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.