A flow microcalorimeter/densimeter system has been commissioned to measure heat capacities and densities of solutions containing radioactive species as a function of temperature. Measurements were made for NaTcO4(aq) at six temperatures (189.15 K to 373.15 K for the heat capacities, 287.43 K to 396.67 K for the densities) over the molality range 0.01 to 0.29 mol-kg–1. Measurements for NaReO4(aq) (NaReO4 is a common nonradioactive analogue for NaTcO4) were made under similar conditions, but for eight temperatures and a more extensive range of molalities, 0.05 to 0.65 mol-kg–1. Heat capacities of NaCl(aq) reference solutions were also measured from 293.15 K to 398.15 K.The heat capacity and density data are analysed using Pitzer's ioninteraction model. Equations for the apparent molar heat capacities and volumes are reported. Values of the NaReO4(aq) partial molar heat capacities are compared to literature values based on integral heats of solution. The agreement between the two sets of NaReO4 results is good below 330 K, but only fair at the higher temperatures. Values of the partial molar volumes have also been derived. Using literature values and the results of our experiments, it is calculated that the disproportionation of hydrated TcO2(s) to form TcO
4–
(aq) and Tc(cr) occurs more readily at high temperatures. The uncertainties introduced by using thermodynamic values for ReO
4–
(aq), in the absence of values for TcO
4–
(aq), are discussed. 相似文献
In an attempt to crystallize Ce[ReO4]4 · xH2O from aqueous solutions of equimolar amounts of Ce[SO4]2 and Ba[ReO4]2 via salt‐metathesis the serendipitous formation of colorless, transparent, rod‐shaped single crystals of CaNa[ReO4]3 was observed as a result of calcium and sodium impurities within the improperly deionized water used. Structure analysis by X‐ray diffraction lead to the conclusion that the title compound crystallizes in the ThCd[MoO4]3 structure type with the hexagonal space group P63/m and the lattice parameters a = 991.74(6) pm, c = 636.53(4) pm, c/a = 0.642 for Z = 2. The crystal structure contains purely oxygen surrounded and crystallographically unique cations, namely Ca2+ in tricapped trigonal prismatic (d(Ca–O) = 6 × 249 pm + 3 × 254 pm), Na+ in octahedral (d(Na–O) = 6 × 241 pm), and Re7+ in tetrahedral coordination (d(Re–O) = 171–173 pm). Furthermore, it was possible to yield an almost phase‐pure microcrystalline powder of the title compound from a melt of equimolar amounts of Na[ReO4] and Ca[ReO4]2 stemming from aquatically obtained precursors. 相似文献
Devising sensors for the perrhenate anion in aqueous media is extremely challenging, and has seldom been reported in the literature. Herein, we report a fluorescence turn-on sensor for the perrhenate anion in aqueous media based on the aggregation-induced emission of a popular ultrafast molecular rotor dye, Thioflavin-T. The selective response towards the perrhenate anion has been rationalized in terms of matching water affinity, with the weakly hydrated perrhenate anion spontaneously forming a contact ion pair with the weakly hydrated ultrafast molecule-rotor-based organic cation, Thioflavin-T, which in turn leads to an aggregate assembly that provides a fluorescence turn-on response towards perrhenate. The sensing response of Thioflavin-T has been found to be quite selective towards the perrhenate anion when tested against anions that are ubiquitously present in the environment, such as chloride, nitrate, and sulfate anions. The formation of self-assembled Thioflavin-T aggregates has also been investigated by time-resolved emission and temperature-dependent measurements. 相似文献
Equilibrium constants () for the ion-pair formation of a complex ion NaL+ with ReO4− in water were determined potentiometrically at 25 °C and the ionic strength (I) of 0 mol dm−3 using a Na+-selective electrode. Here, crown ethers, L, were 15-crown-5 ether (15C5), benzo-15C5, 18-crown-6 ether (18C6) and benzo-18C6. Also, NaReO4 was extracted by the L into 1,2-dichloroethane and then extraction constants (Kex/mol−2 dm6) for the species, NaLReO4, were determined at 25 °C by AAS. These Kex values were resolved into four component equilibrium constants containing KMLA calculated at given I values. Based on these data, extraction-abilities of the L against the perrhenate were discussed in comparison with those of sodium picrate-L systems reported previously. 相似文献
Catalytic deoxydehydration (DODH) of vicinal diols is studied. We find that NH4ReO4 (ammonium perrhenate, APR) catalyzes the DODH of glycols to alkenes by sacrificial alcohol (2,4-dimethyl-3-pentanol) at 140–165 °C. The product yields range from good to excellent and no isomers detected. The catalytic DODH reaction of glycols to alkene is of potential value for the production of chemicals and fuels from the renewable biomass-derived polyols.
Cyclo[8]pyrrole, an octapyrrolic expanded porphyrin with no meso-linking atoms, was found to interact with a series of anions in the solid state and in a chloroform solution. The anion selectivities have been determined relative to a structurally characterised salt, H2cyclo[8]pyrrole2+·I? ·I3 ? , via counter anion exchange. Although cyclo[8]pyrrole demonstrates a general selectivity for sulfate, it interacts well with both the pertechnetate and perrhenate anions. Moreover, it has been shown to act as a phase-transfer catalyst facilitating the extraction of pertechnetate from an aqueous to an organic phase in the presence of sulfate. 相似文献
Complexation between perrhenate ion and N-methyl-N-vinylacetamide and N-methyl-N-vinylamine copolymers in aqueous solutions was studied by high-performance liquid chromatography on monolith ultrashort columns. It was demonstrated that complexation has slow kinetics and strongly depends on the length of alkyl substituent. 相似文献