Crystal structure of BaMn 2 (AsO 4 ) 2 containing discrete [Mn 4 O 18 ] 28- units

In our attempt to search for mixed alkaline-earth and transition metal arsenates, the title compound, barium dimanganese(II) bis-(arsenate), has been synthesized by employing a high-temperature RbCl flux. The crystal structure of BaMn (AsO ) is made up of MnO octa-hedra and AsO tetra-hedra assembled by sharing corners and edges into infinite slabs with composition [Mn (AsO ) ] that extend parallel to the plane. The barium cations reside between parallel slabs maintaining the inter-slab connectivity through coordination to eight oxygen anions. The layered anionic framework comprises weakly inter-acting [Mn O ] tetra-meric units. In each tetra-mer, the manganese(II) cations are in a planar arrangement related by a center of inversion. Within the slabs, the tetra-meric units are separated from each other by 6.614 (2) Å (Mn⋯Mn distances). The title compound has isostructural analogues amongst synthetic Sr ( O ) compounds with = Ni, Co, and = As, P.