Sc(0.43(2))Rb2Mo15S19, a partially Sc-filled variant of Rb2Mo15S19.

The structure of scandium dirubidium pentadecamolybdenum nonadecasulfide, Sc(0.43(2))Rb(2)Mo(15)S(19), constitutes a partially Sc-filled variant of Rb(2)Mo(15)S(19) [Picard, Saillard, Gougeon, Noel & Potel (2000), J. Solid State Chem. 155, 417-426]. In the two compounds, which both crystallize in the R ̅3c space group, the structural motif is characterized by a mixture of Mo(6)S(i)(8)S(a)(6) and Mo(9)S(i)(11)S(a)(6) cluster units (`i' is inner and `a' is apical) in a 1:1 ratio. The two components are interconnected through interunit Mo-S bonds. The cluster units are centred at Wyckoff positions 6b and 6a (point-group symmetries ̅3. and 32, respectively). The Rb(+) cations occupy large voids between the different cluster units. The Rb and the two inner S atoms lie on sites with 3. symmetry (Wyckoff site 12c), and the Mo and S atoms of the median plane of the Mo(9)S(11)S(6) cluster unit lie on sites with .2 symmetry (Wyckoff site 18e). A unique feature of the structure is a partially filled octahedral Sc site with ̅1 symmetry. Extended Hückel tight-binding calculations provide an understanding of the variation in the Mo-Mo distances within the Mo clusters induced by the increase in the cationic charge transfer due to the insertion of Sc.