Local molecular environment drives speciation and reactivity of ion complexes in concentrated salt solution

Nikhil Rampal, Hsiu Wen Wang, Denys Biriukov, Alexander B. Brady, Joerg C. Neuefeind, Milan Předota, Andrew G. Stack

Research output: Contribution to journalArticlepeer-review

11 Scopus citations

Abstract

The speciation and reactivity of aqueous salt solutions are important for a wide variety of applications. However, application of this information is inhibited by broad disagreement about composition, mechanisms, and structure in concentrated solutions especially. Here, neutron diffraction with isotopic substitution measurements on aqueous zinc chloride solutions are used to calibrate molecular dynamics simulations that include effective electronic polarization. This allows us to probe the origin of speciation and reactivity of zinc chloride-water ion complexes, ZnClx(H2O)y2-x (x ≤ 4 and y ≤ 6), by comparing the reactivity of species in concentrated (4.5 m) and dilute (0.01 m) conditions. Within the concentrated solution, it is found that the extended solvation environment is dominated by solvent-separated ion complexes whose presence increases the free energy of activation for interconversion of species while simultaneously enhancing their thermodynamic stability. This concentration-dependent reactivity and stability suggests that other reactions, such as the nucleation of solid phases, will also be affected.

Original languageEnglish
Article number116898
JournalJournal of Molecular Liquids
Volume340
DOIs
StatePublished - Oct 15 2021

Funding

This material is primarily based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division . The research at the Spallation Neutron Source at Oak Ridge National Laboratory, was supported by the Scientific User Facilitates Division, BES, DOE. D.B. and M.P. were supported by the Ministry of Education, Youth, and Sports of the Czech Republic, project LTAUSA17163.

Keywords

  • Concentrated aqueous solutions
  • Ion complexes
  • Neutron diffraction
  • Rare event methods
  • Reaction mechanisms

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