  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 Ag(II) cation
and other paramagnetic transition metal cation are known experimentally.
Recently the high-pressure synthesis of ternary silver(II) fluorides 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, evaluate coupling constants and calculate the
impact of Ag(II) presence on superexchange between the other cations. The
results indicate that the low-pressure form of AgCuF4, the only composed of
stacked layers as the parent AgF2, would hold mainly Ag-Ag and Cu-Cu
superexchange interactions. Upon compression, or with the nickel(II) cation,
the Ag-M interactions in AgMF4 intensify, 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.
