The molecular and crystal structure of psi-retroprogesterone

The crystal structure of synthetic, racemic ψ-retroprogesterone (9α-methyl-19-nor-progesterone) has been determined by X-ray analysis and refined to R = 0.050. The analysis was carried out to establish the relative configuration at positions 9, 10 and 17 in connection with the biological activity of the compound.     

The crystal and molecular structure of 7-con-O-methylnogarol

A crystal structure analysis for 7-con-O-methylnogarol free base, a promising antitumor antibiotic of the nogalamycin family, has been carried out with low temperature X-ray diffraction data. The relative configuration of the anthracycline moiety is C7(S) and C9(S); the sugar moiety is an α-D-3,6-dideoxy-3-dimethylaminoglucose.     

The crystal and molecular structure of pentafluoropropionylbenzoylmethylene triphenylphosphorane

The crystals of pentafluoropropionylbenzoylmethylene triphenylphosphorane that bears two strongly electron-withdrawing groups in alkylidene moiety are monoclinic and its space group is C2/c, with a = 11.271(3)Å, b = 18.253(6)Å, c =23.938(7)Å, β = 91.09(2)°, z = 8. The X-ray diffraction intensity data were collected on a four-circle diffractometer. The structure has been solved by direct method and refined by block-diagonal least-squares method. The final R- index was 0.075 for 3146 independent observed reflexions. In this paper the structure of this ylide is compared with that of corresponding arsonium ylide previously reported. Both ylidic skeleton structures are planar with sp² hybridization. The bond length of P-C(1) is 1.748 (5)Å with bond order. 1.60 while the bond order of As-C(1) in the corresponding arsonium ylide is 1.46, indicating that the phosphonium ylide has a greater contribution of “ylene” structure to the overall structure. As a result the phosphonium ylide should be less reactive than the corresponding arsonium ylide. In both ylides, (he major delocalized canonical forms of negative charge are shown to be 3.     

The crystal and molecular structure of ferricinium tetrachloroferrate

The crystal and molecular structure of ferricinium tetrachloroferrate was studied by X-ray diffraction. The compound crystallizes in space group Pna2₁ with 4 molecules C₁₀H₁₀Cl₄Fe₂ per unit cell. Data analysis was relatively difficult and direct methods of phase determination were very useful in the interpretation of the Patterson synthesis. The two rings in ferricinium are nearly parallel. The structural parameters are very similar to those previously published by others for ferrocene. This molecular structure and its vibrational properties seem to be in contrast to a general rule previously formulated by others for the infrared spectra of cyclopentadienyl compounds.     

The crystal and molecular structure of benzoyl-pentafluoropropionylmethylene triphenylarsorane

Benzoyl-pentafluoropropionylmethylene triphenylarsorane contains two strongly electron-withdrawing groups in alkylidene moiety. Single crystals obtained from CH₃OH-H₂O solution are triclinic, the space group is \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{P}}\bar 1 $\end{document}, with a = 12.292Å, b = 13.457Å, c = 15.318Å, α = 90.562° β = 90.516°, γ = 92.820°, and Z = 4. The X-ray diffraction intensity data were collected with a four-circle diffractometer. The structure has been solved by heavy-atom method and refined by block-diagonal least-squares method. The final R was 0.061 for 8393 independent observed reflections. The ylide carbon is planar sp² hybridized. The bond length of As-C_ylide is 1.888Å, much longer than As = C, and also longer than the corresponding bond length in other arsonium ylides previously reported, indicating a smaller contribution of “double bond” canonical form to the overall structure. On the other hand, the easier delocalization of negative charge due to the two strongly electron-withdrawing groups results in the greater chemical stability.     

The crystal and molecular structure of isoalfileramine dihydrobromide

The crystal and molecular structure of isoalfileramine dihydrobromide has been determined from 3-dimensional single crystal X-ray diffraction data collected by counter techniques. Isoalfileramine is a cyclized derivative of the novel alkaloid, alfileramine, which has been isolated from leaves of Zanthoxylum punctatum Vahl. The crystals of isoalfileramine dihydrobromide were triclinic, space group P1? (No. 2), with two formula units in a unit cell of dimensions a = 16.380(12) Å, b = 9.917(7) A, c = 10.648(7) A, α = 116.39(2)°, β = 91.10(2)° and γ = 101.40(2)°. The structural model, which employed anisotropic thermal parameters only for the bromide ions, was refined using full matrix least squares methods to an R value of 0.089 (R_w = 0.090) for 1053 independent reflections with F² > 3σ(F²). Isoalfileramine dihydrobromide is shown to be a unique pentacycle exhibiting a strained pyran ring. This work was critical in establishing structure for the parent alkaloid, alfileramine, and pointed out the clear structural relationship of alfileramine to tetrahydrocannabinols.     

The crystal and molecular structure of 6-oxadihydrouracil

The crystal and molecular structure of 6-oxadihydrouracil (C₃H₄N₂O₃) has been determined by single crystal x-ray diffraction techniques. The compound crystallizes in the space group P2₁ 2₁ 2₁ with four molecules in a unit cell of dimensions: a = 5.106(1)Å, b = 12.461(2)Å and c = 7.112(1)Å. The structure was solved by direct methods and refined to a final value of R = 0.052. The oxauracil ring is non-planar with the C5 atom assuming tetrahedral geometry and the ring oxygen having oxazinal distances and angle (C-O = 1.43₂Å, N-O = 1.40₈Å, and CON angle of 109.0°). The usual hydrogen bonding patterns associated with the uracil ring are absent in this compound.     

Low temperature nanostructured lithium titanates: controlling the phase composition, crystal structure and surface area

Low temperature lithium titanate compounds (i.e., Li₄Ti₅O₁₂ and Li₂TiO₃) with nanocrystalline and mesoporous structure were prepared by a straightforward aqueous particulate sol–gel route. The effect of Li:Ti molar ratio was studied on crystallisation behaviour of lithium titanates. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that the powders were crystallised at the low temperature of 500 °C and the short annealing time of 1 h. Moreover, it was found that Li:Ti molar ratio and annealing temperature influence the preferable orientation growth of the lithium titanate compounds. Transmission electron microscope (TEM) images showed that the average crystallite size of the powders annealed at 400 °C was in the range 2–4 nm and a gradual increase occurred up to 10 nm by heat treatment at 800 °C. Field emission scanning electron microscope (FE-SEM) analysis revealed that the deposited thin films had mesoporous and nanocrystalline structure with the average grain size of 21–28 nm at 600 °C and 49–62 nm at 800 °C depending upon the Li:Ti molar ratio. Moreover, atomic force microscope (AFM) images confirmed that the lithium titanate films had columnar like morphology at 600 °C, whereas they showed hill-valley like morphology at 800 °C. Based on Brunauer–Emmett–Taylor (BET) analysis, the synthesized powders showed mesoporous structure containing pores with needle and plate shapes. The surface area of the powders was enhanced by increasing Li:Ti molar ratio and reached as high as 77 m²/g for the ratio of Li:Ti = 75:25 at 500 °C. This is one of the smallest crystallite size and the highest surface areas reported in the literature, and the materials could be used in many applications such as rechargeable lithium batteries and tritium breeding materials.     

The crystal and molecular structure of bis-dimethylaminotitanium difluoride tetramer

The crystal structure of [(Me₂N)₂TiF₂₄ has been determined by single-crystal X-ray diffraction. The crystals are tetragonal, I$\text{4}$, a = b = 11.313(5), c = 12.862(4) Å, Z = 2. The titanium atoms display a distorted octahedral coordination and are linked by TiFTi and TiNMe₂Ti bridges to form a tetramer, which possesses a crystallographic inverse tetrad axis at its centre. One fluorine and one dimethylamino group do not participate in the bridging. The principal bond lenghts are TiF(bridging) 2.00(2) and 2.06(2), TiF (terminal) 1.77(2), TiN(bridging) 2.14(3) and 2.19(3), TiN(terminal) 1.99(30) Å. The structure has been refined to R = 0.077 for 231 visually estimated unique reflections.     

The crystal and molecular structure of tetrahydro-thiazole-2-thione

The crystal of tetrahydrothiazole-2-thione (TTT) belongs to monoclinic system. Space group P2₁/n. There are eight molecules in an unit cell with parameters a = 13.844(7)Å, b = 5.614 (2)Å, c = 13.516 (7)Å, β=95.08 (5)°, V =1046.3 (9)ų The three dimensional intensity data were obtained on a Syntex R3 four-circle diffractometer, and the number of the independent diffractions amounted to 1906. The structure was solved by direct method and refined by block-diagonal least-squares method. The final R is 0.082. In crystal, the molecular structure is between 1 and 2 in which S(1), S(2), N and C(1) are coplanar with conjugation. We use CNDO/2 programmes written by ourselves on Eclipse computer to compute the electronic energies, molecular total energies, dipole moments, the charge densities and net charges of each atom of TTT and its N-benzoylated derivative. The color of the acylated TTT and its properties for aminolysis are discussed.