Real and Hypothetical Intermediate-Valence AgII/AgIII and AgII/AgI Fluoride Systems as Potential Superconductors

The fate of compound with AgF2:AgO stoichiometry-A theoretical study

Metal oxyfluorides constitute a broad group of chemical compounds with a rich spectrum of crystal structures and properties. Surprisingly though, none of the ternary oxyfluorides contains a cation from group 11 of the periodic table. Intending to find one, we focused on the silver derivative, the Ag₂OF₂ system, which may be considered as the 1:1 "adduct" of AgF₂ (i.e., an antiferromagnetic positive U charge transfer insulator) and AgO (i.e., a diamagnetic disproportionated negative charge transfer insulator). Here, possible crystal structures of the silver oxyfluoride were studied using evolutionary algorithms based on the density functional theory approach. We analyzed the oxidation states of silver in the low-energy structures, possible magnetic interactions, and energetic stability with respect to the available substrates. Our findings suggest that silver oxyfluoride, if obtained, may form a metastable crystal with cations in three different oxidation states of the same element. Due to the small energy difference, existence of a fully disproportionated metallic compound cannot be ruled out. Finally, we outlined a prospect for the synthesis of polytypes of interest using diverse synthetic approaches, starting from the direct fluorination of Ag₂O.