Colourless crystals of the novel compound BaYb6(Si2O7)2(Si3O10) were prepared using a high-temperature flux-growth technique in air. The crystal structure was solved and refined to R(F) = 2.50 % using single-crystal X-ray diffraction data collected at room temperature. The silicate is monoclinic, space group P21/m (Z = 2), with a = 5.5173(11), b = 27.260(6), c = 6.8150(14) Å, β = 106.73(3)°, V = 981.6(3) Å3. BaYb6(Si2O7)2(Si3O10) represents the first silicate containing both (Si2O7) and (Si3O10) groups in the ratio 2:1 and is isotypic with (NH4)Cd6(P2O7)2(P3O10). Its framework topology is characterised by one horseshoe-shaped trisilicate (Si3O10) group, two symmetrically equivalent (Si2O7) groups with the Si–O–Si angle of 165.3° and staggered conformation, and zigzag chains of edge-sharing distorted YbO6 octahedra (<Yb–O = 2.24 Å>). The Ba atoms occupy narrow channels extending parallel to [100]. The topological features of BaYb6(Si2O7)2(Si3O10) are compared to those of other compounds containing mixed groups (M2O7) and (M3O10). A similarity to BaY4(Si2O7)(Si3O10) is pointed out.

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