville prepared homogeneous glasses ranging in composition from pure GeO₂ to GeO by quenching bulk samples from the melt and by vapor deposition. For compositions in the range of 10–20 mol % excess Ge dissolved in GeO₂, he found that phase separation into amorphous Ge rich and amorphous GeO₂ phases occurred. The results reported here on a 7.5 mol % excess Ge composition using differential scanning calorimetry have shown that a two-step phase separation mechanism is operative. A homogeneous GeGeO₂ glass phase separates at 450°C into amorphous GeO₂ and amorphous GeO. The GeO phase separates at 570°C into crystalline Ge and amorphous GeO₂. The heat measured at 570°C is equal to the sum of the heats of phase separation of GeO and crystallization of Ge. The amorphous GeO₂ crystallizes at 670°C with a heat of crystallization of 4.65 kcal/mol (± 0.5). Additional support for a two-step phase separation mechanism is provided by kinetic arguments based on the viscosity dependence on composition and on the structure of the amorphous GeO phase and its stability relative to the homogeneous GeGeO₂ glass.