Cation coordination polyhedra lead to multiple lengthscale organization in aqueous electrolytes

Area of Science:

• Physical Chemistry
• Materials Science
• Solution Chemistry

Background:

• Understanding correlations in aqueous electrolyte pair distribution functions (PDFs) is challenging.
• Polyoxoanions in electrolytes can influence solution structure through ion-network formation.

Purpose of the Study:

• To investigate the role of cation-coordination polyhedra in NaNO3(aq) and NaNO2(aq) electrolytes.
• To elucidate the origin of multiple lengthscale correlations in electrolyte PDFs.

Main Methods:

• Analysis of pair distribution functions (PDFs).
• Investigating coordination chemistry of polyoxoanions in aqueous solutions.

Main Results:

• A cation-coordination network was identified in NaNO3(aq) and NaNO2(aq).
• Oxygen correlations exhibit two characteristic lengthscales: 3.5-5.5 Å and 5.5-7.5 Å.
• The longer lengthscale (5.5-7.5 Å) is linked to oligomer formation, specifically dimers and their subunits.

Conclusions:

• The coordination chemistry of polyoxoanions induces long-range order in aqueous electrolytes.
• PDF contraction in the 5.5-7.5 Å range is attributed to O⋯O correlations within oligomeric structures.