László Párkányi

Classification of the isostructurality of organic molecules in the crystalline state

Since its discovery by Mitscherlich in 1819, the isomorphism of crystals has been interpreted in various, sometimes controversial ways. This can be attributed to the fact that the word isomorphous refers only to the external similarities between crystalline substances. Identical or quasi-identical packing motifs of related organic substances should therefore be distinguished by a more appropriate terminology. For organic substances, in contrast with inorganic crystals, where the recommended term is isotypic, the term isostructural is unambiguous. The present work attempts to classify the main forms as isostructural and homeostructural. Within the former class, there are two subclasses distinguished by the degree of isostructurality

Catalytic and structural studies of RhI complexes of (−)-(2S,4S)-2,4-bis(diphenylphosphino)pentane. Asymmetric hydrogenation of acetophenonebenzylimine and acetophenone

Abstract Rhodium(I) complexes formed by (−)-(2 S ,4 S )-2,4-bis(diphenylphosphino)pentane (BDPP) are efficient catalysts for the hydrogenation of acetophenone and acetophenonebenzylimine. The composition of the solvent mixture and the reaction temperature have a marked influenced on the enantioselectivity. These effects are thought to be related to the enhanced conformational flexibility of six-membered rings when simple substrates without functional groups are coordinated to the rhodium. X-ray crystallographic studies reveal that in [Rh(( S , S )-BDPP)NBD] + ( 1 ) the ligand is in a chair conformation, and that in [Rh(( S , S )-BDPP)COD] + ( 2 ) the chelate ring is in a δ-skew conformation. Studies of Rh(( S , S )-BDPP)(NBD)Cl ( 3 ) in solution indicate a trigonal bipyramidal structure with a chair conformation of the ring in aromatic solvents and a conformationally labile ring in methanol.

Design of a Monomeric Arsinogallane and Chemical Conversion to Gallium Arsenide

A monomeric arsinogallane containing a covalent gallium-arsenic bond has been prepared, and its molecular structure has been determined by x-ray crystallography. The compound reacted with tert-butanol at ambient temperature to yield the III-V semiconductor gallium arsenide as a finely divided amorphous solid. During the initial stages of the reaction small clusters of gallium arsenide were apparently present in solution. The band gaps of these particles, as observed by their absorption spectra, were larger than that of the bulk material. This work is a step toward the development of new molecular precursors for technologically important materials and the study of quantum size effects in small semiconductor particles.

Crytal and molecular structures of γ-1-phenylsilatrane: some structural features of silatranes

γ-1-phenylsilatrane crystallizes in the monoclinic space group P 2 1 / n , with a 8.475, b 12.949, c 11.122 » and β 90.86°. The structure was determined by direct methods and was refined to R 0.078 for 1687 observed reflexions and 0.081 for all 1813 reflexions. The →Si bond length is 2.132(4), SiC is 1.894(5) ». The mean SiO bond distance is 1.656 A, angle NSiC is 179.0(2)°. The average NSiO, CSiO and OSiO angles are 83.6, 96.4 and 123.5°. By use of published data for six other silatrane molecules, some structural features were established. Thus, the length of the N→Si bond is affected by the other apical substituents of the silicon atom, the number of oxygen atoms attached to it and steric effects. Increase in the length of the dative N→Si bond is accompanied by further distortion of the trigonal bipyramidal configuration and of the tetrahedron around the nitrogen atom. The relatively long SiC( sp 2 ) bond may be due to decrased d π  p π interaction. The crystalline modifications (α, β, ψ) of the 1-phenyl-derivative possibly result from rapid ring-inversion in solution.

Haliclonadiamine, an antimicrobial alkaloid from the sponge Haliclona SP

Abstract The marine sponge Haliclona sp. from Palau contains haliclonadiamine ( 2 ) as the major antimicrobial alkaloid, together with papuamine ( 1 ). The structure of haliclonadiamine ( 2 ) was determined by X-ray analysis.

The molecular structure of 1-fluorosilatrane

Abstract The crystal structure of 1-fluorosilatrane has been determined by X-ray diffraction. The N → Si dative bond length is 2.042(1) A, somewhat longer than that in the 1-chloro derivative (2.023 A). The carbon atoms linked to nitrogen are disordered. The atoms in the close-packed crystal structure are well fixed and have low thermal motion. Deformation electron density calculations show considerable density in the region between the silicon and nitrogen atoms. A mass spectrometric study indicates a strong SiF bond.

Radical Dimerization of 5,5′‐Diphenyl‐3,3′,4,4′‐tetramethoxy‐2,2′‐bipyrrole: π Dimer in the Crystal, σ Dimer in Solution.

The crystalline, spinless π dimer (1.+ ⋅PF6 )2 was obtained by the oxidation of bipyrrole 1 with ferrocenium hexafluorophosphate. The diamagnetic species generated electrochemically in solution was identified as the σ dimer by NMR spectroscopy.

Comparison of the polymorphic modifications of famotidine

The polymorphic modifications of famotidine are described and characterized by their spectroscopic (infrared, X-ray) and some physico-chemical data. In addition to the standard physico-chemical data (melting point, solubility, bulk density) some further properties influencing its use in pharmaceutical technology are also characterized. The methods used to prepare the morphologically homogeneous modifications are also given.

Metabolites of the Palauan sponge Dactylospongia sp.

Abstract A Palauan sponge of the genus Dactylospongia contained four new diastereoisomeric sesquiterpene cyclopentenones, dactylospongenones A-D (3–6) that are related through a ring-contraction to ilimaquinone (2), which was also isolated from the sponge. The same sponge also contained the known metabolite, dictyoceratin-A (7), and a new derivative, dictyoceratin-C (8).

Organometalloidal derivatives of the transition metals: IX. Synthesis and the crystal structure of (η5-C5H5)Fe(CO)2SiMe2-SiPh3

Abstract Reaction of (η5-C5H5)(CO)2FeNa with ClSiMe2-SiPh3 yields (η5-C5H5)-Fe(CO)2SiMe2-SiPh3. The crystal structure of the compound has been determined by X-ray diffraction. The SiSi bond distance is 2.374(1) A, which is longer by 0.018 A than that in Me3Si-SiPh3. This difference is in agreement with spectroscopic data, and is presumably due to the σ-donor property of the silyl group. The SiFe bond length is 2.346(1) A.