Notes Preparation and X-Ray Crystal Structure of [Ru,RhH,(CO),]*

The synthesis and X-ray crystal structure determination of a new ruthenium-rhodium mixed-metal cluster [Ru,RhH,(CO),,] have been performed. The complex crystallises in the space group PT with a = 8.356(8), b = 9.261 (8), c = 13.83(1) A, C( = 82.56(7), p = 80.1 2(7), y = 68.83(7)", and Z = 2. Its 'H n.m.r. properties are also discussed. Tetranuclear mixed-metal carbonyls of ruthenium, cobalt, and rhodium form an exceptionally well defined group of cluster compounds. Of the dodecacarbonyl clusters of the type [Ru,- is entirely unknown.' The compound [CoRh,(CO),,] has been reported to be unstable., The metal combination Ru,Rh, however, is known from several clusters containing C5H5 or C5Me5 ligand~.,-~ In this work the new parent cluster [ R U , R~H , ( C O )~~] has been prepared and characterised by X-ray crystallography and 'H n.m.r. spectroscopy. Results and Discussion The crystal structure of [Ru,RhH,(CO),,J, (l), is shown in the The hydrogen atoms were placed and refined isotropically in Ru(p-H)Ru positions, which were indirectly evidenced as the hydride sites. These positions correspond to those observed in the cobalt and osmium analogues mentioned above. The metalmetal distances corresponding to the bridging hydrides (av. 293.0 pm) are clearly longer than the three others (av. 275.9 pm) and are of the size of hydride-bridged Ru-Ru bond lengths.' The carbonyls also bend away from these bridged Ru-Ru edges as a result of the steric demands of the hydrides. The cis Ru-Ru-C angles of the carbonyls 6, 7, and 11 are significantly larger (1 11.0-1 16.5, av. 113.9") than for 4, 5, 8, 9, 10, and 12 (95.8-98.0, av. 96.9"). This supports the positions of the hydrides being opposite the metal assigned as rhodium in the Computer-simulated space filling models of the cluster were also used to locate the hydrides.'' The models showed 'holes' in the carbonyl coverage only in the three directions where the hydride ligands in the Experimental The literature method was used to prepare [Rh(CO),] -.', Other reagents were obtained from commercial sources. Reactions and manipulations were carried out under a dinitrogen atmosphere using standard Schlenk-tube techniques. Infrared spectra were recorded on a Nicolet 2OSXC FT-IR spectrometer