Complexes containing phosphorus lignads—161: New phosphinite,phosphonite and phosphite derivatives of ruthenium,osmium and iridium

The complexes [MHCl(CO)(PPh₃)₃] (M = Ru or Os) readily undergo substitution at the site trans to the hydride ligand to afford phosphinite-, phosphonite-, or phosphite-containing products [MHCI(CO)(PPh₃)₂L] [L = P(OR)Ph₂, P(OR)₂Ph or P(OR)₃ respectively; R = Me or Et]. The ruthenium complexes alone undergo further substitution to afford complex cations [RuH(CO)(PPh₃)_nL_4?n]⁺ [n = 2, L = P(OMe)₃; n = 1, L = P(OR)₃; n = 0, L = P(OR)₂Ph or P(OR)Ph₂] which were isolated and characterised as their tetraphenylborate salts. Synthesis of the cationic complexes [IrHL₅][BPh₄]₂ [L = P(OR)₃, R = Me or Et] is also reported. Stereochemical assignments based on NMR data are given, and second order ³¹P and high field ¹H NMR patterns are analysed.     

A maximum shear stress theory of plastic failure of fiber-reinforced materials

A theory of plastic behavior of fiber-reinforced composite materials is presented. The theory allows for several failure modes of the composite material, including plastic failure of the matrix material alone and the combined ductile failure of the fibers and the matrix. The latter mode may be readily modified to allow for brittle behavior of the fiber material.     

EPR and saturation transfer EPR spectra at high microwave field intensities

The eight unique EPR signals at the first and second harmonies of the Zeeman modulation are sensitive to the very slow rotational diffusion of spin labeled biomolecules when these signals are recorded under conditions of microwave saturation and finite Zeeman modulation frequencies and amplitudes. Such saturation transfer sensitive spectra have been employed to study contractile proteins, hemoproteins, enzymes, etc. When these species or their supramolecular complexes are characterized by correlation times in the range 10^?8 to 10^?3 s. Published computer simulation reproduce quite well spectra at the longer correlation times and the general sensitivity of spectra to changing rotational correlation time; however, agreement between experimental and calculated spectral shapes is poor for rotational correlation time on the order of 10^?7 s and the dependence of experimental spectra upon microwave field intensity is not reproduced. In the present communication we show that the previously reported discrepancy between experimental and calculated spectra is due to the neglect of higher order cou magnetic interactions modulated by the molecular motion and involving the spin-microwave field interaction. When these “pseudodiagonal” terms of the spin density equation are explicitly included, experimental spectral lineshapes, spectral line positions, and the ratios of amplitudes of the various signal components are quantitatively reproduced. Plots of the ratios of the heights of the high and low field spectral extrema suggest a procedure for calibrating microwave field intensities as these ratios are found experimentally and theoretically to be nearly a linear function of microwave field intensity for intensities in the range 0.15 to 0.5 G. The separation of low and high field extrema was observed to increase with increasing microwave field intensity, suggesting the need to carefully consider saturation effects when determining rotational correlation times from this separation.     

Oxidative cyclization and fragmentation of steroidal alcohols induced by ceric ammonium nitrate

Oxidative cyclizations of steroidal alcohols (1a–1d) using ceric ammonium nitrate (CAN) in aqueous acetonitrile or aqueous acetic acid gave the corresponding cyclic ethers (2a–2d), whereas the tertiary alcohol (4) gave secosteroid (5).     

Ground state shaoe and crossing of near spherical and deformed bands in 182Hg

The energy levels of ¹⁸²Hg have been identified for the first time through comparison of in-beam studies of the reactions ^156,154Gd(³²S, 4n)^184,182Hg and γ-X-ray coincidences. Levels up to 12⁺ in ¹⁸²Hg were established from γ-γ coincidences and singles measurements. The data establish that the ground state shape is near spherical, and that the ground band is crossed by a well-deformed band at 4⁺. In contrast to IBA model predictions that the deformed band will rise in energy in ¹⁸²Hg compared to ¹⁸⁴Hg, the energies of the deformed levels in ¹⁸²Hg continue to drop.     

Chromium tracer diffusion in NiO crystals

Diffusion of ⁵¹Cr in NiO single crystals in air has been studied by the tracer-sectioning technique. In the temperature range 1192–1642°C, the diffusion coefficient can be expressed by the Arrhenius expression D=D_oexp(-Q/RT), with D_o=(8·6±1·2)×10^?3 cm²/sec and Q=67·4±1·1 kcal/mole. The use of a high specific-activity tracer and a special configuration for the diffusion anneal prevented the self-dopling effect found by Seltzer and the evaporation of chromium from the sample surface. The present results, in conjunction with published results on nickel self-diffusion in NiO and interdiffusion in the NiO?Cr₂O₃ system, are used to determine a chromium ion-vacancy binding energy of about 5 kcal/mole in pure NiO.