2 CHLORO-BRIDGED OSMIUM CLUSTERS

The molecular structure of the chloro-bridged tetraosmium cluster, dod ecacarbonyl-1 kappa(3)C, 2 kappa(3)C, 3 kappa(3)C, 4 kappa(3)C-mu-chlo ro-3:4 kappa(2)Cl-tris-mu-hydrido-1:2 kappa(2)H; 1:3 kappa(2)H; 2:4 ka ppa(2)H-tetraosmium(5 Os-Os), [Os-4(mu-Cl)(mu-H)(3)(CO)(12)], consists of a 'butterfly' arrangement of Os atoms, just as in the iodo analogu e. The chloro bridge in the tetraosmium cluster is symmetric, whereas in the pentaosmium cluster, tetradecacarbonyl-1 kappa(3)C, 2 kappa(2)C , 3 kappa(3)C, 4 kappa(3)C, 5 kappa(3)-mu-chloro-2:5 kappa(2)Cl-tris-m u-hydrido-1:2 kappa(2)H; 2:3 kappa(2)H; 2:4 kappa(2)H-pentaosmium(8 Os -Os), [Os-5(mu-Cl)(mu-H)(3)(CO)(14)], it is distinctly asymmetric. Thi s asymmetry is attributed to the trans influence of a carbonyl ligand, which lengthens the trans-Os-Cl bond.