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-CH₃im)(CN)₅]^2- with Mn(III) Schiff base complexes. Their crystal structure and magnetic properties have been characterized. Five complexes, [Mn₂(5-Brsalen)₂Fe(CN)₅(1-CH₃im)]·H₂O (1), [Mn₂(5-Clsalen)₂(H₂O)₂Fe(CN)₅(1-CH₃im)]·H₂O (2), [Mn₂(5-Clsaltn)₂(H₂O)₂Fe(CN)₅(1-CH₃im)] (3), [Mn₂(5-Clsaltmen)₂(H₂O)₂Fe(CN)₅(1-CH₃im)]·H₂O (4), and [Mn₂(5-Brsaltmen)₂(H₂O)₂Fe(CN)₅(1-CH₃im)]·CH₃OH (5), are neutral and trinuclear with two [Mn(SB)]⁺ (SB^2- = Schiff base ligands) and one [Fe(1-CH₃im)(CN)₅]^2-. Complex {[Et₄N][Mn(acacen)Fe(CN)₅(1-CH₃im)]}_n·6nH₂O (6) is one-dimensional with alternate [Mn(acacen)]⁺ and [Fe(CN)₅(1-CH₃im)]^2- units. The two-dimensional complex {[Mn₄(saltmen)₄Fe(CN)₅(1-CH₃im)]}_n[ClO₄]_2n·9nH₂O (7) consists of Mn₄Fe 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 (J) ranging from 4.5 to 6.0 cm^-1, based on the Hamiltonian Ĥ = −2JŜ_Fe(Ŝ_Mn(1) + Ŝ_Mn(2)). Antiferromagnetic interaction has been observed in complex 6, whereas ferromagnetic coupling occurs in complex 7. Complexes 6 and 7 exhibit long-range magnetic ordering with a T_N value of 4.0 K for 6 and T_c of 4.8 K for 7. Complex 6 shows metamagnetic behavior at 2 K, and complex 7 possesses a hysteresis loop with a coercive field of 500 Oe, typical of a soft ferromagnet.