Pressure-Induced Aggregation of Associating Liquids as a Driving Force Enhancing Hydrogen Bond Cooperativity

Abstract

The behavior of hydrogen bonds under extreme pressure is still not well understood. Until now, the shift of the stretching vibration band of the X−H group (X = the donor atom) in infrared spectra has been attributed to the variation in the length of the covalent X−H bond. Herein, we combined infrared spectroscopy and X-ray diffraction experimental studies of two H-bonded liquid hexane derivatives, i.e., 2-ethyl-1-hexanol and 2ethyl-1-hexylamine, in diamond anvil cells at pressures up to the GPa level, with molecular dynamics simulations covering similar thermodynamic conditions. Our findings revealed that the observed changes in the X−H stretching vibration bands under compression are not primarily due to H-bond shortening resulting from increased density but mainly due to cooperative enhancement of H-bonds caused by intensified molecular clustering. This sheds new light on the nature of H-bond interactions and the structure of liquid molecular systems under compression.

Inflection Point in Pressure Dependence of Ionic Conductivity as a Fingerprint of Local Structure Formation

“…In turn, intensified molecular clustering of some associating liquids has been found at elevated pressure. 56 The last example, [P 666,14 ][BOB], has undergone a hidden liquid–liquid transition originating from the self-organization of alkyl cation chains in nonpolar domains. All these examples suggest that the inflection point can be associated with structural self-assembly.…”

“…At the same time, glycerol and [C 8 HIm]­[NTf 2 ] generate strong hydrogen bonds and are therefore expected to form aggregates. In turn, intensified molecular clustering of some associating liquids has been found at elevated pressure . The last example, [P 666,14 ]­[BOB], has undergone a hidden liquid–liquid transition originating from the self-organization of alkyl cation chains in nonpolar domains.…”

High-Pressure and Temperature Effects on the Clustering Ability of Monohydroxy Alcohols

“…However, it was more evident for lower methanol concentrations (note the lack of preference for creating a ring cluster for pure methanol). Finally, our latest paper based on infrared spectroscopy, X-ray diffraction, and molecular dynamics simulations with another force field also demonstrated intensified molecular clustering via H bonds in 2E1H under high pressure . This nice agreement with other studies reflects the validity of the proposed structural models of the studied alcohols at the very wide range of thermodynamic conditions.…”