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Abstract

Silver, a coinage metal alongside copper and gold, uniquely serves as the only "normal
transition metal" in the triad. Whilst copper exhibits a reddish hue and gold displays a
yellow lustre, silver possesses a bright white metallic sheen and surpasses all metals in
electrical conductivity, thermal conductivity and reflectivity. Beyond its common +1
oxidation state, silver can adopt the much rarer +2 state. The Ag2+ cation, with a 4d9
electron configuration and an unpaired 4d electron, exhibits intriguing chemical and
physical properties. It is confined almost exclusively to fluorine environment and together
they form the family of compounds called fluoridoargentates(II). The extreme moisture
sensitivity of Ag2+ demands rigorous handling techniques, resulting in only approximately
a hundred of Ag2+ compounds compared to the thousands of known Ag+ compounds.
Fluoridoargentates(II) display fascinating magnetic properties and have been proposed
as analogues to cuprates, with predictions of unconventional superconductivity. However,
detailed studies has been hampered by difficulties in their preparation. Currently, these
compounds are synthesised via two methods: (i) conventional solid-state synthesis at
temperatures >360 °C, which causes decomposition of the main AgF2 precursors and
contamination with secondary phases, and (ii) solution-based methods using hazardous
anhydrous hydrogen fluoride that also require specialized equipment and offers access only
to a limited subset of compounds. These limitations underscore the need for a roomtemperature
synthetic approach capable of producing phase-pure samples.
To overcome these obstacles and expand Ag2+ chemistry, this thesis introduces
mechanochemistry as a viable synthetic route for fluoridoargentates(II). Mechanochemistry
operates at room temperature without requiring solvents, affording precise control over
milling parameters and enabling access to metastable phases. Whilst mechanochemistry of
oxides is well-established, mechanochemistry of fluorides remains nascent, with
mechanochemistry of fluoridoargentates(II) entirely unexplored at the outset of this work.
This thesis first benchmarked the mechanochemical synthesis using the MAgF4 series
(M = Ba, Sr, Hg, Ca, Cd) of compounds, and resolved their structures and magnetic
properties via synchrotron and neutron powder diffraction. The optimized conditions were
then applied to the alkali metal fluoridoargentates(II) in the MAgF3 and M2AgF4 series (M
= Na, K, Rb, Cs), enabling ccomprehensive structural and magnetic characterization.
Mechanochemistry subsequently enabled discovery of novel phases, including NaAgF3,
Ag2F3, Ag3F4, Ag3YF8, and Ag3BiF8, with structures determined using three-dimensional
electron diffraction complemented by synchrotron and neutron powder diffraction.
Magnetic studies revealed antiferromagnetic and ferromagnetic behaviours, with some
compounds exhibiting synthesis-dependent properties.
Overall, this thesis demonstrates that mechanochemistry is a powerful method for
discovering new fluoridoargentate(II) phases and advancing the understanding of their
structural and magnetic properties. It establishes a foundation for future research on the
Ag2+ cation, potentially uncovering unconventional superconductivity in this system.