Syntheses and crystal structures of hydrated ternary cerium sulfates: Mixed-valence K5Ce2(SO4)(6)center dot H2O and K2Ce(SO4)(3)center dot H2O

摘要

A new chemical and structural interpretation of K5Ce2(SO4)(6)-H2O (I) and a redetermination of the structure of K2Ce(SO4)(3)-H2O (II) is presented. The mixed-valent compound I crystallizes in the space gpup C2/c with a = 17.7321(3), b 7.0599(1), c = 19.4628(4) angstrom, beta = 112.373(1)degrees and Z = 4. Compound I has been discussed earlier with space group Cc. In the structure of 1, there are pairs of edge sharing cerium polyhedra connected by sulfate oxygen atoms in the mu(3) bonding mode. These cerium dimers are linked through edge and corner sharing sulfate bridges, forming layers. The layers are joined by potassium ions which together with the water molecules are placed between the layers. No irregularity in the distribution of the Ce-III and Ce-IV to cause the lost of a crystallographic center of symmetry was detected. We suggest that the charge exerted by the extra f(1) electron for every cerium dimer is delocalized over the Ce1 -O-2-Ce2 moiety in a non-bonding mode. As a result, the oxidations state of each cerium ion is a mean value between III and IV at each atomic position. Compound 11 crystallizes in the space group C2 with a = 20.6149(2), b = 7.0742(1), c = 17.8570(1) angstrom, beta = 122.720(1)degrees and Z = 8. The hydrogen atoms have been located and the absolute structure has been established. Neither hydrogen atom positions nor anisotropic displacement parameters were given in the previous reports. In compound 11, the cerium polyhedra are connected by edge and corner sharing sulfate groups forming a three-dimensional network. This network contains Z-shaped channels hosting the charge compensating potassium ions.