Molecular properties of metal difluorides and their interactions with CO₂ and H₂O molecules: a DFT investigation

A computational study of metal difluorides (MF₂; M = Ca to Zn) and their interactions with carbon dioxide and water molecules was performed. The structural parameter values obtained and the results of AIM analysis and energy decomposition analysis indicated that the Ca-F bond is weaker and less ionic than the bonds in the transition metal difluorides. A deformation density plot revealed the stablizing influence of the Jahn-Teller effect in nonlinear MF₂ molecules (e.g., where M= Sc, Ti, Cr). An anaysis of the metal K-edge peaks of the difluorides showed that shifts in the edge energy were due to the combined effects of the ionicity, effective nuclear charge, and the spin state of the metal. The interactions of CO₂ with ScF₂ (Scc3 geometry) and TiF₂ (Tic2 geometry) caused CO₂ to shift from its usual linear geometry to a bent geometry (η²(C=O) binding mode), while it retained its linear geometry (η¹(O) binding mode) when it interacted with the other metal difluorides. Energy decomposition analysis showed that, among the various geometries considered, the Scc3 and Tic2 geometries possessed the highest interaction energies and orbital interaction energies. Heavier transition metal difluorides showed stronger affinities for H₂O, whereas the lighter transition metal (Sc and Ti) difluorides preferred CO₂. Overall, the results of this study suggest that fluorides of lighter transition metals with partially filled d orbitals (e.g., Sc and Ti) could be used for CO₂ capture under moist conditions. Graphical abstract Interaction of metal difluorides with carbon dioxide and water.