Reaction between cerium trifluoride and elemental fluorine

Reactions between cerium trifluoride and elemental fluorine have been examined by means of the kinetic and crystallographic method. The reactions were performed at 503–573 K under fluorine pressures of 6.7–26.7 kPa for reaction time up to 3 h. Two kinds of CeF4 were synthesized by controlling the reaction condition. One is the metastable CeF4-I synthesized at 523–538 K which returns to CeF3 to release elemental fluorine, and the other is the stable CeF4-II obtained at temperatures higher than ca. 540 K, which never returns to CeF3. X-ray diffraction–Rietveld analysis revealed that the structure of CeF4-I and CeF4-II were monoclinic structure (C12/c1, Z=12, CeF4-I/CeF4-II: a0, 1.26 nm/1.25; b0, 1.06/1.05; c0, 0.82/0.82; β, 126.1/126.3°; cell volume, 8.91×10−28/8.78×10−28 m3) and the cell volume of the CeF4-I was 1.4% larger than that of the CeF4-II. Bond lengths between Ce and F in CeF4-I were somewhat longer than those in CeF4-II. When CeF4 and NaCl were put separately in the reaction container, CeF4-I changed to CeF3 with converting NaCl to NaF, however, CeF4-II never reacted with NaCl.