Steric and Electronic Influences in Os₃(CO)₁₁(PR₃) Structures

The structures of Os₃(CO)₁₁(PR₃) with R = F, OPh, Et, p-C₆H₄Me, o-C₆H₄Me, p-C₆H₄(CF₃) and C₆H₁₁, and with PR₃ = P(OCH₂)₃CMe have been determined. The Os-Os bond lengths in these compounds are compared to the Os-Os lengths for the other structures of Os₃(CO)₁₁(PR₃) clusters reported in the literature. In most cases, the Os-Os bond length remote from the P ligand [range, 2.8666(4)-2.9044(4) Å] and that in the pseudo-trans position [range, 2.8712(5)-2.900(1) Å] show little variation as the steric and electronic properties of the P ligand are varied. The Os-Os length cis to PR₃ shows more variation [range, 2.879(1)-2.9429(4) Å] and is sensitive to both the size and the σ-donor/π-acceptor properties of the PR₃ ligand: larger or better donor PR₃ ligands cause an increase in the Os-Os bond length. The Os-P distances [range, 2.15(2)-2.478(1) Å] show a similar dependence on the steric and electronic properties of the PR₃ ligand.