Synthesis, crystal structure and spectroscopic properties of a novel yttrium(iii) fluoride dimolybdate(vi): YFMo2O7

Abstract

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 Y³⁺ cations in a pentagonal bipyramidal environment consisting of two F⁻ anions in the apical positions and five O²⁻ anions in the equatorial positions. These polyhedra are connected to ¹_∞{[YF^v_2/2O^t_5/1]⁸⁻} chains along [100] by sharing common F⁻ vertices. The likewise crystallographically unique Mo⁶⁺ 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 ¹_∞{[MoO^e_2/2O^v_1/2O^t_2/1]⁻}. Taking a sixth oxygen ligand further away from the Mo⁶⁺ cations into account, the aforementioned chains assemble to corrugated ²_∞{[MoO^e_2/2O^v_3/2O^t_1/1]⁻} layers perpendicular to [010] with the ¹_∞{[YF^v_2/2O^t_5/1]⁸⁻} chains situated between these sheets. Since Y³⁺ 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 Eu³⁺.