Iron(II) Formate [Fe(O₂CH)₂]·1/3HCO₂H: A Mesoporous Magnet − Solvothermal Syntheses and Crystal Structures of the Isomorphous Framework Metal(II) Formates [M(O₂CH)₂]·n(Solvent) (M = Fe, Co, Ni, Zn, Mg)

Recrystallisation of iron( II ) formate dihydrate from formic acid under solvothermal conditions results in single‐crystals of the iron( II ) formate, α‐Fe(O 2 CH) 2 ·1/3HCO 2 H. The crystal structure of this phase has been determined by X‐ray diffraction and reveals an open framework structure with formic acid molecules occupying channels in the lattice which is stable even after removal of the solvent molecules. Magnetic susceptibility and Mössbauer measurements show that the compound undergoes 3D magnetic ordering below T C = 16 K. α‐Fe(O 2 CH) 2 ·1/3HCO 2 H and the corresponding magnesium, cobalt, nickel and zinc formates form an isomorphous series. In contrast to the iron compound, the magnetic behaviour of the cobalt analogue is dominated by antiferromagnetic interactions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)