Observation of exotic water in hydrophilic nanospace of porous coordination polymers

TL;DR

This study reveals the unique structural properties of water confined in hydrophilic nanopores of porous coordination polymers, showing characteristics of both ice and liquid, which could impact applications and fundamental understanding of supercritical water.

Contribution

It provides the first detailed observation of exotic water in hydrophilic PCP nanopores, demonstrating its mixed ice-liquid structural features and potential for new applications.

Findings

Confined water exhibits ordered ice-like structure.

Infrared spectroscopy shows broken hydrogen bonds.

Properties resemble supercritical water in hydrophobic nanospace.

Abstract

The fundamental understanding of water confined in porous coordination polymers (PCPs) is significantly important not only for their applications such as gas storage and separation, but also for exploring the confinement effects in the nanoscale spaces. Here, we report the observation of an exotic water in the well-designed hydrophilic nanopores of PCPs. Single-crystal X-ray diffraction found that nanoconfined water has an ordered structure that is characteristic in ices, but infrared spectroscopy revealed a significant number of broken hydrogen bonds that is characteristic in liquids. We found that their structural properties are quite similar to those of solid-liquid supercritical water predicted in hydrophobic nanospace at extremely high pressure. Our results will open up not only new potential applications of exotic water in PCPs to control chemical reactions but also experimental systems to clarify the existence of solid-liquid critical points.