The structure of the orthorhombic phase of osmium oxide pentafluoride, OsOF5

Abstract

Crystals of osmium oxide pentafluoride, OsOF₅, the first heptavalent osmium compound prepared, are orthorhombic below 32·5°, with four molecules in a unit cell of dimensions a= 9·540, b= 8·669, c= 5·019 Å, space group Pnma. The structure was determined from the isostructural relationship with the actinide hexafluorides, and refined by three-dimensional Fourier and difference syntheses.

The OsOF₅ units of the molecular lattice are distorted from octahedral ligancy. The nature of the distortion is consistent with the greater effective size of the oxygen ligand compared with the fluorine ligands and is indicative of an ordered structure. The chemically significant interatomic distances are: Os–O 1·74 ± 0·03, the trans-Os–F 1·72 ± 0·03, two equatorial Os–F 1·76 ± 0·03, two equatorial Os–F 1·80 ± 0·03 Å.