Synthesis and characterisation of the carboxylate linked osmium clusters [{Os3H(CO)10}2(CO2CH2CO2)], [{Os3H(CO)10}2(CO2C2H4CO2)], [{Os3H(CO)10}2(C4O4)] and [{Os3H(CO)10}2(C4O4){Co2(CO)6}]

Reactions between the activated cluster [Os3(CO)10(NCMe)2] and malonic acid, succinic acid and dicarboxylic acetylene, respectively, lead to the formation of the linked cluster complexes [{Os3H(CO)10}2(CO2CH2CO2)] (1), [{Os3H(CO)10}2(CO2C2H4CO2)] (2), and [{Os3H(CO)10}2(C4O4)] (3) in good yield. Cluster 3 was subsequently treated with [Co2(CO)8] and this results in the addition of a “Co2(CO)6” group giving [{Os3H(CO)10}2(C2O4){Co2(CO)6}] (4). The X-ray crystal structures are reported for 2–4. In each structure the two triangular triosmium units are linked by the carboxylate groups and within each complex the carboxylate groups are chelating and bridge two osmium atoms.