Crystal structure of BaMn2(AsO4)2 containing discrete [Mn4O18]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 BaMn2(AsO4)2 is made up of MnO6 octa-hedra and AsO4 tetra-hedra assembled by sharing corners and edges into infinite slabs with composition [Mn2(AsO4)2]2- that extend parallel to the ab 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 [Mn4O18]28- 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 SrM2(XO4)2 compounds with M = Ni, Co, and X = As, P.