Search results for "bond"
showing 10 items of 3527 documents
Strategies for structure solution and refinement of small organic molecules from electron diffraction data and limitations of the simulation approach
1999
In recent years, a series of non-linear optically active bis(benzylidene) ketones have been synthesized and investigated by electron crystallography. In most cases, structure refinement was possible by combining electron diffraction analysis and quantum-mechanical calculations with maximum-entropy methods. However, when the torsional angles between the phenyl rings and the C=C double bonds are strongly affected by the crystal field, this method fails because packing-energy calculations are not sufficiently sensitive. This problem can be solved by refining the approximate model with SHELXL, if the data set is sufficiently accurate and the model close to the correct structure. Here it is show…
First-principles calculations of the atomic and electronic structure of SrZrO3 and PbZrO3 (001) and (011) surfaces.
2010
We present the results of calculations of surface relaxations, rumplings, energetics, optical band gaps, and charge distribution for the SrZrO(3) and PbZrO(3) (001) and (011) surfaces using the ab initio code CRYSTAL and a hybrid description of exchange and correlation. We consider both SrO(PbO) and ZrO(2) terminations of the (001) surface and Sr(Pb), ZrO, and O terminations of the polar SrZrO(3) and PbZrO(3) (011) surfaces. On the (001) surfaces, we find that all upper and third layer atoms relax inward, while outward relaxations of all atoms in the second layer are found with the sole exception of the SrO-terminated SrZrO(3) (001) surface second layer O atom. Between all (001) and (011) s…
Impurity levels and nonlinear optical properties of doped BaTiO3 from extended cluster LDA calculations
1997
The electronic structures of some transition-metal ions doping the ferroelectric oxide BaTiO3 are calculated through the density functional theory framework (LCAO-LSD ADF method) on extended clusters [XO6Ba8Ti6] embedded in a punctual charge set depicting the crystalline environment. The transition ions X are Fen+(n = 2, 3, 4, 5), Ti3+, Nb4+, and Nb5+. Some related defects like Fe(SINGLE BOND)Vo, where Vo stands for a lacunar oxygen site, are also investigated through a similar process. The positions of impurity levels insides the O2p(SINGLE BOND)Ti3d band gap are obtained from eigenvalues and related optical transition or ionization energies are calculated using excited states. This allows…
Topochemical Reactions of Monomers with Conjugated Triple-Bonds VII Mechanism of Transition from Monomer to Polymer Phase During Solid-State Polymeri…
1972
The lattice-controlled solid-state polymerisation of three different modifications of 2,4-hexadiin-1,6-diol-bis(phenylurethane) was investigated by X-ray and optical methods. The polymerisation is a homogeneous reaction. The polymer grows in the form of single chains within the crystal of the monomer. The chains extend along a definite crystallographic direction. Monomer and polymer are isomorphous and monomer-polymer single crystals of various compositions are obtained up to a quantitative conversion in the case of modification I or III. Phase separation into a mesomorphic polymer and oriented monomer phase was observed on annealing partially polymerised single-crystals of modification II …
Adsorption of Alcohols Onto Zinc Selenide (ZnSe) Crystal Surface
2014
Adsorption behaviour of ZnSe, a popular material used in the manufacture of crystals for total internal reflectance techniques was studied for the adsorption of alcohols from dichloromethane solutions using infrared spectrometry. A series of n-alcohols were used in this study. The results show that the integrated area for the hydrogen bonded OH stretchings decrease and suggests that there is a continuous adsorption of alcohol molecules onto the ZnSe crystal by breaking the hydrogen bonds between alcohol molecules in solution.
Complexation behaviour of hexadentate ligands possessing N2O4and N2O2S2cores: differential reactivity towards Co(ii), Ni(ii) and Zn(ii) salts and str…
2004
Reactions of divalent metal salts of Co, Ni and Zn with 1,2-di(salicylaldimino-o-phenylthio) ethane (H2L1) and 1,2-di(naphthaldimino-o-phenylthio) ethane (H2L2), having N2O2S2 cores, and 1,2-di(O-salicylaldimino-o-hydroxyphenyl) ethane (H2L3), having a N2O4 core, have been explored. Out of the three ligands and the nine products obtained from the corresponding reactions, two ligands and seven products were crystallographically characterized. However, all the ligands and the products were characterized by analytical and spectral methods. Reaction of H2L1 and H2L2 with Co(II) salts results in oxidative cleavage of the C-S bond to produce a Co(III) product bound to two dissimilar tridentate li…
Bis[3-methyl-5-(pyridin-2-yl)-1H-pyrazol-4-yl] selenide methanol hemisolvate
2014
The asymmetric unit of the title compound, C18H16N6Se·0.5CH3OH, contains two independent molecules of bis[3-methyl-5-(pyridin-2-yl)-1H-pyrazol-4-yl] selenide with similar C—Se—C bond angles [99.30 (14) and 98.26 (13)°], and a methanol molecule of solvation. In one molecule, the dihedral angles between pyrazole and neighbouring pyridine rings are 18.3 (2) and 15.8 (2)°, and the corresponding angles in the other molecule are 13.5 (2) and 8.3 (2)°. In the crystal, the selenide and solvent molecules are linked by classical O—H...N and N—H...N hydrogen bonds, as well as by weak C—H...O and C—H...π interactions, forming a three-dimensional supramolecular architecture.
3-(4-Fluorophenyl)-1-methyl-4-(4-pyridyl)quinolin-2(1H)-one
2007
The title compound, C21H15FN2O, was synthesized in the course of our studies of p38 mitogen-activated protein kinase inhibitors. It has been investigated by 1H and 13C NMR spectroscopy and was proven by X-ray crystallographic analysis to be the N-methyl rather than the O-methyl isomer. In the crystal structure, a three-dimensional network is formed consisting of quinolinone aromatic stacking interactions and weak C—H⋯O and C—H⋯N hydrogen bonds.
Ground state and electronic spectrum of Cu(ii) and Cu(iii) complexes of N,N′-1,2-phenylenebis-2-mercaptoacetamide
2009
The electronic structure and the UV-vis spectrum of reduced and oxidized model systems of the N,N'-1,2-phenylenebis(2-mercapto-2-methylpropionamide) copper complex have been studied using a multiconfigurational quantum chemical method (CASSCF/CASPT2). The bonds between Cu and the two sulfur ligand atoms have a large covalent character in the oxidized Cu(III) form. As a result of the increased covalency, the effective charge on the Cu atom is actually smaller in the oxidized form. The electronic spectrum for both oxidation states of the complex is in agreement with the experiment for excitation energies and intensities showing that the theoretical description of the electronic structure is e…
Self-assembled hydrogen-bonded coordination networks in two copper(II) carboxylates with 4-pyridylmethanol
2011
AbstractThe crystal and molecular structure of [Cu(nif)2(4-PM)2]·CH3OH (1) and [Cu(2-Clbz)2(4-PM)2(H2O)] (2), (where nif = niflumate anion, 2-Clbz = 2-chlorobenzoate anion and 4-PM is the 4-pyridylmethanol), have been determinated by X-ray crystallography. The Cu2+ cation in (1), is coordinated by two pairs of oxygen atoms from asymmetric bidentate niflumate anions and by a pair of pyridine nitrogen atoms from monodentate 4-pyridylmethanol ligands in trans position forming an extremely elongated bipyramid. The Cu2+ cation in (2), is coordinated by a pair of oxygen atoms from monodentate 2-chlorobenzoate anions, further by a pair of pyridine nitrogen atoms from monodentate 4-pyridylmethanol …