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.

Metallacycles of increasing size were obtained by reaction of octahedral Fe/Cu/C clusters and anionic ligands, with different donor atoms (O, N, S). They were characterized by X-ray determination IR, 1H NMR and electrochemical studies. The carbidocarbonyl clusters are stable upon electron transfer and the bridging ligand allow electronic communication.Figure optionsDownload as PowerPoint slideHighlights
► A general method for the synthesis of dimeric [Fe4(CO)12Cu2(μ-X)]n− anionic clusters.
► Spectroscopic characterization of the products.
► Solid State structure of the dimers where bridging X = pyrazolate or thiophenolate.
► Electrochemical studies, showing the redox stability of the clusters and partially correcting some previous results.
► Assessment of electronic communication between the metal cluster core, related to the π-donor abilities of the ligands.