Search results for "Tetra"
showing 10 items of 6481 documents
Conductance in isodielectric mixtures. I.n-butyronitrile with dioxane, benzene, and carbon tetrachloride
1974
The conductance of tetrabutylammonium tetraphenylboride, picrate, nitrate, and bromide has been measured at 25°C inn-butyronitrile and in mixtures of this solvent with dioxane, benzene, and carbon tetrachloride covering the range of dielectric constants from 10–24.26. For the picrate, nitrate, and bromide, the association constants at a given dielectric constant are independent of the chemical composition of the solvent. The changes of Walden products with solvent composition, however, are different, depending on which other solvent is mixed with the butyronitrile.
Orbital-Resolved Partial Charge Transfer from the Methoxy Groups of Substituted Pyrenes in Complexes with Tetracyanoquinodimethane—A NEXAFS Study
2012
It is demonstrated that the near-edge X-ray absorption fine structure (NEXAFS) provides a powerful local probe of functional groups in novel charge transfer (CT) compounds and their electronic properties. Microcrystals of tetra-/hexamethoxypyrene as donors with the strong acceptor tetracyano-p-quinodimethane (TMP/HMP-TCNQ) were grown by vapor diffusion. The oxygen and nitrogen K-edge spectra are spectroscopic fingerprints of the functional groups in the donor and acceptor moieties, respectively. The orbital selectivity of the NEXAFS pre-edge resonances allows us to precisely elucidate the participation of specific orbitals in the charge transfer process. Upon complex formation, the intensit…
Rietveld Refinement of Tetragonal V4+–ZrO2 Solid Solutions Obtained from Gels by X-ray Powder Diffraction
2002
Abstract The crystal structure of three tetragonal V x Zr 1− x O 2 solid solutions, with x =0.025, 0.05, and 0.075, prepared by heating dried gel precursors at 450°C in air atmosphere, have been determined by Rietveld refinement on the basis of powder X-ray powder diffractometer data. They contain V 4+ cations surrounded by eight oxygens, four at a distance between 2.079 and 2.093 A and another four at longer distances between 2.369 and 2.348 A. The estimation of the crystal average oxygen position from the X-ray lattice parameter of V x Zr 1− x O 2 conform with the relationship proposed by Howard et al. ( J. Am. Ceram. Soc. 81, 241 (1998)).
Synthesis, crystal structure and magnetic properties of the chiral iron(II) chain [Fe(bpym)(NCS)2]n (bpym = 2,2′-bipyrimidine)
1996
Abstract The iron(II) compound of formula [Fe(bpym)(NCS)2]n (bpym = 2,2′-bipyrimidine) has been synthesized and its crystal structure determined by X-ray diffraction methods. It crystallizes in the tetragonal P41 (No. 76) and P43 space groups, a = 8.849(2), c=16.486(3) A , V=1290.9(5) A 3 , Z=4, D c =1.699 g cm −3 , M r =330.2, F(000)=664, λ( Mo K α)=0.71073 A , μ( Mo K α)=14.8 cm −1 and T=295 K. A total of 2449 reflections was collected over the range 3≤2ϑ≤55°; of these, 1657 were unique and 1321 were considered as observed (13σ(I)) and used in the structural analysis. The final R and Rw residuals were 0.027 and 0.026, respectively. The structure is made up of chiral (Δ and Λ enantiomers c…
Synthesis, Crystal Structure, and Properties of Multicomponent Bis(ethylenedithio)tetrathiafulvalene Charge-Transfer Salts of the [Mo3S7Br6]2- Cluster
2005
A new family of bis(ethylenedithio)tetrathiafulvalene (ET) radical salts has been prepared in the presence of a triangular molybdenum sulfide cluster of formula [Mo 3 S 7 Br 6 ] 2 - , which contains highly electrophilic axialsulfur atoms. A systematic change in the experimental conditions yields five different salts, namely (ETA)2(ET B )[Mo 3 S 7 Br 6 ] 2 . CH 2 Br 2 (1), (ETA)(ET B )Mo 3 S 7 Br 6 ].1.1CH 2 Br 2 (2), (ETA)(ETB)(ET C ){[Mo 3 S 7 Br 6 ]Br}.0.5C 2 H 4 Cl 2 (3), (ET)((n-Bu 4 )N)-[Mo 3 S 7 Br 6 ] (4), and (ET)(Ph4P)[Mo 3 S 7 Br 6 ].0.5CH 3 CN (5), where the ET subscript denotes crystallographically independent molecules. The five compounds have been structurally characterized, a…
Crystal structure and spectroscopic study of [Cu(BPCA)(OH2)(O2CCH3)·H2O complex; BPC = N-2-pyridinylcarbonyl-2-pyridinecarboximidate anion
1989
Abstract The crystal and molecular structure of the [Cu(BPCA)(OH2)(O 2CCH3]·H2O complex (BPCA = N-2-pyridinylcarbonyl-2-pyridinecarboximidate anion) has been determined by X-ray diffraction methods. It crystallizes in the triclinic space group P l with two formula units in a cell of dimensions: a = 7.416(2), b = 8.632(4), c = 13.034(3) A, α = 74.55(3), β = 84.84(3), γ = 81.04(5)°. Least-squares refinement of 2534 reflections with I > 2.5σ(I) and 218 parameters gave a final R = 0.047 and Rw = 0.049. The structure consists of discrete [Cu(BPCA)(OH2)(O2CCH3)] neutral units linked through hydrogen bonding. The coordination geometry around copper ions can be described as tetragonal square pyrami…
Fine-Tuning the Dimerization of Tetraureacalix[4]arenes
2010
Calix[4]arenes substituted by four urea residues at their wide rim form hydrogen-bonded homo- and heterodimeric capsules in apolar solvents. If urea groups are covalently connected to loops or substituted by bulky residues, the dimerization may be restricted to those pairs in which the loops do not overlap and for which the residues are small enough to pass the loops. In the present study, we describe the dimerization properties of tetraureas with one, two (adjacent or opposite), three, or four loops and those bearing (additionally) up to four residues of different size: a = tolyl, b = 3,5-di-tertbutylphenyl, c = 4-propyloxy-3,5-di-(tert-butylphenyl)phenyl, and d=4-[tris-(4-tert-butylphenyl…
A DFT study of the asymmetric (S)-5-(pyrrolidin-2-yl)-1H-tetrazole catalyzed Michael addition of carbonyl compounds to nitroalkenes
2007
Abstract The role of the ( S )-5-(pyrrolidin-2-yl)-1 H -tetrazole in the asymmetric organocatalyzed Michael addition of carbonyl compounds to nitroalkenes has been studied using DFT methods at the B3LYP/6-31G ∗∗ computational level. For the C–C bond-formation step, several reactive channels have been analyzed. The B3LYP/6-31G ∗∗ results, which are in reasonable agreement with the experiments, allow us to explain the stereoselectivity and the increase of the reactivity achieved by an intramolecular HB between the acid hydrogen of the tetrazole moiety and one oxygen atom of the nitroalkene.
Superparamagnetic iron oxide/oleic acid nanoparticles with immobilized organosilicon derivatives ofN-(2-hydroxyethyl)tetrahydroisoquinoline: synthesi…
2013
Superparamagnetic iron oxide/oleic acid nanoparticles bearing lipid-like organosilicon N-(2-hydroxyethyl)-1,2,3,4-tetrahydroisoquinoline derivatives have been synthesized with the aim of their potential biomedical application. X-ray diffraction analysis, Dynamic light-scattering measurements, method of magnetogranulometry and some others have been employed to investigate the morphology and properties of the nanoparticles synthesized. The magnetic core diameter of mixed covered nanoparticles ranged between 4.8 and 9.6 nm. The magnetization analyses showed that the particles are superparamagnetic at room temperature. In vitro cell cytotoxicity and intracellular NO generation caused by the wat…
Electromechanical Properties of Ba(1–x)SrxTiO3 Perovskite Solid Solutions from First-Principles Calculations
2017
Many thanks to M. Maček-Kržmanc, R. A. Evarestov, D. Gryaznov and D. Fuks for fruitful discussions. This study was supported by the ERA-NET HarvEnPiez project.