CHARACTERIZATION OF DECAOSMIUM CARBIDO CARBONYL CLUSTERS SUPPORTED ON MGO

Supported decaosmium carbido carbonyl clusters were prepared by surface-mediated organometallic synthesis from chloroosmium complexes on MgO and by adsorption of [Os10C(CO)24]2- onto thermally activated MgO from THF solution. The supported clusters have been characterized by extended X-ray absorption fine structure (EXAFS) spectroscopy, ultraviolet-visible diffuse reflectance (UV-vis DR) spectroscopy, and infrared spectroscopy. Transmission electron microscope (TEM) images of clusters prepared by surface-mediated synthesis have been obtained. Analysis of the Os L(III) EXAFS data indicates that each preparation yields molecularly dispersed "[Os10C(CO)24]" clusters with structures closely similar to that of the dianion in crystalline [Et4N]2[Os10C(CO)24]. The principal optical absorption of the supported clusters can be assigned to an Os-Os* --> CO "2-pi*" transition by comparison to the UV-vis spectrum of [PPN]2[Os10C(CO)24] in solution. Infrared spectra provide evidence of "[Os10C(CO)24]" clusters in oxidized and reduced states (relative to the dianion) on the MgO surfaces. Apparently, surface-mediated synthesis yields [Os10C(CO)24]n-, n = 0, 1, and 2; and adsorption of [Os10C(CO)24]2- onto MgO yields [Os10C(CO)24]n-, n = 2, 3, and 4. TEM images of supported clusters prepared by surface-mediated synthesis contain high-contrast scattering centers about 10 angstrom in size that are inferred to be decaosmium species.