Three new scandium silicates with framework structures made of octahedra and tetrahedra, KSrScSi2O7, NaBaScSi2O7 and RbBaScSi3O9, were obtained through a high-temperature flux-growth technique. Their crystal structures have been determined from single-crystal intensity data (Mom>Km>α radiation, CCD area detector, 293 K; m>Rm>(m>Fm>) = 3.30, 1.82, 2.00%, respectively). The disilicate KSrScSi2O7 is monoclinic, m>Pm>21/m>nm>, with m>am> 9.446(2), m>bm> 5.478(1), m>cm> 12.537(3) Å, β 104.39(3)°, m>Vm> 628.4(2) Å3, Z = 4. The disilicate NaBaScSi2O7 forms monoclinic crystals with space-group symmetry m>Pm>21/m>mm>, with m>am> 6.845(1), m>bm> 5.626(1), m>cm> 8.819(2) Å, β 109.33(3)°, m>Vm> 320.47(10) Å3, Z = 2. The cyclosilicate RbBaScSi3O9 crystallizes as pseudohexagonal triplets; it is also monoclinic, m>Pm>21/m>nm>, with m>am> 6.957(1), m>bm> 10.199(2), m>cm> 11.881(2) Å, β 90.07(3)°, m>Vm> 843.0(2) Å3, Z = 4. The topologies of KSrScSi2O7 and NaBaScSi2O7 show clear similarities, corresponding to isolated Si2O7 groups, bound to octahedrally coordinated Sc3+. The pseudohexagonal arrangement in RbBaScSi3O9 is based on isolated ScO6 octahedra, each of which is corner-linked to Si3O9 rings. In all three compounds, the alkali and alkaline-earth atoms occupy voids in the resulting three-dimensional frameworks. Results of a Raman spectroscopic study of the two disilicates and of five related novel disilicates are also briefly presented, with a focus on the behavior of the Si2O7 group.
