Structural independence of hydrogen-bond symmetrisation dynamics at extreme pressure conditions

Abstract

The experimental study of hydrogen-bonds and their symmetrization under extreme conditions is predominantly driven by diffraction methods, despite challenges of localising or probing the hydrogen subsystems directly. Until recently, H-bond symmetrization has been addressed in terms of either nuclear quantum effects, spin crossovers or direct structural transitions; often leading to contradictory interpretations when combined. Here, we present high-resolution in-situ 1H-NMR experiments in diamond anvil cells investigating a range of systems containing linear O-H ⋯ O units at pressure ranges of up to 90 GPa covering their respective H-bond symmetrization. We found pronounced minima in the pressure dependence of the NMR resonance line-widths associated with a maximum in hydrogen mobility, precursor to a localisation of hydrogen atoms. These minima, independent of the chemical environment of the O-H ⋯ O unit, can be found in a narrow range of oxygen oxygen distances between 2.44 and 2.45 Å, leading to an average critical oxygen-oxygen distance of $${\bar{r}}_{{{{{{{{\rm{OO}}}}}}}}}^{{{{{{{{\rm{crit}}}}}}}}}=2.443(1)$$ r ¯ OO crit = 2.443 ( 1 ) Å.

Potential energy barrier for proton transfer in compressed benzoic acid

“…The obtained results shed light on previous experiments on compressed benzoic acid, in particular the drastic reduction of the O⋯O distance with pressure. The current findings are also of importance for other high-pressure studies on strongly hydrogen bonded systems, 62 most notably water. 63–65 In particular, it seems that the recently proposed critical O⋯O distance for hydrogen bond symmetrization (ref.…”

“…61 Moreover the distance at which the LP barrier becomes null (2.46 Å) is close to the critical O⋯O distance (2.44 Å) at which hydrogen-bond symmetrization is proposed for a number of inorganic systems. 62 This hints that the energetics of the PT process may be similar regardless of the environment surrounding the hydrogen bond, although more studies are needed to confirm this.…”

“…61 Moreover the distance at which the LP barrier becomes null (2.46 Å) is close to the critical O/O distance (2.44 Å) at which hydrogen-bond symmetrization is proposed for a number of inorganic systems. 62 This hints that the energetics of the PT process may be similar regardless of the environment surrounding the hydrogen bond, although more studies are needed to conrm this. The current results indicate that pressure-induced symmetrization of the hydrogen bond should occur in solid BA, but retrieving this effect requires taking into account the quantum nature of the system.…”

“…[63][64][65] In particular, it seems that the recently proposed critical O/O distance for hydrogen bond symmetrization (ref. 62) might be common also to organic compounds. Benzoic acid is of special interest in this context, as this distance can obtained for this compound at relatively low pressure (p < 20 GPa).…”

Direct Hydrogen Quantification in High-pressure Metal Hydrides

“…Moreover, this and similar methods might be usable for other high-pressure problems like the water transport in the inner regions of Earth [44] using in-situ high-pressure NMR experiments [45][46][47] SUPPLEMENTARY Following are the data tables used to compute the hydrogen concentrations n 1 1 . Noise describes the root mean square noise level in spectral domain far off the resonances.…”