Structures of the radical P[N(SiMe3)2](NPri2), its dimer, cation and chloro derivative

Treatment of PCl[N(SiMe3)2](NPri2) (1) with potassium-graphite in thf afforded the colourless, crystalline diphosphine [P[N(SiMe3)2](NPri2)]2 (2) in good yield. Sublimation of 2 in vacuo yielded the yellow phosphinyl radical P[N(SiMe3)2](NPri2) (3), which upon cooling reverted to 2; the latter in C6D6 at 298 K was a mixture of rac and meso diastereoisomers. The yellow, crystalline phosphenium salt [P[N(SiMe3)2](NPri2)][AlCl4] (4) was obtained from 1 and 1/2Al2Cl6 in CH2Cl2. By single-crystal X-ray diffraction (XRD) the structures of the known compound 1 and of 2 and 4 were determined. The structure of the radical 3, formed by the thermal homolytic dissociation of the diphosphine 2, was determined in the gas phase by electron diffraction (GED), utilising data from UMP2/6-31+G*ab initio calculations. The model of the molecule in the GED structure analysis was described by a set of internal coordinates and an initial set of Cartesian coordinates from ab initio calculations, facilitating the structure analysis. The experimental data were found to be consistent with the presence of a single conformer of the radical in the gas phase. The computed standard homolytic dissociation enthalpy of the P-P bond in the corresponding diphosphine 2, corrected for BSSE, 54 kJ mol(-1), is substantially reduced compared to the dissociation enthalpy of tetramethyldiphosphine by the reorganisation energies of the fragments that form upon dissociation. The intrinsic energy content of the P-P bond in the diphosphine 2 was estimated to be 286 kJ mol(-1), in agreement with the results of previous work on a series of crowded diphosphines.     

Molecular Structures of arachno‐Decaborane Derivatives 6,9‐X2B8H10 (X: CH2, NH,Se) Including a Gas‐Phase Electron‐Diffraction Study of 6,9‐C2B8H14.

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A streaming birefringence study of the flow at the junction of the aorta and the renal arteries

Streaming birefringence with an organic dye (Milling Yellow) was used to investigate the flow near the junction of the renal arteries and the descending aorta in a model of human vessels. The dye concentration was adjusted to give fluid rheological properties, typical of blood. Steady and pulsatile flow were investigated at branch-to-trunk flow ratios of 0.050–0.350. The flow ratio range over which flow separation and simple secondary flows were identified during systole near the renal ostia are reported. Streaming birefringence has the advantage of allowing visualization of the entire flow field. Also, the fluid rather than suspended particles are observed. An important disadvantage, however, is that three-dimensional flows make interpretation difficult.     

The gas-phase molecular structure of silyl chloroacetylene,determined by electron diffraction

The molecular structure of SiH₃CCCl in the gas phase has been investigated using electron diffraction. Mean amplitudes of vibration and perpendicular amplitude correction factors calculated from spectroscopic data enabled refinement of both r_a and r_α structures to be carried out. The r_α refinement leads to a linear skeleton, with r_α parameters: r(Si-C) 181.2(5) pm, r(CC) 123.4(6) pm, r(C-Cl) 162.0(5) pm, r(Si-H) 148.8(12) pm, ∠HSiC 109.4(20)°. The r_a structure shows an apparent angle in the skeleton of 172(3)° (∠CCCl) owing to shrinkage.