Cyclic dimers of variable size, formed from FeCu carbide clusters: Synthesis, structure and electrochemical behaviour of [{Fe4C(CO)12Cu2(μ-X)}2]n−, (X = phenylthiolate, pyrazolate, (n = 2) or diphenolate (n = 4))

The reaction of [Fe4C(CO)12(CuNCMe)2] with anionic units in 1:1 molar ratio systematically yields cyclic dimers of composition [{Fe4C(CO)12Cu2(μ-X)}2]n−, where X are bridging ligands with different size, donor atom and charge: {X = phenylthiolate, PhS−, (n = 2 (1)), pyrazolate, C3H3N2−, (n = 2 (2)), diphenolate, (O–C6H4–C6H4–O2−, n = 4 (3)}. All anions have been characterized by elemental analysis, IR and 1H NMR spectroscopy and by single crystal X-ray diffraction. They share the same structure with the known anion [{Fe4C(CO)12Cu2(μ-Cl)}2]2− (X = Cl, (4)), with the obvious difference in the size of the ring, depending on the number of atoms in the spacer. All these macrocycles display rich electrochemical behaviour, undergoing two reversible reductions and two irreversible monoelectronic oxidations, poorly affected by the substituent and therefore assigned to the Fe4C core. Electronic communication increases in the order 3 ≈ 4 > 1 > 2.