Syntheses, Structures, and Magnetic Properties of a Novel <i>mer</i>-[(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 <i>mer</i>-[Fe­(bbp)­(CN)₃]^2– [<b>1</b>; 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 <b>1</b> 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 (<b>2</b>), a tetranuclear compound {[Ni­(tren)]₂[Fe­(bbp)­(CN)₃]₂}·7MeOH (<b>3</b>), and a one-dimensional heterobimetallic system: {[Ni­(dpd)₂]₂[Fe­(bbp)­(CN)₃]₂}·9MeOH·3H₂O (<b>4</b>) [ntb = tris­(2-benzimidazolylmethyl)­amine, tren = tris­(2-aminoethyl)­amine, and dpd = 2,2-dimethyl-1,3-propanediamine]. The structural data shows that <b>2</b> is a linear complex in which a central Fe^III ion links two adjacent Ni^II ions via axial cyanides, while <b>3</b> is a molecular square that contains cyanido-bridged Ni^II and Fe^III ions at alternate corners. Complex <b>4</b> is a one-dimensional system that is composed of alternating cyanido-bridged Ni^II and Fe^III centers. Compounds <b>2</b>–<b>4</b> 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 <b>2</b>–<b>4