Spectroscopic investigation of the interaction of Co2(CO)8 with MgO and SiO2

Co2(CO)8, when absorbed in the gas phase, in vacuo, on fully dehydrated MgO, forms a variety of carbonyl clusters both neutral and ionic. These clusters disintegrate into monometallic species upon dosing with either CO or NH3, resulting in Co(CO)4- and Co2+(CO)n (n = 2 or 3) with CO and Co(CO)4- and Co2+(NH3)6 with NH3, respectively. The negatively charged species are formed via several routes, including disproportionation and nucleophilic attack by O2- on the carbonyl groups of different cobalt carbonyl clusters. These effects are attributed to the strongly basic nature of the highly dehydroxylated magnesia used in the present investigation. Diffuse reflectance and e.s.r. spectral studies performed in similar conditions on magnesia confirm all these transformations. The results on a highly dehydrated SiO2 surface are quite different: Co2(CO)8 is mostly adsorbed without appreciable chemical modification, giving two isomers containing linear and bridged CO. Only by removing CO by outgassing at the beam temperature, is the total transformation into Co4(CO)12 and possibly Co6(CO)12 observed.