Search results for "MR"

Über polygermane

1980

Abstract The crystal structure of octaphenylcyclotetragermane, (Ph 2 Ge) 4 , has been determined and refined to an R value of 0.046. The symmetry of the molecule approximater D 2d . the Ge 4 ring is nearly planar and square (angle of pucker 3.9°, GeGe 246.5(5) pm). The 8 phenyl groups (GeC 196.2(10) pm) are arranged in two distinct sets (“parallel” touching and perpendicular to the Ge 4 ring) which exchange their positions in solution. The packing of the (Ph 2 Ge) 4 molecules in the crystal resembles a cubic body centred sphere packing. The homocyclic series (Ph 2 Ge) n with n  4, 5, 6 shows 13 C NMR signals in CDCl 3 solution monotonic dependent on the endocyclic GeGeGe angles.

Polycondensed nitrogen heterocycles. Part21. Complete13C NMR assignment of annelated phenanthridines

1986

Two-dimensional nmr techniques were used for the complete assignment of 13C nmr spectra of pyrrolo-[1,2-f]-, pyrazolo[1,5-f]-, and 1,2,4-triazolo[1,5-f]phenanthridines.

Efficient synthesis of copillar[5]arenes and their host–guest properties with dibromoalkanes

2011

An efficient method for the synthesis of copillar[5]arenes was developed with FeCl(3) as catalyst and different 1,4-dialkoxybenzenes and paraformaldehyde as reactants (yields: 50-85%). The host-guest property of (co)pillar[5]arenes and terminal dibromoalkanes was investigated by (1)H NMR measurements and an X-ray study. The complexation behavior of the copillar[5]arenes can be tuned by changing the substituents on the host. A complete complexation selectivity was found between pillar[5]- and pillar[6]arenes, which is an interesting aspect for sensor techniques.

Possibilities of multinuclear NMR in the chemistry of heteroorganic compounds

1994

13C NMR Spectral Identification of Four Cyclolithocholates (3α-Hydroxy-5β-cholan-24-oate Macrolides)

1996

Molecular scale structure and dynamics at an ionic liquid/electrode interface.

2017

After a century of research, the potential-dependent ion distribution at electrode/electrolyte interfaces is still under debate. In particular for solvent-free electrolytes such as room-temperature ionic liquids, classical theories for the electrical double layer are not applicable. Using a combination of in situ high-energy X-ray reflectivity and impedance spectroscopy measurements, we determined this distribution with sub-molecular resolution. We find oscillatory charge density profiles consisting of alternating anion- and cation-enriched layers at both cathodic and anodic potentials. This structure is shown to arise from the same ion-ion correlations dominating the liquid bulk structure.…

A Diferrous Single‐Molecule Magnet

2007

The diferrous complex [Fe2(acpypentO)(NCO)3] (1),(acpypentO– = the anion of 1,5-bis[2-pyridyl(1-ethylimino)]pentane-3-ol) was studied by spectroscopic (dual-mode X-band EPR and 57Fe-Mossbauer) and magnetic (AC magnetic susceptibility) techniques. Complex 1 (A. K. Boudalis et al., Inorg. Chem.2004, 43, 1574) was previously shown to exhibit an intramolecular ferromagnetic coupling with important single-ion anisotropies with marked differences in the single-ion electronic parameters of the two iron sites. In this contribution, additional studies are carried out to probe its dynamic magnetic properties. Mossbauer spectra recorded at liquid helium temperatures indicate slow paramagnetic relaxati…

Magnetic Study of a Pentanuclear {Co 2 III Co 3 II } Cluster with a Bent {Co II 3 } Motif

2014

We have synthesised and structurally characterised a new pentanuclear mixed-valent cobalt cluster of formula [CoII3CoIII2(OH)2(piv)6(L)2(H2O)4] (piv = trimethylacetate, H2L = salicylideneanthranillic acid) from reaction of a dinuclear cobalt pivalate precursor with a Schiff base type ligand under mild reaction conditions. The core structure can be conveniently described as two fused Co3–μ3–OH triangles with a strict unique sharing vertex point. A complete picture of the magnetic behaviour of this compound is presented. Through combined use of susceptibility, magnetisation, and EPR data as well as broken-symmetry DFT calculations, we have supported the magnetic data that show weak and anisot…

Semi-empirical simulations of surface relaxation for perovskite titanates

2000

The (100) and (110) surface relaxations are calculated for SrTiO 3 and BaTiO 3 perovskite thin films. By means of a semi-empirical shell model, the positions of atoms in 16 near-surface layers placed atop a slab of rigid ions are calculated. Surface rumpling and surface-induced dipole moments are calculated for all possible surface terminations. Our results for the (100) surface structure are in good agreement with ab-initio plane-wave pseudopotential calculations and LEED experiments. The surface energy for the Ba-, Sr-, TiO-terminated (110) surfaces is found to be much larger than that for the (100) surface. In contrast, the surface energy for the asymmetric O termination, where outermost…

Relaxation Mechanisms of 5-Azacytosine.

2015

The photophysics and deactivation pathways of the noncanonical 5-azacytosine nucleobase were studied using the CASPT2//CASSCF protocol. One of the most significant differences with respect to the parent molecule cytosine is the presence of a dark (1)(nNπ*) excited state placed energetically below the bright excited state (1)(ππ*) at the Franck-Condon region. The main photoresponse of the system is a presumably efficient radiationless decay back to the original ground state, mediated by two accessible conical intersections involving a population transfer from the (1)(ππ*) and the (1)(nNπ*) states to the ground state. Therefore, a minor contribution of the triplet states in the photophysics o…