Silver indium diphosphate, AgInP2O7

Polycrystalline material of the title compound, AgInP2O7, was synthesized by traditional high-temperature solid-state methods and single crystals were grown from the melt of a mixture of AgInP2O7 and B2O3 as flux in a platinium crucible. The structure consists of InO6 octahedra, which are corner-shared to PO4 tetrahedra into a three-dimensional network with hexagonal channels running parallel to the c axis. The silver cation, located in the channel, is bonded to seven O atoms of the [InP2O7] framework with Ag–O distances ranging from 2.370 (2) to 3.015 (2) Å. The P2O7 diphosphate anion is characterized by a P—O—P angle of 137.27 (9) and a nearly eclipsed conformation. AgInP2O7 is isotypic with the M IFeP2O7 (M I = Na, K, Rb, Cs and Ag) diphosphate family.


Comment
The diphosphates A I M III P 2 O 7 (A I = Li, Na, K, Rb, Cs and Ag; M III = Al, Ga, Cr, Fe, In, Y) are extensively studied for their electrical and optical properties and for its perspective application as magnetic materials (Terebilenko et al. (2010);Hizhnyi et al. (2008); Whangbo et al. (2004); Vitins et al. (2000)). The crystal structures of most of these compounds are known except a few cases in which the crystal growth is difficult. In this context, the present paper reports on the determination of AgInP 2 O 7 crystal structure from X-ray diffraction single-crystal data.
The structure of this phosphate is characterized by a three-dimensional network built up from indum octahedra linked to diphosphate groups by a corner-sharing. Each InO 6 octahedra is surrounded by six PO 4 tetrahedra belonging to five different P 2 O 7 groups (see Fig.1 and Fig.2). As a result of these blocks, assemblage three-dimensional-framework is formed with hexagonal channels, where silver cations reside. Although, the coordination sphere of Ag + cations is composed of seven O 2anions in an irregular geometry, located at Ag-O distances between 2.370 (2) and 3.015 (2) Å (see Fig.2). Furthermore, the diphosphate group contains two distorted PO 4 tetrahedra sharing one corner and display a nearly eclipsed conformation.
Silver indium diphosphate (pyrophosphate) is isostructural to A I FeP 2 O 7 (A I = Na, K, Rb, Cs and Ag) diphosphates family and is categorized as a dichromate type.

Experimental
AgInP 2 O 7 in the form of single crystals was prepared by stoichiometric reaction of AgNO 3 , (NH 4 ) 2 HPO 4 and In 2 O 3 in B 2 O 3 flux. The mixture was heated at 773 K under ambiante atmosphere for 6 h and 973 K for 2 h with intermediate grindings to ensure complete reaction. Subsequent melting at 1323 K followed by slow cooling to room temperature at a rate of 12°K h -1 resulted in colourless crystals of the title compound.

Refinement
The highest and deepest hole residual peak in the final difference Fourier map are located at 0.49 Å and 0.58 Å, respectively from Ag1 atom. The not significants bonds and angles were removed from the CIF file.

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The