Characterization, redox properties and structures of the iron nitridocarbonyl clusters [Fe4N(CO)11{PPh(C5H4FeC5H5)2}]–, [Fe6N(CO)15]3– and [Fe6H(N)(CO)15]2–

The redox condensation of [Fe2(C0)'l2- with [Fe,N(CO),,] - yielded the cluster [Fe,N(CO), ,I3 - . Singlecrystal X-ray analysis showed it to possess an octahedral metal cage, with an interstitial nitride ligand. Under the D, idealized symmetry, all iron vertices are equivalent, being bound to one edge-bridging and two terminal carbonyls. The ion [Fe6N(CO)l,]3- can be oxidized to [Fe,N(~O),,]- or protonated to the hydridic dianion [Fe6H(N)(C0),,]2-. The molecular structure of the latter was determined, and is strikingly similar to that of the parent trianion. Small deformations of the ligand shell or elongations of the Fe-Fe distances are not sufficient to determine the location of the hydride. Electrochemical experiments were consistent with the chemical findings, showing that [Fe,N(CO), ,] - undergoes three irreversible one-electron oxidation steps, ultimately generating [Fe,N(CO),,] -. A lifetime of about 15 s was evaluated for the transient radical [Fe,N(CO), ,I2 - . Thermal activation induces substitution of one carbonyl ligand of [Fe,N(CO),,] - by PPh(C,H,FeC,H,),, yielding [Fe,N(CO), {PPh(C,H,FeC,H,),}] -, the molecular structure of which was also determined. The cluster adopts a butterfly arrangement of iron atoms, having an exposed u,-N atom and the phosphine ligand at a wingtip position. Cyclic voltammetry showed that communication between the two ferrocenyl units of the ligand PPh(C5H4FeCSH5), is rather low in the free state, and is notably improved by co-ordination to the tetrairon cluster. The lSN-labelled [Fe,N(CO), ,I3 - and [Fe,H(N)(CO), ,I2 - complexes were synthesized, and the NMR chemical shifts and IR bands of the interstitial p6-N ligands measured.