Iron-nickel mixed metal nitrido clusters: Synthesis and solid state structure of the anions [HFe5NiN(CO)14]2- and [HFe4Ni2N(CO)13]2-

The two clusters [HFe5NiN(CO)14]2- (1) and [HFe4Ni2N(CO)13]2- (2) were obtained by reaction of [Fe4N(CO)12]- and [Ni6(CO)12]2- in refluxing MeCN and EtCN, respectively, along with other Fe-Ni mixed metal clusters. Their solid state structures were determined on the [PPh4]+ salts, and both have an octahedral metal cage, containing an interstitial nitrogen atom. The two Ni atoms in 2 are cis, with a Ni-Ni separation of 2.724(1) Å. The two anions have different stereochemistry of the carbonyl ligands: in 1, five CO's are semi-bridging, and the remaining nine are terminal; in 2 there are three asymmetric bridging and ten terminal ligands (two for each iron and one for each nickel). The hydride ligands were located in the final difference maps, both bridging a Ni-Fe edge of the clusters but, thanks to the better quality of the diffraction data, the metal-hydrogen distances were refined only in 2. In this cluster, the Fe-H and Ni-H bond lengths are 1.77(2) and 1.79(2) Å, respectively.