Ba2Gd2(Si4O13): a silicate with finite Si4O13 chains.

The title compound, dibarium digadolinium(III) tetrasilicate, crystallized from a molybdate-based flux. It represents a new structure type and contains finite zigzag-shaped C(2)-symmetric Si(4)O(13) chains and Gd(2)O(12) dimers built of edge-sharing GdO(7) polyhedra. The [9+1]-coordinated Ba atoms are located in voids in the atomic arrangement. All atoms are in general positions except for one O atom, which lies on a twofold axis. The structure is compared with those of the few other known tetrasilicates.