Measured and calculated oxidation potentials of 1-X-12-Y-CB11Me10- anions

Cyclic voltammetry of 31 icosahedral carborane anions 1-X-12-Y-CB(11)Me(10)(-) at a Pt electrode in liquid SO(2) revealed a completely reversible one-electron oxidation even at low scan rates, except for the anions with Y = I, which are oxidized irreversibly up to a scan rate of 5.0 V/s, and the anion with X = COOH and Y = H, whose oxidation is irreversible at scan rates below 1.0 V/s. Relative reversible oxidation potentials agree well with RI-B3LYP/TZVPP,COSMO and significantly less well with RI-BP86/TZVPP,COSMO or RI-HF/TZVPP,COSMO calculated adiabatic electron detachment energies. Correlations with HOMO energies of the anions are nearly as good, even though the oxidized forms are subject to considerable Jahn-Teller distortion. Except for the anion with X = F and Y = Me, the oxidation potentials vary linearly with substituent σ(p) Hammett constants. The slopes (reaction constants) are ~0.31 and ~0.55 V for positions 1 and 12, respectively.     

Antiferromagnetic Interactions in 1D Heisenberg Linear Chains of 7‐(4‐Fluorophenyl) and 7‐Phenyl‐Substituted 1,3‐Diphenyl‐1,4‐dihydro‐ 1,2,4‐benzotriazin‐4‐yl Radicals

7‐(4‐Fluorophenyl) and 7‐phenyl‐substituted 1,3‐diphenyl‐1,4‐dihydro‐1,2,4‐benzotriazin‐4‐yl radicals were characterized by X‐ray diffraction analysis and variable‐temperature magnetic susceptibility studies. The radicals pack in 1D π stacks of equally spaced slipped radicals with interplanar distances of 3.59 and 3.67 Å and longitudinal angles of 40.97 and 43.47°, respectively. Magnetic‐susceptibility studies showed that both radicals exhibit antiferromagnetic interactions. Fitting the magnetic data revealed that the behavior is consistent with 1D regular linear antiferromagnetic chain with J=?12.9 cm^?1, zJ′=?0.4 cm^?1, g=2.0069 and J=?11.8 cm^?1, zJ′=?6.5 cm^?1, g=2.0071, respectively. Magnetic‐exchange interactions in benzotriazinyl radicals are sensitive to the degree of slippage, and inter‐radical separation and subtle changes in structure alter the fine balance between ferro‐ and antiferromagnetic interactions.     

Lanthanide transport in stabilized zirconias: interrelation between ionic radius and diffusion coefficient

The diffusion of all stable lanthanides was measured both in calcia stabilized zirconia (CSZ) and in yttria stabilized zirconia (YSZ) in the temperature range between 1,286 and 1,600 degrees C. The lanthanide diffusion coefficients obtained increase with increasing ionic radius. The experimental activation enthalpy of diffusion is near 6 eV for CSZ and between 4 and 5 eV for YSZ and is not strongly affected by the type of lanthanide. The results were correlated with defect energy calculations of the lanthanide diffusion enthalpy using the Mott-Littleton approach. An association enthalpy of cation vacancies with oxygen vacancies of about 1 eV (96 kJ/mol) was deduced in the case of CSZ, while there is no association in the case of YSZ. Furthermore, the change in diffusion coefficients can be correlated to the interaction parameter for the interaction between the lanthanide oxide with zirconia: The higher the interaction parameter, the higher the lanthanide diffusion coefficient.     

A DFT study of the ground state multiplicities of linear vs angular polyheteroacenes

Unrestricted density functional calculations in combination with the broken-symmetry approach and spin-projection methods have been employed to study a series of formally 4n pi antiaromatic linear and angular polyheteroacenes. Calculations show that the linear polyheteroacene molecules have either stable singlet zwitterionic 6-9 or singlet diradical 5 ground states because they sacrifice the aromaticity of the central arene to form two independent cyanines. The corresponding angular compounds 10-14 have robust triplet states, since they cannot create independent cyanines to escape their overall antiaromaticity. An analysis based on the SOMO-SOMO energy splittings, their spatial distributions, and the spin density populations for the triplet states is presented to clarify the factors that determine their ground state multiplicities.     

Adsorption of cobalt ions on the "electrolytic solution/gamma-alumina" interface studied by diffuse reflectance spectroscopy (DRS)

Diffuse reflectance spectroscopy was used for the first time to investigate the adsorption of the [Co(H2O)6]2+ ions on the interface developed between the surface of the gamma-alumina particles and the electrolytic aqueous solutions used for the preparation of cobalt-supported gamma-alumina catalysts by equilibrium deposition filtration. The formation of inner-sphere Co(II) surface complexes in which Co(II) is in octahedral symmetry was confirmed. A deconvolution peak centered at approximately 585 nm was attributed to the exchange of one aqua ligand with one AlxOHy (x = 1, 2, or 3; y = 0 or 1) negatively charged surface group resulting in the formation of mononuclear monosubstituted inner-sphere Co(II) complexes at a Co(II) surface concentration equal to 0.02 micromol of Co(II)/m2. It was inferred that as the surface Co(II) concentration increases the formation of disubstituted and/or trisubstituted surface complexes is favored with respect to the formation of monosubstituted Co(II) surface complexes. A deconvolution peak centered at approximately 640 nm was attributed to the exchange of one or more aqua ligands with bridging hydroxo ligands (Co-O-H). The relative magnitude of this peak increases with the Co(II) surface concentration, reflecting the increasing formation of binuclear, oligonuclear, and multinuclear Co(II) surface complexes and then the formation of the Co(II) surface precipitate.     

Mesostructured selenides with cubic MCM-48 type symmetry: large framework elasticity and uncommon resiliency to strong acids

The metal mesostructured Pt/Sn/Se chalcogenides with cubic MCM-48 type pore symmetry are found to be surprisingly stable in concentrated oxidizing acids. Their metal chalcogenide framework exhibits high flexibility during reversible proton exchange as it expands and contracts in an apparent breathing-like action.     

Anodic oxidation of methyl alpha-dimethylsilyldihydrocinnamate. A novel silicon gamma-aryl effect

The anodic oxidation of methyl 3-phenyl-2-dimethylsilylpropionate occurs at a potential almost 1 V positive of that required to oxidize other alpha-silyl esters. Semiempirical and ab initio calculations on the model compound 1-phenyl-2-trimethylsilylethane indicate that electron removal from these two compounds is highly stereoelectronically dependent. Both molecules exist almost exclusively in a conformation in which the phenyl group and silicon atom are anti and the side chain is perpendicular to the aromatic ring. This conformation has a higher energy HOMO orbital and lower computed ionization potential than the only other significantly populated conformation of 1-phenyl-2-trimethylsilylethane. Finally, the ab initio calculations show that in the cation radical of this model compound the ipso carbon of the aromatic ring and the side chain carbon bound to silicon draw significantly closer together than in the neutral species; an electrostatic potential map of the cation radical shows that the ipso carbon bears the highest degree of positive charge of any of the benzenoid carbons. We interpret these data, taken together, as an indication that this cation radical is stabilized by overlap of the rear lobe of the carbon-silicon bond with the p-orbital of the ipso carbon.     

Preparation of hydroxyapatite via microemulsion route

Hydroxyapatite (HAp) was prepared using a microemulsion route in combination with the pH-shock wave method. The samples as received consisted of amorphous aggregated particles, which had remarkable mesoporosity with a narrow pore size distribution. After being heated at 650 degrees C, the A-type carbonate hydroxyapatite was crystallized at 635 degrees C in particles of similar size (40--120 nm) with no internal porosity. At a higher temperature (900 degrees C) a sintering process took place, resulting in network of a larger particles, consisting of HAp and beta-tricalcium phosphate (beta-TCP). The crystallization of HAp occurs at 635 degrees C with an activation energy of 62.7--72.2 kcalmol(-1).     

Ultra‐Small Plutonium Oxide Nanocrystals: An Innovative Material in Plutonium Science

Apart from its technological importance, plutonium (Pu) is also one of the most intriguing elements because of its non‐conventional physical properties and fascinating chemistry. Those fundamental aspects are particularly interesting when dealing with the challenging study of plutonium‐based nanomaterials. Here we show that ultra‐small (3.2±0.9 nm) and highly crystalline plutonium oxide (PuO₂) nanocrystals (NCs) can be synthesized by the thermal decomposition of plutonyl nitrate ([PuO₂(NO₃)₂] ? 3 H₂O) in a highly coordinating organic medium. This is the first example reporting on the preparation of significant quantities (several tens of milligrams) of PuO₂ NCs, in a controllable and reproducible manner. The structure and magnetic properties of PuO₂ NCs have been characterized by a wide variety of techniques (powder X‐ray diffraction (PXRD), X‐ray absorption fine structure (XAFS), X‐ray absorption near edge structure (XANES), TEM, IR, Raman, UV/Vis spectroscopies, and superconducting quantum interference device (SQUID) magnetometry). The current PuO₂ NCs constitute an innovative material for the study of challenging problems as diverse as the transport behavior of plutonium in the environment or size and shape effects on the physics of transuranium elements.