Synthesis from solutions and properties of various metal fluorides and fluoride salts

Parts of the recent advances in the search of new fluorides or fluoride salts, at the Laboratoire des Fluorures in Le Mans, are presented. Hydrothermal synthesis in sub-critical or super-critical conditions is mainly used to obtain rare earth (RE), Al, Ga, In or 3d transition fluorides or fluoride salts (borates, carbonates, phosphates or silicates). Open structures are obtained by low temperature crystallisation from solutions (δ-(H3O)RE3F10·xH2O) and, probably, by decomposition of hybrid organic–inorganic fluorides D·MF5 (D=diprotonated aliphatic diamine), prepared by micro-wave heating of the solutions. Non-centrosymmetric phases are evidenced in fluoride carbonates and fluoride borates: K4RE2(CO3)3F4 and M2(BO3)(OH)0.75F0.25; the magnetic properties of several iron fluoride phosphates are found to be governed by super or super-superexchange interactions.