Kinetic and equilibrium Fe isotope fractionation between aqueous Fe(II) and Fe(III)

Isotopic fractionation between Fe(III) and Fe(II) in aqueous solutions

By computer simulation and also by analytical methods we have computed the nuclear tunneling enhancement of the rate for ferrous–ferric exchange in water. The model we have examined is the one studied earlier where we treated water as a classical liquid [R. A. Kuharski, J. S. Bader, D. Chandler, M. Sprik, M. L. Klein, and R. W. Impey, J. Chem. Phys. 89, 3248 (1988)]. But now we treat water quantum mechanically and find that the tunneling enhancement is a factor of 60 in the rate constant. Further, as observed experimentally, we find that the isotope shift on the rate when changing from D2O to H2O is approximately a factor of 2. The computer simulation aspects of these calculations employ path integral methods and a novel partitioning of the free energy associated with electron transfer. Our results show that it is insufficient to quantize only the atoms composing the ligands. The quantum dynamics of water molecules beyond the first solvation shell prove quite significant.

Role of nuclear tunneling in aqueous ferrous–ferric electron transfer

Computer simulation of photochemically induced electron transfer

Separation of Copper, Iron, and Zinc from Complex Aqueous Solutions for Isotopic Measurement

A Raman study of ferric chloride hexadydrate (FCHH) in 11.5M HCl solutions has shown the presence of tetrahedral FeCl4− ion as the most prominent species. An appreciable concentration of a polymeric species, which is composed of higher chloroferrate groups of the type FeCl5 · H2O, and a small concentration of lower chloro‐aquoferrate complex ion of the type Fe(H2O)4Cl2+ are also present in the solutions. The saturation of FCHH‐11.5M HCl solution with dry HCl is observed to convert both the polymeric species and the lower chloro‐aquoferrate ions into FeCl4− ions. In hydrated ferric chloride melts the most prominent species exists in the form of tetrahedral FeCl4− ion along with an appreciable concentration of Fe(H2O)4Cl2+ ion. Hydrated ferric chloride melts saturated with LiCl or dry HCl gas, contains only FeCl4− ions. In the case of moderately acidic (≤ 6M HCl) ferric chloride solutions Raman evidence has revealed the presence of a polymeric species along with significant concentrations of lower chloro‐aq...

Raman study of ferric chloride solutions and hydrated melts

A Raman investigation on crystalline ferric nitrate enneahydrate (FNEH) has shown that NO3− and Fe(H2O)63+ ions are present in two distinct environments in the monoclinic unit cell of the crystal. In FNEH melt, it has been found that NO3− and Fe3+ ions form a complex in which water is also coordinated to the Fe3+ ion. Raman evidence is presented which indicates that NO3− ion in the nitrate complex is coordinated to the Fe3+ ion in monodentate fashion, with an appreciable covalency in the Fe3+–ONO2− bond. The addition of water to FNEH melt causes dissociation of the nitrate complex. This complex almost ceases to exist when the water content of the melt is raised to 28 mole of water per mole of the salt. A weak polarized band at ∼407 cm−1 in the Fe(NO3)3 · xH2O system (x ≥ 28) has been attributed to the presence of the hydrolysis product of Fe3+ ions. The effect of dilution and of temperature on this band has also been investigated. It is suggested that the hydrolysis product of the salt exists in the form ...

Raman study of ferric nitrate crystalline hydrate and variably hydrated liquids

Analysis of Raman spectra of concentrated alkali metal hydroxide solutions and the solutions of ZnO in concentrated alkali metal hydroxide solutions has contradicted the tetrahedral structure of zincate ions that has been accepted so far. Two low frequency bands, which were earlier assigned to a tetrahedral structure of zincate ions, have been attributed to the formation of ion pairs between alkali metal ions and OH− ions in concentrated KOH and NaOH solutions. The band at 425 cm−1 originates due to the formation of polynuclear aggregates in the solutions. The results have indicated that the zincate ions exist as linear ZnO22− species.

Shiv Kumar Sharma

Papers

Raman study of ferric chloride solutions and hydrated melts

Raman study of ferric nitrate crystalline hydrate and variably hydrated liquids

Raman study of aqueous zinc oxide‐alkali metal hydroxide system