Structural variations in the ligands around a simple oxo-centered building block, the tetrahedral [M4O]6+ unit, M=Mn and Fe

The structures of two new complexes of the anion of 2,2′-dipyridylamine (dpa) with the tetrahedral [M4O]6+ core (M=Mn, Fe) are presented. The structures are a variation of the basic beryllium acetate structure, in which a central [M4(μ4-O)]6+ unit has each of the six edges of the tetrahedron bridged by a bidentate ligand. The situation is complicated in the present case by the potentially tridentate dpa ligand, such that the third nitrogen atom coordinates to a metal atom in only three of the six ligands, forming complexes in which one metal atom is four-coordinate and three are five-coordinate. Analysis of the three-dimensional structures of the resulting Mn and Fe complexes reveals a surprising form of isomerism.