Open AccessIon association with tetra-n-alkylammonium cations stabilizes higher-oxidation-state neptunium dioxocations
Author(s) -
Shanna L. Estes,
Botao Qiao,
Geng Bang Jin
Publication year - 2019
Publication title -
nature communications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.559
H-Index - 365
ISSN - 2041-1723
DOI - 10.1038/s41467-018-07982-5
Subject(s) - chemistry , aqueous solution , inorganic chemistry , oxidation state , electrolyte , metal , electrochemistry , solvation , redox , ionic bonding , chloride , metal ions in aqueous solution , qualitative inorganic analysis , tetra , ion , electrode , organic chemistry , medicinal chemistry
Extended-coordination sphere interactions between dissolved metals and other ions, including electrolyte cations, are not known to perturb the electrochemical behavior of metal cations in water. Herein, we report the stabilization of higher-oxidation-state Np dioxocations in aqueous chloride solutions by hydrophobic tetra- n -alkylammonium (TAA + ) cations—an effect not exerted by fully hydrated Li + cations under similar conditions. Experimental and molecular dynamics simulation results indicate that TAA + cations not only drive enhanced coordination of anionic Cl – ligands to Np V/VI but also associate with the resulting Np complexes via non-covalent interactions, which together decrease the electrode potential of the Np VI /Np V couple by up to 220 mV (ΔΔ G = −22.2 kJ mol −1 ). Understanding the solvation-dependent interplay between electrolyte cations and metal–oxo species opens an avenue for controlling the formation and redox properties of metal complexes in solution. It also provides valuable mechanistic insights into actinide separation processes that widely use quaternary ammonium cations as extractants or in room temperature ionic liquids.