Crystalline Water Structure in Room-Temperature Clathrate State: Hydrogen-Bonded Pentagonal Rings

TL;DR

This study reveals a novel crystalline water structure in a clathrate state at room temperature, characterized by pentagonal rings and gas-filled cages, advancing understanding of water's interactions with small nonpolar molecules.

Contribution

It introduces a new room-temperature crystalline water structure formed by hydrogen-bonded pentagonal rings in a clathrate state, analyzed through electron microscopy and first-principles calculations.

Findings

Crystalline water forms at room temperature in a clathrate state.

Structure consists of hydrogen-bonded pentagonal rings similar to ice XVII.

Provides insights into water-molecule interactions at ambient conditions.

Abstract

Water hydrogen bonding is extremely versatile; approximately 20 ice structures and several types of clathrate hydrate structures have been identified. These crystalline water structures form at temperatures below room temperature and/or at high pressure. We used transmission electron microscopy to study a new crystalline water structure in a clathrate state that is prepared by sandwiching gas-supersaturated water between graphene layers under ambient conditions. In this clathrate state, water molecules form a three-dimensional hydrogen bonding network that encloses gas-filled cages 2-4 nm in size. We derived the crystalline water structure by recording and analyzing electron diffraction patterns and performing first-principles calculations. The structure consists purely of pentagonal rings and has a topology similar to that of water ice XVII. The study proposed a mechanism for the formation of the clathrate state. The present results improve the understanding of interactions among water and small nonpolar molecules and offer novel insights into the local structures of ambient liquid water.