Lone-pair containment in closed cavities. The MT_e6O₁₃ (M = Mn, Ni, Co) family of ternary oxides

The hydrothermal and ceramic syntheses, single crystal structures and some properties of MnTe6O13, NiTe6O13 and CoTe6O13, are described. These isostructural phases [space group R (3) over bar (No. 148) with a approximate to 10.2 Angstrom and c approximate to 19 Angstrom] contain a dense network of isolated MO6 (M = Mn, Ni, Co) octahedra, TeO4 folded squares and distorted TeO4+1 square-based pyramids, sharing vertices and edges by way of M-O-Te and Te-O-Te bonds. The Te-IV lone pairs are directed into closed cavities formed from 18 Te-centred and 6 MO6 groupings. Magnetic susceptibility data for MnTe6O13, and CoTe6O13 show antiferromagnetic ordering at ca. 13 and 21 K, respectively, which must occur via a superexchange pathway.