An orthorhombic polymorph of the ultraphosphate YP5O14

Single crystals of yttrium pentaphosphate(V), YP5O14, were obtained by solid-state reaction. The orthorhombic title compound belongs to the family of ultraphosphates and is the second polymorph of this composition. It is isotypic with its Ho and Er analogues. The structure contains two bridging Q 2-type PO4 tetrahedra and one branching Q 3-type PO4 tetrahedron, leading to infinite ultraphosphate ribbons running along the a axis. The coordination polyhedron around the Y3+ cation may be described as distorted bicapped trigonal-prismatic. The YO8 polyhedra are isolated from each other. They are linked by corner-sharing to the O atoms of six Q 2-type and of two Q 3-type PO4 tetrahedra into a three-dimensional framework.

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: WM2221).

Comment
Rare earths ultraphosphates exhibit a growing attention because of their potential applications as optical materials, including lasers, phosphors, matrices for the energy up-conversion and more recently for plasma display panels (PDP) as they exhibit an absorption band overlapping the emission spectrum of a Xe-Ne plasma in the VUV region (Rao & Devine, 2000;Moine & Bizarri, 2006). The non-optically active matrix of YP 5 O 14 can be used as host material for such applications and hence needs to be structurally well-characterized. This article deals with the crystal structure refinement of the orthorhombic polymorph that is isotypic with HoP 5 O 14 (Durif, 1972) and ErP 5 O 14 (Katrusiak & Kaczmarek, 1995;Dimitrova et al. 2004).
Two PO 4 tetrahedra are Q 2 type bridging tetrahedra with typical two shorter and two longer P-O bonds (Durif, 1995).
The third PO 4 tetrahedron is a branching Q 3 type tetrahedron and exhibits also characteristic bond lengths ranging from 1.455 (4) to 1.567 (3) Å. These PO 4 groups form infinite ribbons with composition (P 5 O 14 ) 3which can be considered as built of two infinite (PO 3 ) n chains running along the a axis and connected by alternating up and down capping PO 4 tetrahedra (Figs. 1, 2). The repetition unit in these ribbons is P 10 O 28 .

Experimental
Crystals of the title compounds were synthesized by reacting Y 2 O 3 with (NH 4 ) 2 HPO 4 in a graphite crucible. A mixture of these reagents in the molar ratio 1:9 was used for the synthesis. The mixture was first heated at 473 K for 12 h. Then the temperature was raised up to 673 K and was held for 2 days before cooling to room temperature at a rate of 10 K/h. Single-crystals were extracted from the batch by washing with hot water. Besides crystals of the title compound, crystals of the monoclinic polymorph were also obtained (Mbarek et al., 2009).

Refinement
The highest residual peak in the final difference Fourier maps was located 0.26 Å from atom Y1 and the deepest hole was located 0.44 Å from atom P2.  (3)