Sensitivity\nof Mild Hydrothermal Synthesis to the\nReaction Conditions: Targeting Mixed-Metal Hexagonal Tungsten Bronze\nFluorides <i>A</i><sub><i>x</i></sub>M<sup>2+</sup><sub><i>x</i&g

The synthesis of five quaternary hexagonal tungsten bronze\n(HTB)\nfluorides, <i>A</i><sub><i>x</i></sub>M<sup>2+</sup><sub><i>x</i></sub>M<sup>3+</sup><sub>(1–<i>x</i>)</sub>F<sub>3</sub>, (<i>A</i> = Cs and Rb;\nM<sup>2+</sup> = Co<sup>2+</sup>, Ni<sup>2+</sup>, and Zn<sup>2+</sup>; and <i>M</i><sup>3+</sup> = V<sup>3+</sup>) via a mild\nhydrothermal route is reported. The crystal structures and compositions\nwere determined using a combination of single-crystal X-ray diffraction,\nRietveld refinement of powder X-ray diffraction data, and inductively\ncoupled plasma optical emission spectroscopy analysis. This study\nhighlights the sensitivity of the mild hydrothermal method on the\nreaction temperature, solvent system, and quantity of starting reagents\nthat directly influence the selective synthesis of kinetically stabilized\nfluoride materials, including hydrated fluorides, β-pyrochlores,\nand HTB. The magnetic susceptibility and isothermal magnetization\ndata for all five compounds were collected, which revealed the existence\nof a strong antiferromagnetic component in these phases. The presence\nof the Kagome layer in the structure results in geometrical frustration\nand leads to frustration indexes ranging from 7 to 13 for these compounds.