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A. Grenier-a,b, A. Porras-gutierrez-a, A. Desrues-a,b, S. Leclerc-a,b, and O. J. , Borkiewicz c , Henri Groult a,b , Damien Dambournet a,b* a Sorbonne Université, CNRS, Physico-chimie des électrolytes et nano-systèmes interfaciaux

X. , Advanced Photon Source, Science Division

, All syntheses gave pure single-phase MnF2 with rutile-type structure (P42/mnm space group), as shown in Figure S1. Crystallite size estimated from Scherrer's equation from the (110) peak and the yield of the reaction are gathered in Table S1, * Corresponding author: damien.dambournet@sorbonne-universite.fr Optimized synthesis conditions -Solvents: Preliminary syntheses in pure ethanol, pure water and a mixture of ethanol and water