Synthesis and crystal and molecular structure of μ-oxo-bis[trifluoroacetato(p-tolyl)iodine]

Crystal and molecular structure of μ-oxo-bis[trifluoroacetato(p-tolyl)iodine] (I) synthesized by a new procedure was determined by X-ray diffraction analysis. Crystals I are orthorhombic, unstable, space group Pbcn, a=17.684(3), b=8.453(3), c=30.560(4) Å, Z=8. The structure of I was solved by direct and Fourier methods and refined by the full-matrix least-squares procedure in an anisotropic-isotropic approximation to R=0.098 (CAD-4 automatic diffractometer, λCuK_α, 1200 observed reflections with I≥2σ). In molecule I, two iodine atoms have T-configuration of valence bonds with the average bond angles O?I?O 169(1) and O?I?C 86(2)°, average bond lengths I?O_μ 2.009(9), I?O_acet 2.269(9), and I?C_aryl 2.11(1) Å, and the bond angle I?O?I 118.1(5)°. In molecule I, two p-Tol substituents are directed to approximately the same side of the medium plane of the central O?I?O?I?O fragment. Crystal structure I has I...O type intra-and intermolecular nonvalent interactions (secondary bonds).     

Transition metal complexes with tridentate salicylaldimine derived from 3,5-di-t-butylsalicylaldehyde

Several new binuclear Cu^II, Ni^II, OV^IV and Mn^II complexes of tridentate salicylaldimine (H₂L), obtained from 3,5-di-t-butylsalicylaldehyde and o-aminophenol, have been prepared and characterized by analytical, spectroscopic (i.r., u.v.–vis., e.s.r.) techniques, magnetic and thermal measurements. The adduct formation or dissociation of these complexes in the presence of strongly coordinating solvents like pyridine and DMSO did not take place. The complexation of Co^II with H₂L is accompanied by intramolecular electron transfer from the metal to the coordinated ligand yielding the radical ligand Co^III complex (g = 2.003, A ^Co = 10 G). The e.s.r. spectra of the Cu^II, OV^IV and Mn^II complexes in the solid state and in solution are very broad due to intramolecular dipolar antiferromagnetic interactions.     

Role of acid centers of Sn/Mo oxide catalyst in propylene conversion to acetone

Infrared spectroscopic studies of the nature of catalyst centers indicate the presence of Brönsted and Lewis acid centers on the surface. Propylene conversion to acetone proceeds via proton transfer from the surface to propylene with the formation of a (CH₃)₂–C(H)–O–Me type compound, and its subsequent dehydration.

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- , . (CH₃)₂–C(H)–OMe .

     

Examination of intermediates in globular protein unfolding by the tritium labeling method

Unfolding of polypeptide chain of ribonuclease A in urea and guanidinium chloride (GuCl) solutions under equilibrium conditions involves formation of intermediates whose properties (compactness and preservation of the most of the native hydrophobic core, secondary structures, and native-like folding of the polypeptide chain) correspond to the basic characteristics of the “molten globule” state. Intermediates are “damp” molten globules (with water molecules inside the globule). The examinations performed revealed pronounced distinctions in the properties of the intermediates, above all, in their compactness degrees.     

Stereochemical studies—XXVI: Conformational Equilibria of ketals of 2-substituted cyclohexanones

The position of the conformational equilibria in a series of 2-substituted cyclohexanone ketals have been determined by ¹H NMR. For the ethylene ketals 6 the equatorial conformer has been found to be enthalpically preferred. The other ketal system (5, 7–9), in contrast, display predominance of axial conformers. The reasons for this behavior are discussed in terms of rotameric conformations of acetal chains.     

Acoustoelectric effects in carbon nanotubes

We report observations of acoustoelectric effects in carbon nanotubes. We excite sound in &mgr;m long ropes of single walled carbon nanotubes suspended between two metallic contacts by applying radio-frequency electric field. The sound is detected by measuring either the dc resistance of the tubes in a region of strong temperature dependence (in the vicinity of superconducting or metal-insulator transition), or their critical current. We show that, depending on the excitation power, the vibrations produce either electron heating or phase coherence breaking.     

Synthesis, spectroscopic and structural studies of new Schiff bases prepared from 3,5-Bu2t-salicylaldehyde and heterocyclic amines: X-ray structure of N-(3,5-di-tert-butylsalicylidene)-1-ethylcarboxylato-4-aminopiperidine

Two new sterically hindered salicylaldimines, N-(2,2,6,6-tetramethyl-piperidine-4)-3,5-Bu2t-salicylaldimine (I) and N-(1-carboxyethyl piperidine-4)-3,5-Bu2t-salicylaldimine (II), have been prepared and characterized by IR, UV-vis, 1H NMR, 13C NMR techniques and the structure of II has been examined by X-ray crystallography. No intermolecular H-bonding, pi-pi stacking or C--H...pi interactions are observed in the structure. The crystal structure the was mainly governed by intermolecular steric repulsions, due to bulky tert-butyl groups and the tendency of salicylaldimine rings to pack in parallel mode forms one-dimensional columns.     

Measurement of quantum noise in a carbon nanotube quantum dot in the Kondo regime

The current emission noise of a carbon nanotube quantum dot in the Kondo regime is measured at frequencies ν of the order or higher than the frequency associated with the Kondo effect k(B)T (K)/h, with TK the Kondo temperature. The carbon nanotube is coupled via an on-chip resonant circuit to a quantum noise detector, a superconductor-insulator-superconductor junction. We find for hν ≈ k(B)T(K) a Kondo effect related singularity at a voltage bias eV ≈ hν, and a strong reduction of this singularity for hν ≈ 3k(B)T(K), in good agreement with theory. Our experiment constitutes a new original tool for the investigation of the nonequilibrium dynamics of many-body phenomena in nanoscale devices.