Synthesis, crystal structure and spectroscopic properties of a novel yttrium(III) fluoride dimolybdate(VI): YFMo2O7.

Thermal treatment of a mixture of Y2O3, YF3 and MoO3 in a 1 : 1 : 6 molar ratio at 850 °C in evacuated silica ampoules yielded colorless, platelet-shaped single crystals of YFMo2O7. SiO2 was dissolved from the ampoule wall in small amounts, but could be removed from the crude product by treatment with hydrofluoric acid (20%). The title compound crystallizes monoclinically in the space group P2/c with two formula units per unit cell with the dimensions a = 4.2609(2), b = 6.5644(4), c = 11.3523(7) Å, and β = 90.511(2)°. Its crystal structure contains crystallographically unique Y(3+) cations in a pentagonal bipyramidal environment consisting of two F(-) anions in the apical positions and five O(2-) anions in the equatorial positions. These polyhedra are connected to {[YFO](8-)} chains along [100] by sharing common F(-) vertices. The likewise crystallographically unique Mo(6+) cations exhibit a coordination number of five and reside in the centers of distorted square pyramids built up of oxide anions. These entities are fused to chains along [001] by sharing common edges and vertices according to {[MoOOO](-)}. Taking a sixth oxygen ligand further away from the Mo(6+) cations into account, the aforementioned chains assemble to corrugated {[MoOOO](-)} layers perpendicular to [010] with the {[YFO](8-)} chains situated between these sheets. Since Y(3+) represents a non-luminescent rare-earth metal(iii) cation, YFMo2O7 is a suitable host material for doping with luminescence-active lanthanoid(iii) cations, such as Eu(3+).