A. Zwick

A practical, cheap and environmentally friendly preparation of bismuth(III) trifluoromethanesulfonate

A method for large scale preparation of Bi(OTf)3 from Bi2O3 in a weakly hydrated form after freeze-drying.

The spin-crossover phenomenon in the solid state: Do domains play a role? A micro-Raman study

Abstract In order to assess experimentally the extent to which the nucleation-growth mechanism influences the phenomenon of spin-state crossover in the solid state, variable temperature micro-Raman mapping experiments have been conducted for the first time on the spin-crossover complex Fe(pz)[Ni(CN)4]·2H2O. The results point to the absence of domains with dimensions greater than ∼1 micron.

Raman Spectroscopic Study of Aluminum Silicate Complexes at 20°C in Basic Solutions

Raman spectroscopic measurements were performed at ambient temperature onaqueous silica-bearing solutions (0.005 < mSi < 0.02; 0 < pH < 14). The spectraare consistent with the formation of monomeric Si(OH)o4, SiO(OH)−3 andSiO2(OH)2−2 species at acid to neutral, basic, and strongly basic pH, respectively.Raman spectra of aqueous Al-bearing solutions at basic pH confirm thepredominance of the Al(OH)−4 species in a wide concentration range (0.01 < mAl < 0.1).Raman spectra of basic solutions (12.4 < pH < 14.3), containing both Al andSi, exhibit a strong decrease in intensities of SiO(OH)−3, SiO2(OH)2−2, andAl(OH)−4 bands in comparison with Al-free Si-bearing and Si-free Al-bearingsolutions of the same metal concentration and pH, suggesting the formation ofsoluble Al—Si complexes. The amounts of complexed Al and Si derived fromthe measurements of the Al and Si band intensities in strongly basic solutions(pH ∼ 14) are consistent with the formation, between Al(OH)−4 andSiO2(OH)2−2, of the single Al—Si dimer SiAlO3(OH)3−4 according to the reactionSiO2(OH)2−2 + Al(OH)−4 ⇔ SiAlO3(OH)3−4 + H2OAt lower pH (∼ 12.5) the changes in band intensities are consistent with theformation of several, likely more polymerized, Al—Si complexes.

Raman spectroscopic study of arsenic speciation in aqueous solutions up to 275°C

Raman spectroscopic measurements were performed on As2O3–H2O solutions (0.02⩽[As]⩽5.2 mol kg-1) at temperatures from 20 to 275°C. At 20°C the spectrum of arsenic solutions of low concentration (0.02–0.5 mol kg-1) is the same over a wide range of pH (0–8). It only exhibits a polarized band at 700 cm-1 with a depolarized shoulder at 655 cm-1. These bands can be attributed to the pyramidal molecule As(OH)30. The spectrum of these solutions does not change significantly with increasing temperature. The only change consists in a small shift of the two bands towards low wavenumbers. In solutions of medium As concentration (1 mol kg-1), a broadening of the 700 cm-1 band towards low wavenumbers is observed. This can be explained by the formation of a non-dehydrated dimeric species which forms via hydrogen bridging bonds. At higher As concentrations (2–5.2 mol kg-1), a new band appears at 525 cm-1, the intensity of which increases with increasing As concentration and temperature. By comparison with the spectrum of fused arsenic oxide, this band can be attributed to As—O—As bonds. This suggests that polymeric species are present in concentrated As solutions. In the most concentrated solutions (4.1 and 5.2 mol kg-1), a new band occurs at 380 cm-1, which can be attributed to the symmetric stretching of the As4O6 tetrahedron.

Conductive thin films of θ-(BETS)4[Fe(CN)5NO] on silicon electrodes – new perspectives on charge transfer salts

An alternate electrodeposition method using large surface silicon electrodes as anodes to prepare thin films of radical cation salts has been developed. We report on its use for the preparation of the radical cation salt containing the BETS molecule [BETS=bis(ethylenedithio)tetraselenafulvalene] and the photochromic nitroprusside [Fe(CN)5NO]2− anion, i.e. θ-(BETS)4[Fe(CN)5NO]. The use of various techniques, such as SEM/EDX, XPS, X-ray, IR and Raman, unambiguously confirmed that the film is made of the θ-(BETS)4[Fe(CN)5NO] phase previously obtained as single crystals on platinum electrodes. These results show that it is possible to electrodeposit cation radical salts on silicon wafers. In addition, this new method of electrodeposition proves to be extremely useful for preparing the large amounts of product (several hundreds of milligrams) often required for physical measurements.

Thermal stability of enzymes: influence of solvatation medium (a Raman spectroscopy study)

Abstract Conformational studies of two enzymes (invertase and lysozyme), their interactions with their solvent and the effect of alkali halides on conformational changes have been performed by means of Raman spectroscopy. It has been demonstrated that the protective effect against thermal denaturation, exhibited by the studied salts can be correlated to a parameter (Δω) obtained from the Raman spectra of the enzymes in solution. From a qualitative point of view, the higher the protective effect is, the more Δω decreases.

Raman Spectroscopic Study of Aluminum Silicate Complextion in Acidic Solutions from 25 to 150°C

AbstractRaman spectroscopic measurements were performed on aqueous acid to neutral silica-bearing solutions (0.005 ≤ mSi ≤ 0.02, 0 ≤ pH ≤ 8) and Al–silica solutions at temperature from 20 to 150°C. At 20°C, the spectrum of silica-bearing solutions exhibits only the bands of water and a completely polarized band at 785 cm−1. This band is attributed to the ν1 band of the tetrahedral Si(OH)4 molecule. In

Selective Photoswitching of the Binuclear Spin Crossover Compound {[Fe(bt)(NCS)~2]~2(bpm)} into Two Distinct Macroscopic Phases

{\text{Si(OH)}}_{\text{4}} {\kern 1pt} {\kern 1pt} - {\kern 1pt} {\text{AlCl}}_3 {\kern 1pt} - {\kern 1pt} {\text{HCl}}