Cyanide-Bridged Mn(III)−Fe(III) Bimetallic Complexes Based on the Pentacyano(1-methylimidazole)ferrate(III) Building Block:  Structure and Magnetic Characterizations

Seven cyanide-bridged bimetallic complexes have been synthesized by the reaction of [Fe(1-CH<sub>3</sub>im)(CN)<sub>5</sub>]<sup>2-</sup> with Mn(III) Schiff base complexes. Their crystal structure and magnetic properties have been characterized. Five complexes, [Mn<sub>2</sub>(5-Brsalen)<sub>2</sub>Fe(CN)<sub>5</sub>(1-CH<sub>3</sub>im)]·H<sub>2</sub>O (<b>1</b>), [Mn<sub>2</sub>(5-Clsalen)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>Fe(CN)<sub>5</sub>(1-CH<sub>3</sub>im)]·H<sub>2</sub>O (<b>2</b>), [Mn<sub>2</sub>(5-Clsaltn)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>Fe(CN)<sub>5</sub>(1-CH<sub>3</sub>im)] (<b>3</b>), [Mn<sub>2</sub>(5-Clsaltmen)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>Fe(CN)<sub>5</sub>(1-CH<sub>3</sub>im)]·H<sub>2</sub>O (<b>4</b>), and [Mn<sub>2</sub>(5-Brsaltmen)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>Fe(CN)<sub>5</sub>(1-CH<sub>3</sub>im)]·CH<sub>3</sub>OH (<b>5</b>), are neutral and trinuclear with two [Mn(SB)]<sup>+</sup> (SB<sup>2-</sup> = Schiff base ligands) and one [Fe(1-CH<sub>3</sub>im)(CN)<sub>5</sub>]<sup>2-</sup>. Complex {[Et<sub>4</sub>N][Mn(acacen)Fe(CN)<sub>5</sub>(1-CH<sub>3</sub>im)]}<i><sub>n</sub></i>·6nH<sub>2</sub>O (<b>6</b>) is one-dimensional with alternate [Mn(acacen)]<sup>+</sup> and [Fe(CN)<sub>5</sub>(1-CH<sub>3</sub>im)]<sup>2-</sup> units. The two-dimensional complex {[Mn<sub>4</sub>(saltmen)<sub>4</sub>Fe(CN)<sub>5</sub>(1-CH<sub>3</sub>im)]}<i><sub>n</sub></i>[ClO<sub>4</sub>]<sub>2</sub><i><sub>n</sub></i>·9<i>n</i>H<sub>2</sub>O (<b>7</b>) consists of Mn<sub>4</sub>Fe units which are further connected by the phenoxo oxygen atoms. Magnetic studies show the presence of ferromagnetic Mn(III)−Fe(III) coupling in the trinuclear compounds with the magnetic coupling constant (<i>J</i>) ranging from 4.5 to 6.0 cm<sup>-1</sup>, based on the Hamiltonian <i>Ĥ</i> = −2<i>J</i><i>Ŝ</i><sub>Fe</sub>(<i>Ŝ</i><sub>Mn(1)</sub> + <i>Ŝ</i><sub>Mn(2)</sub>). Antiferromagnetic interaction has been observed in complex <b>6</b>, whereas ferromagnetic coupling occurs in complex <b>7</b>. Complexes <b>6</b> and <b>7</b> exhibit long-range magnetic ordering with a <i>T</i><sub>N</sub> value of 4.0 K for <b>6</b> and <i>T</i><sub>c</sub> of 4.8 K for <b>7</b>. Complex <b>6</b> shows metamagnetic behavior at 2 K, and complex <b>7</b> possesses a hysteresis loop with a coercive field of 500 Oe, typical of a soft ferromagnet.