X-Ray diffraction and magnetic studies on a series of isostructural divalent metal chloranilates with zigzag polymeric chain structures and on a dinuclear iron(III) chloranilate

Abstract

The reaction of iron(III) ion with chloranilic acid (2,5-dichloro-3,6-dihydroxycyclohexa-2,5-diene-1,4-dione) in hot aqueous solution in air generated a product in which the iron, surprisingly, is in the +II oxidation state as is indicated by structural, magnetic and Mössbauer spectral studies. Single crystal X-ray studies of the product of composition [Fe(C₆Cl₂O₄)(H₂O)₂]·H₂O reveal a 1-dimensional zigzag polymeric structure with iron(II) ions carrying two cis water ligands linked together by bridging chloranilate anions. Hydrogen bonding between lattice water and the chains, together with close stacking of C₆Cl₂ units from adjacent chains, leads to a very compact 3-dimensional network. The same product can be generated directly from iron(II) ion. Weak ferromagnetic coupling between high spin iron(II) centres with J = +0.47 cm⁻¹ is observed. Isostructural crystalline materials can be obtained in which Fe^II has been replaced by Mn^II, Zn^II and Cd^II, a complete structural refinement being carried out in the latter case. Very weak antiferromagnetic coupling between high spin metal centres is observed in the manganese case (J = −0.17 cm⁻¹). The structure of a previously reported iron(III) chloranilate, [Fe₂(C₆Cl₂O₄)₃(H₂O)₄]·4H₂O, has been determined by single crystal X-ray diffraction, revealing a dinuclear structure with one bridging chloranilate, two cis water ligands and one chelating, “terminal” chloranilate per iron(III) centre.