Fig. 1: Identification and control of proton ordering in a chiral cyclic BI hexamer. | Nature Communications

Fig. 1: Identification and control of proton ordering in a chiral cyclic BI hexamer.

From: Anomalous rotational-symmetry breaking in proton arrangement of surface-confined cyclic hydrogen bonds revealed by atomic force spectroscopy

Fig. 1

The −8.5°-L (state 1) and +8.5°-R (state 4) configurations are the two ground states, each hosting cyclic H-bonds with coexisting localized and quantum-delocalized protons. Rotating (denoted as Rot) the ground-state hexamer by ±17° changes the adsorption registry and yields the intermediate +8.5°-L (state 2) and −8.5°-R (state 3) configurations, in which proton delocalization is suppressed. A collective six-proton transfer (CPT) converts 2–4 or 3–1, reversing the cyclic H-bonding directionality and restoring the delocalized protons. For clarity, only the imidazole ring of BI is shown: N (blue) and H (red). R and L denote the chirality of the cyclic H-bonds. PIMD calculations reveal asymmetric proton sharing in non-classical H-bonds (blue shading), contrasted with localized protons in classical H-bonds (pink/orange shading).

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