Host–guest properties of the trinuclear arene–ruthenium cluster cation [H₃Ru₃(C₆H₆)(C₆Me₆)₂(O)]⁺

The trinuclear arene–ruthenium cluster cation [H₃Ru₃(C₆H₆)(C₆Me₆)₂(O)]⁺, containing a μ₃-oxo cap and three arene ligands that span a hydrophobic pocket above the metal skeleton, has been crystallised as tetrafluoroborate salt in the presence of various guest molecules. The host–guest complexes have been characterised by single-crystal X-ray structure analysis. With chloroform as the guest molecule, a CHCl₃ molecule sits perfectly in the hydrophobic pocket, the hydrogen atom being encapsulated inside the cavity. When dioxane is added during the crystallisation process, the cluster forms infinite chains which are connected by a complex network of hydrogen bonds involving the μ3-oxo ligand, water and dioxane molecules. Interestingly, in the presence of phenol, a water molecule is hydrogen-bonded between the μ₃-oxo ligand and the phenol molecule, forming a one-dimensional μ₃-O … H₂O … HO hydrogen-bonded chain. Finally, with benzoic acid, a head-to-tail host–guest chain is obtained, the phenyl ring being incorporated in the hydrophobic pocket, while the acid group is hydrogen-bonded to the μ3-oxo ligand.