Fe-Cu octahedral carbide clusters and the replacement of their labile halide ligands: Synthesis, solid state structure, substitution and electrochemnical reactivity of [Fe5C(CO)14(CuBr)]2-,[Fe4C(CO)12(CuCl)2]2-, è(Fe4Cu2C(CO)12(mu-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(-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 deriv. [Fe5C(CO)14(CuBr)]2- (4) or the solvento complexes [Fe5C(CO)14(Cu(THF))]- (5) and [Fe4C(CO)12(Cu(NCMe))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 Cu atoms in a pseudo-linear geometry, where one of the coordination positions is occupied by the interstitial carbide. The two Cu atoms in the Fe4Cu2 clusters are always in cis geometry and, in the dimer [{Fe4Cu2C(CO)12(-Cl)}2]2-, they are joined through chlorides. The role of the different metal centers in detg. the redox activity of the heteronuclear Fe-Cu clusters 1, 2, and 3 was studied by electrochem. methods. In the chloro bridged dimer 3, the two Fe4Cu2C cluster units resulted electronically not communicating.