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

Two cyano-bridged Ni(II)−Fe(III) complexes {(H<sub>3</sub>O)[Ni(H<sub>2</sub>L)]<sub>2</sub>[Fe(CN)<sub>6</sub>]<sub>2</sub>·[Fe(CN)<sub>6</sub>]·6H<sub>2</sub>O}<i><sub>n</sub></i> (<b>1</b><b>)</b> and [K(18-C-6)(H<sub>2</sub>O)<sub>2</sub>][Ni(H<sub>2</sub>L)]<sub>2</sub>[Fe(CN)<sub>6</sub>]<sub>3</sub>·4(18-C-6)·20H<sub>2</sub>O (<b>2</b><b>)</b> (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 <b>1</b> has a zigzag one-dimensional structure, in which two <i>trans</i>-CN<sup>-</sup> ligands of each [Fe(CN)<sub>6</sub>]<sup>3-</sup> link two <i>trans</i>-[Ni(H<sub>2</sub>L)]<sup>4+</sup> groups, and in turn, each <i>trans</i>-[Ni(H<sub>2</sub>L)]<sup>4+</sup> links two [Fe(CN)<sub>6</sub>]<sup>3-</sup> in a trans fashion. Complex <b>2</b> is composed of cyano-bridged pentanuclear molecules with moieties connected by the <i>trans</i>-CN<sup>-</sup> ligands of [Fe(CN)<sub>6</sub>]<sup>3-</sup>. 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.