Nuclear field shift effect of lead in ligand exchange reaction using a crown ether
Abstract
Lead isotopes were fractionated by the liquid-liquid extraction technique between an aqueous phase and a crown ether. After purification by ion-exchange chemistry, the 207Pb/206Pb and 208Pb/206Pb isotopic ratios were measured by multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Isotope fractionations > 0.05‰ have been found. The conventional equilibrium mass-dependent isotope effect estimated by an ab initio calculation was smaller than the Pb isotope fractionation experimentally obtained. Conventional mass-dependent isotope fractionation is not a valuable explanation for our results. The nuclear field shift effect, which results from the isotopic change in the nuclear size and shape, was also estimated by an ab initio method combined with a finite nucleus model. The nuclear field shift effect calculated was in agreement with our experimental results. Therefore, this study reports the first nuclear field shift effect of Pb in an equilibrium ligand exchange reaction.