Syntheses, Structures, and Magnetic Properties of a Novel mer-[(bbp)Fe^III(CN)₃]^2– Building Block (bbp: bis(2-benzimidazolyl)pyridine dianion) and Its Related Heterobimetallic Fe(III)–Ni(II) Complexes

A new symmetrical tricyanide building block mer-[Fe­(bbp)­(CN)₃]^2– [1; bbp = bis­(2-benzimidazolyl)­pyridine dianion] has been prepared and structurally and magnetically characterized. It forms a new low-spin meridionally capped {Fe^IIIL­(CN)₃} fragment with the tridentate bbp ligand. The reaction of 1 with Ni^II salts in the presence of various ancillary ligands affords several new cyanido-bridged complexes: a trinuclear complex {[Ni­(ntb)­(MeOH)]₂[Fe­(bbp)­(CN)₃]­[ClO₄]₂}·2MeOH (2), a tetranuclear compound {[Ni­(tren)]₂[Fe­(bbp)­(CN)₃]₂}·7MeOH (3), and a one-dimensional heterobimetallic system: {[Ni­(dpd)₂]₂[Fe­(bbp)­(CN)₃]₂}·9MeOH·3H₂O (4) [ntb = tris­(2-benzimidazolylmethyl)­amine, tren = tris­(2-aminoethyl)­amine, and dpd = 2,2-dimethyl-1,3-propanediamine]. The structural data shows that 2 is a linear complex in which a central Fe^III ion links two adjacent Ni^II ions via axial cyanides, while 3 is a molecular square that contains cyanido-bridged Ni^II and Fe^III ions at alternate corners. Complex 4 is a one-dimensional system that is composed of alternating cyanido-bridged Ni^II and Fe^III centers. Compounds 2–4 display extensive hydrogen bonding and moderately strong π–π stacking interactions in the solid state. Magnetic studies show that ferromagnetic exchange is operative within the Fe^III_LS(μ-CN)­Ni^II units of 2–4.