Structural distortion and disorder in pseudo-trigonal noncentrosymmetric K4Ce(CO3)(3)O.2H(2)O

The crystallisation of a new rare earth carbonate K4Ce(CO3)(3)O.2H(2)O is o bserved at the interface between a solution of K2CO3 and a CeF3 nutrient po wder at 180 degreesC. The structure is determined from X-ray crystal diffra ction data. The cell is orthorhombic (Amm2 space group, a(O) = 4.1741(5), b (O) = 16.305(2), c(O) = 9.395(1) Angstrom, Z= 2) and derives from a trigona l cell (a(H) approximate to 9.40 and c(H) = 4.174 Angstrom). The Ce4+ ions adopt an eight-fold coordination with six oxygen atoms from three carbonate groups in a mean plane; the last two oxygen atoms link the CeO8 polyhedra in order to build infinite chains along the a axis. (C) 2001 Elsevier Scien ce Ltd. Ah rights reserved.