6H2O System Research Articles

Crystal field analysis and electric dipole intensity parameters for holmium in Na 3[Ho(oxydiacetate) 3]· 2NaClO 4·6H 2O

Locations and assignments of 104 crystal-field levels have been made for Ho 3+ in the trigonal Na 3[Ho(oxydiacetate) 3]·2NaClO 4·6H 2O system. These energy levels span the 0–36100 cm −1 energy region, and they were located and assigned from axial and orthoaxial (σ and π polarized) absorption measurements on single crystals. The assigned levels are analyzed in terms of a 26-parameter hamiltonian in which six of the parameters are defined to represent the 4f-electron-crystal-field interactions for Ho 3+ ions located at sites with trigonal dihedral ( D 3) symmetry. Quantitative line intensities have been determined for 59 individual 4f → 4f (crystal-field) transitions observed in the low-temperature (10 K) absorption spectra, and these intensity data have been analyzed in terms of a general parametric model for 4f → 4f transition intensities in lanthanide systems. The energy and intensity parametrizations provide a basis for calculating the 4f → 4f absorption spectra of Ho 3+ in Na 3[Ho(oxydiacetate) 3]·2NaClO 4·6H 2O over a wide spectral range, and excellent agreement between calculated and experimentally measured spectra is obtained.

Phase transitions in the (Ni,Zn)TiF 6 · 6H 2O system

Measurements of the transformation rates and the characteristic temperatures of the trigonal ≡ monoclinic structural change in (Ni 1− x Zn x )TiF 6 · 6H 2O show a double transition up to x = 0.5. The relationships between the phase changes generally observed in the ABF 6 · 6H 2O system and the internal motions of the octahedral ionic complexes are discussed, and a phase diagram for the mixed nickel/zinc fluorotitanate is established.

Optical spectra, energy levels and crystal-field analysis of Sm3+in Na3[Sm(oxydiacetate)3] · 2NaClO4· 6H2O

Locations and assignments of 144 crystal-field energy levels are reported for Sm3+ in the trigonal Na3[Sm(oxydiacetate)3] · 2NaClO4 · 6H2O system. These energy levels span the 0–36 000 cm-1 energy region, and they were located and assigned from optical emission spectra and from axial and orthoaxial (σ- and π-polarized) absorption measurements on single crystals. The principal SL parentages of the assigned levels span at least 20 Russell-Saunders terms within the 4f 5 electronic configuration of Sm3+, and these assigned levels represent nearly half the total number of crystal-field energy levels predicted to occur within the 0–36 000 cm-1 region. The assigned levels are analysed in terms of a 26-parameter electronic hamiltonian in which six of the parameters are defined to represent the 4f-electron/crystal-field interactions for Sm3+ located at sites with trigonal dihedral (D 3) symmetry. Of the 26 parameters, 22 (including the six crystal-field parameters) are used in fitting calculated energy levels to the experimental data, and excellent calculated-versus-experimental energy level fits are achieved. Fitted values obtained in this study for the Sm3+ ‘free-ion’ energy parameters are compared to those reported previously for Sm3+ in LaF3 and LaCl3. Quantitatively determined line strengths are reported for 50 (4f → 4f) crystal-field transitions observed in the single-crystal absorption spectra of Na3[Sm(oxydiacetate)3] · 2NaClO4 · 6H2O at 10 K.

Hydroformylation of formaldehyde catalyzed by cobalt-rhodium bimetallic systems

The hydroformylation of formaldehyde to glycolaldehyde and its hydrogenation to ethylene glycol on using either Co-Rh bimetallic carbonyl clusters or mixtures of cobalt and rhodium derivatives as catalyst precursors has been investigated. The effect on activity and selectivity of varying the Co/Rh ratio of the Rh 4(CO) 12-CoCl 2·6H 2O system has also been studied. A limiting molar selectivity in C 2-oxygenated products (glycolaldehyde and ethylene glycol) of ca. 65% has been obtained in the most favorable conditions. Attempts to drive the reaction toward ethylene glycol in a one-batch process led to significantly lower selectivities in C 2 species, due to concomitant hydrogenation of formaldehyde to methanol. The latter represented the major competitive reaction in all the experiments. Under the adopted experimental conditions, all the investigated systems deactivate with time, owing to reduction to [Rh(CO) 4] − and/or [Co(CO) 4] −; this is further accelerated by an increase of the reaction temperature, probably because of formation of methylamines from decomposition of the dimethyl formamide used as reaction solvent. The most relevant effect on selectivity of the Co(II) salts in this system seems to be due to their oxidizing behavior toward rhodium carbonyl anionic species and their consequent capacity to buffer for some time the rhodium in a yet unknown oxidation state x (probably +1 > x > −0.2), for which hydroformylating rather than hydrogenating behavior prevails.

Study on combined latent-and sensible-heat thermal energy storage. 1st report Charging and discharging characteristics.

A combined type latent-and sensible-heat thermal energy storage is proposed, and its performance is investigated experimentally and theoretically. The dominant characteristics of this system are verified by comparison with proto-types, such as the sensible and the latent thermal energy storage types. The solidification and melting experiments are performed using a water-n-octerdencane and -CaCl2 6H2O systems. The charging and discharging characteristics and the basis of performance evaluation are clarified.