Superexchange interactions in AgMF4 (M = Co, Ni, Cu) polymorphs

Abstract

Abstract Magnetic properties of silver(II) compounds have been of interest in recent years. In covalent compounds, the main mechanism of interaction between paramagnetic sites is the superexchange via the connecting ligand. To date, little is known of magnetic interactions between Ag(II) cations and other paramagnetic centres. It is because only a few compounds bearing a Ag(II) cation and other paramagnetic transition metal cation are known from experimental work. Recently the high-pressure synthesis of ternary silver(II) fluoridometallates with 3d metal cations AgMF4 (M = Co, Ni, Cu) was predicted to be feasible. Here, we investigate the magnetic properties of these compounds in their diverse polymorphic forms. Using well-established computational methods we predict superexchange pathways in AgMF4 compounds, evaluate coupling constants and calculate the impact of the Ag(II) presence on superexchange between the other cations. The results indicate that the low-pressure form of AgCuF4, the only one composed of stacked layers like the parent AgF2, would show mainly Ag–Ag and Cu–Cu superexchange interactions. Upon compression, or with the nickel(II) cation, the Ag–M interactions in AgMF4 compounds are intensified, which is emphasized by an increase of Ag–M superexchange coupling constants and Ag–F–M angles. All the strongest Ag–M superexchange pathways are quasi-linear, leading to the formation of antiferromagnetic chains along the crystallographic directions. The impact of Ag(II) on M–M superexchange turns out to be moderate, due to factors connected to the crystal structure.