Strong, yet split hydrogen bonding with ice rules in delafossite (H/D)RhO₂

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 RhIIIO2 layers. Bragg and real-space X-ray and neutron scattering analysis, vibrational and solid-state NMR spectroscopy, and density functional theory–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. , Synthesis of NaRhO2, HRhO2 and DRhO2 NaRhO2 was synthesized by combining powdered Na2CO3 (5 wt% excess, Aesar 99.95%) and Rh2O3 (Sigma 99.8%) in an agate mortar and pestle and hand grinding for 30 minutes before loading into an Al2O3 crucible and heating to 850 Â°C in a muffle furnace for 15 hours with a heating and cooling rate of 130 Â°C h^–1^ HRhO2 was synthesized from NaRhO2 (according to HxRhO2—Na1–xRHO2) by ion-exchange of Na^+^ for H^+^ using cerium ammonium nitrate (NH4)2Ce(NO3)6 (Sigma â‰¥ 99.99%). 50 mg of NaRhO2 was dispersed in solutions of varying molar concentrations of (NH4)2Ce(NO3)6  in ultra-pure H2O at 60 Â°C with continuous stirring for 100 hours.[1] Ion exchange was assumed to occur at a 1/1 molar ratio. Complete exchange was achieved using a 5/1 molar excess of (NH4)2Ce(NO3)6. The synthesis of DRhO2 was identical except for the use of D2O (Sigma 99.9 atom%) instead of H2O. X-ray Diffraction Synchrotron X-ray diffraction (..., # Strong, yet split hydrogen bonding with ice rules in delafossite (H/D)RhO~2~ Dataset DOI: [10.5061/dryad.1rn8pk17j](https://doi.org/10.5061/dryad.1rn8pk17j) ## Description of the data and file structure The data was collected to understand the structure of the materials HRhO2 and DRhO2. The collected data includes X-ray and neutron Bragg diffraction and neutron diffuse scattering data as well as solid state 1H and 2H NMR. Structural files for HRhO2 and DRhO2 are also provided. ### Files and variables ## Crystallographic Information Files ### HRhO2 File: HRhO2_298K_XRD-NPD.cif Description: crystallographic information file describing the structure of HRhO2. Data was generated from a joint Rietveld refinement against synchrotron X-ray and neutron Bragg diffraction data for HRhO2 at 298 K. Variables include: chemical name, measurement temperature, unit cell parameters, symmetry space group, symmetry equivalent positions, atom site labels, atom site symbols, atom site multiplicit..., ,