Reactions of CS₂ with metal cluster carbonyls of the iron triad: Reaction of [Os₆(CO)₁₈] and X-ray crystal structure of [Os₄(CO)₁₂(CS)S]

The reaction of [Os₆(CO)₁₈] with excess CS₂ in heptane at 165 °C under CO pressure gives the known compounds [Os₃(CO)₈(CS)S₂] (1) and [Os₃(CO)₉S₂] (2), and also [Os₄(CO)₁₂(CS)S] (3). A single crystal X-ray diffraction study shows that in (3) the four Os atoms adopt a 'butterfly' configuration, but with an Os ⋯ Os separation of 3.598(2) Å across the 'backbone', which is non-bonding. Three of the Os atoms are capped by a μ₃-S ligand, while a CS ligand, which acts as a four-electron donor, lies on the other side of the metal framework. The carbon atom of this ligand is co-ordinated to all four metal atoms but the sulphur atom is only co-ordinated to one. The molecule (3) crystallises in space group P1 with a = 14.834(6), b = l0.048(5), c = 7.682(5) Å, α = 108.84(3), β = 92.99(3), γ = 95.64(3)° and Z = 2. The structure was solved by a combination of direct methods and Fourier difference techniques, and refined by blocked-cascade least squares to R = 0.058 for 3 249 observed diffractometer data.