The cluster [H2OS4(CO)(13)] may be reduced with K/Ph2CO to generate an anion which reacts with [M(eta(6)-C6H5R)(MeCN)(3)](2+) (M=Os. Ru: R=H. Me) affording the capped clusters [H2OS4M(CO)(12)(eta(6)-C6H5R)] (M=Os, R=H (1); M=Ru, R=H (2); M=Os. R=Me (3)) with the arene ligand on one of the axial site of a trigonal bipyramid. The Os clusters 1 and 3 transform into the more stable equatorial isomers, 4 and 5, respectively, in 24 h. The structure of 5 has been confirmed by a single crystal X-ray diffraction study, and all the complexes have been characterised spectroscopically. The axial isomers may be carbonylated or hydrogenated to generate the edge-bridged tetrahedral clusters [H2OS4M(CO)(13)(eta(6)-C6H5R)] (M=Os, R=H (6); M=Ru, R=H (7); M=Os, R=Me (8)) and the known clusters [H4OS4M(CO)(12)(mu(6)-C6H6)] (M=Os (9); Ru (10)). The structure of 7 has been confirmed by an X-ray diffraction analysis. The axial isomer 1 reacts with PPh2Me to yield the addition product [H2Os5(CO)(12)(eta(6)-C6H6)PPh2Me] (11), whereas the mixed osmium-ruthenium analogue undergoes a transformation to the 'spiked' tetrahedral [H3Os4Ru(CO)(12)(mu(3)-sigma,sigma,eta(6)-C6H5)PPh2Me] (12). Deprotonation of the axial isomers 1 and 2 and subsequent reaction with [AuPPh3](+) yields [HOs4M(CO)(12)(C6H6)(AuPPh3)] (M=Os (13); Ru (14)). As well as spectroscopic characterisation cluster, the structures of 11, 12 and 13 have been established by X-ray diffraction experiments. In a related series of reactions the cluster monoanion [Os-4(CO)(13)X](-) (X=Cl (15), Br (16), I(17)) may be capped using the monocation [Ru(eta(5)-C5H5)(MeCN)(3)](+) affording [HOs4Ru(CO)(13)(eta(5)-C5H5)] (18), which is readily deprotonated and further capped with [AuPPh3](+) to afford the neutral cluster [Os-4(CO)(13)Ru(eta(5)-C5H5)AuPPh3] (20). The structures of 15, 18 and 20 have been established crystallographically. The cluster anion [Os-4(CO)(13)X](-) may be reduced with K/Ph2CO and the resulting anionic complex coupled with [Ru(eta(5)-C5H5)(MeCN)(3)](+), providing another route to [Os4Ru(CO)(13)(eta(5)-C5H5)](-) (19). This anionic complex may also be coupled with [Ru(eta(6)-C6H6)(MeCN)(3)](2+) affording [Os4Ru(CO)(13)(eta(6)-C6H6)] (21) which has also been structurally characterised. (C) 2003 Elsevier Science B.V. All rights reserved.