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)].6H(2)O}(n) (1) and [K(18-C-6)(H2O)2]-[Ni(H2L)](2)[Fe(CN)(6)](3).4(18-C-6).20H(2)O (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.