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 drying the products formed in the reaction of the respective lanthanide oxide with perchloric acid (70%). According to X‐ray powder investigations, they all crystallize with the hexagonal space group P6₃/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 undertaken successfully (a = 933.61(3) pm, c = 584.88(2) pm; R_p = 0.207, R_Bragg = 0.068). The structure of Er(ClO₄)₃ was refined from neutron diffraction 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.