Experimental and Theoretical Investigation of Isotope Fractionation of Zinc between Aqua, Chloro, and Macrocyclic Complexes

Abstract : This work reports on the chemical isotope fractionation of Zn(II) by a solvent extraction method with the crown ether dicyclohexano-18-crown-6. The (m)Zn/(64)Zn ratios (m = 66, 67, and 68) were analyzed by multiple-collector inductively coupled plasma mass spectrometry. The relative deviations of the (66)Zn/(64)Zn ratios relative to the unprocessed material (delta(66)Zn) was determined to be -0.51 to -0.32 in the acidity region 1.0-6.0 mol dm(-3) (M) HCl. The acidity dependence or delta(m)Zn was explained by the isotope exchange reactions between Zn(II) species (Zn(2+), ZnCl(+), ZnCl(2), ZnCl(3)(-), and ZnCl(4)(2-)) and the mole fractions of them. The magnitude of delta(m)Zn due to the related Zn(II) species estimated by quantum chemical calculations was in agreement with delta(m)Zn experimentally obtained. Contribution of nuclear field shift to the isotope fractionation was estimated to be less than 10% of delta(m)Zn by quantum chemical calculations.