Ordo ab Chao: Crystallographic Disorder as a Window into Ionic Liquid Structure

Authors

• Joseph Cooper, Ave Maria University
• Marija Scheuren, Ave Maria University
• Lara I. Teodoro, Ave Maria University
• Christopher M. Butch, State University of New York at Oswego
• Raychell A. Jerdo, State University of New York at Oswego
• Kylie M. Allen, State University of New York at Oswego
• Mariana E. Toner, State University of New York College at Oswego
• Matthias Zeller, Purdue University
• Arsalan Mirjafari, State University of New York College at Oswego
• Patrick C. Hillesheim, Illinois State UniversityFollow

Document Type

Article

Publication Date

2026

Publication Title

Crystal Growth & Design

Keywords

cations, crystallization, diseases and disorders, salts, solvents

Abstract

Despite being intended to resist crystallization, ionic liquids (ILs) quite frequently form solids, albeit with low melting points. The design motifs that lower melting points can leave measurable signatures in the solid state, manifesting as crystallographic disorder, and often give rise to metastable liquid states. While sometimes treated as experimental complications, such features provide a valuable window into the structural origins of IL phase behavior. Herein, we report a crystallographic study of a series of benzylated ILs that crystallize either directly or from long-lived supercooled melts. Single-crystal X-ray diffraction, supported by computational modeling and statistical analyses, provides structural evidence that conformational heterogeneity and interaction degeneracy can impede the propagation of long-range order. Competition among multiple energetically similar CH₃···π and related π-mediated interactions generates complex crystallographic landscapes in which multiple local arrangements coexist, leading to the formation of metastable liquid states prior to crystallization. Notably, across the series of structures examined, cations that successfully crystallize converge on a recurring effective molecular volume, achieved through static packing, conformational flexibility, or crystallographic disorder. Viewed in this context, disorder is not incidental but mechanistically informative, encoding how ILs accommodate volume, distribute interactions, and navigate the boundary between liquid persistence and crystalline order.

Funding Source

Acknowledgment is made to the Donors of the American Chemical Society Petroleum Research Fund (66195-UNI10) for support of this research. This work is supported by the National Institute of General Medical Sciences of the National Institutes of Health (Award No. R15GM153057). This article was published Open Access thanks to a transformative agreement between Milner Library and ACS.

Creative Commons License

This work is licensed under a Creative Commons Attribution 4.0 International License.

DOI

10.1021/acs.cgd.6c00247

Comments

First published in Crystal Growth & Design (2026): https://doi.org/10.1021/acs.cgd.6c00247. Supporting information available on publisher's site.

Recommended Citation

Cooper, J., Scheuren, M., Teodoro, L. I., Butch, C. M., Jerdo, R. A., Allen, K. M., Toner, M. E., Zeller, M., Mirjafari, A., & Hillesheim, P. C. (2026). Ordo ab Chao: Crystallographic Disorder as a Window into Ionic Liquid Structure. Crystal Growth & Design. https://doi.org/10.1021/acs.cgd.6c00247