Survey of the phase formation in the Yb2O3Ga2O3MO and Yb2O3Cr2O3MO systems in air at high temperatures (M: Co,Ni, Cu,and Zn)

The phase relations in the Yb₂O₃Ga₂O₃CoO system at 1300 and 1200°C, the Yb₂O₃Ga₂O₃NiO system at 1300 and 1200°C, the Yb₂O₃Ga₂O₃CuO system at 1000°C and the Yb₂O₃Ga₂O₃ZnO system at 1350 and 1200°C, the Yb₂O₃Cr₂O₃CoO system at 1300 and 1200°C, the Yb₂O₃Cr₂O₃NiO system at 1300 and 1200°C, the Yb₂O₃Cr₂O₃CuO system at 1000°C, and the Yb₂O₃Cr₂O₃ZnO system at 1300 and 1200°C were determined in air by means of a classical quenching method. YbGaCoO₄ (a = 3.4165(1) and c = 25.081(2) Å), YbGaCuO₄ (a = 3.4601(4) and c = 24.172(6) Å), and YbGaZnO₄ (a = 3.4153(5) and c = 25.093(7) Å), which are isostructural with YbFe₂O₄ (space group: $\text{R}\text{3}\text{m, a = 3.455(1)}$ and c = 25.109(2) Å, were obtained as stable phases. In the Yb₂O₃Ga₂O₃NiO system and the Yb₂O₃Cr₂O₃MO system (M: Co, Ni, Cu, and Zn), no ternary stable phases existed.     

X-ray microanalysis and high-resolution transmission electron microscopy of the reduced titanium-niobium oxides

Phase relationships in TiNb₂O₇ and Ti₂Nb₁₀O₂₉ reductions at 1400°C were investigated by means of X-ray microanalytical electron microscopy and high-resolution transmission electron microscopy (TEM). Compositions of phases present in equilibrium were obtained by applying thin-crystal approximation by which $\text{Nb}\text{Ti}$ ratios in different phases were determined; their oxygen content was inferred from structural considerations. In this manner, phase relationships in that portion of the TiO₂NbO₂NbO_2.5 equilibrium diagram with 2.417 ≥ x (in MeO_x) ≥ 2 were defined. Data obtained, in combination with high-resolution electron microscopy observations, confirmed that the reduction reaction, in part, is a heterogeneous process controlled by outward diffusion of both metal and oxygen atoms. Recombination of the diffused particles leads to the formation of separate crystals. The original block structure phase undergoes transformation in a quasihomogeneous manner either to an isomorphous phase in the binary NbO system or to a structurally related lower composition oxide. A new superstructure Me₂₅O₆₀(Ti_7.16Nb_42.84O₁₂₀) has been detected as an intermediate metastable phase, generated in the reduction of TiNb₂O₇ to stable Me₁₂O₂₉(Ti_1.53Nb_10.47O₂₉) and MeO₂(Ti_0.52Nb_0.48O₂) phases. Consideration of phase relationships among Me₂₅O₆₀, Me₁₂O₂₉, and MeO₂ suggests a chemical mechanism for the reaction concerned. The Me₂₅O₆₀ superstructure has a monoclinic symmetry with cell parameters a = 19.0 Å, b = 3.8 Å, c = 26.6 Å, α = 90°, β = 90°, γ = 78.5°, as determined from the structure image calculations.     

Die chemie der schweren carben-analogen R2M,M = Si,Ge, Sn: X. 7-sila-norbornadiene: reaktionen mit halogenen und thermolyse in genewart von metallorganischen oder organischen halogeniden

The 7-sila norbornadienes (I–IV) react rapidly with halogens at −20 to +20°C to yield Me₂SiHal₂ (Hal = Cl, Br, I) and the naphthalene or benzene derivatives (V–VIII). Bromine in CCl₄ at 0°C, however, caused surprising rearrangement in I giving the 2-bromosilylated naphthalene (IX), since an attack at the alkene group seemed to be preferred. Methylation and methoxylation of IX gave respectively X and XI. Careful hydrolysis of IX yielded the disiloxane VII. Insertions of Me₂Si into the SiHal, SiH, SiC, or SnC bonds were not observed at 160–200°C, whereas insertions into SnCl or SnH bonds occurred smoothly via a one-step mechanism. Halogen is abstracted from different CHal bonds leading to Me₂SiHal₂ and sometimes to Me₄Si₂Hal₂. The degradation of the silylene precursors in these cases is always first order and resembles that of spontaneous thermolysis.     

The phase relations in the In2O3A2O3BO systems at elevated temperatures [A: Fe or Ga, B: Cu or Co]

The phase relations in the In₂O₃Fe₂O₃CuO system at 1000°C, the In₂O₃Ga₂O₃CuO system at 1000°C, the In₂O₃Fe₂O₃CoO system at 1300°C, and the In₂O₃Ga₂O₃CoO system at 1300°C were determined by means of a classical quenching method. InFeCuO₄ (a = 3.3743(4) Å, c = 24.841(5) Å), InGaCuO₄ (a = 3.3497(2) Å, c = 24.822(3) Å), and InGaCoO₄ (a = 3.3091(2) Å, c = 25.859(4) Å) having the YbFe₂O₄ crystal structure, In₂Fe₂CuO₇ (a = 3.3515(2) Å, c = 28.871(3) Å), In₂Ga₂CuO₇ (a = 3.3319(1) Å, c = 28.697(2) Å), and In₂FeGaCuO₇ (a = 3.3421(2) Å, c = 28.817(3) Å) having the Yb₂Fe₃O₇ crystal structure, and In₃Fe₃CuO₁₀ (a = 3.3432(3) Å, c = 61.806(6) Å) having the Yb₃Fe₄O₁₀ crystal structure were found as the stable ternary phases. There is a continuous series of solid solutions between InFeCoO₄ and Fe₂CoO₄ which have the spinel structure at 1300°C. The crystal chemical roles of Fe³⁺ and Ga³⁺ in the present ternary systems were qualitatively compared.     

Sesquiterpenoids — XVI: Conformations of cycloheptane and α-methylene-γ-lactone rings in sesquiterpenoids: X-ray determination of the constitution,absolute stereochemistry,and conformation of euparotin bromoacetate

The molecular structure of euparotin, a highly oxygenated sesquiterpene of the guaianolide type, has been determined by crystal-structure analysis of euparotin bromoacetate. The bromo-derivative crystallizes from benzene-petrol as a benzene solvate, C₂₂H₂₅O₈Br·$\text{1}\text{2}$C₆H₆, crystals of which are monoclinic, of space group C2, with a = 34·85, b = 7·04, c = 10·90 Å, β = 106°35′, and Z = 4. The atomic co-ordinates were determined by Fourier and least-squares calculations which employed 1947 photographic |F₀| values and converged at R = 12·8% with isotropic thermal parameters for the C and O atoms and anisotropic parameters for the Br atom. The absolute configuration was established by the anomalous-dispersion effect. The cycloheptane ring of the sesquiterpenoid has a conformation which is closer to a twist chair (C₂) than a chair (C_s) form, and a survey shows that this is also true for other perhydroazulene sesquiterpenoids. In the α-methylene-γ-lactone of euparotin and several other sesquiterpenoids the CCCO torsion angle has the same sign as the C(α)C(β)C(γ)-O torsion angle, establishing the basis for Stöcklin et al's correlation between the position and stereochemistry of lactone fusion and the sign of the Cotton effect of the n → π* transition of the CCCO chromophore.     

Effect of gadolinium substitution on the linear thermal expansion of barium sodium niobate

Ba₂NaNb₅O₁₅ (BSN) exhibits a large thermal contraction in its c-axis between 350° and 750°C. This behaviour contributes to a serious cracking problem during its crystal growth. The substitutions of Gd for Ba and/or Na in BSN can be made with either anion or cation compensation. The former, namely, type A, compositions were found to eliminate the thermal contraction behaviors, and had small variations in their linear thermal expansion coefficients, α, between 50° and 650°C. With good ferroelectric and dielectric properties, they showed potentials to replace the BSN crystal in electro-optic devices.     

The structure of (dichloro) (DI-μ-acetato)(bis-triphenyl phosphine) dimolybdenum(II)

The title compound was obtained in crystalline form suitable for X-ray structure determination. It forms crystals in the monoclinic space group P2₁/c with two centrosymmetric molecules in a unit cell of dimensions, a = 10.888(1) Å, b = 10.182(2) Å, c = 17.929(4) Å, β = 104.33(1)°. The central Mo₂Cl₂(O₂C)₂P₂ core has effectively C_2h-symmetry with the following principal dimensions: MoMo = 2.091(1) Å, MoCl = 2.405 Å, MoP = 2.566(2) Å, MoO(av.) = 2.103[4] Å, MoMoP = 104.38(7)°, and MoMoCl = 116.23(8)°.     

Studies of alkylmetal alkoxides of aluminium,gallium and indium : IV. The molecular structure of dimethylaluminium t-butoxide dimer by gas phase electron diffraction

The electron diffraction data for gaseous dimethylaluminium t-butoxide dimer are consistent with a molecular model of effective D_2h symmetry. The Al₂O₂ ring is planar and the three valencies of the O atoms are lying in a plane. The t-butyl groups undergo nonhindered or slightly hindered internal rotation. The most important bond distances and valence angles are: AlO = 1.864(6), AlC = 1.962(15), OC = 1.419(12), CC = 1.533(5) Å, ∠AlOAl = 98.1(0.7), ∠CAlC = 121.7(1.7) and ∠OCC = 110.4(0.5)°.     

Struktur und Bindung in Übergangsmetall-Fluoriden MIIMeIVF6: Neutronenbeugungs-Strukturuntersuchungen an CaSnF6, FeZrF6, und CrZrF6

Compounds M^IIMe^IVF₆ requently undergo phase transitions from the cubic ordered ReO₃ to the trigonal LiSbF₆ structure when lowering the temperature. In case of a strongly Jahn-Teller unstable cation in the M^II position additional phases may occur. Results of powder neutron-diffraction studies on CaSnF₆, FeZrF₆, and CrZrF₆ at different temperatures are reported. The high-temperature phases have the space group Fm3m; the F^? ligands are either statistically displaced from the M^IIMe^IV directions or undergo a strong thermal motion perpendicular to these directions ($\text{?M}{}^{\mathrm{<mtext>II</mtext>}}\text{}\text{FMe}{}^{\mathrm{IV}}$: 165–180°). The thermal ellipsoids of the CrF bonds are strongly indicative of a dynamical Jahn-Teller effect in addition. In the low-temperature phases of CaSnF₆ and FeZrF₆ (space group $\text{R}\text{3}$) the $\text{?M}{}^{\mathrm{<mtext>II</mtext>}}\text{}\text{FMe}{}^{\mathrm{IV}}$ is more distinctly bent (?155–160°). CrZrF₆ undergoes two reversible phase transitions, which are determined to occur at 415 ± 5 K (cubic → tetragonal, dynamic to static Jahn-Teller distortion of CrF₆ octahedra and 150 ± 10 K (tetragonal → (pseudo)monoclinic).     

The crystal structure of triphenyltin isothiocyanate

The crystal structure of Ph₃SnNCS has been determined by single crystal X-ray diffraction. The crystals are monoclinic, P2₁, a = 19.02(3), b = 11.67(2), c = 15.49(2)Å;, β = 95.64(10)°, Z = 8. The molecules are arranged in infinite zig-zag S…SnNCS…Sn&.sbnd; chains similar to those in Me₃SnNCS, but with slightly longer SnN, shorter SnS bonds, and almost planar SnC₃ units. Principal mean bond lengths and angles are: SnN, 2.22(5); NC, 1.17(8); CS, 1.58(7); SSn, 2.92(1); SnC, 2.09(3); CC, 1.38(2)Å; SnNCm 161(4); CSSn, 97(3); SSnN, 175(3) and CSnC, 119.8(1.5)°.     

Skew-trapezoidal bipyramidal diorganotin(IV) bischelates. Crystal structure of dimethylbis(2-pyridinethiolato-N-oxide)tin(IV)

Dimethylbis(2-pyridinethiolato-N-oxide)tin(IV), Me₂Sn(2-SPyO)₂, crystallizes in space group P2₁/c with a 9.877(3), b 11.980(4), c 13.577(3) Å, β 109.1(2)° and Z = 4. The structure was refined to R_F = 0.036 for 2263 Mo-K_α observed reflections. The coordination geometry at tin is a skew-trapezoidal bipyramid, with the oxygen [SnO 2.356(3), 2.410(4) Å] and sulfur [SnS 2.536(1), 2.566(1) Å] atoms of the chelating groups occupying the trapezoidal plane and the methyl groups [SnC 2.106(6), 2.128(7) Å] occupying the apical positions. The methyl-tin-methyl skeleton is bent [CSnC 138.9(2)°]. The SSnS angle is 77.8(1)°, but the OSnO angle is opened to 136.7(1)° to accommodate the intruding methyl groups. The carbontincarbon angles predicted from quadrupole splitting (^119mSn Mössbauer) and one-bond ¹¹⁹Sn¹³C coupling constant (solution ¹³C NMR) data agree closely with the experimental value.     

Röntgenographische,thermoelektrische, und IR-spektroskopische Untersuchung des Spinellsystems LixMn1−xV2O4

The spinels of the system Li_xMn_1?xV₂O₄ (0 ? x ? 1) have been prepared at 700–750°C from LiV₂O₄ and MnV₂O₄. The lattice constants decrease linearly with increasing x. In the region x>0.75, the d-electrons of V should be delocalized as the VV distances are lower than the critical VV separation of 2.94 Å. Experimentally, the samples with x>0.6 show no IR absorption bands and the Seebeck coefficient is near zero. The Seebeck coefficient can be described with a model of intermediate polarons and can be expressed by the equation $\text{Θ = 198}\text{log}\text{[1 +}\text{(1 ? x)}{}^5\text{x}\text{]}$.     

Author index for volume 47

The phase diagram of the pseudo-ternary MnV₂O₆LiVMoO₆MoO₃ system has been determined with DTA and X-ray phase analysis. Its outstanding feature is the very large range of stability of the quaternary solid solution α-ML? described by the formula Mn_1?x?yLi_y?_xV_2?2x?yMo_2x+yO₆ (? = cation vacancy), and crystallizing in the monoclinic brannerite-type structure. In this solution y may vary between 0 and 1, which corresponds to the entire miscibility of MnV₂O₆ and LiVMoO₆; x may change between 0 and x_max depending on y (if, e.g., y equals 0.00, 0.40, 0.84, or 1.00, x_max is 0.45, 0.28, 0.16, or 0.00, respectively). Depending on composition, α-ML? is stable up to 540–710°C. Other features of the diagram, including the liquidus, are described in detail. The dependence of unit cell dimensions on composition of α-ML? has been determined. On passing from MnV₂O₆ to LiVMoO₆, the lattice parameter b and unit cell volume increase, c and c sin β decrease, and a changes insignificantly. These changes are interpreted by taking into account the ionic radii of the components and the specific details of the brannerite-type structure. ML? solid solutions were prepared using the amorphous citrate precursor method.     

The molecular structure of [dimethyl(phenyl)silyl]tris(trimethylsilyl)methane

The structure of the crowded molecule (Me₃Si)₃C(SiMe₂Ph) has been determined by single crystal X-ray diffraction. The steric strain manifest itself mainly in lengthening of the Me₃SiC and Me₂PhSiC bonds (average length 1.920(6) $\text{,ac>A}\text{?}$) and closing up of the CSiC angles within the Me₃Si and Me₂PhSi groups (average 105.2(10)°), with correspondingly large C(1)SiC angles (113.5(13)°; C(1) is the central carbon atom).     

Mono-, di-, and tetra-aurated derivatives of barbituric acid,including a new type of polynuclear gold compound. Crystal structure of 1,3-bis(triphenylphosphinegold)-5,5-diethylbarbituric acid

Reaction of barbituric acid (2,4,6-pyrimidinetrione) or its derivatives with LAuCl (L = triphenylphosphine) gave 3-LAu-5,5-diethyl-, 1,3-(L'Au)₂-5,5-diethyl- (L′ = L or L′ = Cy₃P), 1,3-dimethyl-5,5-bis(LAu)-, or 1,3,5,5-tetrakis-(LAu)barbituric acid, which were characterized as N-, N,N′-, C,C′-, or N,N′,C,C-gold derivative,s respectively, by IR, ¹H, ¹³C and ³¹P NMR spectroscopy. In the case of 1,3-(LM)(L″M)-5,5-diethylbarbituric acid compounds with M = gold and L″ either Cy₃P, Ph₃As, or (4-tolyl)₃P, or ML = ML″ = HgMe were prepared. An X-ray diffraction study of 1,3-(LAu)₂-5,5-Et₂-pyrimidin-2,4,6-trione · 3C₆H₆ revealed that (a) the heterocyclic ring is planar, (b) there is no inter- or intra-molecular Au ⋯ Au interaction, and (c) the coordination around each gold atom is approximately linear (PAuN 178.3(4)°, with AuN 2.022(12) and AuP 2.233(5) Å. The molecular parameters are compared with those for barbituric acid and other barbiturates.     

Selective self-assembly synthesis of MnV2O6·4H2O with controlled morphologies and study on its thermal decomposition

The MnV₂O₆·4H₂O with rod-like morphologies was synthesized by solid-state reaction at low heat using MnSO₄·H₂O and NH₄VO₃ as raw materials. XRD analysis showed that MnV₂O₆·4H₂O was a compound with monoclinic structure. Magnetic characterization indicated that MnV₂O₆·4H₂O and its calcined products behaved weak magnetic properties. The thermal process of MnV₂O₆·4H₂O experienced three steps, which involves the dehydration of the two waters of crystallization at first, and then dehydration of other two waters of crystallization, and at last melting of MnV₂O₆. In the DSC curve, the three endothermic peaks were corresponding to the two steps thermal decomposition of MnV₂O₆·4H₂O and melting of MnV₂O₆, respectively. Based on the Kissinger equation, the average values of the activation energies associated with the thermal decomposition of MnV₂O₆·4H₂O were determined to be 55.27 and 98.30?kJ?mol^?1 for the first and second dehydration steps, respectively. Besides, the thermodynamic function of transition state complexes (??H ^??, ??G ^?? , and ??S ^?? ) of the decomposition reaction of MnV₂O₆·4H₂O were determined.     

Syntheses and structural aspects of rigid aryl- palladium(II) and -platinum(II) complexes. X-ray crystal structure of o,o′-bis[(dimethylamino)methyl]phenyl- platinum(II) bromide

The tridentate monoanionic ligand o,o′-(Me₂NCH₂)₂C₆H₃ (NCN′) has been used to synthesize novel aryl-palladium(II) and -platinum(II) complexes [PtR(NCN′)] and [MX(NCN′)] (M = Pt, Pd). Three synthetic procedures are described, namely: (i) reaction of the cationic complex [M(NCN′)(H₂O)]⁺ with KX or NaX to give [MX(NCN′)] (X = Cl, I, O₂CH, NCS, NO₂, NO₃); (ii) displacement reactions using AgX with [MBr(NCN′)] to give [MX(NCN′)] (X = CN, O₃SCF₃. O₂CMe, O₂CCF₃) and (iii) transmetallation reactions of [PtBr{C₆H₃(CH₂NMe₂)₂-o,o′}] with organolithium to give [PtR{C₆H₃(CH₂NMe₂)₂-o,o′}] (R = Ph, o-, m-, p-tolyl, CCPh, CC-p-tolyl). All complexes have been characterized by elemental analysis, and IR, ¹H and ¹³C NMR spectroscopy.An X-ray diffraction study has shown that [PtBr{C₆H₃(CH₂NMe₂)₂-o,o′}] (2) has a square-planar structure, in which the tridentate ligand is bonded via C(ipso) (PtC 1.90(1) Å), and two mutually trans-N donor atoms (PtN(1) 2.07(1), PtN(2) 2.09(1) Å). The fourth site trans to C(ipso) is occupied by bromine (PtBr 2.526(2) Å). The two chelate rings (NPtC(ipso) 82.9(5) and 81.5(5)°) are distinctly puckered, with the two NMe₂ groups on opposite sides of the aryl plane. The PtC bond in 2 is shorter than analogous bonds in other arylplatinum(II) complexes, as a result of (i) the rigid structure of the tridentate ligand and (ii) the presence of two hard N donor atoms trans to one another across the platinum centre.     

Phase equilibria and thermodynamics of coexisting phases in rare-earth element-iron-oxygen systems. III. The europium-iron-oxygen system

X-ray and microstructural analysis methods were used to study the possibility of cationic nonstoichiometry in intermediate phases of the ferroperovskite-ferrogarnet type of the Eu₂O₃Fe₂O₃ system. It is shown that at 1350°C europium ferroperovskite has a narrow range of nonstoichiometry in the direction of excess iron oxide. The character of phase changes in the EuFeO system during changes in P_O2 has been studied; the equilibrium pressure of oxygen on ferrogarnet and magnetite has been calculated, and an equilibrium phase diagram of the type log P_O2 = f(composition) at 1473°K has been constructed. The relative stability of europium ferroperovskite and ferrogarnet has been evaluated.     

Molecular structure and conformational composition of gaseous 1,1-dichloro-2-bromomethyl-cyclopropane and 1,1-dichloro-2-cyanomethyl-cyclopropane as determined by electron diffraction

The molecular structure of the title compounds have been investigated by gas-phase electron diffraction. Both molecules exist as about equal amounts of the two gauche conformers. There is no evidence for the presence of a syn conformer, but small amounts of this form cannot be excluded. Some of the important distance (r_a) and angle (∠_α) parameters for 1,1-dichloro-2-bromomethyl-cyclopropane are: r(CH) = 1.095(19) Å, r(C₁C₂) = 1.476(11) Å, r(C₂C₃) = 1.517(31) Å, r(CCH₂Br) = 1.543(32) Å, r(CCl) = 1.752(6) Å, r(CBr) = 1.950(13) Å, ∠CCBr = 110.5(1.9)°, ∠ClCCl = 111.9(6)°, ∠CCC = 117.5(1.3)°, σ₁ (CC torsion angle between CBr and the three-membered ring for gauche-1) = 116.2(5.6)°, σ₂ = −132.7(7.6). For 1,1-dichloro-2-cyanomethyl-cyclopropane the parameter values are: r(CH) = 1.101(16) Å, r(C₁C₂) = 1.498(9) Å, r(C₂C₃) = 1.544(21) Å, r(C₂C₄) = 1.497(33) Å, r(CCN) = 1.466(26) Å, r(CN) = 1.165(8) Å, r(CCl) = 1.754(5) Å, ∠CCCN = 113.7(2.0)°, ∠CCC = 122.8(1.6)°, ClCCl = 112.5(4)°, σ₁ = 113(13)°, σ₂ = −124(10)°.     

Notable features in the molecular structure of W2(OCH2-t-Bu)6(NCNMe2)3: Three different modes of bonding for NCNMe2(2-) ligands

Hydrocarbon solutions of W₂(OCH₂-t-Bu)₆(HNMe₂)₂(MM) and Me₂NCN (?3 equiv) react at 0°C to give a compound of formula W₂(OCH₂-Bu-t)₆(NCNMe₂)₃. The crystal and molecular struture of the latter compound, deduced from an X-ray study, reveals the loss of the WW triple bond (WW = 3.85 Å) and the formal reduction of each Me₂NCN molecule to a 2- ligand for which three different modes of bonding are seen.