Intramolecular Dynamics of Tetranuclear Iridium Carbonyl Cluster Compounds. Part III. Crystallographic and dynamic evidence for the intermediate of the ‘merry-go-round’ process in nonacarbonyl-μ3-(1,3,5-trithiane)-tetrairidium

The title complex crystallises in two C_3v, isomeric forms differing in carbonyl-ligand arrangement. In solution, the isomer 1b with three edge-bridging carbonyls on a common face of the metal tetrahedron converts via an endothermic equilibrium into the isomer 1u with no bridging carbonyls. The latter was shown by ¹³C-NMR to be the intermediate of the ‘merry-go-round’ process which exchanges the sites of the basal CO's.