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

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 mZn/64Zn ratios (m = 66, 67, and 68) were analyzed by multiple-collector inductively coupled plasma mass spectrometry. The relative deviations of the 66Zn/64Zn ratios relative to the unprocessed material (δ66Zn) 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 of δmZn was explained by the isotope exchange reactions between Zn(II) species (Zn2+, ZnCl+, ZnCl2, ZnCl3−, and ZnCl42−) and the mole fractions of them. The magnitude of δmZn due to the related Zn(II) species estimated by quantum chemical calculations was in agreement with δmZn experimentally obtained. Contribution of nuclear field shift to the isotope fractionation was estimated to be less than 10% of δmZn by quantum chemical calculations.