A thermodynamic study of struvite+water system

Equilibrium analysis of the system with MgNH₄PO₄·6H₂O (struvite) is taken as an interesting example of two-phase system where a change in solid phase composition (conversion) is affected by hydrolytic phenomena. The problem is presented in a comprehensive manner, based on results obtained from calculations made according to iterative computer program. The complex nature of phenomena occurred, with side effects resulting from presence of carbonate species, is explained. The analytical and physicochemical aspects of the matter are considered.     

Phase equilibria and isomorphism in the LiVWO<Subscript>6</Subscript>-NaVWO<Subscript>6</Subscript> system

Compounds of composition Li _x Na_{1 − x} VWO₆ (0 ≤ x ≤ 1), which are synthetic analogues of brannerite-type minerals, were produced for the first time by solid-state synthesis at high temperatures. The structure of the compounds and their unlimited miscibility in the solid phase in the LiVWO₆-NaVWO₆ binary system were determined by X-ray diffraction. The phase equilibrium diagram was studied by differential thermal analysis together with thermodynamic modeling. It was found that the system under investigation is described by the regular solid solutions model.     

Alkaline Earth Cluster Compounds AE[W6I14] and the Solvate [Ca(C2H6SO)6][W6I14]

Alkaline earth tungsten iodide clusters AE[W₆I₁₄] with AE = Mg, Ca, Sr, Ba and the solvated compound [Ca(C₂H₆SO)₆][W₆I₁₄] were prepared and structurally characterized. A new synthesis was employed, starting from W₆I₂₂, which is an exceptional compound among binary tungsten iodides because it is soluble in common polar organic solvents. As evidence for the wide range of the applicability of W₆I₂₂, we report the synthesis of the new AE[W₆I₁₄] compounds in comparison to a solid‐state reaction departing from W₃I₁₂.     

A full dimensional direct ab initio dynamics study of the electron capture by SF6

The dynamics of electron capture by sulfur hexafluoride (SF₆) have been investigated by means of full dimensional direct ab initio dynamics calculations at the HF/6-311G(d)+sp (a diffuse sp-function is further added to sulfur atom) level. A rigid SF₆ structure and narrow Franck–Condon region for electron capture was assumed in choosing initial conditions for the trajectories. The direct ab initio dynamics calculations for the electron capture processes by SF₆ indicated that the SF⁻₆ ion formed by the vertical electron attachment to SF₆ decomposes into SF⁻₅ and F via short-lived complex formation (SF⁻₆). The lifetime of SF⁻₆ was distributed from 0.1–0.2 ps, which is quite short as lifetime of the intermediate complex. The dynamics calculations showed that 12% of the total available energy is partitioned into the relative translational mode between SF₅⁻ and F. The effect of solid phase on the dynamics has been examined by introducing a model bath-relaxation time for energy dispersion. There was a possibility that the SF₆⁻ anion exists in solid phase. The mechanism of the electron capture by SF₆ in gas phase and in solid phase was discussed on the basis of the results.     

Convergent solid phase peptide synthesis. II. Synthesis of the 1–6 apamin protected segment on a NBB-resin. Synthesis of apamin

The article deals with the use of the NBB-resin for synthesis of protected segments followed by solid phase segment condenstaion. Solid phse synthesis on a NBB-resin of the segment 1–6 of apamin yielded either the (1–6) apamin-OH segment after photolysis or (1–6) apamin-NH-NH₂ after hydrazinolysis. The two protected segments were purified on Sephaex LH-20 followed by Bio-Beads S-X1 chromatography and respectively coupled onto a resin on which the 7–18 sequence of apamin was assembled stepwise with the standard solid phase procedure. On a portion of the resin, stepwise synthesis was continued to complete apamin. After HF treatment, deprotection of the cysteines, formation of the disulfide bonds and purification, biologically active apamin was obtained in the three cases.     

Hexagonal Bipyramidal [Ta2B6]−/0 Clusters: B6 Rings as Structural Motifs

It has been a long‐sought goal in cluster science to discover stable atomic clusters as building blocks for cluster‐assembled nanomaterials, as exemplified by the fullerenes and their subsequent bulk syntheses. ¹ , ² Clusters have also been considered as models to understand bulk properties, providing a bridge between molecular and solid‐state chemistry. ³ Because of its electron deficiency, boron is an interesting element with unusual polymorphism. While bulk boron is known to be dominated by the three‐dimensional (3D) B₁₂ icosahedral motifs, ⁴ new forms of elemental boron are continuing to be discovered. ⁵ In contrast to the 3D cages commonly found in bulk boron, in the gas phase two‐dimensional (2D) boron clusters are prevalent. ⁶ – ⁸ The unusual planar boron clusters have been suggested as potential new bulking blocks or ligands in chemistry. ^6a Herein we report a joint experimental and theoretical study on the [Ta₂B₆]⁻ and [Ta₂B₆] clusters. We found that the most stable structures of both the neutral and anion are D_6h bipyramidal, similar to the recently discovered MB₆M structural motif in the Ti₇Rh₄Ir₂B₈ solid compound. ⁹      

Facile reduction of aromatic nitro/azido functionality on solid support employing Al/NiCl2·6H2O and Al/NH4Cl: synthesis of pyrrolo[2,1-c][1,4]benzodiazepines

An efficient and mild method for the reduction of aromatic nitro and azido groups on solid support using Al/NiCl₂·6H₂O and Al/NH₄Cl is described. This solid phase reduction technique has been applied towards the synthesis of DNA binding pyrrolo[2,1-c][1,4]benzodiazepine antitumour antibiotics.     

Reactions of carbonyl clusters with heterobidentate ligands. Synthesis and structural characterization of H4Ru4(CO)10[k2(P,S)-Ph2P(2-CH3SC6H4)] and Rh6(CO)14[k2(P,S)-Ph2P(2-CH3SC6H4)] clusters

Two new disubstituted derivatives of the clusters Rh₆(CO)₁₆ and H₄Ru₄(CO)₁₂ with the heterobidentate ligand [Ph₂P(2-CH₃SC₆H₄)] were synthesized. Structures of these compounds were completely characterized both in solid phase and solution. The H₄Ru₄(CO)₁₀[k²(P,S)-Ph₂P(2-CH₃SC₆H₄)] cluster is an example of a structure, in which a chelating coordination of a heterobidentate ligand results in the occurrence of a center of asymmetry associated with the substituted metal atom. This type of polynuclear complexes is of interest for obtaining essentially new catalysts for asymmetric synthesis on the basis of cluster compounds.     

Synthese,Kristallstruktur und festkörper‐NMR‐spektroskopische Untersuchung neuer Oxonitridosilicate der Mischkristallreihe Ba4−xCaxSi6N10O

The new oxonitridosilicates Ba_4?xCa_xSi₆N₁₀O have been synthesized by means of high‐temperature synthesis in a radio‐frequency furnace, starting from calcium, barium, silicon diimide and amorphous silicon dioxide. The maximum reaction temperature was at about 1450 °C. The solid solution series Ba_4?xCa_xSi₆N₁₀O with a phase width 1.81 ≤ x ≤ 2.95 was obtained. The crystal structure of Ba_1.8Ca_2.2Si₆N₁₀O was determined by X‐ray single‐crystal structure determination (P2₁3, no. 198), a = 1040.2(1) pm, Z = 4, wR2 = 0.082). It can be described as a highly condensed network of corner‐sharing SiN₄ and SiON₃ tetrahedra, the voids of which are occupied by the alkaline earth ions. The structure is isotypic with that of BaEu(Ba_0.5Eu_0.5)YbSi₆N₁₁. In the ²⁹Si solid‐state MAS‐NMR spectrum two isotropic resonances at ?50.0 and ?53.6 ppm were observed.     

Analysis on holdup during processing UF6

Holdup in processing UF₆ is analyzed in the present article. Under normal operation conditions of temperature and pressure, UF₆ stays in gas phase. While if water moisture ingresses, chemical reaction between UF₆ and moisture results in solid or liquid productions that can deposit on structure surfaces. The present report focuses on the chemistry of holdup and how to measure it, and safeguards and criticality safety concerns. An available statistic theoretical model is also discussed.     

Über die Chemie der Glasrußbildung durch Oxydation von gasförmigem SiCl4 und GeCl4 bei hohen Temperaturen

About the Chemistry of the Formation of Glass-soot by Oxidation of Gaseous SiCl₄ and GeCl₄ at High Temperatures By the oxidation of gaseous mixtures of SiCl₄ and GeCl₄ at temperatures of 2023 K finely grained glass-soot is formed. For the preparation of compounds according to the composition Si_1?xGe_xO₂ (0 ≤ x ≤ 1) the existence of a solid continuous phase was proved by infrared spectroscopy and electron microscopy. The experimentally during the process of oxidation determined degrees of conversion are compared with thermodynamical calculations, considering different kinds of formation of the solid phase.     

Zur Löslichkeit von Cobalt(IV) in Li8SiO6

On the Solubility of Cobalt(IV) in Li₈SiO₆ Li₈SiO₆ dissolves up to 2 at.‐%, cobalt(IV). Crystals of such solid solutions are transparent and of deep ruby red colour. Cobalt concentrations as determined by ICP‐OES, EDX and magnetic susceptibility measurements are in good accordance. The X‐ray powder diffraction and the magnetic properties confirm integration of Co⁴⁺ into the lithiumoxosilicate. These new results are indicating that the ruby red phase, previously addressed as “Li₈CoO₆”, is in fact cobalt doped Li₈SiO₆.     

Phase polymorphism of [Ni(DMSO)6](BF4)2 studied by differential scanning calorimetry

The tetrafluoroborate of hexadimethylsulfoxidenickel(II) was synthesized and studied by differential scanning calorimetry. Seven solid phases of [Ni(DMSO)₆](BF₄)₂ were revealed. Specifically, six phase transitions of the first order were detected between the following solid phases: stable KIb → stable KIa at T _C6 = 335 K, metastable KIIb → metastable KIIa at T _C5 = 368 K, metastable KIII → overcooled phase KI at T _C4 = 378 K, metastable KIIa → overcooled phase KI at T _C3 = 396 K, stable KIa → stable KI at T _C2 = 415 K and stable KI → stable K0 at T _C1 = 433 K. [Ni(DMSO)₆](BF₄)₂ begins decomposition at 440 K with loss of one DMSO molecule per formula unit forming [Ni(DMSO)₅](BF₄)₂ (phase L0) which melts next in two steps in the temperature range 550–593 K. From the entropy changes connected both with melting and with phase transitions, it can be concluded that phases KI, overcooled KI and K0 are orientationally dynamically disordered (ODIC) crystals. Stable phases KIb, KIa and metastable phase KIII are ordered solid phases. Metastable phase KIIa and metastable phase KIIb are more or less ordered solid phases.     

Phase equilibria in the system FeVO4−Fe2WO6 in the solid state

A diagram of the phase equilibria established in the solid state in the system FeVO₄?Fe₂WO₆ was plotted on the basis of X-ray phase analysis and DTA. This system, one of the intersections of the three-component system Fe₂O₃?V₂O₅?WO₃, does not appear to be a real two-component system in the solid state.     

Cs2LiLuCl6: Zwei Formen mit zwei Umwandlungen im festen Zustand

Cs₂LiLuCl₆: Two Modifications with Two Transitions in the Solid State At ambient temperature Cs₂LiLuCl₆ crystallizes with the trigonal HT-K₂LiAlF₆ structure type (?6L-type”? form I, L). With increasing temperature a reversible, reconstructive solid to solid first order phase transition to the cubic-face centered K₂NaAlF₆-type (?elpasolite”?, form II) occurs at ≈? 325°C with a negative volume discontinuity. Above ≈? 510°C up to the melting point (≈? 675°C) again the 6L-type is observed (form I, H). The likewise reversible phase transition proceeds with a positive volume discontinuity. In both phase transitions 60° rotations occur within densest packed layers with [0 0.1] as rotation axis.     

Photoredox Activation of SF6 for Fluorination

We report the first practical use of SF₆ as a fluorinating reagent in organic synthesis. Photoredox catalysis enables the in situ conversion of SF₆, an inert gas, into an active fluorinating species by using visible light. Under these conditions, deoxyfluorination of allylic alcohols is effected with high chemoselectivity and is tolerant of a wide range of functional groups. Application of the methodology in a continuous‐flow setup achieves comparable yields to those obtained with a batch setup, while providing drastically increased material throughput of valuable allylic fluoride products.     

Phase equilibrium in the Pb2SnSb2S6-SnS system

The Pb₂SnSb₂S₆-SnS system was studied over a wide range of concentrations using a set of physicochemical methods (powder X-ray diffraction, DTA, microstructure examination, and microhardness measurement). A phase diagram for the title quasi-binary join was constructed for the first time. The phase diagram is of the eutectic type; the eutectic coordinates are 25 mol % SnS and 775 K. The extents of solid solutions based on the terminal components were determined to be 10 mol % SnS and 5 mol % Pb₂SnSb₂S₆. Alloys having compositions in the SnS-based solid solution region are semiconductors.     

Reactions of rhodium carbonyl clusters with heterobidentate ligands. Synthesis and structural characterization of the Rh6(CO)15[(C6H5)2PC6H4N(CH3)2] and {Rh6(CO)15[(C6H5)2PC6H4NH(CH3)2]}[GaX4] cluster compounds

The reaction of heterobidentate 4-(dimethylamino)phenyldiphenylphosphine with labile cluster Rh₆(CO)₁₅(NCMe) yielding a new monosubstituted cluster Rh₆(CO)₁₅(Ph₂PC₆H₄NMe₂) was described. The reactions of the resulting cluster with GaX₃ compounds were studied. The structure of all obtained compounds was completely characterized both in a solid phase and in a solution by X-ray diffraction analysis, mass spectrometry, and IR and polynuclear NMR spectroscopy.     

Biology‐Oriented Combined Solid‐ and Solution‐Phase Synthesis of a Macroline‐Like Compound Collection

Macrolines constitute a class of natural products that has more than 100 members and displays diverse biological activities. These compounds feature a cycloocta[b]indole scaffold that represents an interesting target structure for biology‐oriented synthesis (BIOS). We have presented a solid‐phase synthesis of isomerically pure cycloocta[b]indoles by employing the Pictet–Spengler reaction and the Dieckmann cyclization as key steps. The scope of this reaction sequence was investigated in more detail by using various additional diversification procedures, such as Pd‐catalyzed Sonogashira or Suzuki couplings on a solid phase, thus allowing, for example, the generation of 10‐substituted cycloocta[b]indole derivatives. Finally, solution‐phase decoration of the cycloocta[b]indole skeleton by reduction and saponification was evaluated, thereby further extending the scope of the solid‐phase synthesis.     

Polymorphie von SrTa2O6

Polymorphism of SrTa₂O₆ Orthorhombic SrTa₂O₆ is a new low temperature modification related to orthorhombic CaTa₂O₆. SrTa₂O₆(orh.) was obtained when the wellknown modification SrTa₂O₆(TTB) which is related to the tetragonal tungsten bronzes was heated in the presence of a transporting agent (chlorine) or a mineralizer (melt of B₂O₃) at temperatures below 1150°C. It could be prepared by the reaction of a 1:1 mixture of Sr(NO₃)₂ or SrCO₃ with Ta₂O₅ in a sealed quartz glass tube as well. SrTa₂O₆(orh.) also occurred as an intermediate phase of the reaction of the corresponding 1:2 mixture at temperatures below 900°C (e. g. 840°C). Indexing of Guinier powder patterns led to the following unit cell: a = 11.006 Å, b = 7.638 Å, c = 5.622 Å. At temperatures above 1220°C SrTa₂O₆(orh.) changes (in air) to SrTa₂O₆(TTB). A reversal of this transition could not be achieved without the presence of a mineralizer or a transporting agent. Ca_xSr_1?xTa₂O₆ solid solutions of the low temperature form could not definitely be established. However, at 1300°C solid TTB solutions of Ca_xSr_1?xTa₂O₆ were formed. For x > 0.05 the TTB unit cells are orthorhombically distorted. For x ≥ 0.85 the x-ray powder patterns of the solid solutions looked like the one of CaTa₂O₆(orh.) and no TTB-structure was observed at 1300°C.