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A new restraint scheme for Rietveld refinement based on Morse bond energy potential is introduced, in which the asymmetry of the Morse potential allows the refinement to `break' the incorrectly placed bonds. The analysis of bond-length distributions at different values of restraint strength reveals a visible difference in behavior of wrong and correct structures, which can be detected using robust statistical methods. This fact is employed as a basis for a novel structure verification criterion. The approach is demonstrated on known difficult cases of acetolone and γ-quinacridone and used for the Rietveld refinement of N-(6-phenylhexanoyl)glycyl-L-tryptophanamide, an organic molecule of a potential anxiolytic containing 32 non-H atoms and 14 single bonds. The results are verified using density functional theory calculations with periodic boundary conditions. [ABSTRACT FROM AUTHOR]

The reaction of CpCo(1,3-C3B2Me5H) ( 1) with CpTl affords the thallium derivative CpCo(1,3-C3B2Me5)Tl ( 2). The structures of 1 and 2 were determined by X-ray diffraction at 100 K. An 'extra' hydrogen atom in 1 occupies a C-H ···B bridging position. According to DFT calculations, 1 exists as a mixture of two enantiomers with an enantiomerization barrier of only 0.5 kcal mol-1. The transition state has Cs symmetry with an endo-CH hydrogen atom. The isomeric iso- 1with the Co-H ···B bridge is less stable than 1 by 10 kcal mol-1.The formation of 1 and iso- 1 from C3B2Me5H and CpCo(C2H4)2 have almost equal activation energies. The isomerization of iso- 1 to 1 was shown to proceed as a two-step hydrogen transfer. The bonding of the 'extra' hydrogen atom in the related CHB-bridged carborane nido-2,3,5-C3B3R5H2 and metallacarboranes M(C5R5)(C3B2R′5H) (R, R′ = H, Me; M = Co, Rh, Ir) as well as their hydridic isomers MH(C5R5)(C3B2R′5) was compared. According to energy decomposition analysis, the bonding of the parent anion [CpCo(1,3-C3B2H5)]- with metal cations becomes stronger in the following order: K+ < Na+ < Tl+ < Li+ < [RuCp]+. The attractive interactions between the [CpCo(1,3-C3B2H5)]- and Tl+ fragments are 68 % electrostatic and 32 % covalent. [ABSTRACT FROM AUTHOR]

The structures of tricarbonyl(formylcyclopentadienyl)manganese(I), [Mn(C6H5O)(CO)3], (I), and tricarbonyl(formylcyclopentadienyl)rhenium(I), [Re(C6H5O)(CO)3], (II), were determined at 100 K. Compounds (I) and (II) both possess a carbonyl group in a trans position relative to the substituted C atom of the cyclopentadienyl ring, while the other two carbonyl groups are in almost eclipsed positions relative to their attached C atoms. Analysis of the intermolecular contacts reveals that the molecules in both compounds form stacks due to short attractive π(CO)...π(CO) and π(CO)...π interactions, along the crystallographic c axis for (I) and along the [201] direction for (II). Symmetry-related stacks are bound to each other by weak intermolecular C-H...O hydrogen bonds, leading to the formation of the three-dimensional network. [ABSTRACT FROM AUTHOR]

The article describes a comparison between experimental and calculated electron density functions of p(r) of the titled compound in crystals for an isolated dimer. It discusses the theory on the application of atoms in molecules as it allowed visualization of the electron lone pair (Lp) of tin and the calculations of some bond energies and other atomic charges. It has demonstrated the stereochemical activity of the Lp, having the volume estimated to be at 10 Å3.

The article discusses a study on the crystal and molecular structures of the compounds [Mn(C5H4I(CO)3], [Re(C5H4I)(CO)3], [Mn2(C12H8(CO)6] and [Re2(C12H8(CO)6]. Zigzag chains are formed by the molecules in the four metal-organic compounds. Weak intermolecular hydrogen bonds join the said chains. Also cited are the methods used to prepare the compounds.

The article discusses a study on the crystal and molecular structures of monohalogenated ferrocenes C5H5FeC5H4X (X = Cl, Br and I) and a second polymorph of C5H5FeC5H4I. It describes the 1-chloroferrocene and 1-bromoferrocenes as isomorphous crystals. The arrangement of molecules in the triclinic form of 1-iodoferrocene is in zigzag tetramers. Crystallographic data shows the stability of the monoclinic form.

The crystal structures of Cr(PhCN)2 (2), (PhCN)Cr(PhCH3) (3) and (PhCN)Cr(PhCF3) (4) prepared by means of the Metal Vapor Synthesis (MVS) technique have been determined. Compounds (2), (3) and (4) crystallize as discrete sandwich complexes having intrinsic C2v(mm2), C5(m) and C1(1) symmetries, respectively. The X-ray diffraction study has revealed a synperiplanar conformation for (2) and (3), and a synclinal conformation for (4) with a torsion angle (Cipso1-Centroid1-Centroid2-Cipso2) of φ = 63.5°. The angles between the ligand planes are 2.2, 3.9 and 1.8°, respectively. The Cr atom is slightly (by 0.04-0.06 Å) displaced towards the substituents from the line connecting the centers of the opposite aromatic rings. The Cr-Cipso distances are 2.115 (2)-2.137 (2), 2.112 (2) and 2.185 (3) Å for CN, CF3 and CH3 groups, respectively. The CN groups as well as the H atoms lie out of the C6 ring planes and are bent towards the Cr atom, but the C atom of the CH3 group also lying out of the C6 ring plane is bent away from the Cr atom. The C atom of the CF3 group is essentially coplanar to the C6 ring plane. There are no unusual intermolecular contacts in the structures of (2)-(4). [ABSTRACT FROM AUTHOR]

The novel title furazan-containing macrocycle (systematic name: 6,9,14,17-tetraoxa-2,3,5,7,16,18-hexaazatricyclo[13.3.0.- 04.8]octadeca-4,7,15,18-tetraene), C8H10N6O4, (I), is the first macrocycle where the furazan rings are connected via a hydrazine group. In spite of the strain in the 12-membered macrocycle of (I), the geometry of the furazan fragment is the same in (I) and in its acyclic analogue 1,8-bis(5-aminofurazan-4-yloxy)-3,6-dioxaoctane, C10H16N6O6, (II). In both compounds, the participation of the furazan rings in intermolecular hydrogen bonding equalizes the N-O bonds within the furazan rings, in contrast with rings which do not participate in such interactions. [ABSTRACT FROM AUTHOR]

Relates the results of x-ray structural investigations for the compounds N,N-Dimethyl-N'-[(1E,2E)-3-(4-nitrophenyl)prop-2-enylidene]benzene-1,4- diamine and N,N,-dimethyl-4-[(1E,3E)-4-(4-nitrophenyl) buta-1,3-dienyl]-1-naphthylamine. Dihedral angle between the slightly pyramidal dimethylamine substituent and the aromatic ring.

Discusses the structures of the compounds 3,5-Bis[4-(diethylamino)benzylidene]-1-methyl-4-piperidone and 3,5-bis-[4-(diethylamino)cinnamylidene)-1-methyl-4-piperidone. Conjugation between donor and acceptor parts; Dihedral angles between the planar part of the heterocycle.

Compares the crystal structure of four 3-cyanodifurazanyl ethers. Geometric parameters of four 3-cyanodifurazanyl ethers; Influence of different functional groups on difurazanyl ether; Examination of the displacement ellipsoids of four 3-cyanodifurazanyl ethers.

Discusses the synthesis and X-ray structural investigation of (E)-(4-hydroxyphenyl)(4-nitrophenyl)diazene, (E)-(4-methoxyphenyl)(4-nitrophenyl)diazene and (E)-[4-(6-bromohexyloxy)phenyl](4-cyanophenyl)diazene. Trans geometry of the azobenzene core; Conformations of the alkyl tails; Crystal structure of the compounds.

A series of indole- and carbazole-substituted pyridinium iodide salts has been synthesized and characterized. X-ray analysis revealed that the iodide salt of the indole-substituted cation ( E)-4-(1 H-indol-3-yl­vinyl)- N-methyl­pyridinium (IMPE+), C16H15N2+·I−, (I), has two polymorphic modifications, (I a) and (I b), and a hemihydrate structure, C16H15N2+·I−·0.5H2O, (II). Until now, only one crystal modi­fication has been identified for the ( E)-4-(9-ethyl-9 H-carbazol-3-yl­vinyl)- N-methyl­pyridinium (ECMPE+) iodide salt, C22H21N2+·I−, (III). Crystals of (I a) and (I b) comprise stacks of antiparallel cations with iodide anions located in the channels between the stacks. Due to the presence of the water mol­ecules, the packing in (II) is quite different to that found in (I a) and (I b), and positional disorder involving a statistical superposition of two rotamers of IMPE+, with different orientations of the indole fragment, was found. Crystals of (III) contain two independent ECMPE+ rotamers with different orientations of their carbazole substituents. The cations are packed in stacks, with the iodide anions located in the channels between the stacks. In (III), the iodide was found to be disordered over two sites, with occupancies of 0.83 and 0.17. [ABSTRACT FROM AUTHOR]

A combinatorial chemistry approach has been used to synthesize an array of Schiff bases, five of which, namely N-[( E,2 E)-3-(4-methoxy­phenyl)-2-propenyl­idene]-3-nitro­aniline, C16H14N2O3, (1 a), N-[( E,2 E)-3-(4-methoxy­phenyl)-2-propenyl­idene]-4-nitro­aniline, C16H14N2O3, (2 a), N-{( E,2 E)-3-[4-(di­methyl­amino)­phenyl]-2-propenyl­idene}-3-nitro­aniline, C17H17N3O2, (1 b), N-{( E,2 E)-3-[4-(di­methyl­amino)­phenyl]-2-propenyl­idene}-4-nitro­aniline, C17H17N3O2, (2 b), and N-{( E,2 E)-3-[4-(di­methyl­amino)­phenyl]-2-propenyl­idene}-2-methyl-4-nitro­aniline, C18H19N3O2, (3 b), have been structurally characterized. A stack structure is observed for (1 a) and (1 b) in the crystal phase. Experimental and calculated molecular structures are discussed for these compounds which belong to a chemical class having potential applications as non-linear optical materials. [ABSTRACT FROM AUTHOR]

Although the two polymorphic modifications, (I) and (II), of the title compound, C13H10N2O, crystallize in the same space group ( P21/ c), their asymmetric units have Z′ values of 1 and 2, respectively. These are conformational polymorphs, since the mol­ecules in phases (I) and (II) adopt different rotations of the phenyl ring with respect the central 2-cyano­carboxy­amino­prop-2-enyl fragment. Calculations of crystal packing using Cerius2 [Molecular Simulations (1999). 9685 Scranton Road, San Diego, CA 92121, USA] have shown that (I) is more stable than (II), by 1.3 kcal mol−1 for the crystallographically determined structures and by 1.56 kcal mol−1 for the optimized structures (1 kcal mol−1 = 4.184 kJ mol−1). This difference is mainly attributed to the different strengths of the hydrogen bonding in the two forms. [ABSTRACT FROM AUTHOR]

Two phenyl-substituted carboranes, 3-phenyl-1,2-dicarba- closo-dodecaborane(12), C8H16B10, (I), and 1-phenyl-1,7-dicarba- closo-dodecaborane(12), C8H16B10, (II), were found to be isostructural. Comparison of the bond angles at the ipso-C atoms of the phenyl substituent for (I) and (II) [117.71 (3) and 118.45 (10)°, respectively] indicates that electron donation of the carborane cage for B- and C-substituted carboranes is different. [ABSTRACT FROM AUTHOR]

The combinatorial chemistry approach has been used to synthesize an array of Schiff bases. The structures of five of these Schiff bases have been confirmed by X-ray analysis [Nesterov, Timofeeva, Borbulevych, Antipin & Clark (2000). Acta Cryst. C 56, 971-975]. In two cases, the reaction conditions were not sufficient to obtain the products in question. In one case, a molecular complex, C10H10O2·­C6H5N3O4, of the starting products 4-methoxy­cinnam­aldehyde and 2,4-di­nitro­aniline was found. X-ray analysis revealed hydrogen-bond formation between the mol­ecules of these reagents in the crystal. In the other case, X-ray analysis demonstrated that no chemical reaction occurred under the reaction conditions, and only one starting reagent, 4-(di­methyl­amino)­cinnam­aldehyde, C11H13NO, was found in the precipitate. [ABSTRACT FROM AUTHOR]

The structures of the potential non-linear optical (NLO) materials N-[2-(iso­propyl­amino)-5-nitro­phenyl]­acet­amide, (I) C11H15N3O3, and N-[2-(butyl­amino)-5-nitro­phenyl]­acet­amide, (II) C12H17N3O3, have been investigated by X-ray analysis. To compare them with the structure of N-[2-(di­methyl­amino)-5-nitro­phenyl]­acet­amide, (III) C10H13N3O3, a known NLO compound, we had to redetermine the structure of (III), since it was described only briefly in the literature. There are two mol­ecules in the asymmetric unit of compound (I), which have different orientations of the substituents with respect to the benzene ring. The packing of mol­ecules in (II) and (III) contains stacks but both (I) and (II) crystallize in a centrosymmetric space group, which renders them inappropriate for NLO applications. [ABSTRACT FROM AUTHOR]

The title compound, C13H12N2OS, was prepared by condensation of 4-methoxycinnamaldehyde and thioacetamide in ethanol at room temperature. Its investigation was undertaken as part of our search for new non-linear optical compounds. The π-conjugated title molecule is almost planar, the dihedral angle between the central planar 2-cyano-5-(4-methoxy­phenyl)penta-2,4-diene fragment and the thioacetamide group being 9.2 (6)°. Molecules are linked by N-H⋯N and N-H⋯O hydrogen bonds forming a two-dimensional motif. [ABSTRACT FROM AUTHOR]

The low-temperature study of the title compound, (C36H30NP2)2[Cu2Br4], revealed the nature of rotational disorder which has been observed at room temperature for the [Cu2Br4]2− anion. The centrosymmetric anion has a planar structure with slightly distorted trigonal coordination of the Cu atoms. [ABSTRACT FROM AUTHOR]