Solvation of the Morpholinium Cation in Acetonitrile. Effect of an Anion

TL;DR

This study uses molecular dynamics simulations to analyze how morpholinium cations are solvated in acetonitrile, highlighting the influence of anions like acetate on solvation structures for potential electrolyte applications.

Contribution

It provides detailed structural insights into morpholinium cation solvation in acetonitrile and examines the effect of acetate anions, validated against high-level quantum calculations.

Findings

Nitrogen in the morpholine ring is a key electrophilic site.

Acetate anions weaken cation solvation by occupying space near nitrogen.

Favorable solvation in acetonitrile supports electrolyte development.

Abstract

Ionic liquids constitute a fast growing class of compounds finding multiple applications in science and technology. Morpholinium-based ionic liquids (MBILs) and their mixtures with polar molecular co-solvents are interesting as sustainable electrolyte systems for electrochemistry. We investigate local structures of protic and propton-free morpholinium cations in acetonitrile (ACN) using semi-empirical molecular dynamics (MD) simulations. An impact of an anion (acetate) on the cation solvation regularities is discussed. Unlike oxygen, nitrogen of the morpholine ring is a strong electrophilic binding center. This site is responsible for the interactions of the cation with the solvent and with the anion. In protic MBILs, the role of nitrogen is delegated to the proton, which is linked to nitrogen. The acetate anion weakens solvation of the cation due to occupation of space near nitrogen or proton. The analysis reveals a favorable solvation of MBILs in ACN, which is a prerequisite for a new high-performance electrolyte system. The reported structural data are validated through a point-to-point comparison with the MP2 post-Hartree-Fock theory.