Five-coordinate pentafluorobenzothiolate osmium(IV) complexes [Os(SC6F5)4(P(C6H4X-4)3)] (X = OCH3, CH3, F, Cl or CF3): Solid and solution structural characterization

The reactions of OsO₄ with excess of HSC₆F₅ and P(C₆H₄X-4)₃ in ethanol afford the five-coordinate compounds [Os(SC₆F₅)₄(P(C₆H₄X-4)₃)] where X = OCH₃ 1a and 1b, CH₃ 2a and 2b, F 3a and 3b, Cl 4a and 4b or CF₃ 5a and 5b. Single crystal X-ray diffraction studies of 1 to 5 exhibit a common pattern with an osmium center in a trigonal-bipyramidal coordination arrangement. The axial positions are occupied by mutually trans thiolate and phosphane ligands, while the remaining three equatorial positions are occupied by three thiolate ligands. The three pentafluorophenyl rings of the equatorial ligands are directed upwards, away from the axial phosphane ligand in the arrangement “3-up” (isomers a). On the other hand, ³¹P{¹H} and ¹⁹F NMR studies at room temperature reveal the presence of two isomers in solution: The “3-up” isomer (a) with the three C₆F₅-rings of the equatorial ligands directed towards the axial thiolate ligand, and the “2-up, 1-down” isomer (b) with two C₆F₅-rings of the equatorial ligands directed towards the axial thiolate and the C₆F₅-ring of the third equatorial ligand directed towards the axial phosphane. Bidimensional ¹⁹F–¹⁹F NMR studies encompass the two sub-spectra for the isomers a (“3-up”) and b (“2-up, 1-down”). Variable temperature ¹⁹F NMR experiments showed that these isomers are fluxional. Thus, the ¹⁹F NMR sub-spectra for the “2-up, 1-down” isomers (b) at room temperature indicate that the two S-C₆F₅ ligands in the 2-up equatorial positions have restricted rotation about their C–S bonds, but this rotation becomes free as the temperature increases. Room temperature ¹⁹F NMR spectra of 3 and 5 also indicate restricted rotation around the Os–P bonds in the “2-up, 1-down” isomers (b). In addition, as the temperature increases, the ¹⁹F NMR spectra tend to be consistent with an increased rate of the isomeric exchange. Variable temperature ³¹P{¹H} NMR studies also confirm that, as the temperature is increased, the a and b isomeric exchange becomes fast on the NMR time scale.     

Synthesis and structure of [C6N4H20]0.5[B5O6(OH)4]: A new organically templated pentaborate with white-light-emission

A new organically templated pentaborate [C₆N₄H₂₀]_0.5[B₅O₆(OH)₄] (1a) was prepared by reactions of triethylenetetramine (TETA) with excess boric acid in aqueous solution and characterized by elemental analysis, FTIR, TG-DTA, powder X-ray diffraction and photoluminescence spectroscopy. The structure of 1a was determined by a single-crystal X-ray diffraction. It crystallizes in the monoclinic system with space group P2(1)/c, a=9200(3) Å, b=14.121(5) Å, c=10.330(4) Å, β=91.512(4)°, V=1341.4(9) Å³, and Z=4. The luminescent properties of the compound were studied, and a green-blue luminescence occurs with an emission maximum at 507 nm upon excitation at 430 nm. The photoluminescence of 1a can be modified from green-blue to white by means of a simple heat-treatment process. The white-light-emission of sample 1c makes the pentaborate a good candidate for display and lighting applications in the white LED.     

The PtP(C6H11)3(C2H4)2 mediated activation of aldehyde CH bonds via chelate-assisted oxidative addition reactions

Hydrocarbon solutions of PtPCy₃(C₂H₄)₂ (Cy = cyclohexyl) react rapidly with 8-quinolinecarboxaldehyde (1 equiv.) to yield tricyclohexylphosphine quinolinecarboxyl platinum hydride (1) and CH₂CH₂ (2 equiv.). Compound 1 reacts with CCl₄ in hydrocarbons to give PtPCy₃(NC₉H₆CO)Cl (2) and CHCl₃. The compound PtPCy₃(C₂H₄)₂ also reacts with Ph₂P(C₆H₄-o-CHO) and Ph₂As(C₆H₄-o-CHO) to give PCy₃PtPh₂P(C₆H₄-o-CO)(H) (3) and PCy₃PtPh₂As(C₆H₄-o-CO)(H) (4), respectively. Compounds 1, 2, 3, and 4 were characterized by infrared and ¹H NMR spectra, and the crystal structure of 3 was determined by X-ray diffraction. Crystals of 3 are monoclinic, with space group P2₁/n and Z = 4 with the unit cell dimensions a 9.7936(17), b 14.844(35), c 23.530(64) Å, β 91.817 (18)°, and V 3419.09(1.36) ų. The structure is refined to final discrepancy factors of R = 0.055, and R_w = 0.064. The molecular structure of 3 is that ligating atoms are in a plane containing Pt. The position of the hydride was not located crystallographically, but the ¹H NMR spectrum of 3, supports the presence of a terminal hydride that is cis to the carbonyl. The IR band of 3 at 2023 cm^?1 which is assigned to ν(PtH), and the hydride cleavage reaction of 1 with CCl₄, provide evidence for the PtH bond.     

Allylstannation of α-, β- and γ-diketones mediated by allylbutyltin halides: Bu2(CH2=CHCH2) SnCl and Bu(CH2 =CHCH2) SnCl2

Butane-2,3- (1a), pentane-2,4- (1b) and hexane-2,5-dione (1c) react with Bu₂(CH₂=CHCH₂)SnCl in the presence of water to give monoallylated keto-ols (2a, 2b) and/or diallylated diols (3a, 3b, 3c), this depending upon the employed molar ratio [diketone]/[allyltin chloride]. Bu(CH₂=CHCH₂)SnCl₂ reacts with neat 1c in a one-pot synthesis to give mixtures of heterocyclic compounds: 2,5-diallyl-2,5-dimethyltetrahydrofuran (4), and 3-chloro-1,5-dimethyl-8-oxabicyclo [3,2,1] octane (5). Compound 4 is also obtained in high yield from the corresponding diol 3c by cyclodehydration promoted by RSnCl₃ (R = Me and Bu).     

Reactivity of 2,3-bis(2-pyridyl)pyrazine with [Re2(CO)8(CH3CN)2]: Molecular structures of [Re2(CO)8(C14H10N4)] and [Re2(CO)8(C14H10N4)Re2(CO)8]

The reaction of the labile compound [Re₂(CO)₈(CH₃CN)₂] with 2,3-bis(2-pyridyl)pyrazine in dichloromethane solution at reflux temperature afforded the structural dirhenium isomers [Re₂(CO)₈(C₁₄H₁₀N₄)] (1 and 2), and the complex [Re₂(CO)₈(C₁₄H₁₀N₄)Re₂(CO)₈] (3). In 1, the ligand is σ,σ′-N,N′-coordinated to a Re(CO)₃ fragment through pyridine and pyrazine to form a five-membered chelate ring. A seven-membered ring is obtained for isomer 2 by N-coordination of the 2-pyridyl groups while the pyrazine ring remains uncoordinated. For 2, isomers 2a and 2b are found in a dynamic equilibrium ratio [2a]/[2b]  =  7 in solution, detected by ¹H NMR (−50 °C, CD₃COCD₃), coalescence being observed above room temperature. The ligand in 3 behaves as an 8e-donor bridge bonding two Re(CO)₃ fragments through two (σ,σ′-N,N′) interactions. When the reaction was carried out in refluxing tetrahydrofuran, complex [Re₂(CO)₆(C₁₄H₁₀N₄)₂] (4) was obtained in addition to compounds 1-3. The dinuclear rhenium derivative 4 contains two units of the organic ligand σ,σ′-N,N′-coordinated in a chelate form to each rhenium core. The X-ray crystal structures for 1 and 3 are reported.     

Reduction reactions of the metallocene complex (η-C5H4CMe2C9H7)2ZrCl2

The preparation and characterization of the substituted bis(cyclopentadienyl) zirconium dichloride complexes (η⁵-C₅H₄CMe₂C₉H₇)₂ZrCl₂ (1a, b) is reported. The isomer mixture of 1a, b was treated with different reducing agents such as sodium and n-butyllithium under various reaction conditions. In these reactions CC and CH activation and cleavage reactions were observed. In combination with methylaluminoxane (MAO) 1a, b and 3 showed low activities as homogeneous ethylene polymerization catalysts and no activities towards propylene. Compounds 2 and 3 were characterized by NMR spectroscopy and X-ray crystallography.     

Syntheses, crystal structures and spectroscopic properties of KEu[AsS4], K3Dy[AsS4]2 and Rb4Nd0.67[AsS4]2

Three rare earth compounds, KEu[AsS₄] (1), K₃Dy[AsS₄]₂ (2), and Rb₄Nd_0.67[AsS₄]₂ (3) have been synthesized employing the molten flux method. The reactions of A₂S₃ (A = K, Rb), Ln (Ln = Eu, Dy, Nd), As₂S₃, S were accomplished at 600 °C for 96 h in evacuated fused silica ampoules. Crystal data for these compounds are: 1, monoclinic, space group P2₁/m (no. 11), a = 6.7276(7) Å, b = 6.7190(5) Å, c = 8.6947(9) Å, β = 107.287(12)°, Z = 2; 2, monoclinic, space group C2/c (no. 15), a = 10.3381(7) Å, b = 18.7439(12) Å, c = 8.8185(6) Å, β = 117.060(7)°, Z = 4; 3, orthorhombic, space group Ibam (no. 72), a = 18.7333(15) Å, b = 9.1461(5) Å, c = 10.2060(6) Å, Z = 4. 1 is a two-dimensional structure with ²_∞[Eu(AsS₄)]⁻ layers separated by potassium cations. Within each layer, distorted bicapped trigonal [EuS₈] prisms are linked through distorted [AsS₄]³⁻ tetrahedra. Each Eu²⁺ cation is coordinated by two [AsS₄]³⁻ units by edge-sharing and bonded to further two [AsS₄]³⁻ units by corner-sharing. Compound 2 contains a one-dimensional structure with ¹_∞[Dy(AsS₄)₂]³⁻ chains separated by potassium cations. Within each chain, distorted bicapped trigonal prisms of [DyS₈] are linked by slightly distorted [AsS₄]³⁻ tetrahedra. Each Dy³⁺ ion is surrounded by four [AsS₄]³⁻ moieties in an edge-sharing fashion. For compound 3 also a one-dimensional structure with ¹_∞[Nd₀.₆₇(AsS₄)₂]⁴⁻ chains is observed. But the Nd position is only partially occupied and overall every third Nd atom is missing along the chain. This cuts the infinite chains into short dimers containing two bridging [As₄]³⁻ units and four terminal [AsS₄]³⁻ groups. 1 is characterized with UV/vis diffuse reflectance spectroscopy, IR, and Raman spectra.     

Polymer-supported calix[4]arenes for sensing and conversion of NO2/N2O4

The use of simple calix[4]arenes 1a,b for NO₂/N₂O₄ sensing and conversion is demonstrated, both in solution and in the solid state. Upon reacting with these gases, compounds 1a,b encapsulate reactive NO⁺ cations within their cavities with the formation of deeply colored (λ_max∼570 nm) charge-transfer complexes 2a,b. Further functionalization of the calix[4]arene platform is reported for attachment to solid supports. Polymer-supported calixarene material 3 was prepared, which reversibly traps NO₂/N₂O₄ with the formation of nitrosonium storing polymer 4. Material 4 was effectively used for nitrosation of amides.     

Structure cristalline de La3ReO8

Lanthanum rhenium oxide, La₃ReO₈, crystallizes in the monoclinic system, space group C2₁ with the unit-cell dimensions a = 17.535(11), b = 11.889(7), c = 12.816(8) Å, γ = 90°, Z = 16. Single-crystal diffraction data were collected on an automatic four-circle diffractometer. The structure, determined by Patterson and Fourier methods, has been refined by full-matrix least-squares calculations to an R value of 0.09 for 4206 independent observed reflections. The presence of two superstructures along the a and b axes has made the determination of positions of oxygen atoms very difficult. It can be visualized as isolated ReO₆ octahedra defining tunnels, parallel to the b axis, occupied by a double chain of edge-shared La₄O tetrahedra.     

Carbomolybdate clusters formed by carbonyl insertion into molybdenum-oxygen bonds. Structural investigation of the [RMo4O15X] core (R = ---C9H4O, X = OCH3; R = ---C14H10, X = ---C7H5O2; R = C14H8, X = ---OH)

[C₄H₉)₄N]₂[Mo₂O₇] reacts with a variety of organic species containing α-diketone groups to give tetranuclear complexes of general composition [RMo₄O₁₅X]³⁻. The complexes [(C₄H₉)₄N]₃[(C₉H₄O)Mo₄O₁₅(OCH₃)] (I), [(C₄H₉)₄N]₃[(C₁₄H₁₀)Mo₄O₁₅(C₆H₅CO₂)] (11) and [(C₄H₉)₄N]₃[(C₁₄H₈)Mo₄O₁₅(OH)] (III) were synthesized from the reactions of dimolybdate with ninhydrin, benzil and phenanthraquinone, respectively. Complex II may also be prepared from dimolybdate and benzoin in acetonitrile-methanol solution, from which it co-crystallizes with the binuclear species [(C₄H₉)₄N]₂[Mo₂O₅(C₆H₅C(O)C(O)C₆H₅)₂] · CH₃CN · CH₃OH (IV). Complexes I–III exhibit the tetranuclear core, previously described for the α-glyoxal derivatives [(C₄H₉)₄N]₃[(HCCH)Mo₄O₁₅X], where X = F⁻ or HCO₂⁻. The ligands may be formally described as diketals, formed by insertion of ligand carbonyl subunits into molybdenum-oxygen bonds. The structures I–III differ most dramatically in the identity and coordination mode of the anionic ligand X⁻ which occupies a position opposite the diketal moiety relative to the [Mo₄O₁₁]²⁺ central cage. Thus, I exhibits a doubly bridging methoxy group in this position, while II possesses a benzoate ligand with an unusual μ₃-O,O′coordination mode. Complex III presents a hydroxy-group unsymmetrically bonded to three of the molybdenum centres. The stereochemical consequences of the various coordination modes are discussed. Crystal data: Compound I, monoclinic space group Pc, a = 24.888(2), b = 12.897(3), c = 24.900(3) Å, β = 101.94(2)°, D_calc = 1.28 g cm⁻¹ for Z = 4. Structure solution and refinement based on 8695 reflections with F_o 6σ(F_o) (Mo-K_α, λ = 0.71073 Å) converged at a conventional discrepancy factor of 0.060. Compound II, orthorhombic space group Pbca, a = 20.426(6), b = 26.916(6), c = 32.147(7) Å, V = 17673.2(20) ų, D_calc = 1.33 g cm⁻³ for Z = 8; 5224 reflections, R = 0.076. Compound III, tetragonal space group I4₁/a, a = b = 48.129(6), c = 13.057(2) Å, V = 30246.2(12) ų, D_calc = 1.35 g cm⁻³ for Z = 16; 5554 reflections, R = 0.053. Compound IV, orthorhombic space group Pnca, a = 16.097(4), b = 16.755(4), c = 25.986(7) Å, V = 7008.1(13) ų, Z = 4, D_calc = 1.18 g cm⁻³ ; 2944 reflections, R = 0.061.     

(C6H6)n-kohlenwasserstoffe: Eigenschaften und darstellung einer hexacyclischen C18H18-verbindung

The synthesis of the hexacyclic C₁₈H₁₈-compound 2 and its spectroscopic and chemical properties are reported. By temperature-dependent NMR, protons H^6,7 and H^17,18 are shown to be differently influenced by the dynamic equilibrium 2a ? 2b. At 130°, 2 decomposes into benzene and tetracyclo-(5.3.2.0^2,5.0^6,8)dodeca-3 (4).     

Structures of C4

Linear (1), cyclic (2) and bicyclic (3) alternatives are considered as possible ground-state structures for C₄. At the highest levels of theory, MP4SDQ/6-31¹//HF/6-31¹, 3, with two π electrons is found to be most stable.     

Reactions of bis(alkynyl)silanes with HB(C6F5)2: Formation of boryl-substituted silacyclobutene derivatives

Treatment of R₂Si(CC-SiMe₃)₂ [1a (Me), 1b (Ph)] with HB(C₆F₅)₂ at low temperature (253 K (a), 273 K (b)) gives the -B(C₆F₅)₂ substituted silacyclobutene products (4a,b) under kinetic control. Upon warming to room temperature they disappear to form the thermodynamically favoured isomeric silole derivatives (2a,b). Similar treatment of Me₂Si(CC-R¹)₂ [5a (R¹ = Ph), 5b (R¹ = tert-butyl) with HB(C₆F₅)₂ at room temperature gave the stable -B(C₆F₅)₂ substituted silacyclobutene derivatives 6 and 7, respectively. Subsequent photolysis resulted in a Z- to E-isomerization of the substituted exocyclic CC double bonds in these products. The silacyclobutene derivative E-6 was characterized by an X-ray crystal structure analysis.     

Reactions of tungsten and molybdenum propargyl complexes with Co2(CO)8, Co4(CO)12, and Cp2Mo2(CO)4. A crossover study of formation of (CO)3 Cp(CO)2

The nature of the protonation reaction of (

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o(CO)₃ (M = Mo, W; R = Me, Ph, p-MeC₆H₄) (2) (obtained from (CO)₃CpMCH₂CCR (1) and Co₂(CO)₈) to give (CO)₃ Cp(CO)₂ (3) was further investigated by a crossover experiment. Thus, reaction of an equimolar mixture of 2b (M = W, Cp = η⁵-C₅H₅, R = Ph) and 2e (M = W, Cp = η⁵-C₅H₄Me; R = p-MeC₆H₄) with CF₃COOH affords only 3b (same M, Cp, and R as 2b) and 3e (same M, Cp, and R as 2e) to show an intramolecular nature of this transformation. Reaction of (CO)₃CpWCH₂CCPh (1b) with Co₄(CO)₁₂ was also examined and found to yield 2b exclusively. Treatment of 1 with Cp₂Mo₂(CO)₄ at 0–5°C provides thermally sensitive compounds, possibly (CO)₂Cp

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oCp(CO)₂ (5), which decompose at room temperature to give Cp₂Mo₂(CO)₆ as the only isolated product.     

New binuclear vanadium(III) and (IV) squarate species: synthesis, structure and characterization of [V(OH)(H2O)2(C4O4)]2·2H2O and (NH4)[(VO)2(OH)(C4O4)2(H2O)3]·3H2O

Two new vanadium squarates have been synthesized, characterized by infrared and thermal behavior and their structures determined by single crystal X-ray diffraction. Both structures are made of discrete, binuclear vanadium entity but in 1, [V(OH)(H₂O)₂(C₄O₄)]₂·2H₂O the vanadium atom is trivalent and the entity is neutral while in 2, (NH₄)[(VO)₂(OH)(C₄O₄)₂(H₂O)₃]·3H₂O, the vanadium atom is tetravalent and the entity is negatively charged, balanced by the presence of one ammonium ion. Both molecular anions are bridged by two terminal μ₂ squarate ligands. 1 crystallizes in the triclinic system, space group P-1, with lattice constants a=7.5112(10) Å, b=7.5603(8) Å, c=8.2185(8) Å, α=106.904(8)°, β=94.510(10)°, γ=113.984(9)° while 2 crystallizes in the monoclinic system, space group C2/c, with a=14.9340(15) Å, b=6.4900(9) Å, c=17.9590(19) Å and β=97.927(12)°. From the magnetic point of view, V(III) binuclear species show ferromagnetic interactions at low temperatures. However, no anomalies pointing to magnetic ordering are observed down to 2 K.     

Hydroxy- and boronic-acid-functionalized carbosilanes: Synthesis and solid state structure of Si(C6H4-4-SiMe2((CH2)3OH))4

Consecutive synthesis methodologies for the preparation of carbosilanes (Ph)(Me)Si((CH₂)₃B(OH)₂)₂ (2), Si(C₆H₄-4-SiMe₂((CH₂)₃B(OH)₂))₄ (5), (Ph)(Me)Si((CH₂)₃OH)₂ (3), and Si(C₆H₄-4-SiMe_3−n((CH₂)₃OH)_n)₄ (6a, n = 1; 6b, n = 2; 6c, n = 3) are reported. Boronic acids 2 and 5 are accessible by treatment of (Ph)(Me)Si(CH₂CHCH₂)₂ (1) or Si(C₆H₄-4-SiMe₂(CH₂CHCH₂))₄ (4a) with HBBr₂·SMe₂ followed by addition of water, while 3 and 6 are available by the hydroboration of 1 or Si(C₆H₄-4-SiMe_3−n(CH₂CHCH₂)_n)₄ (4a, n = 1; 4b, n = 2; 4c, n = 3) with H₃B·SMe₂ and subsequent oxidation with H₂O₂.The single molecular structure of 6a in the solid state is reported. Representative is that 6a crystallized in the chiral non-centrosymmetric space group P2₁2₁2₁ forming 2D layers due to intermolecular hydrogen bond formation of the HO functionalities along the crystallographic a and c axes.     

Chiral chelate phosphanes: XI. Application of cyclopentane-based C2 chiral bis(phosphane) ligands C5H8(PR2)2 to Pt---Sn-catalyzed styrene hydroformylation

Treatment of [(1,5-C₈H₁₂)PtCl(X)] (X=Cl, CH₃, CH₂CMe₃) with C₂ chiral cyclopentane-1,2-diyl-bis(phosphanes) C₅H₈(PR₂)₂, either as racemic mixtures or as resolved enantiomers, afforded the chelate complexes [C₅H₈(PR₂)₂Pt(Cl)(X)] (X=Cl: R=Ph (1), N-pip (2), OPh (3); X=CH₃: R=Ph (4), N-pip (5), OPh (6); X=CH₂CMe₃: R=Ph (7), N-pip (8), OPh (9); ‘N-pip’=N(CH₂)₅), (+)-[(1R,2R)-C₅H₈{P(OPh)₂}₂PtCl₂] [(R,R)-3], (−)-[(1S,2S)-C₅H₈{P(OPh)₂}₂PtCl₂] [(S,S)-3], (−)-[(1R,2R)-C₅H₈(PPh₂)₂Pt(Cl)(X)], and (+)-[(1S,2S)-C₅H₈(PPh₂)₂Pt(Cl)(X)] (X=CH₃: (R,R)-4, (S,S)-4; X=CH₂CMe₃: (R,R)-7, (S,S)-7). Reacting 4, 6, and 7 with AgO₃SCF₃ led to triflate derivatives [C₅H₈(PR₂)₂Pt(X)(OSO₂CF₃)] [X=CH₃: R=Ph (11), OPh (12); X=CH₂CMe₃: R=Ph (13)] with covalently bonded OSO₂CF₃ ligands. The unusual Pt₂ complex [μ-Cl{C₅H₈(PPh₂)₂PtCH₃}₂]O₃SCF₃ (14) containing an unsupported single Pt---Cl---Pt bridge was also isolated. In the presence of SnCl₂, complexes 1, 3, 4, 6, 7, and 9 are catalysts for the hydroformylation of styrene forming 2- and 3-phenylpropanal together with ethylbenzene. Except for 1, they also catalyze the consecutive hydrogenation of the primary propanals to alcohols. High regioselectivities towards 2-phenylpropanal (branched-to-normal ratios ≥91:9) were obtained in hydroformylations catalyzed by 3 and 4, for which the influence of varied CO/H₂ partial pressures, catalyst-to-substrate ratios and different reaction temperatures and times on the outcome of the catalytic reaction was also studied. When tin-modified complexes (R,R)-3, (S,S)-3, and (S,S)-4 were used as optically active Pt(II) catalysts, an only low stereoselectivity for asymmetric hydroformylation (e.e.<18%) was observed. The Pt---Sn complexes [C₅H₈(PR₂)₂Pt(CH₃)(SnCl₃)] [R=Ph (15), OPh (17)], resulting from SnCl₂ insertion into the Pt---Cl bonds of 4 or 6, undergo rapid degradation in solution, forming mixtures composed of [C₅H₈(PR₂)₂Pt(X)(Y)] with R=Ph or OPh and X/Y=Cl/SnCl₃ (16, 18), Cl/Cl (1, 3), and SnCl₃/SnCl₃ (19, 20), respectively. In the presence of SnCl₂, triflate complex 11 also becomes a catalyst for styrene hydroformylation and consecutive hydrogenation of the aldehydes to alcohols. The crystal structures of 11 complexes — 2, 5, 7, 8, 9, 10 (the previously prepared [C₅H₈{P(N-pip)₂}₂Pt(CH₂CMe₃)₂]), 13, 14, 16, (R,R)-3, and (S,S)-3 — were determined by X-ray diffraction.     

Stereoconvergent synthesis of C1-C17 and C18-C25 fragments of bafilomycin A1

The effective syntheses of the enantiomerically pure C1-C17 2 and C18-C25 3 fragments as promising synthetic intermediates of bafilomycin A₁, 1 have been achieved.     

Phase transitions in K3AlF6

Phase transitions in the elpasolite-type K₃AlF₆ complex fluoride were investigated using differential scanning calorimetry, electron diffraction and X-ray powder diffraction. Three phase transitions were identified with critical temperatures , and . The α-K₃AlF₆ phase is stable below T₁ and crystallizes in a monoclinic unit cell with a=18.8588(2)Å, b=34.0278(2)Å, c=18.9231(1)Å, β=90.453(1)° (a=2a_c−c_c, b=4b_c, c=a_c+2c_c; a_c, b_c, c_c—the basic lattice vectors of the face-centered cubic elpasolite structure) and space group I2/a or Ia. The intermediate β phase exists only in very narrow temperature interval between T₁ and T₂. The γ polymorph is stable in the T₂<T<T₃ temperature range and has an orthorhombic unit cell with a=36.1229(6)Å, b=17.1114(3)Å, c=12.0502(3)Å (a=3a_c−3c_c, b=2b_c, c=a_c+c_c) at 250 °C and space group Fddd. Above T₃ the cubic δ polymorph forms with a_c=8.5786(4)Å at 400 °C and space group . The similarity between the K₃AlF₆ and K₃MoO₃F₃ compounds is discussed.     

Synthesis and crystal structure of new uranyl tungstates M2(UO2)(W2O8) (M=Na, K), M2(UO2)2(WO5)O (M=K, Rb), and Na10(UO2)8(W5O20)O8

The solid-state reactions of UO₃ and WO₃ with M₂CO₃ (M=Na, K, Rb) at 650°C for 5 days result, accordingly the starting stoichiometry, in the formation of M₂(UO₂)(W₂O₈) (M=Na (1), K (2)), M₂(UO₂)₂(WO₅)O (M=K (3), Rb (4)), and Na₁₀(UO₂)₈(W₅O₂₀)O₈ (5). The crystal structures of compounds 2, 3, 4, and 5 have been determined by single-crystal X-ray diffraction using Mo(Kα) radiation and a charge-coupled device detector. The crystal structures were solved by direct methods and Fourier difference techniques, and refined by a least-squares method on the basis of F² for all unique reflections. For (1), unit-cell parameters were determined from powder X-ray diffraction data. Crystallographic data: 1, monoclinic, a=12.736(4) Å, b=7.531(3) Å, c=8.493(3) Å, β=93.96(2)°, ρ_cal=6.62(2) g/cm³, ρ_mes=6.64(1) g/cm³, Z=4; 2, orthorhombic, space group Pmcn, a=7.5884(16) Å, b=8.6157(18) Å, c=13.946(3) Å, ρ_cal=6.15(2) g/cm³, ρ_mes=6.22(1) g/cm³, Z=8, R1=0.029 for 80 parameters with 1069 independent reflections; 3, monoclinic, space group P2₁/n, a=8.083(4) Å, b=28.724(5) Å, c=9.012(4) Å, β=102.14(1)°, ρ_cal=5.83(2) g/cm³, ρ_mes=5.90(2) g/cm³, Z=8, R1=0.037 for 171 parameters with 1471 reflections; 4, monoclinic, space group P2₁/n, a=8.234(1) Å, b=28.740(3) Å, c=9.378(1) Å, β=104.59(1)°, ρ_cal=6.13(2) g/cm³,  g/cm³, Z=8, R1=0.037 for 171 parameters with 1452 reflections; 5, monoclinic, space group C2/c, a=24.359(5) Å, b=23.506(5) Å, c=6.8068(14) Å, β=94.85(3)°, ρ_cal=6.42(2) g/cm³,  g/cm³, Z=8, R1=0.036 for 306 parameters with 5190 independent reflections. The crystal structure of 2 contains linear one-dimensional chains formed from edge-sharing UO₇ pentagonal bipyramids connected by two octahedra wide (W₂O₈) ribbons formed from two edge-sharing WO₆ octahedra connected together by corners. This arrangement leads to [UW₂O₁₀]²⁻ corrugated layers parallel to (001). Owing to the unit-cell parameters, compound 1 probably contains similar sheets parallel to (100). Compounds 3 and 4 are isostructural and the structure consists of bi-dimensional networks built from the edge- and corner-sharing UO₇ pentagonal bipyramids. This arrangement creates square sites occupied by W atoms, a fifth oxygen atom completes the coordination of W atoms to form WO₅ distorted square pyramids. The interspaces between the resulting [U₂WO₁₀]²⁻ layers parallel to plane are occupied by K or Rb atoms. The crystal structure of compound 5 is particularly original. It is based upon layers formed from UO₇ pentagonal bipyramids and two edge-shared octahedra units, W₂O₁₀, by the sharing of edges and corners. Two successive layers stacked along the [100] direction are pillared by WO₄ tetrahedra resulting in sheets of double layers. The sheets are separated by Na⁺ ions. The other Na⁺ ions occupy the rectangular tunnels created within the sheets. In fact complex anions W₅O₂₀¹⁰⁻ are built by the sharing of the four corners of a WO₄ tetrahedron with two W₂O₁₀ dimmers, so, the formula of compound 5 can be written Na₁₀(UO₂)₈(W₅O₂₀)O₈.