BaMnII 2MnIII(PO4)3

The title compound, barium trimanganese tris(orthophosphate), was synthesized hydrothermally. Its structure is isotypic with the lead and strontium analogues AMnII 2MnIII(PO4)3 (A = Pb, Sr). Except for two O atoms on general positions, all atoms are located on special positions. The Ba and one P atom exhibit mm2 symmetry, the MnII atom 2/m symmetry, the MnIII atom and the other P atom .2. symmetry and two O atoms are located on mirror planes. The crystal structure contains two types of chains running parallel to [010]. One chain is linear and is composed of alternating MnIIIO6 octahedra and PO4 tetrahedra sharing vertices; the other chain has a zigzag arrangement and is built up from two edge-sharing MnIIO6 octahedra connected to PO4 tetrahedra by edges and vertices. The two types of chains are linked through PO4 tetrahedra into an open three-dimensional framework which contains channels parallel to [100] and [010] in which the BaII ions are located. The alkaline earth cation is surrounded by eight O atoms in the form of a slightly distorted bicapped trigonal prism.

The title compound, barium trimanganese tris(orthophosphate), was synthesized hydrothermally. Its structure is isotypic with the lead and strontium analogues AMn II 2 Mn III -(PO 4 ) 3 (A = Pb, Sr). Except for two O atoms on general positions, all atoms are located on special positions. The Ba and one P atom exhibit mm2 symmetry, the Mn II atom 2/m symmetry, the Mn III atom and the other P atom .2. symmetry and two O atoms are located on mirror planes. The crystal structure contains two types of chains running parallel to [010]. One chain is linear and is composed of alternating Mn III O 6 octahedra and PO 4 tetrahedra sharing vertices; the other chain has a zigzag arrangement and is built up from two edge-sharing Mn II O 6 octahedra connected to PO 4 tetrahedra by edges and vertices. The two types of chains are linked through PO 4 tetrahedra into an open three-dimensional framework which contains channels parallel to [100] and [010] in which the Ba II ions are located. The alkaline earth cation is surrounded by eight O atoms in the form of a slightly distorted bicapped trigonal prism.

Comment
Investigating functional compounds by means of the hydrothermal process, particularly phosphates, we have succeeded to synthesize and structurally characterize new mixed-cation orthophosphates with open frameworks, e.g. the isotypic pair Ag 2 M 3 (HPO 4 )(PO 4 ) 2 (M = Co, Ni) (Assani et al., 2011a,b) that is closely related to the alluaudite structure. Others investigated phosphates include compounds crystallizing in the AMn II 2 Mn III (PO 4 ) 3 (A = Pb, Sr) structure type (Alhakmi et al. (2013a,b) with rarely observed mixed-valent Mn II/III cations (Adam et al., 2009). The present article reports on synthesis and crystal structure of the isotypic barium analogue, BaMn II 2 Mn III (PO 4 ) 3 . All atoms of this structure are in special positions, except two oxygen atoms (O3, O4) in general position of space group Imma. The connection of the metal-oxygen polyhedra, viz. BaO 8 polyhedra, MnO 6 octahedra and PO 4 tetrahedra is shown in Fig. 1. The framework of the crystal structure consists of two isolated PO 4 tetrahedra linked to MnO 6 octahedra, building two types of chains running along [010]. The first chain is formed by alternating Mn III O 6 octahedra and PO 4 tetrahedra sharing vertices. The second chain is built up from two edge-sharing Mn II O 6 octahedra leading to the formation of Mn II 2 O 10 dimers that are connected to two PO 4 tetrahedra by a common edge. These two types of chains are linked together by common vertices of PO 4 tetrahedra to form an open three-dimensional framework that delimits two types of tunnels parallel to [100] and [010] where the Ba II ions are located (Fig. 2). The coordination sphere of the Ba II ion is that of a bicapped trigonal prism.

Experimental
The hydrothermal treatment of a reaction mixture of barium, manganese and phosphate precursors in a proportion corresponding to the molar ratio Ba: Mn: P = 1: 3: 3 has allowed to isolate brown block-shaped crystals corresponding to the title compound as well as a parallelepipedic colourless crystals which were identified to be the known manganese phosphate Mn 5 (HPO 4 ) 2 (PO 4 ) 2 . 4H 2 O (Moore & Araki, 1973). The hydrothermal reaction was conducted in a 23 ml Teflonlined autoclave, filled to 50% with distilled water and under autogeneous pressure at 463 K for five days.

Refinement
The highest peak and the deepest hole in the final Fourier map are at 0.82 Å and 1.00 Å away from Ba1.

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 cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes. Refinement. Refinement of F 2 against all reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on all data will be even larger.