New total synthesis of dl-physostigmine (dl-eserine) via regioselective NaBH4-reduction of imides

The regioselective NaBH₄/H⁺ reduction of α,α-disubstituted succinimides offers a method for a short and stereoselective total synthesis of dl-physostigmine in which the key-step is the formation of the B-ring via amine substitution on a ω-carbinol-lactam.     

Practical optical resolution of dl-muscone using tartaric acid derivatives as a chiral auxiliary

A simple and practical synthesis of (R)-(−)-muscone was achieved by optical resolution of dl-muscone using tartaric acid derivatives. The acetalization of dl-muscone with N,N′-dibenzyl-l-tartaramide in the presence of Sc(OTf)₃ and methyl orthoformate furnished a diastereomeric mixture of acetals, which were readily separated by simple recrystallization. Diastereomerically pure acetal was hydrolyzed to give optically pure muscone and recovered N,N′-dibenzyl-l-tartaramide.     

Mono- and di-nuclear rhodium complexes of meso- and dl-1,1,4,7,10,10-hexaphenyl-1,4,7,10-tetraphosphadecane. Stereochemical control of reactivity and complexation geometry

Thermolysis of meso- and dl-1,1,4,7,10,10-hexaphenyl-1,4,7,10-tetraphosphadecane (200°C, 10 min) followed by fractional crystallisation from ethanol/dichloromethane gives two sharp-melting diastereomers. The higher melting compound, herein shown to be the meso-isomer, reacts with 1,5-cyclooctadiene-2,4-pentanedionatorhodium and HBF₄ to give the dinuclear rhodium complex (3). This underwent hydrogenation slowly in methanol solution with deposition of rhodium metal and formation of a mononuclear complex (5) with four coordinated phosphorus nuclei, also obtained by independent synthesis. This proved to be highly susceptible to oxidation, forming a dioxygen complex (6) with P(1) and P(3) mutually trans. The lower melting dl-isomer likewise formed a dinuclear rhodium complex (4) on reaction with 1,5-cyclooctadiene-2,4-pentanedionatorhodium and HBF₄. This reacted more rapidly than complex 3 with hydrogen forming a mononuclear dihydride (7) and metallic rhodium. In the presence of cyclohexene, a tetracoordinate phosphinerhodium complex (9) was formed. This reacted with oxygen to give dioxygen complex (10), although here P(1) and P(4) are mutually trans, and with carbon monoxide to give a five-coordinate monocarbonyl (11).The corresponding dirhodium bis-cyclooctadiene complex of 1,1,4,8,11,11-hexaphenyl-1,4,8,11-tetraphosphaundecane (13) (a single diastereomer of unknown stereochemistry), reacted with hydrogen in methanol to form a dinuclear solvate without reductive degradation.     

Low-temperature phases of the solid electrolyte Ag26I18W4O16

Single crystal X-ray diffraction photographs taken with a Buerger precession camera, at temperatures 250, 214, and 122 K, corroborate the existence of three low-temperature phases of Ag₂₆I₁₈W₄O₁₆. These phases are labeled α′, β, and γ in order of decreasing temperature. The α′ phase is monoclinic, space group P2₁, Z = 2; the β phase is triclinic, space group $\text{P}\text{1}$ or P1, Z = 2; and the γ phase is triclinic, space group P1, Z = 1. Lattice constants at the aforementioned temperatures are given. Twins in the β and γ phases are related by the albite and pericline laws, as are twins in the feldspars. The highest symmetry known to be attained by the (W₄O₁₆)^8? entity is 2(C₂), which, strictly, it must lose at the transition to the α′ phase.     

The synthesis and crystal structure of α-Ca3UO6

Single crystals of α-Ca₃UO₆ were grown from a UO₃CaCl₂CaO melt by the slow cooling method from 950°C. The crystal structure was determined by means of X-ray diffraction with R = 0.032 and R_w = 0.019. The structure of α-Ca₃UO₆ is of Mg₃TeO₆ type. α-Ca₃UO₆ is rhombohedral with a = 6.729 (1)Å, α = 90.30 (1)°, Z = 2, D_c = 4.955 g/cm³, D_m = 4.79 g/cm³, space group $\text{R}\text{3}$. Uranium and calcium atoms are six-coordinated. At 1200°C rhombohedral α-Ca₃UO₆ irreversibly transforms to monoclinic β-Ca₃UO₆.     

One pot synthesis using supported reagents system KSCN/SiO2-RNH3OAc/Al2O3: synthesis of 2-aminothiazoles and N-allylthioureas

A simple and efficient method has been developed for the synthesis of 2-aminothiazoles and N-allylthioureas from commercially available materials in one pot by using a supported reagents system, KSCN/SiO₂-RNH₃OAc/Al₂O₃, in which α-halo ketone reacts first KSCN/SiO₂ and the product, α-thiocyanatoketone, reacts with RNH₃OAc/Al₂O₃ to give the final product, 2-aminothiazoles, in good yield and allyl bromide reacts with KSCN/SiO₂ and the product, allyl isothiocyanate, reacts with RNH₃OAc/Al₂O₃ to give N-allylthiourea.     

Esr spectra and magnetic constants of α-Al2O3:Co,H

ESR spectra of the defect α-Al₂O₃:Co²⁺, H⁺ are reported and used to derive the magnetic tensors g and A. This defect is shown to exist in several types, and models in the framework of the α-Al₂O₃ structures are proposed.     

Characterization and evaluation of Fe2O3/Al2O3 oxygen carrier prepared by sol–gel combustion synthesis

The sol-gel combustion synthesis (SGCS) for oxygen carrier (OC) to be used in chemical looping combustion (CLC) was first designed and experimented in this work, which is a new method of OC synthesis by combining sol-gel technique and solution combustion synthesis. Cheap hydrated metal nitrates and urea were adopted as precursors to prepare Fe₂O₃/Al₂O₃ OC at the molar ratio to unity (Fe1Al1), which was characterized through various means, including Fourier transforms infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential thermal analysis (DTA), X-ray diffractor (XRD), and N₂ isothermal adsorption/desorption method. FTIR analysis on the chemical structure of the dried gel of Fe1Al1 indicated that urea was partly hydrolyzed and the hydrated basic carbonate was formed by the combination of groups such as (Fe(_1−yAl_y)_1−xO_1−3x, CO₃²⁻ and -OH-. By analyzing the staged products during SGCS, calcination was found as a necessary step to produce Fe₂O₃/Al₂O₃ OC with separate phases of α-Fe₂O₃ and α-Al₂O₃. Through TGA-DTA, the decomposition of the dried gel was found to undergo five stages. The analysis of the evolved gases from the gel decomposition using FTIR partially confirmed the staged decomposition and assisted a better understanding of the mechanism of SGCS. XRD identification further substantiated the necessity of calcination to synthesize Fe₂O₃/Al₂O₃ OC with separate phases of α-Fe₂O₃ and α-Al₂O₃, though it was not necessary for the synthesis of single phase α-Fe₂O₃ and α-Al₂O₃. Structural characterization performed on N₂ adsorption analyzer displayed that the pore shape of Fe1Al1 particles was heterogeneous. Finally, H₂ temperature-programmed reduction (TPR) of Fe1Al1 products in TGA indicated that the reduction reaction of Fe1Al1 OC after calcination was a single step reaction from α-Fe₂O₃ to Fe, and calcination benefited to improve the transfer rate of the lattice oxygen from the OC to fuel H₂. Furthermore, four times of reduction and oxidization (redox) reaction by alternating with H₂ and air demonstrated the synthesized OC had good reactivity and sintering-resistance, much suitable to be used in the realistic CLC. Overall, the SGCS method was found superior to other existent methods to prepare Fe₂O₃/Al₂O₃ OC for CLC application.     

The local structure and composition of Ba4Nb2O9-based oxycarbonates

X-ray powder-diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), infrared spectroscopy (IR), thermogravimetry (TG) and mass spectroscopy (MS) were performed to investigate the composition and the crystal structure of tetra-barium di-niobate (V) Ba₄Nb₂O₉. The TG, MS and IR studies revealed that the compound is a hydrated oxycarbonate. Assuming that the carbonate stoichiometrically replaces oxygen, the composition of the low-temperature α-modification, obtained by slow cooling from 1100 °C, corresponds to Ba₄Nb₂O_8.8(CO₃)_0.2·0.1H₂O, while the quenched high-temperature γ-modification has the Ba₄Nb₂O_8.42(CO₃)_0.58·0.38H₂O composition. The α-phase has a composite incommensurately modulated structure consisting of two mutually interacting [Ba]_∞ and the [(Nb,□)O₃]_∞ subsystems. The composite modulated crystal structure of the α-phase can be described with the lattice parameters a=10.2688(1) Å, c=2.82426(8) Å, q=0.66774(2)c* and a superspace group Rm(00γ)0s. The HRTEM analysis demonstrates the nanoscale twinning of the trigonal domains parallel to the {1 0 0} crystallographic planes. The twinning introduces a one-dimensional disorder into the [(Nb,□)O₃]_∞ subsystem, which results in an average P2c crystal structure of the α-phase. Possible places for the carbonate group in the structure are discussed using a comparison with other hexagonal perovskite-based oxycarbonates.     

An organosilyl derivative of trivacant tungstophosphate. Synthesis, characterization and crystal structure determination of α-A-[NBu4]3[PW9O34(C2H5SiO)3(C2H5Si)]

In the presence of NBu₄ⁿBr acting as phase-transfer reagent, organosilicon trichloride C₂H₅SiCl₃ reacts in acetonitrile with the trivacant tungstophosphate sodium salt β-A-Na₈H[PW₉O₃₄]·24H₂O to give hybrid organosilyl polyoxotungstate derivative α-A-[NBu₄ⁿ]₃[PW₉O₃₄(C₂H₅SiO)₃(C₂H₅Si)]. X-ray single crystal structural analysis indicates that the title compound is monoclinic, space group Cc, with lattice constants a=26.828(5), b=22.459(5), c=17.517(4) Å, β=103.19(3)°, V=10,276(4) Å³, Z=4, R=0.0462. According to the result of X-ray single crystal diffraction and chemical analysis, the hybrid polyanion consists of one α-A-[PW₉O₃₄]⁹⁻ framework on which are grafted simultaneously three RSiO groups through six Si-O-W bridge bonds, each of which is attached to the fourth RSi group through three Si-O-Si bridge bonds. The hybrid polyanion becomes a partial saturated, closed cage structure and also has an assembly of virtual C_3V symmetry.     

ESR spectra and magnetic constants of α-Al2O3:Co2+,H+ and α-Al2O3 :Co2+,X+

New anisotropic ESR spectra of Co²⁺ doped sapphire, different from hitherto known, are reported. The new spectra which are observed, beside the well-known spectra of α-Al₂O₃:Co²⁺, are shown to form two sets, each one consisting of six spectra (1–6) and (7–12). The spectra of both sets are proven to be interrelated by B_3a symmetry. g and A tensors for each set will be given. Evidence is given that the two sets are to be assigned to the defects α-Al₂O₃:Co²⁺,H⁺ and α-Al₂O₃:Co²⁺,X⁺. The former is concluded to consists of a Co²⁺ ion at the substitutional site (c) and a proton located in a potential minimum along a straight line between O^2- ions situated in O²⁺ triangles above and below the CO²⁺ ion. The potential function for the proton has been calculated by quantum-chemical calculations to clucidate the geometrical structure of the paramagnetic center. The α-Al₂O₃:Co²⁺,X⁺ could not be fully analyzed but some evidence is presented, that X⁺ might be alkali ions.     

The luminescence of Cs3Bi2Cl9 and Cs3Sb2Cl9

The luminescence properties of Cs₃Bi₂Cl₉, α-Cs₃Sb₂Cl₉, and β-Cs₃Sb₂Cl₉ are reported and compared with those of Cs₃Bi₂Br₉. The first two compounds have comparable luminescence properties which can be described in terms of a band model. Deep center emission is observed for both compounds, whereas edge emission is observed only for Cs₃Bi₂Cl₉. The optical transitions of β-Cs₃Sb₂Cl₉ are localized on the Sb³⁺ ion. The orientation of the lone-pair orbitals of the ns² ions seems to play an important role in the formation of the cationic valence band. The α-β transformation must therefore have a considerable influence on the spectral properties of Cs₃Sb₂Cl₉.     

Kinetics of thermal decomposition of Co3O4 powder and single crystals

Kinetics of thermal decomposition in vacuum of Co₃O₄ powder as well as single crystals has been investigated. Discrepancies with the results of previous authors have been discussed. Decomposition of Co₃O₄ proceeds through formation of a compact layer of CoO and hence diffusion is the rate-limiting factor. The experimental curves α(t) be described for 0.05 < α < 0.85 using a modified Ginstling-Brounshtein equation: 1 ? 2α/3 ? (1 ? α)^2/3 = ktⁿ where the activation energy varies with the degree of decomposition.     

Influence of the preparation history of α-Fe2O3 on its reactivity for hydrogen reduction

TG experiments on the hydrogen reduction of α-Fe₂O₃ were carried out to elucidate the influence of the preparation history of the oxide on its reactivity. α-Fe₂O₃ samples were prepared by the thermal decomposition of seven iron salts in a stream of oxygen, air or nitrogen at temperatures of 500–1200°C for 1 h. Thirteen metal ions such as Cu²⁺, Ni²⁺, etc. were used as doping agents. The reactivity of the oxide was indicated by the initial reduction temperature (T_i. α-Fe₂O₃ prepared at lower temperatures showed lower T_i values and the reduction proceeded stepwise (Fe₂O₃ → Fe₃O₄ → Fe). T_i values increased with the rise in the preparation temperature of the oxide. The oxides prepared at higher temperatures showed that two reduction steps (Fe₂O₃ → Fe₃O₄ → Fe) proceed simultaneously. the preparation in oxygen gave higher T_i than that in air or nitrogen. The doping by metal ions, except Ti⁴⁺, lowered the T_i of α-Fe₂O₃. The Cu²⁺ ion showed the lowest T_i, while Ti⁴⁺ showed the highest T_i and the inhibition effect.The reduction process was expressed by two equations; Avrami—Erofeev's equation for α-Fe₂O₃ → Fe₃O₄ and Mampel's equation for Fe₃O₄ → Fe.     

Neutron powder diffraction on α-Tl4CrI6 and β-Tl4CrI6

α-Tl₄CrI₆ (a = 9.132(1), c = 9.667(1) Å, $\text{Z = 2,}\text{P4}\text{mnc}$ at 293 K) adopts a distorted Tl₄HgBr₆ structure. In α-Tl₄CrI₆ there occurs a random distribution of Jahn-Teller distorted octahedra which are elongated perpendicular to the c axis. Between 77 and 4.2 K a phase transition occurs. In β-Tl₄CrI₆ (a = 12.941(3), b = 12.596(3), c = 9.602(2) Å, Z = 4, Cccm at 4.2 K) the directions of elongation of the octahedra are ordered. The structure is very much related to that of α-Tl₄CrI₆. A three-dimensional magnetic ordering takes place at 2.7(2) K. The magnetic space group at 1.2 K is C_I22′2′. The magnetic moments (3.48(6) μ_B) are parallel to (0 0 1) and have an angle of 41(9)° with the a axis. Four magnetic sublattices are present, forming two independent magnetic lattices which have no interaction due to the antiparallel ordering.     

Structure and luminescence of the α-LnNb3O9-type rare earth niobates

α-LnNb₃O₉ (Ln = La, Pr, Nd) compounds have been prepared hydrothermally from acidic solutions. In comparison to the previously reported orthorhombic β modifications, α-LnNb₃O₉ compounds are monoclinic. The structure of α-PrNb₃O₉ was determined with a = 5.3784(6), b = 7.602(2), c = 16.344(2) Å, and β = 92.21(1)°, space group $\text{P2}{}_1\text{c}$. It is built of double and single chains of corner-shared NbO₆ octahedra extended along the b axis. Praseodymium atoms reside in tunnels along the b axis and are in eight-coordination with oxygen. All α-LnNb₃O₉ compounds can be irreversibly converted to the β modification by heating in air to 1200°C. The X-ray excited luminescence of Sm-, Eu-, Tb-, and Dy-doped α-LaNb₃O₉ is also reported.     

Ph2S2-CaH2 in N-methyl-2-pyrrolidone as an efficient protocol for chemoselective cleavage of aryl alkyl ethers

CaH₂ was been found, for the first time, as a mild reducing agent to generate thiophenolate anion from Ph₂S₂ in N-methyl-2-pyrrolidone (NMP) for deprotection of aryl alkyl ethers. Excellent chemoselctivity was observed for substrates having chloro and nitro groups without displacement of the chlorine atom and the nitro group. Selective ether cleavage took place in the presence of α,β-unsaturated carbonyl and nitro groups without reduction and conjugate addition (to the α,β-unsaturated carbonyl group).     

The α-AlB12 structure

The crystal structure of α-AlB₁₂, reported recently by Higashi, Sakurai, and Atoda is confirmed by an independent investigation of a different crystal. The space group is P4₁2₁2 (or P4₃2₁2) and our lattice parameters are a = 10.161(7)Å, c = 14.283(8)Å. The structure was partially solved by Patterson methods, when the full structure was communicated to us by Higashi et al. Utilizing 2393 reflections, our structure refinement yields an R value of 2.6% with very low standard deviations for structural parameters (0.0001 for atomic coordinates of boron atoms). Within the standard deviations there is excellent agreement with all parameters determined by Higashi et al. It is found, nevertheless, that the structural parameters of α-AlB₁₂ do not serve to account for the reported Debye-Scherrer patterns of “BeB₆,” “LiB₆,” or β-tetragonal boron, all of which have the same cell dimensions and space group as α-AlB₁₂.     

Crystal structure of KSbP2O8

KSbP₂O₈ crystallizes in the rhombohedral system, space group $\text{R}\text{3}$, with a = 4.7623(4) Å, c = 25.409(4)Å, and Z = 3. The structure was determined from 487 reflexions collected on a NONIUS CAD4 automatic diffractometer with MoK^?α radiation. The final R index and weighted R_w index are 0.030 and 0.038, respectively. This structure is built up from layers of SbO₆ octahedra and PO₄ tetrahedra sharing corners. These (SbP₂O^?₈)_n layers are very similar to the (ZrP₂O^2?₈)_n layers in the well-known α-ZrP compound.