Search results for "Bonding"

Crystal structure of 1-hy­droxy-2,2,6,6-tetra­methyl­piperidin-1-ium tri­fluoro­methane­sulfonate

2015

In the cation of the title salt, C9H20NO+·CF3O3S−, the six-membered heterocyclic ring displays a chair conformation. In the crystal, centrosymmetric pairs of cations and anions are linked by N—H...O and O—H...O hydrogen bonds to form rings with aR44(14) graph-set motif.

Speciation of trialkyltin(IV) cations in natural fluids

2004

The hydrolysis of (CH(3))(3)Sn(+), (C(2)H(5))(3)Sn(+) and (C(3)H(7))(3)Sn(+) has been studied in a Synthetic Seawater (SSW) ionic medium simulating the major composition of natural seawater, at different salinities (5 less than or equal to S less than or equal to 45), and at t = 25 degreesC. Interactions with anionic components of SSW, considered as single sea salt, are determined by means of a complex formation model. By potentiometric measurements (ISE-H(+) and ISE-F(-) electrodes), the model has been extended to also consider interactions of organotins with carbonate and fluoride ions, which are other important components of seawater. Literature and new values of hydrolysis constants in …

ChemInform Abstract: New Ionic Liquid-Modified Silica Gels as Recyclable Materials for L-Proline- or H-Pro-Pro-Asp-NH2-Catalyzed Aldol Reaction.

2008

L-proline and the tripeptide H–Pro–Pro–Asp–NH2 (1) have been supported, by adsorption, onto the surface of modified silica gels functionalized with a monolayer of covalently attached 1,2-dimethyl-imidazolium chloride, tetrafluoroborate or hexafluorophosphate ionic moieties, respectively. Three different linkers were used to attach the ionic liquid moiety to the surface of these supports. The resulting materials have been used as catalysts for the aldol reaction between acetone and several substituted benzaldehydes. Good yields and enantioselectivities, comparable to or better than those obtained under homogeneous conditions, were obtained. These materials are easily recovered by filtration,…

Post-Processing via Cation Exchange Cartridges: Versatile Options

2012

New 68Ge/68Ga radionuclide generators provide the positron emitter 68Ga (T½ = 67.7 min) as an easily available and relatively inexpensive source of a PET nuclide for labeling of interesting targeting vectors. However, currently available “ionic” 68Ge/68Ga radionuclide generators are not necessarily optimized for the routine synthesis of 68Ga-labeled radiopharmaceuticals in a clinical environment. Post-processing of 68Ge/68Ga generators using cation exchange resins provides chemically and radiochemically pure 68Ga with 97±2% within less than 4 min, with 68Ge almost completely removed, and ready for online labeling. This simple, fast, and efficient technology can be extended for new applicati…

Crystal Structures and Thermal Behavior of Bis(dibenzyldimethylammonium) Tetrabromometallates(II) [M = Mn(II), Co(II) and Zn(II)] and Their Solvates

2007

Six new A2MBr4 structures [A = dibenzyldimethylammonium cation,M = Mn(II), Co(II) or Zn(II)] were crystallized with or without solvent molecules from acetonitrile, methanol and/or aqueous solutions. The isomorphous compounds [(Bz2Me2N)2][MnBr4]·CH3CN·H2O (1) and [(Bz2Me2N)2]-[ZnBr4]·CH3CN·H2O (4) crystallize in the triclinic space group P1̄ from acetonitrile solutions. The solvent molecules participate in the hydrogen bonding network inside the crystal structure. [(Bz2Me2N)2][CoBr4]·0.5CH3CN (2) crystallizes from an acetonitrile solution in the monoclinic space group P21/c. The solvent molecules fill the voids of the crystal structure. Compound 2 is isostructural with the previously reporte…

1993

The synthesis and the thermotropic phase behavior of the dipolar amphiphiles C 5 H 5 N + (CH 2 ) m OCOPhPHCOO(CH 2 ) m N + C 5 H 5 and the polymeric amphiphile [(CH 2 ) 6 OPhPhO(CH 2 ) 6 OCOCH([CH 2 ] 6 N + C 5 H 5 )COO] n are described

A quantum chemical topological analysis of the c-c bond formation in organic reactions involving cationic species

2014

ELF topological analysis of the ionic Diels-Alder (I-DA) reaction between the N,N-dimethyliminium cation and cyclopentadiene (Cp) has been performed in order to characterise the C-C single bond formation. The C-C bond formation begins in the short range of 2.00-1.96 Åvia a C-to-C pseudoradical coupling between the most electrophilic center of the iminium cation and one of the two most nucleophilic centers of Cp. The electron density of the pseudoradical center generated at the most electrophilic carbon of the iminium cation comes mainly from the global charge transfer which takes place along the reaction. Analysis of the global reactivity indices indicates that the very high electrophilic c…

Ab initio molecular orbital study of the substituent effect on phosphine–borane complexes

1998

Abstract Ab initio molecular orbital calculations have been used to study the substituent effect on H 3 BPH n Me 3− n and Me 3− n H n BPH 3 ( n =0–3) phosphine–borane complexes. The ab initio results show that successive methyl substitution on the phosphine favours complex formation, contrary to successive methyl substitution on the borane. The natural bond orbitals partitioning scheme suggests that, in general, there is no correlation between the charge transfer and the complexation energies. It also shows the shortening of the P–H and P–C bond lengths, upon complexation, is due to the increasing `s' character of these bonds.

Theoretical CASPT2 study of the excited state double proton transfer reaction in the 7-azaindole dimer

2006

Accurate CASPT2 calculations on the excited state double proton transfer reaction in the 7-azaindole dimer have been performed on different symmetric and asymmetric pathways along the protons interchange. The presence of a conical intersection connecting the initially photoinduced singlet excited state with a charge transfer state leading both to asymmetric ionic and neutral structures promotes a step-wise mechanism, probably taking place through the ionic intermediate. The concerted path is computed slightly higher in energy in the gas phase.

Polyoxometalate-Based Molecular Materials.

1998

Molecule-based materials with active physical properties, in particular electrical, magnetic, and optical, are a focus of contemporary materials chemistry research. Certainly, one reason for this interest has been the realization that these materials can exhibit cooperative properties typically associated with the inorganic network solids, as for example metallic conduction or even superconductivity,1 ferromagnetism,2 and nonlinear optical properties.3 With respect to the electrical properties, many important achievements were obtained in the 1970s with the discovery of the first molecule-based metal in 1972,4 namely the π-electron donor-acceptor complex [TTF][TCNQ] (TTF ) tetrathiafulvalen…