Abstract

Two series of hydrated fluorides have been prepared by a “chimie douce” process. For the first family, more than twenty five compounds of δ-ALn₃F₁₀,xH₂O (A⁺ = alkaline ions, NH₄⁺, H₃O⁺ and Ln = lanthanide) have been prepared. They crystallize in the Fdm space group (a ≈ 15.4 Å and Z = 16) and are isotypic with δ-(H₃O)Yb₃F₁₀,xH₂O (x = 1). The diamond-type structure of these phases (diamond stacking of octahedral units of antiprisms, called UOA_[8]), creates cavities and tunnels where the water molecules can move.

The second family, γ-ThLn₂F₁₀,H₂O (Ln³⁺ = Er³⁺, Dy³⁺ and Yb³⁺) results from the substitution of Ln³⁺ and A⁺ by a tetravalent cation. The new compound γ-ThEr₂F₁₀,H₂O (Fmm space group, a = 10.739(1) Å and Z = 8) is isotypic with γ-KYb₃F₁₀. Water molecules are located inside the tunnels (8c sites) of a CCP stacking of UOA_[8] through which they can move.

For both series, the thermal stability and the zeolitic behaviour, studied by DTA/TGA and X-ray thermodiffractometry, are reported and a low zeolitic water capacity, around 2–4% in mass, is observed.