Metalloid derivatives for oganic synthesis the preparation of urazole and thiourazole derivatives

Silicon isocyanates are introduced as versatile reagents for the mild and efficient conversion of hydrazines to urazole derivatives.     

The effect of fluoride ion concentration on apatite formation and on its crystal habit

The effect of fluoride ions on the rate of apatite [ca_10(PO4)6(F,OH)₂] formation and on its crystal habit was investigated. It was found that both at high and at low fluoride concentrations the rate formations is retarded. At two optimal concentrations, namely at 3.4 and 5.5 fluoride: apatite excess of the stoichiometric ratio, the rate is the highest. The crystal habit of the apatite formed at high fluoride concentrations is hexagonal plate-like, while the apatite formed at low fluoride concentrations is dendritic or needle-like. The concentrations of fluoride in the crystals were determined by specific fluoride electrode technique.     

Photogalvanic cell based on the photolysis of rubidium anions in THF

A photogalvanic cell composed of two half cells of the type [Rb-THF]_I and [Rb-THF, crown ether (or kryptand)]_II is reported. Photocurrents and photovoltages, recorded at low temperatures, in the order of 6 nA and 80 mV, respectively are obtained with light excitation at wavelenghts above 640 nm. The corresponding values with excitation above 320 nm, are 30 nA and 250 mV, respectively.     

Synthesis and characterization of β-fused porphyrin-BODIPY dyads

Novel dyads in which a porphyrin ring is directly fused through two β-pyrrolic carbons to a BODIPY^® moiety have been prepared using a stepwise approach starting from the copper(II) complex of pyrrolo[2,3-c]-5,10,15,20-tetraphenylporphyrin. Formylation and reaction with 3,5-dimethylpyrrole afforded 8; subsequent BF₂ complexation gave the TPP-BODIPY^® dyad in reasonable yields. Demetalation in TFA/H₂SO₄ led to the corresponding free base 12, opening the way to the subsequent preparation of the Zn complex 13. Both 12 and 13 exhibited complex optical spectra with an intensely red-shifted Q-band. Luminescence spectra displayed a very intense band around 700 nm making these species suitable as near-IR dyes and sensors in biological media. Optical analyses of 12, using the INDO/SCI technique, were performed to obtain information to establish the origin of the novel optical properties. These studies showed that the optical properties of 12 cannot be attributed to deformation of the molecular skeleton, but derive from the increased extension of the conjugation between the TPP and BODIPY^® π-systems.     

Chalcogen-chalcogen bonds in edge-sharing square-planar d8 complexes. Are they possible?

A theoretical study of the formation of X-X bonds in complexes with the general formula [M(2)(mu-X)(2)L(4)] (M = group 10 and X = group 16 elements) having d(8) transition-metal atoms is presented. The existence of two energy minima for some complexes, with short and long X-X distances, is shown by density functional theory calculations, and the factors responsible for it are analyzed, including a strong influence of the nature of the metals and ligands on the relative stability of the two isomers. The influence of the bite angle of chelating terminal ligands and the nature of the donor atom on the relative stabilities of the two isomers are also discussed.     

Mesoscopic monodisperse ferromagnetic colloids enable magnetically controlled photonic crystals

We report here the first synthesis of mesoscopic, monodisperse particles which contain nanoscopic inclusions of ferromagnetic cobalt ferrites. These monodisperse ferromagnetic composite particles readily self-assemble into magnetically responsive photonic crystals that efficiently Bragg diffract incident light. Magnetic fields can be used to control the photonic crystal orientation and, thus, the diffracted wavelength. We demonstrate the use of these ferromagnetic particles to fabricate magneto-optical diffracting fluids and magnetically switchable diffracting mirrors.     

Isospin Dependence in Nuclear Multifragmentation Within Site Percolation and Nucleation Pictures

The isospin dependence, recently observed in Sn + Sn reactions at 40 MeV/nucleon, is discussed within the framework of two simple nuclear multifragmentation models, namely the site percolation and the nucleation-evaporation models. It is shown that both the models are able to discriminate between ¹¹²Sn+ ¹¹²Sn and ¹²⁴Sn+ ¹²⁴Sn reactions. The nucleation-evaporation model succeeds to reproduce nicely the experimental data, but the site percolation model fails in doing that, even if the cluster noncompactive effect is taken into account. The calculations indicate that the data are originated mainly from a single source.     

Nucleon Finite Volume Effect and Nuclear Matter Properties in a Relativistic Mean-Field Theory

Effects of excluded volume of nucleons on nuclear matter are studied, and the nuclear properties that follow from different relativistic mean-field model parametrizations are compared. We show that, for all tested parametrizations, the resulting volume energy al and the symmetry energy J are around the acceptable values of 16 MeV and 30 MeV, and the density symmetry L is around 100 MeV. On the other hand, models that consider only linear terms lead to incompressibility Ko much higher than expected. For most parameter sets there exists a critical point （pc, δc）, where the minimum and the maximum of the equation of state are coincident and the incompressibility equals zero. This critical point depends on the excluded volume parameter r. If this parameter is larger than 0.5 fm, there is no critical point and the pure neutron matter is predicted to be bound. The maximum value for neutron star mass is 1.85M⊙, which is in agreement with the mass of the heaviest observed neutron star 4U0900-40 and corresponds to r = 0.72 fm. We also show that the light neutron star mass （1.2M⊙） is obtained for r ≌ 0.9 fro.     

Synthesis and Raman spectroscopic characterisation of hydrotalcite with CO32− and VO3− anions in the interlayer

Infrared and Raman spectroscopy were used to characterise synthetic mixed carbonate and vanadate hydrotalcites of formula Mg₆Al₂(OH)₁₆(CO₃)²⁻, (VO₄)³⁻·4H₂ O. The spectra were used to assess the molecular assembly of the cations and anions in the hydrotalcite structure. The spectra may be conveniently subdivided into spectral features based on (1) the carbonate anion (2) the hydroxyl units and (3) water units. Bands were assigned to the hydroxyl stretching vibrations of water. Three types of carbonate anions were identified: (1) carbonate hydrogen‐bonded to water in the interlayer, (2) carbonate hydrogen‐bonded to the hydrotalcite hydroxyl surface and (3) free carbonate anions. It is proposed that the water is highly structured in the hydrotalcite, as it is hydrogen‐bonded to both the carbonate and the hydroxyl surface. The spectra were used to assess the contamination of carbonate in an open reacting vessel in the synthesis of vanadate hydrotalcites of formula Mg₆Al₂(OH)₁₆(CO₃)²⁻, (VO₄)³⁻·4H₂ O. Bands have been assigned to vanadate anions in the infrared and Raman spectra associated with V O bonds. Copyright © 2007 John Wiley & Sons, Ltd.