Effects of ligand substitution on the metal-metal bonding in triosmium carbonyl clusters. The crystal and molecular structures of Os₃(μ₃-S)₂(CO)₉ and Os₃(μ₃-S)₂(CO)₈PMe₂Ph

The molecular structures of the compounds Os₃(μ₃-S)₂(CO)₉, I, and Os₃(μ₃-S)₂(CO)₈PMe₂Ph, II, have been determined by single-crystal X-ray diffraction methods. For I: space group P1, a = 6.745 (2) Å, b = 9.503 (2) Å, c = 13.592 (3) Å, α = 82.42 (2)°, β = 84.58 (2)°, γ = 69.61 (2)°; V = 808.4 (4) ų, Z = 2, ρ_calcd = 3.64 g/cm³. The structure was solved by a combination of Patterson and difference Fourier techniques. Full-matrix least-squares refinement on 2137 reflections (F_o² ≥ 3.0σ(F)₂) yielded the final residuals R_F = 0.032 and R_wF = 0.038. The molecule contains an open triangular cluster of three metal atoms with two equivalent metal-metal bonds Os(1)-Os(2) = 2.814 (1) Å and Os(1)-Os(3) = 2.812 (1) Å. There are two inequivalent triply bridging sulfido ligands, and each metal atom has three linear terminal carbonyl ligands. For II: space group P1, a = 9.316 (2) Å, b = 11.346 (1) Å, c = 13.592 (3) Å, α = 71.65 (1)°, β = 71.63 (2)°, γ = 79.67 (1)°, V = 1164.5 (3) ų, Z = 2, ρ_calcd = 2.84 g/cm³. This structure was solved by a combination of Patterson and difference Fourier techniques. Full-matrix least-squares refinement on 2834 reflections (F_o² ≥ 3.0σ(F)₂) yielded the final residuals R_F = 0.040 and R_wF = 0.041. The structure of II is similar to that of I except that a PMe₂Ph ligand has been substituted for an equatorially positioned carbonyl ligand on one of the exterior metal atoms of the cluster in a position trans to one of the metal-metal bonds. The two metal-metal bonds are significantly different. The one trans to the phosphine ligand is 2.856 (1) Å while the other is 2.770 (1) Å. The structures of I and II are compared with that of Os₃(μ₃-S)₂(CO)₈CS, III, which shows distortions in the metal-metal bonding that are similar to II. The cause of these distortions is attributed to a trans influence of the substituted ligand and is believed to be largely σ inductive in nature. © 1983 American Chemical Society.