From One-dimensional Chain to Pentanuclear Molecule. Magnetism of Cyano-Bridged Fe(III)−Ni(II) Complexes

Two cyano-bridged Ni(II)−Fe(III) complexes {(H₃O)[Ni(H₂L)]₂[Fe(CN)₆]₂·[Fe(CN)₆]·6H₂O}_n (1) and [K(18-C-6)(H₂O)₂][Ni(H₂L)]₂[Fe(CN)₆]₃·4(18-C-6)·20H₂O (2) (L = 3,10-bis(2-aminoethyl)-1,3,6,8,10,12-hexaazacyclotetradecane, 18-C-6 = 18-crown-6-ether) have been synthesized and characterized structurally and magnetically. Complex 1 has a zigzag one-dimensional structure, in which two trans-CN^- ligands of each [Fe(CN)₆]^3- link two trans-[Ni(H₂L)]⁴⁺ groups, and in turn, each trans-[Ni(H₂L)]⁴⁺ links two [Fe(CN)₆]^3- in a trans fashion. Complex 2 is composed of cyano-bridged pentanuclear molecules with moieties connected by the trans-CN^- ligands of [Fe(CN)₆]^3-. Magnetic studies show the existence of ferromagnetic Ni(II)−Fe(III) interactions in both complexes. The intermetallic magnetic coupling constant of both complexes was analyzed by using an approximate model on the basis of the structural features.