Syntheses, structures, and electrochemical properties of four complexes based on 4-ferrocenylbutyrate ligand

Four ferrocenyl complexes with the formulas {[Mn(η2-OOC(CH2)3Fc)2(bbbm)]·CH3OH}n (1), {[Co(OOC(CH2)3Fc)(η2-OOC(CH2)3Fc)(bbbm)]·CH3OH}n (2), {[Ni(OOC(CH2)3Fc)2(bbbm)(CH3OH)2]·2CH3OH}n (3) and [Pb6(μ2-OOC(CH2)3Fc)2(μ3-OOC(CH2)3Fc)2(μ2-η2-OOC(CH2)3Fc)2(η2-OOC(CH2)3Fc)2(μ4-O)2] (4) (Fc = (η5-C5H5)Fe(η5-C5H4), bbbm = 1,1-(1,4-butanediyl)bis-1H-benzimidazole) have been synthesized and characterized by single crystal X-ray diffraction. Owing to the different conformations of the bbbm units in complexes 1 (or 2) and 3, complexes 1 and 2 possess 1D helical chain structure with 21 screw axes along the b-direction, while complex 3 shows a 1D linear chain structure with ferrocenylbutyrate groups hanging on the chain. Complex 4 is a hexanuclear complex and exhibits a nano-scale wheel-like framework with six Pb(II) ions as a core and eight 4-ferrocenylbutyrate ligands as branches. The cyclic voltammetric studies show that the formal potentials of the four complexes are close to the free ferrocenylbutyrate ligand, which indicates that the coordination of the metal ions to the ferrocenyl ligand does not have significant effects on the redox potential of the ferrocenylbutyrate ligand. Further investigations suggest that the redox processes of the ferrocenylbutyrate ligand and complexes 1–4 are all chemically quasi-reversible processes and controlled by diffusion.