Rietveld refinement of the crystal structures of Rb(2) XSi(5)O(12) (X = Ni, Mn)

The synthetic leucite silicate framework mineral analogues Rb(2) XSi(5)O(12) {X = Ni [dirubidium nickel(II) penta­silicate] and Mn [dirubidium manganese(II) penta­silicate]} have been prepared by high-temperature solid-state synthesis. The results of Rietveld refinements, using X-ray powder diffraction data collected using Cu Kα X-rays, show that the title compounds crystallize in the space group Pbca and adopt the cation-ordered structure of Cs(2)CdSi(5)O(12) and other leucites. The structures consist of tetra­hedral SiO(4) and XO(4) units sharing corners to form a partially substituted silicate framework. Extraframework Rb(+) cations sit in channels in the framework. All atoms occupy the 8c general position for this space group. In these refined structures, silicon and X atoms are ordered onto separate tetra­hedrally coordinated sites (T-sites). However, the Ni displacement parameter and the Ni—O bond lengths suggest that for the X = Ni sample, there may actually be some T-site cation disorder.