Title: Mechanochemical Synthesis and Magnetic Properties of the Mixed-Valent Binary Silver(I,II) Fluorides, AgI2AgIIF4 and AgIAgIIF3

Abstract: Fluoridoargentates(II) represent a fascinating class of silver(II) compounds that exhibit structural and magnetic similarities to cuprate superconductors. However, their synthesis is challenging, leaving their properties largely unexplored. In this study, mechanochemistry is introduced as a new technique for the synthesis of fluoridoargentates(II), which avoids the use of anhydrous HF or heating, and employs simple equipment. Furthermore, by ball milling of commercially available precursors, AgF and AgF2, we obtained the first two examples of binary mixed-valent silver(I,II) phases, AgI2AgIIF4 and AgIAgIIF3. While the AgI2AgIIF4 phase was obtained at room temperature, the AgIAgIIF3 phase is metastable and required milling under cryogenic conditions. Using synchrotron powder X-ray diffraction, it was found that AgI2AgIIF4 crystallizes in the P21/c space group and is isostructural to beta-K2AgF4. Here, double-bridged [AgF6]4- octahedra form chains that propagate along the a-crystallographic direction, giving a quasi-1D canted antiferromagnetic character, as shown by magnetic susceptibility. The AgIAgIIF phase adopts the P-1 space group, is isostructural to AgCuF3 and shows features of a one-dimensional antiferromagnet. It is expected that this facile synthetic approach will enable the expansion of silver(II) chemistry and accelerate the search for a silver analogue to cuprate superconductors.