Dipotassium trimanganese(II) tetrakis(hydrogenphosphite), K2[Mn3(HPO3)4].

The title compound is a new mixed alkali/3d metal phosphite. It exhibits a layered structure formed by linear Mn(3)O(12) trimer units which contain face-sharing MnO(6) octahedra interconnected by (HPO(3))(2-) phosphite oxoanions. The K(+) cations located between the anionic [Mn(3)(HPO(3))(4)](2-) sheets are ninefold coordinated. The presence of the alkaline ion leads to the highest symmetry and shortest interlayer distance compared with two previous compounds showing the same anionic framework and having ammonium salts as cations. The compound crystallizes in the space group R3m, with two crystallographically independent Mn atoms occupying sites of 3m and 3m symmetry. All the other atoms, except for the phosphite O atoms, are located on special positions with 3m symmetry.