A cadmium hydroxide complex of a N3S-donor ligand containing two hydrogen bond donors: synthesis, characterization, and CO2 reactivity

Treatment of the ebnpa (N-2-(ethylthio)ethyl-N,N-bis((6-neopentylamino-2-pyridyl)methyl)amine) ligand with a molar equivalent amount of Cd(ClO(4))(2).5H(2)O in CH(3)CN followed by the addition of [Me(4)N]OH.5H(2)O yielded the cadmium hydroxide complex [(ebnpaCd)(2)(mu-OH)(2)](ClO(4))(2) (1). Complex 1 has a binuclear cation in the solid-state with secondary hydrogen-bonding and CH/pi interactions involving the ebnpa ligand. In acetonitrile, 1 forms a binuclear/mononuclear equilibrium mixture. The formation of a mononuclear species has been confirmed by conductance measurements of 1 at low concentrations. Variable temperature studies of the binuclear/mononuclear equilibrium provided the standard enthalpy and entropy associated with the formation of the monomer as DeltaH degrees = +31(2) kJ mol(-1) and DeltaS degrees = +108(8) J mol(-1) K(-1), respectively. Enhanced secondary hydrogen-bonding interactions involving the terminal Cd-OH moiety may help to stabilize the mononuclear complex. Treatment of 1 with CO(2) in acetonitrile results in the formation of a binuclear cadmium carbonate complex, [(ebnpaCd)(2)(mu-CO(3))](ClO(4))(2) (2).     

Elastic constants of B-A1 composites by ultrasonic velocity measurements

The complete orthotropic elastic-stiffness matrix of unidirectional, Borsic-filament-reinforced aluminum composites was experimentally evaluated for three different volume fractions by ultrasonic velocity measurements on thin plates. Longitudinal- and shear-velocity measurements were made in appropriate symmetry directions by direct contact or liquid-immersion techniques. The elastic constants determined by this pulsed through-transmission method were in agreement with micromechanical theories based on the properties of the constituent materials. Agreement was also found between engineering constants determined by mechanical testing and those calculated from the ultrasonic data. Finally, measurement of the ultrasonic-wave velocity has also been shown to be a rapid nondestructive-test method for determining filament-volume fraction in a fabricated part.     

NMR spectra of halopermethylpolysilanes

Proton NMR spectra were determined for the series X(SiMe₂)_nX (n = 3, 4, 6 and X  F, Cl, I) and Me(SiMe₂)₆X. Fluorine-19 NMR spectrafor the fluorosilanes of these series were also determined. The chemical shift of the methyl protons of the SiMe₂X group appears at higher field as the chain length increases. This chemical shift also is at higher field for monohalopolysilanes than for the corresponding dihalopolysilanes. These observations are consistent with increased donation from halogens to vacant polysilane orbitals with increased chain length and with transmission of the effect of a second halogen through the silicon chain.     

Kinematically-complete study of pion production by the reaction 1H(p, π+p)n at 800 MeV

The differential cross section d⁵σ/dp₁dΩ₁dΩ₂ has been measured in a kinematically-complete study of the reaction ¹H(p, π⁺p)n at 800 MeV, for several pairs of coplanar angles. The spectra at all observed angle pairs are dominated by the formation of the δ⁺⁺ isobar, with a tendency of forward peaking in the pion angular distribution.     

Anion radicals of some fluorobiphenyls

Potassium 4,4′-difluorobiphenylide, 4-fluorobiphenylide and potassium 3,3′-difluorobiphenylide are stable at −80° in the tetrahydrofuran. 4-Chlorobiphenyl, 4-bromobiphenyl and 4,4′-dibromobiphenyl apparently react with potassium at low temperatures to form radicals which decompose immediately by halide elimination. The ESR spectra of the 4,4′-difluorobiphenylide and 3,3′-difluorobiphenylide radicals and the polarographic behaviour, p-band positions, and results of LCAO---MO calculations for the parent, neutral compounds are reported.     

High-sensitivity atomic magnetometer unaffected by spin-exchange relaxation

Alkali-metal magnetometers compete with SQUID detectors as the most sensitive magnetic field sensors. Their sensitivity is limited by relaxation due to spin-exchange collisions. We demonstrate a K magnetometer in which spin-exchange relaxation is completely eliminated by operating at high K density and low magnetic field. Direct measurements of the signal-to-noise ratio give a magnetometer sensitivity of 10 fT Hz(-1/2), limited by magnetic noise produced by Johnson currents in the magnetic shields. We extend a previous theoretical analysis of spin exchange in low magnetic fields to arbitrary spin polarizations and estimate the shot-noise limit of the magnetometer to be 2x10(-18) T Hz(-1/2).     

Dimethylsilyl- and methylene-bridged aromatic groups : II. Phosphorescent triplet states

The zero-field splitting parameters D and E, or D, were measured by electron spin spectroscopy for the triplet states of bis(4-biphenylyl)dimethylsilane, 4,4′-bis-(4-biphenylyldimethylsilyl)biphenyl, 1,2-diphenyltetramethyldisilane, several monosilanes, bis(4-biphenylyl)methane, 4,4′-bis(4-phenylbenzyl)biphenyl, and dimethyldiphenylmethane. The zero-field splitting values of compounds having biphenyl subunits bridged with either SiMe₂- or CH₂-groups, compared with those of mono- and disubstituted biphenyls, show that the triplet electrons are localized mainly on one biphenyl group in each of the bridged compounds on the time scale of the ESR observations.