Potassium ditin(IV) tris[phosphate(V)], KSn2(PO4)3

The title compound, KSn2(PO4)3, belongs to the NASICON-type family of phosphates with the space group R . Its structure is constructed by very regular [with P—O distances ranging from 1.513 (6) to 1.522 (6) Å] PO4 tetrahedra and SnO6 octahedra on the 3. axis, which are linked by O atoms, forming an [Sn2(PO4)3] framework. The K atoms occupy the . axis sites and are located in the voids of this arrangement. The crystal studied was a merohedral twin with twin law (010 100 00) and a component ratio of 0.580 (7):0.420 (7).


Crystal data
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: FI2111).
the ionic conductivity properities which may due to the complex and subtle interactions between NASICON framework and mobile ions. The NASICON-type structure with a flexible three-dimensional framework of PO 4 tetrahedra sharing comers with MO 6 octahedra, is amenable to a wide variety of chemical substitutions at the various crystallographic positions, thus yielding a large number of closely related compounds, such as NaFeNb(PO 4 ) 3 (Zatovskii, et al., 2006) and K 2 Ca 2 (SO 4 ) 3 (Boujelben, et al., 2007). In order to inrich this family of compounds, we synthesis the compound KSn 2 (PO 4 ) 3 by the high-temperature reaction and determine the crystal structure from single-crystal X-ray diffraction analysis.KSn 2 (PO 4 ) 3 is isostructure with Na (Alamo & Rodrigo, 1992) and Rb (Zhao et al., 2011) analog crystals which crystallizes in the trigonal space group R-3.
A projection of the crystal structure of KSn 2 (PO 4 ) 3 is given in Fig. 2. It is characterized by the presence of PO 4 tetrahedra and SnO 6 octahedra, linked by sharing corner O atoms, to establish a three-dimentional [Sn 2 (PO 4 ) 3 ] framework. Furthermore, this framwork delimits two types of channels in which the K atoms are located to compensate the negative charges.
The PO 4 tetrahedra are quite regular, with the P-O distance ranging from 1.513 (6) to 1.522 (6) Å, while the SnO 6 octahedra is quite regular too, with the Sn-O distance ranging from 2.003 (6) to 2.045 (6) Å.

Experimental
Compound KSn 2 (PO 4 ) 3 has been prepared by a high-temperature method in air. A powder mixture of K 2 CO 3 , SnO 2 and NH 4 H 2 PO 4 in the molar ratio of K: Sn: P = 15: 1: 15 was first ground in an agate mortar and then transferred to a platinum crucible. The sample was gradually heated in air at 1173 K for 24 h. After that, the intermediate product was slowly cooled to 773 K at the rate of 2 K h -1 , and finally quenched to room temperature. The obtained crystals were colorless with a prismatic shape.

Refinement
The KSn 2 (PO4) 3 crystal studies was twinned by merohedry. For refinement the twin law (0 1 0 1 0 0 0 0 1) was used; the twin component ratio refined to 0.580 (7): 0.420 (7). The highest peak in the difference electron density map equals to 2.23 e/Å 3 at the distance of 0.05 Å from Sn1 site while the deepest hole equals to -2.99 e/Å 3 at the distance of 0.99 Å from Sn2 site.