Polarized Neutron Diffraction as a Tool for Mapping Molecular Magnetic Anisotropy: Local Susceptibility Tensors in CoII Complexes

Polarized neutron diffraction (PND) experiments were carried out at low temperature to characterize with high precision the local magnetic anisotropy in two paramagnetic high‐spin cobalt(II) complexes, namely [Co^II(dmf)₆](BPh₄)₂ ( 1 ) and [Co^II₂(sym‐hmp)₂](BPh₄)₂ ( 2 ), in which dmf=N,N‐dimethylformamide; sym‐hmp=2,6‐bis[(2‐hydroxyethyl)methylaminomethyl]‐4‐methylphenolate, and BPh₄^?=tetraphenylborate. This allowed a unique and direct determination of the local magnetic susceptibility tensor on each individual Co^II site. In compound 1 , this approach reveals the correlation between the single‐ion easy magnetization direction and a trigonal elongation axis of the Co^II coordination octahedron. In exchange‐coupled dimer 2 , the determination of the individual Co^II magnetic susceptibility tensors provides a clear outlook of how the local magnetic properties on both Co^II sites deviate from the single‐ion behavior because of antiferromagnetic exchange coupling.     

Synthesis,crystal structures,spectral, electrochemical and magnetic properties of di-µ-phenoxido-bridged dinuclear copper(II) complexes with N-salicylidene-2-hydroxybenzylamine derivatives: axial coordination effect of dimethyl sulphoxide molecule

The template reaction of salicylaldehyde and its substituted derivatives and 2-hydroxy-5-bromobenzylamine or 2-hydroxy-5-chlorobenzylamine with copper(II) acetate in dimethyl sulphoxide (dmso) afforded eight dinuclear Cu(II) complexes, [Cu₂(L)₂(dmso)₂] (H₂ L = N-salicylidene-2-hydroxy-5-bromobenzylamine, N-salicylidene-2-hydroxy-5-chlorobenzylamine and their 5-bromo, 5-nitro and 5-methyl-substituted salicylidene derivatives). These Cu(II) complexes were characterised by IR and UV-VIS-NIR spectroscopy, electric conductivity, cyclic voltammetry, and temperature dependence of magnetic susceptibilities (4.5–300 K). In the THF solution, the complexes are nonelectrolytes and exhibit a characteristic CT band due to phenoxido-bridging at 360–384 nm. In the cyclic voltammograms, an irreversible reduction process was observed at ?1.18–1.54 V vs Fc/Fc⁺. Single-crystal X-ray crystallography revealed that two Cu(II) ions were bridged by the two phenoxido-oxygen atoms of the two Schiff-base ligands with axial coordination of dmso molecules forming a square pyramid with a Cu-Cu distance of 3.0628(8)–3.0931(6) °A. In accordance with the crystal structures, the magnetic interaction between the two Cu(II) ions is relatively anti-ferromagnetic with ?2J value of 386–575 cm^?1. The axial coordination effect of the dmso molecule was discussed in relation to the correlation between the Cu-O-Cu angle and the ?2J value.     

Direct observation of the formation of a cyclic poly(alkyl sorbate) via chain-growth polymerization by an N-heterocyclic carbene initiator and ring-closing without extreme dilution

1,3-Di-tert-butylimidazol-2-ylidene (NHCtBu), which is one of the typical N-heterocyclic carbene (NHC), was found to initiate the anionic chain-growth polymerization of methyl sorbate (MS) in toluene at −20°C. The polymerization was accelerated by an aluminum Lewis acid, that is, methylaluminum bis(2,6-di-tert-butyl-4-methylphenoxide) (MAD), to afford cyclic poly(MS)s. Subsequently, thiol-ene click reactions of poly(MS)s with two different alkanethiols were performed using a photoradical initiator to obtain graft-like polymers, which was for the microscopic observation of the chains directly by transmittance electron microscope (TEM). The contamination of linear polymers was hardly observed. This means that the polymers synthesized by our synthetic strategy were indeed cyclic polymers. We also compared the theoretical and experimental chain diameter and width for the graft-like cyclic polymers, where these values were dependent on the molecular weight of the cyclic polymers regulated by the feed monomer/initiator ratio and length of the alkanethiols, respectively.     

Relativistic segmented contraction basis sets with core-valence correlation effects for atoms 57La through 71Lu: Sapporo-DK-nZP sets (n?=?D, T, Q)

For the 15 lanthanide atoms ₅₇La through ₇₁Lu, we report Sapporo-DK-nZP sets (n?=?D, T, Q), which are natural extensions of the Sapporo-(DK)-nZP sets for lighter atoms and efficiently incorporate the correlation among electrons in the N through P shells as well as the relativistic effect. The present sets well describe the correlation among the 4s and 4p electrons, which are important in the excitation of 4f electrons. Atomic test calculations of ₅₇La, ₅₈Ce, ₅₉Pr, and ₆₀Nd at configuration interaction with the Davidson correction level of theory confirm high performance of the present basis sets. Molecular test calculations are carried out for ₅₇LaF and ₇₀YbF diatomics at the coupled-cluster level of theory. The calculated spectroscopic constants approach smoothly to the experimental values as the quality of the basis set increases.     

Effects of vibrations on particle motion near a wall: Existence of attraction force

The effects of small vibrations on a particle oscillating near a solid wall in a fluid cell, relevant to material processing such as crystal growth in space, have been investigated experimentally and theoretically. Assuming the boundary layer around the particle to be thin compared to the particle radius at high vibration frequencies, an inviscid fluid model was developed to predict the motion of a spherical particle placed near a wall of a rectangular liquid-filled cell subjected to a sinusoidal vibration. Under these conditions, a non-uniform pressure distribution around the particle results in an average pressure that gives rise to an attraction force. Theoretical expressions for the attraction force are derived for the particle vibrating normal to and parallel with the nearest cell wall. The magnitude of this attractive force has been verified experimentally by measuring the motion of a steel particle suspended in the fluid cell by a thin wire. Experiments performed at high frequencies showed that the mean particle position, when the particle is brought near a cell wall, shifts towards the same wall, and is dependent on the cell amplitude and frequency, particle and fluid densities.     

Shock reaction of hexane at 77, 193, and 273 K with special reference to shock pressure

Shock waves generated by projectile impacts were transmitted into hexane and the shocked hexane was analyzed by TCD-GC, FID-GC, GCMS, and FABMS for produced aliphatic hydrocarbons. The projectile length and its velocity were varied from 10 to 40 mm and from 220 to 1040 m/s, respectively. The initial temperature of the hexane was 77, 193 and 273 K. The major products detected throughout the reactions were hydrogen, light alkanes from C to C, and light alkenes from C to C. The minor products were heavy alkanes from C to C and soot-like materials. Experiments with varied projectile length revealed that the shock reaction occurred only while the shock wave was transmitted through hexane (about seconds). This short reaction time may be responsible for a lower yield of branched products in the shock reaction compared with yield produced by hexane pyrolysis in previous studies. In the shock reaction of hexane, the dehydrogenation was one of the important reactions and the recombination of hexyl radicals might play a role in the formation of -C. Experiments with varied initial temperature suggested that the molar yield of products depends not on the shock temperature but on the shock pressure, and that the reaction mechanisms for solid hexane and for liquid hexane are not identical. As the shock pressure increased, the relative yield of heavy products increased while that of light products decreased. This could be interpreted mainly by considering the activation volumes of the reaction involved. Received 12 September 1997 / Accepted 14 October 1997     

The effect of shock pressures on the inactivation of a marine Vibrio sp.

The effect of shock pressures on the inactivation of a marine Vibrio sp. was studied experimentally and numerically. In the experiment, an aluminum impactor plate accelerated by a gas gun was used to induce shock waves in a sealed aluminum container with cell suspension liquid inside. The shock pressures in the container were measured by a piezofilm gauge. Several 10–100 MPa of pressure were measured at the shock wave front. An FEM simulation, using the Johnson–Cook model for solid aluminum and the Tait equation for the suspension liquid, was carried out in order to know the generation mechanism of shock pressures in the aluminum container. The reflection, diffraction and interaction of shock waves at the solid–liquid boundaries in the aluminum container were reasonably predicted by the numerical simulation. The changes in shock pressures obtained from the computational simulation were in good agreement with those from the experiment. The number of viable cells decreased with the increase of peak pressures of the shock waves. Peak pressures higher than 200 MPa completely inactivated the cells. At this pressure, the cell structures were deformed like the shape of red blood cells, and some proteins leaked from the cells. These results indicate that the positive and negative pressure fluctuations generated by shock waves contribute to the inactivation of the marine Vibrio sp.