Magnesia-Supported Tetrairidium Clusters Derived from [Ir4(CO)12]

The chemistry of iridium clusters formed from [Ir[sub 4](CO)[sub 12]] on basic MgO surfaces was investigated with infrared and extended X-ray absorption fine structure (EXAFS) spectroscopies. The chemistry of iridium carbonyls on MgO is comparable to that of iridium carbonyls in basic solutions. The adsorption of [Ir[sub 4](CO)[sub 12]] on MgO with high, intermediate, and low surface hydroxyl group concentrations led to the formation of structures that are suggested on the basis of infrared spectra to be [Ir[sub 4](CO)[sub 11]COH(O)]. [HIr[sub 4](CO)[sub 1 1]][sup [minus]], and [Ir[sub 8](CO)[sub 22]][sup 2[minus]], respectively, where (O) represents oxygen of the MgO surface. Decar bonylation of the iridium carbonyl clusters on MgO led to the formation of iridium clusters. The reaction of [[sub 4](CO)[sub 12]] with highly dehydroxylated MgO followed by treatment in flowing He at 325[degree]C for 2 h and flowing H[sub 2] at 300[degree]C for 2 h at 1 atm led to formation of clusters that are modeled on the basis of EXAFS spectra as predominantly Ir[sub 4] tetrahedra. The reactions of [Ir[sub 4](CO)[sub 12]] with highly hydroxylated MgO followed by treatment in flowing He at 325[degree]C for 2 h and flowing H[sub 2] at 300[degree]C for 2 h at 1 atmmore » led to the formation of larger iridium clusters, with average diameters of about 12 A. 56 refs., 8 figs., 4 tabs.« less