Strong, Yet Split Hydrogen Bonding with Ice Rules in Delafossite (H/D)RhO ₂

Despite remaining enigmatic, strong hydrogen bonding provides an advanced design handle for tailoring the properties of functional materials. Here, 3R-(H/D)RhO₂ delafossites (prepared by ion exchange of Na⁺ from NaRhO₂) contain H/D in linear coordination with O, linking Rh^IIIO₂ layers. Bragg and real-space X-ray and neutron scattering analysis, vibrational and solid-state NMR spectroscopy, and density functional theory (DFT)-based electronic structure calculations have been employed to understand the nature of the hydrogen bonding. Despite short distances between H/D and the two O to which they are bonded, a clear double-minimum corresponding to a shorter and longer (H/D)-O distance is established. The triangular lattices formed by H/D appear to display ice-like disorder, corroborated by low-temperature heat capacity measurements.