Magnetic isotope effect and theory of atomic orbital hybridization to predict a mechanism of chemical exchange reactions

Abstract

A novel approach is suggested to investigate the mechanisms of chemical complexation reactions based on the results of Fujii with co-workers; they have experimentally observed that several metals and metalloids demonstrate mass-independent isotope fractionation during the reactions with the DC18C6 crown ether using solvent-solvent extraction. In this manuscript, the isotope fractionation caused by the magnetic isotope effect is used to understand the mechanisms of chemical exchange reactions. Due to the rule that reactions are allowed for certain electron spin states, and forbidden for others, magnetic isotopes show chemical anomalies during these reactions. Mass-independent fractionation is suggested to take place due to the hyperfine interaction of the nuclear spin with the electron spin of the intermediate product. Moreover, the sign of the mass-independent fractionation is found to be dependent on the element and its species, which is also explained by the magnetic isotope effect. For example, highly negative mass-independent isotope fractionation of magnetic isotopes was observed for reactions of DC18C6 with SnCl(2) species and with several Ru(III) chloro-species, and highly positive for reactions of this ether with TeCl(6)(2-), and with several Cd(II) and Pd(II) species. The atomic radius of an element is also a critical parameter for the reaction with crown ether, particularly the element ions with [Kr]4d(n)5s(m) electron shell fits the best with the DC18C6 crown ring. It is demonstrated that the magnetic isotope effect in combination with the theory of orbital hybridization can help to understand the mechanism of complexation reactions. The suggested approach is also applied to explain previously published mass-independent fractionation of Hg isotopes in other types of chemical exchange reactions.

Metal Stable Isotope Signatures as Tracers in Environmental Geochemistry

“…It occurs during kinetically controlled processes linked to radical-pair reactions in which singlet–triplet conversions take place and where reactions rates of isotopes can vary strongly based on presence or absence of nuclear spin and magnetic moment. Depending on the fate of specific radical-pairs in the reaction network, in which some pathways are allowed for certain electron spin states and forbidden for others, , the reaction products can be strongly enriched or depleted in odd-mass relative to even-mass isotopes. The MIE has been reported in laboratory experiments for many different elements (C, O, Mg, Si, S, Ca, Zn, Ge, Br, Sn, Hg, U) mainly by Buchachenko. , Since very specific reaction conditions are required for the MIE to be expressed and preserved in the reaction products, its relevance for natural isotope signatures affected by element cycling under environmental conditions is unclear.…”

Chemical kinetic isotope fractionation of mercury during abiotic methylation of Hg(II) by methylcobalamin in aqueous chloride media

“…The MIF can take place if the intermediate products can change their state from the singlet to triplet one. It is possible in the presence of light for HgCl 2 (easier) and HgCl 3 − species and is much more difficult for HgCl 4 2− species (Epov, 2011a).…”

Mechanisms of Oxidation‐Reduction Reactions Can Be Predicted by the Magnetic Isotope Effect

“…According to the recently published paper [14], the magnitude of the MIF should depend on the strength of the ligand field. As it was demonstrated in previous sections, paramagnetic complexes are more responsible for the electron transfer in oxidation-reduction reactions.…”

“…These mechanisms for few reactions are described below in detail based on MIE electron transfer and type of ligands. This is the second paper describing reaction mechanisms using MIE, as the first one described ligand exchange (or complexation) reactions [14].…”