Incoherent neutron quasi-elastic scattering studies of the anisotropic self-diffusion in nematic and smectic a phases of ethyl 4-(4′acetoxy benzylidene) aminocinnamate (EABAC)

Incoherent quasi-elastic neutron scattering spectra have been measured down to low scattering vectors (Q >) 0.14 Å^?1) on magnetically aligned specimens of the nematic and smectic A phases of EABAC. Data were obtained for Q || n and Q⊥n where n denotes the direction of the unique axis) giving the diffusion coefficients D_|| and D_⊥ for the two phases as follows (in units of 10^?7 cm² s^?1); nematic: D_|| = 15.8 ± 2.0, D_⊥ = 12.3 ± 0.8; smectic A: D_|| = 4.3 ± 0.4, D_⊥ = 4.9 ± 0.8. The anisotropy is reversed between the phases and the molecules are more mobile in the nematic phase as expected. In the smectic A experiments with Q || n an apparent inconsistency between low and high Q results is interpreted as evidence for the existence of some slow motion other than translational diffusion which requires further investigation. Preliminary measurements were made to explore the application of the “fixed window” method for determining the temperature dependence of the diffusion coefficients.     

The first structural and spectroscopic characterization of a neptunyl polyoxometalate complex

The reaction between PW9O349- and NpO2+ has yielded the first structurally characterized neptunyl(V) polyoxometalate complex, [Na2(NpO2)2(A-PW9O34)2]14-. This complex is isostructural with the uranyl(VI) analogue, and there is also spectroscopic evidence for its existence in solution. The complex is readily extracted into toluene, and this may have significance in the sequestering and/or separation of the neptunyl ion in terms of nuclear waste management.     

Synthesis, X-ray structure and properties of a new nitrite-bound copper(II) complex with 2-(3,5- dimethylpyrazol-1-ylmethyl)pyridine in a CuN4(O) coordination

Synthesis and characterization of a nitrite-bound copper(II) compound [CuL⁴)₂(ONO)]ClO₄ have been achieved (L⁴ = 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine]. The bidentate ligand L⁴ provides a pyridine and a pyrazole donor site; however, they are separated by a methylene spacer. The complex has been structurally characterized and it belongs to only a handful of complexes having nitrito-bound mononuclear copper(II) centre. The metal atom has a distorted square pyramidal geometry with the copper atom displaced from the equatorial plane by 0.25 Å. In MeCN solution the green complex exhibits a broad ligand-field transition at 655 nm with a shoulder at 675 nm and in dichloromethane-toluene glass (80 K) it exhibits an EPR spectral feature characteristic of the unpaired electron in the d_x²−y² orbital. Variable-temperature (80–300 K) magnetic susceptibility measurements in the solid state as well as room temperature measurement in MeCN solution reveal mononuclear magnetically dilute copper(II) centre. When examined by cyclic voltammetry (MeCN solution) it displays electrochemically irreversible Cu^II---Cu^I response [cathodic peak potential, E_pc (V vs saturated calomel electrode (SCE)): −0.32]. An oxidative response is observed at 1.14 V, probably due to bound-nitrite oxidation and is partially removed to generate a solvated complex at the electrode surface. The latter species gives rise to reversible Cu^II---Cu^I redox response [ ].     

Electrophilic lactonization as a tool in acyclic stereocontrol. Synthesis of serricornin

Several electrophilic lactonization procedures have been explored as a means of functionalizing olefinic carboxylic acids with relative asymmetric induction, Iodolactonization of δ,? -unsaturated acids under conditions of thermodynamic control exhibits good 1,2- and 1,3-, but not 1,4-induction in the formation of δ-lactones. Mercurilactonization proceeds with good stereocontrol in the formation of both γ- and δ-lactones (1,2-induction), but suffers from the difficulty of elimination during reductive demercuration; phenylselenolactonization with N-(phenylseleno)phthalimide is apparently kinetically controlled, affording high induction with 10, a strongly sterically biased substrate leading to a δ-lactone, but not with 16, which leads to a γ-lactone. In contrast, hydroxymethyllactonization proceeds with good stereocontrol in the case of 26, the ester of 10, but not with the analogous ester of 16. The lactones resulting from cyclization of 10 and 13 were converted in stereospecific fashion into each of the stereoisomers of(±)-serricornin.     

A versatile synthesis of functionalised 2-aminoquinolines by mercury controlled cyclisation of 2-vinylphenylthioureas

4-(4-Hydroxyphenyl)-2-phenylamino-1,8-naphthyridine was prepared via cyclisation of N-phenyl-N′-3-(4-hydroxyphenethen-1-yl)pyridin-2-ylthiourea in the presence of mercuric oxide. Derivatives of 4-methyl-2-aminoquinolines were prepared in a similar manner from 2-vinylphenylthioureas.     

Formation of new oxide glasses by laser spin melting and free fall cooling

Glass spherules have been made by laser spin melting and free fall cooling techniques from ceramic rods. Thus, the materials were not in contact with a container at any time. Glasses of 100 to 800 μm diameter were formed from at least 80 wt% of the oxides Al₂O₃, Ga₂O₃, In₂O₃, La₂O₃, ZrO₂, HfO₂, Nb₂O₅ and Ta₂O₅ with 20 or less weight percent of CaO + SiO₂. The best glass formers were in the Nb₂O₅- and Ta₂O₅-based systems. The indices of refraction of most of the glasses and Abbe numbers of many were measured.