Synthesis, stability and zeolitic behavior of δ­ALn3F10,xH2O and γ­ThLn2F10,H2O phases (Ln = lanthanide)

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 A 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) A 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.