A new target for synthesis of sandwiched beryllium, magnesium, and calcium dimers: C5H7-M-M-C5H7 and C4H4P-M-M-C4H4P

Group 2 bis-element sandwiches formed by homoleptic open sandwiches with formula C₅H₇-M-M-C₅H₇ and C₄H₄P-M-M-C₄H₄P (M = Be, Mg, and Ca) have been studied at the B3LYP/cc-PVDZ and BP86/6-311G(d,p) levels of theory. The predicted M-M bond distances are much shorter than in the equivalent isolated M-M dimer and indicate substantial Be-Be, Mg-Mg, and Ca-Ca bonding. An NBO analysis shows that each M-M unit contains a single covalent bond and that the unit is linked to the open pentadienyl and phospholyl ring via ionic bonds. We thus predict that these new compounds are viable synthetic targets.     

Potential-controlled electrodeposition of gold dendrites in the presence of cysteine

Crystalline Au dendrites were formed by electrodeposition on a glassy carbon electrode from a solution of HAuCl(4) containing cysteine. The Au dendrites possessed a hierarchical architecture with three-fold symmetry; they comprised trunks, branches, and nanorod leaves, which all grew along the <111> direction.     

Thermal Instability in a Porous Medium Layer Saturated with a Viscoelastic Nanofluid

The onset of convection in a horizontal layer of a porous medium saturated with a viscoelastic nanofluid was studied in this article. The modified Darcy model was applied to simulate the momentum equation in porous media. An Oldroyd-B type constitutive equation was used to describe the rheological behavior of viscoelastic nanofluids. The model used for the viscoelastic nanofluid incorporates the effects of Brownian motion and thermophoresis. The onset criterion for stationary and oscillatory convection was analytically derived. The effects of the concentration Rayleigh number, Prandtl number, Lewis number, capacity ratio, relaxation, and retardation parameters on the stability of the system were investigated. Oscillatory instability is possible in both bottom- and top-heavy nanoparticle distributions. Results indicated that there is competition among the processes of thermophoresis, Brownian diffusion, and viscoelasticity that causes the convection to set in through oscillatory rather than stationary modes. Regimes of stationary and oscillatory convection for various parameters were derived and are discussed in detail.     

Heterocyclic benzoxazole-based liquid crystals

The synthesis, characterization, and mesomorphic properties of a new type of heteronuclear compounds 1a-c and a Pd complex 1d derived from benzoxazole as the core group are reported. These compounds were prepared by the ring closure reaction of 4-alkoxybenzoic acid 4-[(4-alkoxy-2-hydroxyphenylimino)methyl]phenyl esters 6 in the presence of lead(IV) acetate. All the compounds were characterized by ¹H and ¹³C NMR spectroscopies and elemental analysis. The phase behaviour of these mesogenic compounds was characterized and studied by differential scanning calorimetry and polarizing optical microscopy. All the compounds 1a exhibited nematic (N) and/or smectic C (SmC) phases, as expected for rod-like molecules; however, the compounds 1b and 1c exhibited crystal phases. For those compounds 1a having shorter carbon chains (n = 1, 3, 4) nematic phases were observed, whereas for compounds having longer carbon chains (n = 6, 7, 8, 10, 12, 14) smectic C behaviour was also observed at lower temperatures. The greater aspect ratio (l/d) of compounds 1a compared with 1b and 1c was found to be required for the observation of liquid crystallinity. The fluorescent properties of these compounds were also examined. All λ_max peaks of the absorption and photoluminescence spectra of compounds 1a-1c occurred at c. 316-322 nm and 371-382 nm, respectively. The quantum yields of some compounds were relatively low, and also slightly solvent-dependent.     

The Effect of Temperature,Agitation and Content of Gold on the Thickness of Electroplated Gold at Various Current Densities

The effect of temperature, agitation, and content of gold in the solution on the thickness of electroplated gold at various current densities can be easily explained by their effect on the limiting current. Diffusion coefficient of aurocyanide ion, thickness of diffusion layer, and the activity of aurocyanide ion in the bulk solution are the three major factors to affect the limiting current. It was found that the change of temperature will affect both diffusion coefficient and thickness of diffusion layer. However, the thickness of diffusion layer is mainly determined by the means of agitation.     

Nickel Boride Catalysts in Organic Synthesis (IV). The Effect of Water Washing on P-2 Nickel Boride Catalyst

Water washing of P-2 nickel boride brings about a new catalyst designated as P-2W nickel boride. This P-2W catalyst is more reactive than P-1 or P-2 in the hydrogenation of cyclohexanone and nitrobenzene. The P-2W, however, is less selective than P-2 in the hydrogenation of cyclic olefins.     

Imaging nonequilibrium atomic vibrations with x-ray diffuse scattering

We use picosecond x-ray diffuse scattering to image the nonequilibrium vibrations in the lattice following ultrafast laser excitation. We present images of nonequilibrium phonons in InP and InSb throughout the Brillouin zone which remain out of equilibrium up to nanoseconds. The results are analyzed using a Born model that helps identify the phonon branches contributing to the observed features in the time-resolved diffuse scattering. In InP this analysis shows a delayed increase in the transverse-acoustic (TA) phonon population along high-symmetry directions accompanied by a decrease in the longitudinal-acoustic phonons. In InSb the increase in TA phonon population is less directional.