K9Y3[Si12O32]F2.

Single-crystals of the title compound, nona-potassium triyttrium dodeca-silicate difluoride, were obtained from flux synthesis experiments in the system SiO2-Y2O3-KF. The crystal structure belongs to the group of single-layer silicates and is based on silicate sheets parallel to (110). A single layer contains secondary (Q (2)) and tertiary (Q (3)) silicate tetra-hedra in the ratio 1:2 and is build up from six-, eight- and twelve-membered rings. The linkage between neighboring layers is achieved by two crystallographically independent Y(3+) cations, which are coordinated by six oxygen ligands in form of distorted octa-hedra. Charge compensation is accomplished by incorporation of additional F(-) anions and K(+) cations in the structural channels, forming anion-centred [F2K7] groups. Apart from one K(+) and one Y(3+) cation (each with site symmetry -1), the 30 crystallographically independent atoms reside on general positions.