Crystal structure of BaMnB₂O₅ containing structurally isolated manganese oxide sheets

In an attempt to search for mixed alkaline-earth and transition metal pyroborates, the title compound, barium manganese(II) pyroborate, has been synthesized by employing a flux method. The structure of BaMnB2O5 is composed of MnO5 square pyramids that form Mn2O8 dimers by edge-sharing and of pyroborate units ([B2O5]^4-) that are composed of two corner-sharing trigonal-planar BO3 units. These building blocks share corners to form ∞ ²[MnB2O5]^2- layers extending parallel to (100). The Ba²⁺ cations reside in the gap between two manganese pyroborate slabs with a coordination number of nine. The title compound forms an interesting spiral framework propagating along the 21 screw axis. The structure is characterized by two alternating layers, which is relatively rare among known transition-metal-based pyroborate compounds.