Crystal structure of dodecacarbonyldi-iodotriosmium

Abstract

Crystals of [Os₃(CO)₁₂I₂] are monoclinic, space group P2₁/n, with Z= 2 in a unit cell of dimensions a= 10.329(7), b= 11.579(11), c= 9.334(7)Å, and β= 100.07(2)°. The structure has been elucidated by heavy-atom methods from 2 015 diffracted intensities measured on a four-circle diffractometer, and refined to R 0.062. The molecule is required crystallographically to be centrosymmetric. It comprises a straight chain of three osmium atoms, with the iodine atoms occupying equatorial sites, trans to one another, on the terminal Os atoms. Each Os atom has an octahedral configuration and, apart from the two iodine atoms, all the other sites are occupied by carbonyl ligands. The equatorial ligands on the terminal atoms are staggered with respect to the four carbonyl groups on the central Os atom, while the two terminal carbonyl groups are collinear with the molecular axis. The Os–Os distance is 2.93, Os–I 2.77, and the mean Os–C and C–O distances are 1.95 and 1.14 Å As has been observed in other compounds of this type, the equatorial carbonyl groups on the terminal metal atoms lean inwards towards the central metal atom.