X-ray diffraction analysis on the structure of the glasses in the system PbOSiO2

The structures of PbO·SiO₂ and 2PbO·SiO₂ glasses have been analyzed by use of X-ray diffraction data and pair function method. For PbO·SiO₂ glass, a model consisting of chains of PbO₃ pyramids and silicate chains showed good agreement with the observed RDF. For 2PbO·SiO₂ glass, the present authors reported previously a model in which chains of PbO₃ pyramids are connected with SiO₄ tetrahedra, while the chromatographic analyses of silicate anions by Götz et al. and Smart et al. showed that silicate anions are distributed from monomer to polymer in the glass. We reexamined the structure of this glass referring to these results. Three representative models containing isolated SiO₄, Si₄O₁₂ rings and (SiO₃)_n chains respectively as well as PbO₃ chains were constructed and the RDFs were calculated with changing structure parameters. These three models showed satisfactory agreement with the observed data, showing that silicate anions are distributed from monomer to polymer in 2PbO·SiO₂ glass and an increase of SiO₂ content leads to polymerization of silicate anions to longer chains up to PbO·SiO₂ composition, while the chains of PbO₃ pyramids remain unchanged.     

Ab initio calculation on the (Si2O7)6− bitetrahedra

The total energy surface of the (Si₂O₇)^6? ion is calculated from the bend and torsion angles in the SiOSi axis. The results are discussed and compared with the experimental data. The ab initio calculation of (SiO₄)^4?, as well as the calculation of the charge distributions for all species were made and discussed.     

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.     

High resolution 29Si NMR study of the structure and devitrification of lead-silicate glasses

High speed magic-angle rotation of glass samples in the strong polarizing field of a superconducting magnet yields high-resolution ²⁹Si NMR spectra. Using this technique glasses of various composition, PbO·SiO₂, (PbO)₂·SiO₂, and (PbO)₄·SiO₂ were studied and the influence of thermal treatment followed. Crystallization of PbO·SiO₂ glass has been found to be a complex process leading to a structure identical with that of the mineral alamosite. The ²⁹Si NMR spectrum of crystalline alamosite consists of three lines in agreement with the structure determined by X-ray diffraction.     

Na<Subscript>3</Subscript>Tb<Subscript>3</Subscript>[Si<Subscript>6</Subscript>O<Subscript>18</Subscript>] · H<Subscript>2</Subscript>O,a synthetic analogue of microporous mineral gerenite

Crystals of a new silicate, Na₃Tb₃[Si₆O₁₈] · H₂O, space group \(P\bar 1\), are obtained under hydrothermal conditions. The formula of the compound is determined in the course of structure solution. The silicate is a synthetic analogue of the gerenite mineral (Ca_1.21Na_0.57)(Y_2.24Dy_0.68)Si₆O₁₈ · 2H₂O, whose structure contains six-membered rings formed by SiO₄ tetrahedra. The [Si₆O₁₈] rings are connected by TbO₆ octahedra into a mixed microporous framework with voids filled by Na atoms and water molecules. The new silicate differs from gerenite by the occupation of the Ca position by Na atoms and population of the pores sandwiched between six-membered rings. By virtue of conditions of hydrothermal synthesis in the absence of Ca and excess of Na in the system, an additional Na position appears in the void. It is populated statistically, and in gerenite it was occupied by water molecules only. In the new structure, the position of water is split into two statistically populated positions. The inclusion of Na atoms in additional positions in framework pores and their high thermal vibrations are indicative of ion-exchange properties of the structure. Possible paths of ion exchange are discussed.     

Raman spectroscopic study of scandium in sodium silicate glasses

Glasses in the Na₂OSiO₂Sc₂O₃ system have been studied by Raman and difference Raman spectroscopy. Addition of Sc₂O₃ to sodium silicate glasses results in new vibrational bands at 1025 cm^?1 and 360 cm^?1. The high frequency band is interpreted to be due to Sc⁺³ quasi-complexes formed by Sc⁺³ ions coordinated by SiO₄^?4 tetrahedra having non-bridging oxygens. The discrete character of the scandium-produced bands implies incipient separation of Sc⁺³-enriched silicate structures from purely silicate structures.     

Crystal structures of dioxonium hexafluorotantalate and dioxonium hexafluoroniobate complexes with tetrabenzo-30-crown-10

Two isostructural complexes of dioxonium [H₅O₂]⁺ with tetrabenzo-30-crown-10 of the compositions [(tetrabenzo-30-crown-10 · H₅O₂)][TaF₆] (I) and [(tetrabenzo-30-crown-10 · H₅O₂)][NbF₆] (II) are studied using X-ray diffraction. The complexes crystallize in the monoclinic crystal system (space group C2/c, Z = 4). The unit cell parameters of these compounds are as follows: a = 15.6583(12) Å, b = 15.2259(13) Å, c = 16.4473(13) Å, and β = 99.398(6)° for complex I and a = 15.7117(12) Å, b = 15.2785(15) Å, c = 16.5247(15) Å, and β = 99.398(7)° for complex II. These complexes belong to the ionic type. The dioxonium cation [H₅O₂]⁺ in the form of the two-unit cluster [H₃O · H₂O]⁺ is stabilized by the strong hydrogen bond OH?O [O?O, 2.353(4) Å] and encapsulated by the crown ether. Each oxygen atom of the dioxonium cation also forms two oxygen bonds O?O(crown). The crown ether adopts an unusual two-level (pocket-like) conformation, which provides a complete encapsulation of the oxonium associate. The interaction of the cationic complex with the anion in the crystal occurs through contacts of the C-H?F type.     

Synthesis,Crystal Structure,and Free Radical Scavenging Activity of 4-Aminopyridinium 3,5-Dinitrobenzoate

The crystal structure of 4-aminopyridinium 3,5-dinitrobenzoate, C₁₂H₁₀O₆N₄, has been determined by single-crystal X-ray diffraction technique. The title compound crystallizes in the monoclinic sp. gr. P21/n with the unit cell parameters: a = 7.4726(3) Å, b = 23.0898(9) Å, c = 8.0744(4) Å, V = 1338.64(10) ų, Z = 4. The asymmetric unit of the compound consists of one 3,5-dinitrobenzoate anion and 4-aminopyridine cation. The adjacent anions and cations are linked through two N?H···O hydrogen bonds, N2?H2A···O5 and N₂?H2B···O6, to form an infinite chain of anions and cations, extended along the [010] direction.     

Crystal structures of strontium and barium ethylenediaminetetraacetato cobaltates(III), Sr[CoEdta]2·9H2O and Ba[CoEdta]2·8H2O: Comparison of the structures of complexes in the series M’[CoEdta]2·nH2O (M’ = Mg, Ca, Sr, Ba; n = 7–10)

Cobalt(III) complexes, namely, Sr[CoEdta]₂·9H₂O (I) and Ba[CoEdta]₂·8H₂O (II) (where Edta ^4- is the ethylenediaminetetraacetate ion), are synthesized. The crystal structures of these compounds are determined using X-ray diffraction. Crystals of compound I are triclinic, a = 6.514(1) Å, b = 11.410(2) Å, c = 12.317(2) Å, α = 67.87(1)°, β = 88.73(2)°, γ = 84.22(2)°, V = 843.63(3) ų, Z = 1, space group P1, and R = 0.0295 for 4130 reflections with I > 2σ(I). Crystals of compound II are monoclinic, a = 6.543(2) Å, b = 12.895(3) Å, c = 19.489(4) Å, β = 95.24(3)°, V = 1637.5(5) ų, Z = 2, space group P2₁, and R = 0.050 for 3016 reflections with |F| > 3σ(|F|). The structures of compounds I and II are compared with those of the previously studied complexes Mg[CoEdta]₂·10H₂O (III) and Ca[CoEdta]₂·7H₂O (IV). The crystal structure of the cobalt(III) complex with the strontium cation (I) is topologically similar to the crystal structure of cobalt(III) complex with the calcium cation (IV). The former structure is built up of the two symmetrically independent homochiral anionic complexes [CoEdta]^? (A _I and B _I), the aqua cations [Sr(H₂O)₈]²⁺, and the molecules of crystalization water w _cr. The structure of compound II involves two independent anions [CoEdta]^? (A _II and B _II) with different chiralities (i.e., they are kryptoracemates). The A _II anions are linked via the barium cations into {Ba(H₂O)₇[CoEdta]} _1∞ ⁺ chain agglomerates due to the incorporation of two terminal oxygen atoms O_u of the anions neighboring in the chain into the coordination sphere of the barium atom. All four structures (I–IV) contain stacks composed of the [CoEdta]^? homochiral anions forming layers aligned parallel to the (001) plane. The aqua cations [Sr(H₂O)₈]²⁺, [Mg(H₂O)₆]²⁺, and [Ca(H₂O)₇]²⁺ or the partially hydrated barium cations [Ba(H₂O)₇(O_u)₂]²⁺ (in structure II), as well as water molecules w _cr, are located between the anion layers. The octahedral environment of the cobalt(III) atoms consists of donor atoms (2N and 4O) of the Edta ^4? ligand. The Co-N bonds in the A _I, B _I, A _II, and B _II anions [the mean bond lengths are 1.927(4), 1.921(4), 1.910(6), and 1.921(6) Å, respectively] are considerably longer than the Co-O bonds [the mean bond lengths are 1.908(5), 1.902(5), 1.904(6), and 1.908(6) Å, respectively]. The mean distances Sr-O_w and Ba-O_w in the strontium and barium polyhedra are 2.609(4) and 2.834(8) Å, respectively. The mean distance Ba-O_u is 2.814(7) Å.     

NMR studies on rapidly solidified SiO2Al2O3 and SiO2Al2O3Na2O-glasses

²⁷Al and ²⁹Si MAS NMR studies were performed on roller-quenched SiO₂Al₂O₃-glasses with Al₂O₃ contents ranging from 10 to 60 mol% and on SiO₂Al₂O₃Na₂O glasses containing 10 mol% Al₂O₃ and 2.5 to 10 mol% Na₂O. Pure aluminium silicate glasses show NMR peaks at 0, 30 and 60 ppm. The frequency distribution of the different Al-sites is not affected by the glass composition. In glasses of the system SiO₂Al₂O₃Na₂O the 30 ppm peak decreases to zero as the Na₂O content increases. The 30 ppm peak is assigned to distorted triclustered AlO-tetrahedra, rather than to fivefold coordinated Al. Triclustering of tetrahedra may provide for charge neutrality in glasses with molar excess of Al₂O₃ over Na₂O. As charge balance is increasingly achieved by addition of alkali ions, the tendency of tetrahedral triclustering is reduced, reflected by the disappearance of the 30 ppm peak in glasses containing ≥ 7.5 mol% Na₂O.     

(C2N2H10)2Mg(HP2O7)2·2H2O synthesis and crystal structure

(C₂N₂H₁₀)₂Mg(HP₂O₇)₂·2H₂O, is a new inorganic organic hybrid structure. It has been synthetized using wet chemistry. Its crystal structure consists of cis- and trans-edge sharing [MgO₄(H₂O)₂] octahedra resulting in chains, which are linked via [HP₂O₇] units to form [Mg(HP₂O₇)₂(H₂O)₂]⁴⁻ layers. The Mg²⁺ cations and the ethylendiammonium cations are located on centers of inversion. The ethylendiammonium cations are alternately located in the interlayer space. The cohesion of the crystal is well ensured by coulombic interactions between anions and cations and by several hydrogen bonds. The diphosphate anion shows an eclipsed conformation.     

Fracture toughness-composition relationship in some binary and ternary glass systems

Measurements of the critical stress intensity factor K_Ic are reported for glasses in the Na₂OSiO₂, PbOSiO₂, ZnOB₂O₃, PbOB₂O₃, Na₂OGeO₂ and 20Na₂O?(80 ? x) B₂O₃ ? xSiO₂ systems. The variations of K_Ic with composition are not directly related to the simultaneous variations of Young's modulus. A tentative interpretation is given.     

Two Novel Purely Inorganic Coordination Polymers Constructed From Bivalent Transition Metal Ions and Paratungstate Clusters

Abstract  

The new polymeric compounds (NH₄)₈[Cu(H₂O)₂H₂W₁₂O₄₂]·10H₂O (1) and (NH₄)₄[Co(H₂O)₂][Co(H₂O)₄]₂[H₂W₁₂O₄₂]·8H₂O (2) have been synthesized in aqueous solution and characterized by elemental analysis, TG analysis. Single crystal X-ray diffraction revealed that the [H₂W₁₂O₄₂]¹⁰⁻ (named paratungstate-B) units act as tetradentate and octadentate ligands, respectively. In compound 1, two neighboring paratungstate-B clusters are linked by [Cu(H₂O)₂]²⁺ units leading to the formation of 1D chain. In crystal of 2, each cobalt ion links two paratungstate-B clusters, while each [H₂W₁₂O₄₂]¹⁰⁻ block is surrounded by two [Co(H₂O)₂]²⁺ and four [Co(H₂O)₄]²⁺ bridging cations resulting a 2D sheet formed parallel to the [10[`1]] [10\bar{1}] plane.     

On the constitution of silicate groupings in binary lead silicate glasses

Direct chemical methods have been used to determine the type and the percentage of silicate groupings present in binary lead silicate glasses within the composition range 4PbO · SiO₂PbO · SiO₂. The results obtained indicate that the constitution and the relative amounts of various silicate groupings change with the changing total amount of SiO₂ in the glass. Glasses containing small amounts of SiO₂ are characterized by the presence of few low-molecular silicate units; increasing the percentage of SiO₂ promotes the formation of higher polymerized silicate groupings. The results are discussed with regard to stoichiometry, and are consistent with Hägg's concept of glassiness.     

KNa2Tm[Si8O19] · 4H2O,a new layered silicate related to rhodezite-shlykovite-delhayelite-umbrianite-guenterblassite-hilleshaymite: Topology-symmetry analysis of the OD-family and structure prediction

Crystals of a new silicate KNa₂Tm[Si₈O₁₉] · 4H₂O, space group P12/m1 (the chemical formula was determined in the course of structure solution), are obtained under hydrothermal conditions. KNa₂Tm[Si₈O₁₉] · 4H₂O is the first synthetic representative of the family, which contains the following well-known and recently discovered minerals: rhodezite, delhayelite (fivegite, hydrodelhayelite), mountainite, shlykovite (cryptofillite), and guenterblassite (umbrianite, hilleshaymite). A crystal chemical analysis within the extended OD theory revealed the similarity of the structures of the family, including the new simplest representative and the factors responsible for structural diversity, namely, different symmetry of sheets of octahedra connected with layers of tetrahedra, which are distinguished in all the structures, and different patterns of symmetry relation between the sheets. Hypothetic structures with a higher degree of disordering are deduced. Crystals with these structures can be found in nature or obtained synthetically.     

Effect of Al2O3 on the viscosity and structure of calcium silicate-based melts containing Na2O and CaF2

The effect of Al₂O₃ on viscosity in the calcium silicate melt-based system containing Na₂O and CaF₂ was investigated and correlated with the melt structure using FTIR (Fourier transform infrared) spectroscopy, XPS (X-ray photoelectron spectroscopy), and Raman spectroscopy. Substituting SiO₂ with Al₂O₃ modified the dominant silicate network into a highly structured alumino-silicate structure with the aluminate structure being particularly prevalent at 20 mass% of Al₂O₃ and higher. As the melts become increasingly polymerized with higher Al₂O₃ content, the fraction of symmetric Al–O⁰ stretching vibrations significantly increased and the viscosity increased. XPS showed a decrease in the amount of non-bridged oxygen (O^?) but an increase in bridged oxygen (O⁰) and free oxygen (O^2?) with higher Al₂O₃. Although changes in the structure and viscosity with higher CaO/(SiO₂ + Al₂O₃) were not significant, the symmetric Al–O⁰ stretching in the [AlO₄]^5?-tetrahedral units decreased. The apparent activation energy for viscous flow varied from 118 to 190 kJ/mol.     

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?.     

New framework hydrous silicate K3Sc[Si3O9] · H2O related to the high-temperature anhydrous silicate K3Ho[Si3O9] and symmetry analysis of a phase transition with prediction of structures

Crystals of a new framework silicate K₃Sc[Si₃O₉] · H₂O, space group Pm2₁ n (nonstandard setting of space group Pmn2₁ = C _2v ⁷), are obtained under hydrothermal conditions. The structure is determined without preliminary knowledge of the chemical formula. The absolute configuration is determined. The structure is close to that of the high-temperature K₃Ho[Si₃O₉] phase, which was obtained upon the heating of K₃HoSi₃O₈(OH)₂. This structural similarity is due to the specific conditions of synthesis and an analogous formula, where holmium is replaced by scandium. A symmetry analysis shows that the high local symmetry of a block (rod) is responsible for the first-order phase transition of both the order-disorder (OD) and displacement type. The number of structures in which the simplest and high-symmetry layers are multiplied by different symmetry elements are predicted.     

Hydrothermal crystallization and X-ray structure determination of a new decavanadate with mixed cations [Mn(H2O)6]2[N(CH3)4]2[V10O28]·2H2O

A new decavanadate with mixed cations, [Mn(H₂O)₆]₂[N(CH₃)₄]₂[V₁₀O₂₈]·2H₂O (1), was crystallized from a hydrothermal reaction between MnCO₃ and V₂O₅ in the presence of N(CH₃)₄Br at 100°C. The structure of 1, as determined by x-ray single crystal analysis, consists of cations and anions of hexa-aqua manganese [Mn(H₂O)₆]²⁺, tetramethyl ammonium [N(CH₃)₄]⁺ and decavanadate [V₁₀O₂₈]^6–. The extended H-bonding between the [Mn(H₂O)₆]²⁺ and [V₁₀O₂₈]^6– ions gives rise to a pseudo- two-dimensional network in the crystal lattice x-ray crystallographic data for 1: monoclinic P2₁/n, a = 9.1499(5), b = 12.8725(7), c = 18.625(1) Å, = 92.252(1)°, V = 2192.0(2) ų, MZ = 2, and D _calcd = 2.22 g cm^–3.     

Crystal growth,structure and characterization of diglycine zinc dipicrate: Centrosymmetric crystal exhibiting second harmonic generation efficiency

A new cadmium coordination polymer, formulated as [Cd(L)(phen)]_n, were prepared by hydrothermal reactions based on 3,4-dibromothiophene-2,5-dicarboxylic acid (H₂L) and 1,10-phenanthroline (phen) mixed organic linkers. In the complex, adjacent Cd²⁺ ions are linked by L^2? anions to form a one-dimensional (1D) [CdL]_n chain with [Cd₂(COO)₂] as the secondary building unit (SBU). These adjacent chains are further stacked together by direct C?Br···Br halogen bonds interactions, generating a two-dimensional (2D) supramolecular structure. From the viewpoint of topology, the 2D supramolecular network can be rationalized to a 3,4-connected 3,4L13 net with {4.6²}₂{4².6².8²} topology.