Kinetic iron stable isotope fractionation between iron (-II) and (-III) complexes in solution

Details Kinetic iron stable isotope fractionation between iron (-II) and (-III) complexes in solution Kinetic iron stable isotope fractionation between iron (-II) and (-III) complexes in solution

Sep 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001e%26psl.192...81m&link_type=abstract

Earth and Planetary Science Letters, Volume 192, Issue 1, p. 81-92.

Computer Science

14

Scientific paper

Iron stable isotope fractionation between tris(2,2'-bipyridine) iron-II ([FeII(bipy)3]2+) and iron-III chloride complexes has been measured using plasma source mass spectrometry. The experimental protocol involves complexing FeII ion with 2,2'-bipyridine in a FeII/FeIII chloride solution and then separating the FeII and FeIII solution species in 6 M HCl on an anion exchange resin. Large isotopic variations of ɛ57Fe and ɛ56Fe are experimentally measured in the two separated solution fractions, with isotopic fractionations increasing from Δ(FeII-FeIII)=25 to 174 ɛ units for 57Fe/54Fe and 17 to 117 ɛ units for 56Fe/54Fe. The increase in fractionations correlates with a decrease in the mole fraction of FeII in the solution (Fe*=(FeII)/[(FeII)+(FeIII)]) that results from the dissociation and breakdown of [FeII(bipy)3]2+ complex in 6 M HCl solution. The data variations are mainly ascribed to a kinetic fractionation occurring during this dissociation reaction. Mass balance calculations, assuming that a Rayleigh law describes the overall isotopic trends, suggest a kinetic fractionation of ca. 1.010 (~100 ɛ units). The magnitude of this fractionation is attributed to the rupturing of the strong covalent bonds between 2,2'-bipyridine and FeII ion. The experimental data confirm that the coordination chemistry of iron exhibits a profound control on its isotopic behaviour and that kinetic fractionations may play an important role in its isotope geochemistry, as was also found in the pioneering experimental studies of the sulphur isotopic system in solution.

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