Binary metal(II)-pyromellitate coordination polymers, M₂(pm) (M = Co, Fe, Mn): Synthesis, structures and magnetic properties

The hydrothermal synthesis, structures and magnetic properties of the isostructural coordination polymers _∞³[M^II₂(pm)], M = Co, Fe or Mn and pm = pyromellitate, 1,2,4,5-benzenetetracarboxylate, are described. The structure consists of ID chains of edge-sharing MO₆ octahedra that are connected into layers via O-C-O bridges. The layers are held together by the pyromellitate (pm^4-) backbone to give a 3D structure where each ligand participates in an unprecedented 12 coordination M-O bonds to ten metal atoms. The Fe and Mn analogues are antiferromagnets whereas the Co compound displays a more complex behaviour, existing in one of three magnetic ground states at low temperature (collinear antiferromagnetism, canted antiferromagnetism and field induced ferromagnetism).