Synthesis, crystal structure determination of a novel phosphate AgZnFe(PO) with an alluaudite-like structure.

Single crystals of AgZnFe(PO) [silver zinc iron phosphate (1.64/1.64/1.36/3)] have been synthesized by a conventional solid-state reaction and structurally characterized by single-crystal X-ray diffraction. The title compound crystallizes with an alluaudite-like structure. All atoms of the structure are in general positions except for four, which reside on special positions of the space group, 2/. The Ag cations reside at full occupancy on inversion centre sites and at partial occupancy (64%) on a twofold rotation axis. In this structure, the unique Fe ion with one of the two Zn cations are substitutionally disordered on the same general position (Wyckoff site ), with a respective ratio of 0.68/0.32 (occupancies were fixed so as to ensure electrical neutrality for the whole structure). The remaining O and P atoms are located in general positions. The three-dimensional framework of this structure consists of kinked chains of edge-sharing octa-hedra stacked parallel to [10]. These chains are built up by a succession of [O] ( = Zn/Fe or Zn) units. Adjacent chains are connected by the PO anions, forming sheets oriented perpendicular to [010]. These inter-connected sheets generate two types of channels parallel to the axis, in which the Ag cations are located. The validity and adequacy of the proposed structural model of AgZnFe(PO) was established by means of bond-valence-sum (BVS) and charge-distribution (CHARDI) analysis tools.