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Updated: Jan 8, 2026

A Microfluidic Approach for the Study of Ice and Clathrate Hydrate Crystallization
Published on: August 18, 2022
Water Confined in Sub-Nanochannels of Supramolecular Crystals Exhibiting Ice-Water-Like Phase Transition near Room
Xue-Wei Pan1, Jia-Yi Yuan1, Lu Zhai1
1State Key Laboratory of Materials-Oriented Chemical Engineering and College of Chemistry and Molecular Engineering, Nanjing Tech University, Nanjing, 211816, P. R. China.
Abstract:
Water is a remarkable yet enigmatic substance with a unique array of anomalous properties, and nanoconfined water exhibits behavior starkly distinct from its bulk counterpart. Herein, two new isomorphic supramolecular polar crystals, [M(18-crown-6)]3[Al(ox)3]·9H2O (M+ = K+ for 1; NH4 + for 2) are reported, self-assembled from the cake-shaped [M(18-crown-6)]+ cations (18-crown-6 = 1,4,7,10,13,16-hexaoxacyclooctadecane) and Werner-type [Al(ox)3]3- coordination anions (ox2- = oxalate). The crystals contain tetranuclear supramolecular clusters and double-stranded helical water chains, undergoing an isostructural phase transition near room temperature. This transition stems from volume-conserving rotational motion of crown ether rings and an order-to-disorder transformation of lattice water molecules. Strikingly, 1 and 2 exhibits colossal negative thermal expansion behavior (β = -345.3 m K-1 for 1 and -261.8 m K-1 for 2) between 293-333 K, linked to the disordering of lattice water molecules, a process analogous to the structural transition from hexagonal ice to liquid water. This is the rare example of water confined within sub-nanochannels exhibiting characteristics of an ice-to-water transition. The findings deepen insights into the functional significance of nanoconfined water in biological systems and propose pathways to modulate physical properties in supramolecular materials.
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