A program set for direct calculation of vibrational states of crystal structures in a molecular approach

A Crystal program set intended for calculation of vibrational states of finite arbitrary crystal structures on a personal computer and an MVS-1000 supercomputer is described. Examples of calculated frequency histograms for models of different sizes are reported.     

X-ray and molecular mechanics studies on the crystal and molecular structure of the leucoacetate of ventilatone A

Molecular details of the leucoacetate of ventilatone A have been obtained by X-ray crystallographic and molecular mechanics calculations. In the crystalline state (space group P1,Z=2) the two independent molecules of the asymmetric unit appear to be disordered as some unusual geometrical features are evident. As these two molecules are related by a pseudo center of symmetry details of space group assignment are presented. Evidence of bond order in the molecules is supported by previously published spectroscopic data.     

Dissymetrization of molecular crystals: a driving force for property formation

Phenomena of dissymetrization of molecular crystals are reviewed which lead to sector wise polar properties. Orientational disorder of prolate‐type dipolar molecules taking place at attachment sites can produce partial polar alignment of dipoles in corresponding growth sectors of molecular crystals nucleating into topologically centric packings. As a result bi‐polar crystals are obtained. In case of native polar groups, Monte Carlo simulations predict a basic behaviour for pyroelectric molecular crystals: the dipoles belonging to sectors of either the plus or minus direction of the unique axis show a non‐vanishing probability to be gradually reversed. Domain reversal may start upon a single orientational defect developing into complete sector reversal. Basic features of growth induced stochastic polarity formation are confirmed by scanning pyroelectric microscopy, phase sensitive second harmonic generation microscopy and x‐ray scattering. Real systems comprise channel‐type inclusion compounds, single component molecular crystals, solid solutions and long chain proteins in natural tissues. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The crystal and molecular structure of a dioxan photoadduct of 3-dehydro-gibberellin A1 methyl ester

The three-dimensional structure of a dioxan photoadduct of 3-dehydro-gibberellin A₁ methyl ester has been established as (2′S)-3-[dioxanyl-(2′)]-3-epi-gibberellin A₁ methyl ester (1) by X-ray analysis. The compound crystallizes in the orthorhombic space group P2₁2₁2₁ with four molecules in the unit cell of dimensions a = 9.751, b = 22.189, c = = 10.064 Å. The final R-value is 0.103 for 1151 reflections.     

The molecular and crystal structure of the Steroidal Alkaloid Aculeamine

A new solanocapsine-type alkaloid named aculeamine has been isolated from roots of Solanum aculeatum and its structure has been established by X-ray analysis as 22,26-epimino-23β-methoxy-16α,23-epoxy-5α,25αH,25βH-chloestane-3β-ol. The compound crystallizes in the hexagonal space group P6₁ with the lattice parameters a = b = 16.706, c = 17.056 Å, α = β = 90°, γ = 120°. The final residual value was R = 0.079.     

The crystal and molecular structures of cyclohexanone thiosemicarbazone

Cyclohexanone thiosemicarbazone (Hchtsc) crystallizes in the triclinic crystal system with space group P (No. 2) and the following unit cell parameters: a = 6.2989(2), b = 7.9730(3), and c = 9.4118(2) Å = 79.607(3), = 85.519(2), and = 73.50(2)° V = 445.60(2) ų, Z = 2. The lengths of the bonds C(1)–S, C(1)–N(1), C(1)–N(2), and N(2)–N(3) suggest electron delocalization in all four. The S atom is trans to N(3), and this E configuration is stabilized by intramolecular hydrogen bonding between N(3) and the N(1)H₂ group. Two intermolecular hydrogen bonds involving the S atom and the N(1)–H(1b) and N(2)–H(2) groups give rise to a polymeric chain of molecule pairs.     

The x-ray crystal and molecular structure of glechomafuran

The X-ray crystal structure of glechomafuran (1,10,4,5-diepoxy-7,8-furanogermacrane), a natural product obtained from seeds ofSmyrnium olusatrum L., has been determined in order to establish the correct relative configuration of the molecule. Crystals are monoclinic, space groupP2₁ witha=6.785(4),b=12.325(9),c=16.390(6) Å,=97.89(4)°, and four molecules in the unit cell. The two epoxides are found to be ,-attached, and the associated methyl groups are positionedsyn to each other. The furan ring is essentially flat, and shows no evidence of any double bond delocalization.     

The crystal and molecular structure of 2-S-methylthiouracil

2-S-Methylthiouracil crystallizes in the triclinic space group P with unit cell dimensions a = 5.508(4), b = 7.175(3), c = 8.522(2) Å, = 80.83(2), = 80.43(3), = 76.86(3)°, and Z = 2. The molecule exists in the crystal in the lactam form and is essentially planar. The molecular packing consists of molecules linked in centrosymmetric hydrogen-bonded pairs. The effects of methylation and subsequent metallation on the 2-thiouracil structure are discussed.     

The molecular and crystal structure of p-methyl-phenyl glyoxylacid-m-trifluoro-anilide

Using X-ray crystal structure analysis of the title compound the positions of all atoms (including all A atoms) were localized in the triclinic unit cell with the parameters a = 14.68₆ Å, b = 7.70₀ Å, c = 7.89₈ Å, α = 122.5°, β = 105.4°, γ = 87.7°, space group P1. The existence of an intramolecular H N … O(1) bridge was inferred, the H-bridge acceptor of which predominantly is the π-electron density of the carbonyl group in agreement with the results of the X-ray crystal structure analysis of p-methyl-phenyl-glyoxyl-acid-p-chloroanilide (HOEHNE , SEIDEL ). Moreover, the existence of H-bridgelike interactions of the two phenyl hydrogen atoms H(6) and H(15) to the carbonyl oxygen O(2) could be proved. These interactions stabilize the conformation of the two phenyl rings in the molecule.     

A novel method of temperature control for a crystal growth puller

A facile method to control the contracting rate of the thermal expansible bars for pulling crystal is first suggested. The thermal expansible bars, set in a modified Dewar flask whose vacuum degree is controlled, are heated to designed temperature and then switch off the power to let it cool down at a desired rate, which depends largely on the changeable vacuum degree. This new approach is expected to completely eliminate the effects, which possibly reduces the smooth extent of thermal expansion, caused by the minor temperature fluctuations during crystal growth process and to realize the utmost smooth and slow pulling rate. It is expected to install this apparatus in optical floating zone furnace, instead of traditional motor, to grow peritectic crystal, such as crystal Bi‐2223, since for the peritectic reaction, in principle, the extremely slow growing rate is considerably essential.     

The crystal and molecular structures of isoperezone, aminoperezone, and isoaminoperezone: a comparative study of their crystal packing

The crystal structures of isoperezone (1), aminoperezone (2), and isoaminoperezone (3) have been determined by single-crystal X-ray diffraction. Compound (1) yields orange crystals, orthorhombic space group P2₁2₁2₁ with unit cell dimensions a = 6.271(6), b = 30.373(7), c = 7.257(1) Å, and Z = 4; compound (2) yields purple crystals, orthorhombic space group P2₁2₁2₁ with unit cell dimensions a = 6.498(3), b = 7.500(1) c = 29.200(6) Å, and Z = 4; compound (3) yields purple crystals, monoclinic space group P2₁ with unit cell dimensions a = 7.354(1), b = 7.511(1), c = 13.283(1) Å, = 102,07(1)°, and Z = 2. The side chains in (1)–(3) are oriented out of the plane of the quinone ring at an angle of 124, 144, and 97°, respectively. The molecules in the crystal are held together by hydrogen-bonding networks and van der Waals interactions.     

The crystal and molecular structure of the steroidal alkaloid 20-epi-kibataline

The major constituent of the alkaloid fraction of the leaves of Paravallaris macrophylla Pierre has found to be the new paravallarine-type steroidal alkaloid 20-epi-kibataline. The structure of this steroidal alkaloid has been determined by X-ray analysis. The compound crystallizes in the monoclinic space group P2₁ with the lattice parameters a = 11.286, b = 14.250, c = 6.206 Å, β = 97.88°. The final R value was 0.067.     

Refinement of the crystal and molecular structure of tetraacetylethane by neutron diffraction

The structure of tetraacetylethane has been determined by neutron diffraction. The compound exists in the dienolic form, the enolic hydrogen being intramolecularly bonded to a neighbouring oxygen in a clearly asymmetric mode. The acetylacetonate residues are essentially planar.     

High frequency dynamics of an orientationally disordered molecular crystal

The dynamic structure factor of the polycrystalline plastic crystal 1-cyanoadamantane has been measured in the THz frequency region by inelastic X-ray scattering as a function of the exchanged momentum Q in the range 1–10 nm⁻¹ and as a function of the temperature in the two solid disordered phases: plastic crystal and glassy crystal. We find that the dispersion of the acoustic excitations is crystal-like in the two phases and that the attenuation Γ(Q) shows a negligible T dependence similarly to structural glasses and a Q^α behavior with 1.15 < α < 1.50 at variance with structural glasses characterized by a Q² dependence.     

A stability diagram for crystal growth from the vapor – a review

Stability of the solid‐vapor interface is investigated. Surface roughening and evolution of flat faces at the growth interface is considered in terms of relation between gradient of temperature in the crystal and gradient of concentration in the vapor. Stability diagram is proposed, based on experimental data. The diagram summarizes the various forms and structures, which can be obtained using a typical system for growth from the vapor. The critical lines for constitutional supersaturation and appearance of low and high index faces were plotted. This attempt to the problem of stability of the growth interface differs from the former investigations mainly in looking for dependence between temperature field and concentration field rather than between more absolute parameters like temperature and supersaturation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)