A new mixed-valence lead(II) mangan-ese(II/III) phosphate(V): PbMn(II) 2Mn(III)(PO4)3.

The title compound, lead trimanganese tris(orthophosphate), has been synthesized by hydro-thermal methods. In this structure, only two O atoms are in general positions and all others atoms are in the special positions of the Imma space group. Indeed, the atoms in the Wyckoff positions are namely: Pb1 and P1 on 4e (mm2); Mn1 on 4b (2/m); Mn2 and P2 on 8g (2); O1 on 8h (m); O2 on 8i (m). The crystal structure can be viewed as a three-dimensional network of corner- and edge-sharing PO4 tetra-hedra and MnO6 octa-hedra, building two types of chains running along the b axis. The first is an infinite linear chain, formed by alternating Mn(III)O6 octa-hedra and PO4 tetra-hedra which share one vertex. The second chain is built up from two adjacent edge-sharing octa-hedra (Mn(II) 2O10 dimers) whose ends are linked to two PO4 tetra-hedra by a common edge. These chains are linked together by common vertices of polyhedra in such a way as to form porous layers parallel to (001). These sheets are bonded by the first linear chains, leading to the appearance of two types of tunnels, one propagating along the a axis and the other along b. The Pb(II) ions are located within the inter-sections of the tunnels with eight neighbouring O atoms in form of a trigonal prism that is capped by two O atoms on one side. The three-dimensional framework of this structure is compared with similar phosphates such as Ag2Co3(HPO4)(PO4)2 and Ag2Ni3(HPO4)(PO4)2.