Search results for "MR"

Comparative ab initio calculations of SrTiO3 and CaTiO3 polar (111) surfaces

2012

We present the results of calculations of SrTiO3 and CaTiO3 polar (111) surface relaxations, rumplings, energetics, optical band gaps, and charge distributions using the ab initio code CRYSTAL and a hybrid description of exchange and correlation. We have calculated the surface relaxation of the two possible terminations (Ti and SrO3 or CaO3) of the SrTiO3 and CaTiO3 (111) surfaces. According to our calculations, atoms of the first surface layer relax inwards for Ti-, SrO3-, and CaO3-terminated (111) surfaces of both materials. The only exception is outward relaxation of the SrO3-terminated SrTiO3 (111) surface upper layer Sr atom. For both Ti-terminated SrTiO3 and CaTiO3 (111) surfaces our …

DSC, Dilatometric, Dielectric, and1H NMR Studies of Phase Transitions and Molecular Motions in [N(C2H5)4]3M2Cl9 (M = Sb, Bi) Crystals

1995

Results in the dependence of stoichiometry of obtained tetraethylammonium (TEA) chloroantiomonate and chlorobismuthate salts on the molar ratio of reactants used in the synthesis are presented. Seven tetraethylammonium salts are obtained: (TEA) 6 M 8 Cl 30 , TEAMCI 4 , (TEA) 3 M 2 Cl 9 (M = Sb, Bi) and (TEA) 2 SbCl 5 . Preliminary X-ray diffraction studies on (TEA) 3 M 2 Cl 9 (M = Sb, Bi) show that they are isomorphous, crystallizing at room temperature in monoclinic symmetry. The dilatometric, dielectric, and DSC studies show that (TEA) 3 Bi 2 Cl 9 undergoes two phase transitions at T c2 = 144 K and at T c1 = 322 K while (TEA) 3 Sb 2 Cl 9 undergoes three transitions at T c3 = 185, T c2 = 2…

Microscopic origin of the nonexponential dynamics in a glassy crystal

2003

The origin of the slow relaxation and of the dynamic heterogeneity is studied for an orientation-ally disordered crystal, orthocarborane, composed of quasi-icosahedrally shaped molecules. Multidimensional deuteron magnetic resonance reveals that large jump angles dominate their complex, anisotropic reorientational motion. It involves a sequence of small-angle tilts about locally preferred axes as well as symmetry adapted threefold jumps. The intrinsic dynamics of this glassy crystal is nonexponential and can be fully accounted for in terms of the tilt and jump motion.

Structure, phase transitions and molecular motions in ferroelastic (C4H8NH2)SbCl6·(C4H8NH2)Cl

2002

The crystal structure at 293 K of the new pyrrolidinium chloroantimonate (V) analogue, (C4H8NH2)SbCl6(C4H8NH2)Cl, has been determined by x-ray diffraction as monoclinic, space group P21/c, Z = 8. The crystal is built up of isolated SbCl6- anions, two types of inequivalent pyrrolidinium cation and isolated Cl- ions. It undergoes five solid-solid phase transitions: at 351/374 K of first-order type (cooling/heating, respectively), at 356 and 152 K second order and at 135/141 and 105/134 K first order, detected by differential scanning calorimetry, dilatometric and dielectric measurements. The ferroelastic domain structure appears between 152 and 135 K. The proton nuclear magnetic resonance sec…

1H NMR, DSC, dielectric, and dilatometric studies of phase transitions and molecular dynamics in N (C2H5)4SbCl4

1994

The results of dielectric, dilatometric, 1H NMR, and DSC studies on N(C2H5)4SbCl4 crystals are presented. The title compound undergoes two phase transitions at Tc1 = 272 K reversible of first order and at Tc2 = 393 K irreversible. The values of transition entropies and enthalpies are compared with those of other tetraethylammonium halogenoantimonates and bismuthates (III). The spin-lattice relaxation times and the values of the second moments of the 1H NMR line for the N(C2H5)4SbCl4 crystal are measured in the temperature range of 70 to 400 K. Two minima of T1 are observed. They are attributed to CH3 group reorientations. The activation energies for the processes are determined.

Synthesis and Electrochemistry of Aluminum Porphycenes. Crystal and Molecular Structure of Methyl-σ-Bonded Aluminum Etioporphycene

1997

The synthesis and characterization of three monomeric aluminum porphycenes with anionic or σ-bonded axial ligands is reported. The investigated compounds are represented as ( EtioPc ) Al ( CH 3) and ( EtioPc ) AlX where EtioPc represents the dianion of etioporphycene and X = Cl − or OH −. Each synthesized complex was characterized by mass spectrometry. 1 H NMR, IR and UV-visible spectroscopies as well as by electrochemistry. Comparisons are made between the properties of complexes in the aluminum etioporphycene series and related chloro- or methyl σ-bonded Al ( III ) porphyrins containing octaethylporphyrin ( OEP ) or tetraphenylporphyrin ( TPP ) macrocycles. Comparisons are also made betw…

1979

2D NMR spectra have been measured at variable temperatures between −100°C and +110°C in a sample of melt crystallized deuterated polyethylene (PE). The line shape could be decomposed into a central part originating from deuterons in the amorphous regions and outer parts from crystalline regions of PE. The “NMR crystallinity” determined from this separation was 72% in agreement with the X-ray crystallinity of 74%. Changes of the crystalline NMR line shape were interperted in terms of oscillations around the chain axis, the r.m.s. oscillation amplitude varying from 5° at 40°C to 12° at 110°C. The central part of the NMR line shape indicates the existence of a “narrow” and a “medium” component…

Additional Proof for the Structure of the New Flavone Galangustin (Bucegin) Obtained by 13C-NMR Spectroscopy

2010

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.

Tetranitroresorcin[4]arene: synthesis and structure of a new stereoisomer

2009

The direct reaction between 2-nitroresorcinol and acetaldehyde in alkaline medium yields tetranitro-C1-resorcin[4]arene in a moderate 8.2% overall yield which was characterized by single crystal X-ray crystallography, 1H NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS). In solution and in the solid state, the product adopts a unique, thermally stable and unprecedented rcct-boat conformation.