Determine the inner-hydrogen configuration of adsorbed H₂Pc

Determine whether the two inner hydrogen atoms of H₂Pc adsorbed in the flower configuration on In₂O₃(111) occupy the pair of pyrrolic nitrogen atoms aligned across or parallel to the molecule’s vertical distortion.

Background

The STM and nc-AFM measurements establish the adsorption site, orientation, and distortion of H₂Pc on In₂O₃(111), but the strong contrast variation across the molecular center prevents the inner hydrogen positions from being assigned unambiguously.

The unresolved orientation matters because it specifies the detailed protonation configuration of the macrocycle in its distorted adsorption geometry.

References

Whether in F site the two inner H atoms sit on the pair of pyrrolic N atoms across or parallel to the vertical distortion cannot be determined from the present STM and AFM data.

— The absence of a central metal ion destabilizes phthalocyanine on In$_2$O$_3$(111)  (2609.08742 - Waidbacher et al., 8 Sep 2026) in Discussion, first paragraph