| 1. |
- Langer, Vratislav, 1949, et al.
(författare)
-
2-{[(3-Fluorophenyl)amino]methylidene}-3-oxobutanenitrile and 5-{[(3-fluorophenyl)amino]methylidene}-2,2-dimethyl-1,3-dioxane-4,6-dione: X-ray and DFT studies
- 2010
-
Ingår i: Acta Crystallographica Section C: Crystal Structure Communications. - 0108-2701 .- 1600-5759. ; C66:8, s. o392-o395
-
Tidskriftsartikel (refereegranskat)abstract
- In the crystal structures of the title compounds, C11H9FN2O, (I), and C13H12FNO4, (II), the molecules are joined pairwise via different hydrogen bonds and the constituent pairs are crosslinked by weak C-H...O hydrogen bonds. The basic structural motif in (I), which is partially disordered, comprises pairs of molecules arranged in an antiparallel fashion which enables C-H...N≡C interactions. The pairs of molecules are crosslinked by two weak C-H...O hydrogen bonds. The constituent pair in (II) is formed by intramolecular bifurcated C-H...O/O' and combined inter- and intramolecular N-H...O hydrogen bonds. In both structures, F atoms form weak C-F...H-C interactions with the H atoms of the two neighbouring methyl groups, the H...F separations being 2.59/2.80 and 2.63/2.71 Å in (I) and (II), respectively. The bond orders in the molecules, estimated using the natural bond orbitals (NBO) formalism, correlate with the changes in bond lengths. Deviations from the ideal molecular geometry are explained by the concept of non-equivalent hybrid orbitals. The existence of possible conformers of (I) and (II) is analysed by molecular calculations at the B3LYP/6-31+G** level of theory.
|
|
| 2. |
- Langer, Vratislav, 1949, et al.
(författare)
-
2-Anilinomethylene-3-oxobutanenitrile: an X-ray and density functional theory study
- 2006
-
Ingår i: Acta Crystallographica Section C: Crystal Structure Communications. - 0108-2701 .- 1600-5759. ; C62:9, s. o554-o546
-
Tidskriftsartikel (refereegranskat)abstract
- Molecules of the title compound, C11H10N2O, are effectively planar. In the crystal structure, they are stabilized primarily by electrostatic interactions, as the dipole moment of the molecule is 4.56 D. In addition, the molecules are linked by weak C-H...N and C-H...O hydrogen bonds. An analysis of bonding conditions in the molecule was carried out using natural bond orbital (NBO) formalism.
|
|
| 3. |
- Langer, Vratislav, 1949, et al.
(författare)
-
anti-2-Hydroxy-2-methyl-1-tetralone oxime: X-ray and density functional theory study
- 2006
-
Ingår i: Acta Crystallographica Section C: Crystal Structure Communications. - 0108-2701 .- 1600-5759. ; C62:4, s. o199-o202
-
Tidskriftsartikel (refereegranskat)abstract
- Crystals of the title racemic compound, C11H13NO2, consist of two types of molecules (conformers); one molecule has an exocyclic OH group in an equatorial position and the other has this group in an axial position. Consequently, the hydrogen-bond schemes for the two molecules are different. The molecules with equatorial OH groups create infinite parallel chains (formed by the same enantiomer), connected by centrosymmetric dimers of molecules (of mixed enantiomers), both with axial OH groups. Possible interconversion of the conformers and the flexibility of the molecule were studied by means of different MP2 and density functional theory (DFT) methods. The optimization of the structure by the DFT method confirmed the types of the hydrogen bonds.
|
|
| 4. |
- Langer, Vratislav, 1949, et al.
(författare)
-
Crystal and electronic structure of aqua(N-salicylidene-methylester-L-glutamato)Cu(II) monohydrate
- 2004
-
Ingår i: Zeitschfrift für Kristallographie. - : Walter de Gruyter GmbH. - 0044-2968. ; 219:2, s. 112-116
-
Tidskriftsartikel (refereegranskat)abstract
- The absolute structure of the title compound, CuNC13H17O7, has been determined. The crystal structure consists of the molecular units Cu(N-sal-5-met-L-glu)(H2O) connected by a three-dimensional network of hydrogen bonds. The coordination polyhedron in the complex is approximately square-pyramidal with a pentacoordinated Cu(II) atom. The base of the pyramid is formed by nitrogen and oxygen atoms belonging to the molecule, while the apex of the pyramid contains a weakly bonded oxygen atom of the carboxylic group of another molecule. The B3LYP/SVP method and basis set in Gaussian98 was used for quantum chemical calculation of the nature of CuX (X = O, N) bonds. While the calculated dissociation energy of the weakly bonded crystalline water is only 17.2 kJ/mol, the bonding energy of the water molecule coordinating to the Cu atom is 62.3 kJ/mol.
|
|
| 5. |
- Langer, Vratislav, 1949, et al.
(författare)
-
(E)-Methyl 2-[(2-fluorophenyl)aminomethylene]-3-oxobutanoate: X-ray and density functional theory (DFT) study
- 2009
-
Ingår i: Acta Crystallographica Section C: Crystal Structure Communications. - 0108-2701 .- 1600-5759. ; C65:4, s. o183-o185
-
Tidskriftsartikel (refereegranskat)abstract
- The title compound, C12H12FNO3, a potential precursor for fluoroquinoline synthesis, is essentially planar, with the most outlying atoms displaced from the best-plane fit through all non-H atoms by 0.163(2) and 0.118(2) Å. Molecules are arranged in layers oriented parallel to the (011) plane. The arrangement of the molecules in the structure is controlled mainly by electrostatic interactions, as the dipole moment of the molecule is 5.2 D. In addition, the molecules are linked by a weak C-H...O hydrogen bond which gives rise to chains with the base vector [1,1,1]. Electron transfer within the molecule is analysed using natural bond orbital (NBO) analysis. Deviations from the ideal molecular geometry are explained by the concept of non-equivalent hybrid orbitals.
|
|
| 6. |
- Langer, Vratislav, 1949, et al.
(författare)
-
Ethyl 1-ethyl-7-fluoro-4-oxo-1,4-dihydroquinoline-3-carboxylate: X-ray and DFT studies
- 2011
-
Ingår i: Acta Crystallographica Section C: Crystal Structure Communications. - 0108-2701 .- 1600-5759. ; 67:10, s. o421-o424
-
Tidskriftsartikel (refereegranskat)abstract
- The basic building unit in the structure of the title compound, C14H14FNO3, is pairs of molecules arranged in an antiparallel fashion, enabling weak C-H...O interactions. Each molecule is additionally involved in π-π interactions with neighbouring molecules. The pairs of molecules formed by the C-H...O hydrogen bonds and π-π interactions form ribbon-like chains running along the c axis. Theoretical calculations based on these pairs showed that, although the main intermolecular interaction is electrostatic, it is almost completely compensated by an exchange-repulsion contribution to the total energy. As a consequence, the dominating force is a dispersion interaction. The F atoms form weak C-F...H-C interactions with the H atoms of the neighbouring ethyl groups, with H...F separations in the range 2.59-2.80 Å.
|
|
| 7. |
- Langer, Vratislav, 1949, et al.
(författare)
-
Novel type of Cu(II) complex containing Schiff base
- 2004
-
Ingår i: Abstracts, ECM-22, 26-31 August 2004, Budapest, Hungary, Acta Cryst.. - 9639319406 ; A60, s. 221-
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Recently, special interest has been devoted to the group ofcopper(II) complexes containing Schiff bases, derived fromsalicylaldehyde and various amino acids, and N-, or O- donorneutral ligands due to their biological activities. From this group of substances the structures of (N- salicylidene-racglutamato)(1-methylimidazole)Cu(II), (N-salicylidenerac-glutamato)(2-methylimidazole)Cu(II), (N-salicylidene-L-glutamato)(2-ethylimidazole)Cu(II) and aqua(Nsalicylidene-methylester-L-glutamato)Cu(II)monohydrate have been determined. Electronic structure of these compounds has been investigated by the B3LYP method. A continuation of these studies is a new complex transbis(ethanol)tetrakis(imidazole)Cu(II)(2+) bis[µ-(N-salicylidene-L-glutamato-N,O)-κO:κO´-(imidazole)Cu(II)](2-)presented here.This complex has quite spectacular structural features. Bothions are located on inverse centre. The cation is mononuclear, while the anion is binuclear. The quantum chemical calculation of the electronic structure has also been done by the B3LYP method.
|
|
| 8. |
- Langer, Vratislav, 1949, et al.
(författare)
-
X-ray and DFT studies of a mono- and binuclear copper(II) ionic compound containing a Schiff base
- 2012
-
Ingår i: Acta Crystallographica Section C: Crystal Structure Communications. - 0108-2701 .- 1600-5759. ; 68:Part 11, s. M326-
-
Tidskriftsartikel (refereegranskat)abstract
- In the structure of trans-bis(ethanol-kappa O) tetrakis(1H-imidazole-kappa N-3)copper(II) bis[mu-N-(2-oxidobenzylidene)-D,L-glutamato]-kappa O-4(1),N,O-2':O-2';kappa O-4(2)':O-1,N,O-2'-bis[(1H-imidazole-kappa N-3)cuprate(II)], [Cu(C3H4N2)(4)(C2H6O)(2)][Cu-2(C15H14N3O5)(2)], both ions are located on centres of inversion. The cation is mononuclear, showing a distorted octahedral coordination, while the anion is a binuclear centrosymmetric dimer with a square-pyramidal copper(II) coordination. An extensive three-dimensional hydrogen-bonding network is formed between the ions. According to B3LYP/6-31G* calculations, the two equivalent components of the anion are in doublet states (spin density located mostly on Cu II ions) and are coupled as a triplet, with only marginal preference over an open-shell singlet.
|
|
| 9. |
- Sladkovicova, Mariana, et al.
(författare)
-
DFT and neutron diffraction study of 1,6-anhydro-beta-D-glucopyranose (levoglucosan)
- 2007
-
Ingår i: Central European Journal of Chemistry. - : Walter de Gruyter GmbH. - 1895-1066. ; 5:1, s. 55-70
-
Tidskriftsartikel (refereegranskat)abstract
- Geometries of 27 generated conformers of levoglucosan were optimized in vacuo at DFT level of theory combining several functionals with high quality basis sets. For the sake of comparison a reference molecular and crystal geometry obtained from 30 K single crystal neutron diffraction data was used. Analysis of the conformers' geometries revealed that in all stable conformers intramolecular two- or three centre hydrogen bonds were formed. Relative energy of the conformer, which approximated the molecule in the crystal structure the most, was only similar to 3 kcal/mol higher, than the energy of the most stable conformer in vacuo. The largest discrepancies between the geometries calculated in vacuo and experimental geometry concentrated in the vicinity of anomeric C1. These differences were reduced by involving O1 to intermolecular hydrogen bond using a simple model of the respective hydrogen bond in the crystal.
|
|
