Carbonyl-nitrido mixed-metal clusters: Synthesis, reactivity, electrochemical behavior and solid-state structure of [Co5MoN(CO)(14)](2-) and [Co5MoN(CO)(14)AuPPh3](-)

The dianionic cluster [Co5MoN(CO)14]2− (1) was synthesized from [Co6N(CO)15]− and [Mo2(CO)10]2− in refluxing acetonitrile. The solid-state structure of the [Ph4P]+ salt was determined. It consists of an octahedral metal cage, enclosing a six-coordinate nitrido ligand. Typical bond lengths are: Co−N 1.88 Å, Mo−N 2.03 Å, Co−Co 2.61 Å and Co−Mo 2.84 Å, showing that there is very little, if any, preferential interaction of the interstitial atom with that of molybdenum. The cluster reacts with Au(PPh3)Cl in THF at room temperature forming the derivative [Co5MoN(CO)14{AuPPh3}]− (2). The gold atom caps an MoCo2 face of the octahedron, with short Au−Co (2.68 Å) and long Au−Mo (3.16 Å) bonds, showing that both metal atoms are necessary for coordination, but AuI binds better with the cobalt atoms. Electrochemical studies have pointed out that cluster 1 has good redox capabilities in that it is able to support reversibly the progressive addition of three electrons. EPR measurements on the corresponding trianion confirm the lack of preferential interaction between the Mo site and the interstitial nitride atom.