A new mixed-valence lead(II) manganese(II/III) phosphate(V): PbMnII 2MnIII(PO4)3

The title compound, lead trimanganese tris(orthophosphate), has been synthesized by hydrothermal 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 tetrahedra and MnO6 octahedra, building two types of chains running along the b axis. The first is an infinite linear chain, formed by alternating MnIIIO6 octahedra and PO4 tetrahedra which share one vertex. The second chain is built up from two adjacent edge-sharing octahedra (MnII 2O10 dimers) whose ends are linked to two PO4 tetrahedra 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 PbII ions are located within the intersections 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.

The title compound, lead trimanganese tris(orthophosphate), has been synthesized by hydrothermal 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 edgesharing PO 4 tetrahedra and MnO 6 octahedra, building two types of chains running along the b axis. The first is an infinite linear chain, formed by alternating Mn III O 6 octahedra and PO 4 tetrahedra which share one vertex. The second chain is built up from two adjacent edge-sharing octahedra (Mn II 2 O 10 dimers) whose ends are linked to two PO 4 tetrahedra 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 intersections 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 Ag 2 Co 3 (HPO 4 )(PO 4 ) 2 and Ag 2 Ni 3 (H-PO 4 )(PO 4 ) 2 .

Related literature
For compounds with related structures see: Assani et al. (2011a,b,c); Moore & Ito (1979). For applications of related compounds, see: Trad et al. (2010). For compounds with mixed-valence manganese(II/III) lead(II) triphosphates(V), see: Adam et al. (2009) Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010 with Ima2 space group (Assani et al., 2011a(Assani et al., , 2011b. The structure of this compound is an open frameworks such as that observed in the alluaudite. On the basis of crystallographic considerations, the later phosphates structure represents similarities with the well known alluaudite structure. Accordingly, both structures can be represented by the general formula A(1) A(2)M(1)M(2) 2 (PO 4 ) 3 as it has been established by Moore & Ito, 1979, in the case of alluaudite related compounds. This model is written according to decreasing size of the discrete sites. Mainly, the A sites can be occupied by either mono-or divalent medium-sized cations while the M cationic site corresponds to an octahedral environment generally occupied by the transition metal cations. This fact, particularly in the case of the alluaudite structure, has offered a great field of application as positive electrode in the lithium and sodium batteries (Trad et al., 2010).
In accordance with the forefront of our research, a focus of investigation is associated with the mixed cation orthophosphates belonging to the above-mentioned compounds. Hence, by means of the hydrothermal method, we have recently synthesized and structurally characterized numerous phosphates corresponding to the general formula A(1) A(2)M(1) 2 M(2)(PO 4 ) 3 (Assani et al., 2011c). The present paper is devoted to one of them, namely, PbMn 2+ 2 Mn 3+ (PO 4 ) 3 , with manganese mixed valence, rarely encountered in the literature (Adam et al., 2009).
A partial three-dimensional plot of the crystal structure of the title compound is represented in Fig. 1, illustrating the connection of the metal-oxygen polyhedra. All atoms of this structure are in special positions, except two oxygen atoms (O3,O4) in general position of the Imma space group. The crystal structure network consists of single phosphate PO 4 tetrahedron linked to MnO 6 octahedra, building two types of chains running along the b axis. The first chain is formed by an alternating Mn III O 6 octahedron and PO 4 tetrahedron which share one vertex. The second chain is built up from two adjacent edge sharing octahedra (Mn II 2 O 10 , dimers) whose ends are linked to two PO 4 tetrahedra by a common edge. These two types of chains are linked together by common vertex of plyhedra to form porous sheets parallel to the (0 0 1) plane. The three dimensional framework delimits two types of tunnels parallel to a and b directions where the lead atoms are located as shown in Fig.2

Experimental
The crystal of the title compound is isolated from the hydrothermal treatment of the reaction mixture of lead, manganese and phosphate precursors in a proportion corresponding to the molar ratio Pb:Mn:P = 1: 3:3. The hydrothermal reaction was conducted in a 23 ml Teflon-lined autoclave, filled to 50% with distilled water and under autogeneous pressure at 483 K for five days. After being filtered off, washed with deionized water and air dried, the reaction product consists of a brown sheet shaped crystals corresponding to the title compound besides a light brown powder.

Refinement
The highest peak and the deepest hole in the final Fourier map are at 0.78 Å and 0.76 Å, respectively, from Pb1. The not significant bonds and angles were removed from the CIF file.