Fe-Cu octahedral carbide clusters, and the replacement of their labile halide ligands: synthesis, solid state structure, substitution and electrochemical reactivity of [Fe5C(CO)14(CuBr)]2-, [Fe4C(CO)12(CuCl)2]2-, [{Fe4Cu2C(CO)12(m-Cl)}2]2-, [Fe5C(CO)14(CuOC4H8)]- and [Fe4C(CO)12(CuNCMe)2]

The reactions between [Fe6C(CO)16]2− and CuCl, in refluxing THF, yield [Fe5C(CO)14(CuCl)]2− (1), [Fe4C(CO)12(CuCl)2]2− (2), or [{Fe4Cu2C(CO)12(μ-Cl)}2]2− (3), depending on the Fe6/CuCl ratio. The chloro ligands of these clusters can be displaced either spontaneously, or by metal-assisted substitution, to give the bromo derivative [Fe5C(CO)14(CuBr)]2− (4) or the solvento complexes [Fe5C(CO)14(CuTHF)]− (5) and [Fe4C(CO)12(CuNCMe)2] (6). The latter can be also obtained directly, by metal substitution from [Fe6C(CO)16]2− and [Cu(NCMe)4]BF4, or by polyhedral expansion from [Fe4C(CO)12]2−. All the clusters are octahedral, with the copper atoms in a pseudo-linear geometry, where one of the coordination positions is occupied by the interstitial carbide. The two copper atoms in the Fe4Cu2 clusters are always in cis geometry and, in the dimer [{Fe4Cu2C(CO)12(μ-Cl)}2]2−, they are joined through chlorides. The role of the different metal centres in determining the redox activity of the heteronuclear Fe–Cu clusters 1, 2, 3, has been studied by electrochemical methods. In the bridged dimer 3, the two Fe4Cu2C cluster units resulted electronically not communicating.