The co-ordination of the six-membered crown thioethers 1,3,5-trithiane, 2-methyl-, 2,4-dimethyl-, 2,4,6-trimethyl-, 2-benzyl- and 2,4,6-tribenzyl-1,3,5-trithiane and the nine-membered crown thioether 1,4,7-trithiacyclononane to the cobalt skeleton of various Co₃C clusters was studied. With trithiane and its derivatives complexes of the type [Co₃(CO)₆(µ₃-SCHR¹SCHR²SCHR³)](R = Cl, Me or Ph; R¹– R³= H, Me or CH₂Ph) were obtained, whereas the nine-membered crown thioether gave compounds of the type [Co₃(CO)₅(µ-CO)(µ₃-CR){(SCH₂CH₂)₃}]. The molecular and crystal structures of several representatives have been investigated by single-crystal X-ray diffraction. It has been shown that the trithiane ligand invariably occupies the axial co-ordination sites on the three cobalt atoms, while the trithiacyclononane chelates on one cobalt atom. The intermolecular networks of hydrogen-bonding interactions of the C–H ⋯ O type between the thioether hydrogens and the CO ligands have been investigated and compared with those present in other crystalline clusters carrying thioether ligands.