sentences:  These isomers are sometimes termed Baker, Baker-Figgis or rotational isomers, These involve different rotational orientations of the Mo3O13 units, which lowers the symmetry of the overall structure.The term "lacunary" is applied to ions which have a fragment missing, sometimes called defect structures.Examples are the (XM11O39)"n"− and (XM9O34)"n"− formed by the removal from the Keggin structure of sufficient Mo and O atoms to eliminate 1 or 3 adjacent MO6 octahedra.