Magnetic interactions as a pivotal determinant in stabilizing a novel Ag ^II Ag ^III F ₅ polymorph with high-spin Ag ^III

Based on theoretical calculations, we introduce a new Ag^IIAg^IIIF₅ monoclinic polymorph with a rare high-spin Ag^III. Our analysis of the experimental X-ray diffraction data available in the literature reveals that this polymorph was likely prepared in the past in a mixture with the triclinic form of the same compound. Theoretical calculations reproduce very well the lattice parameters of both forms. Calculations suggest that under ambient conditions, the monoclinic form is the more energetically stable phase of Ag₂F₅. We predict a strong one-dimensional antiferromagnetic superexchange between silver cations of different valences with superexchange constant of -207 meV (hybrid functional result). The polymorph with high-spin Ag^III owes its stability over the one with low-spin Ag^III, to these magnetic interactions. Analysis of the electronic band structure shows that it is also a good candidate for an altermagnet.