Guiding Principles for the Rational Design of Hybrid Materials: Use of DFT Methodology for Evaluating Non-Covalent Interactions in a Uranyl Tetrahalide Model System

Abstract

Together with the synthesis and experimental characterization of 14 hybrid materials containing [UO₂ X₄ ]^2- (X=Cl^- and Br^- ) and organic cations, we report on novel methods for determining correlation trends in their formation enthalpy (ΔH_f ) and observed vibrational signatures. ΔH_f values were analyzed through isothermal acid calorimetry and a Density Functional Theory+Thermodynamics (DFT+T) approach with results showing good agreement between theory and experiment. Three factors (packing efficiency, cation protonation enthalpy, and hydrogen bonding energy [ $E_{H,\mathrm{norm}}^{\mathrm{total}}$ ]) were assessed as descriptors for trends in ΔH_f . Results demonstrated a strong correlation between $E_{H,\mathrm{norm}}^{\mathrm{total}}$ and ΔH_f , highlighting the importance of hydrogen bonding networks in determining the relative stability of solid-state hybrid materials. Lastly, we investigate how hydrogen bonding networks affect the vibrational characteristics of uranyl solid-state materials using experimental Raman and IR spectroscopy and theoretical bond orders and find that hydrogen bonding can red-shift U≡O stretching modes. Overall, the tightly integrated experimental and theoretical studies presented here bridge the trends in macroscopic thermodynamic energies and spectroscopic features with molecular-level details of the geometry and electronic structure. This modeling framework forms a basis for exploring 3D hydrogen bonding as a tunable design feature in the pursuit of supramolecular materials by rational design.

Keywords: Crystal Engineering; Hybrid Materials; Hydrogen Bonding; Periodic Density Functional Theory.