In order to deeply explore the issues related to hydrogen bond symmetry, an international research team led by Thomas Meier, a researcher at the High Pressure Science and Research Center (HPSTAR) in Beijing, has recently performed high-pressure in situ NMR spectroscopy measurements on a series of different samples and discovered a unified law regarding the symmetrization of hydrogen bonds - the symmetrization of hydrogen bonds in different systems The symmetries of hydrogen bonds all occur at the critical point where the hydrogen atoms flow fastest, and all correspond to almost the same spacing of the oxygen atoms (nearest neighbors to the hydrogen atoms).

The study was published in Nature Communications on June 1.

Hydrogen bonds are ubiquitous in nature, forming the backbone of living matter by stabilizing DNA molecules, and are key to the existence and discovery of new materials, and the study of hydrogen bonds is one of the drivers of contemporary condensed matter research. Systems stabilized by hydrogen bonds usually exhibit a wealth of physical phenomena such as phase transitions, superionic states or high-temperature superconductivity. These phenomena often occur when hydrogen bonding tends to be symmetric, i.e., when the hydrogen atom is located at the geometric center between two heavier atoms (e.g., figure).

Hydrogen bonding in substances containing linear hydrogen bonds is asymmetric at atmospheric pressure, and as the pressure increases, the asymmetric hydrogen bonds tend to converge to symmetry. The symmetrization of hydrogen bonds in different systems at high pressure is usually accompanied by different compressive properties, or changes in physical properties such as transport properties, so researchers often correlate the symmetrization of hydrogen bonds with changes in structural phase transitions, high and low spin transitions of substances, etc. However, these correlative interpretations are often contradictory.

Previously, direct studies of hydrogen atoms in diamond-topped anvils using conventional methods such as diffraction or spectroscopy have been limited by the detection techniques themselves, resulting in a lack of insight into the underlying physical mechanisms of hydrogen bond symmetry in these materials.

Nuclear magnetic resonance spectroscopy is a widely used diagnostic method in chemistry and materials science. However, studies using NMR spectroscopy under high pressure conditions, especially ultrahigh pressure conditions approaching one million atmospheres, face great challenges. To address these challenges, Meier and co-workers have explored and improved on the development of this high-pressure technique. In that work, they performed high-pressure in situ NMR spectroscopy studies of ice VII phase/X phase, magnesium silicate phase D, and iron-bearing and iron-free aluminum hydroxides, supplemented by high-pressure X-ray diffraction measurements, using a self-developed high-pressure NMR technique. It was found that in each of these different systems, hydrogen bonding symmetry occurs at an almost equal critical distance to the nearest neighboring oxygen atom of the hydrogen atom, completely independent of the chemical, structural or even quantum mechanical properties of the sample or the hydrogen bonding environment under study.

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