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The hydrothermal synthesis, structures and magnetic properties of the isostructural coordination polymers ∞3[M2II(pm)], M=Co, Fe or Mn and pm=pyromellitate, 1,2,4,5-benzenetetracarboxylate, are described. The structure consists of 1D chains of edge-sharing MO6 octahedra that are connected into layers via O&z.sbnd;C&z.sbnd;O bridges. The layers are held together by the pyromellitate (pm4−) backbone to give a 3D structure where each ligand participates in an unprecedented 12 coordination M&z.sbnd;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). [Copyright &y& Elsevier]