Synthesis and structure of anhydrous rare-earth perchlorates M(ClO4)(3) (M= La, Ce-Er, Y): Derivatives of the UCl3 type of structure

Anhydrous perchlorates M(ClO4)(3) (M = La, Ce-Er, Y) were obtained by dryin g the products formed in the reaction of the respective lanthanide oxide wi th perchloric acid (70%). According to X-ray powder investigations, they al l crystallize with the hexagonal space group P6(3)/m isostructural with the hydrogensulfates of the lighter lanthanides. For the example of Pr(ClO4)(3 ) a full profile Rietveld refinement based on X-ray powder data has been un dertaken successfully (a = 933.61(3) pm, c = 584.88(2) pm; R-p = 0.207, R-B ragg = 0.068). The structure of Er(ClO4)(3) was refined from neutron diffra ction data (a = 919.7(1) pm, c = 559.8(1) pm; R-p = 0.190, R-Bragg = 0.106) . High temperature X-ray powder investigations show that thermal expansion occurs mainly in the (001) plane while the c axis remains nearly constant.