W0248

High Pressure Structural Studies of Ru₃(CO)₁₂. Carla Slebodnick, Jing Zhao, Ross J. Angel, Brian E. Hanson, College of Sciences Crystallography Laboratory, Depts. of Chemistry and Geological Sciences, Virginia Polytechnic Institute and State Univ. Blacksburg, VA 24061.

The pressure dependence of the structures of M₃(CO)₁₂ (M = Fe, Ru, Os) is being explored at pressures ranging from 0-8 GPa. Depending on the metal, solid state structures of M₃(CO)₁₂ adopt either an anticubooctahdral geometry of D_3h symmetry (Ru₃(CO)₁₂, Os₃(CO)₁₂) or an icosahedral geometry of C_2v symmetry (Fe₃(CO)₁₂). Extensive calculations suggest that a third intermediate geometry of D₃ symmetry is sterically favored.¹ This third geometry is a proposed intermediate in solution state dynamics.²

The structure of these complexes at high pressure will give further insight into the role of steric effects on structure. If steric repulsion between the intramolecular carbonyls dictates structure, then a phase transition to the intermediate geometry of D₃ symmetry is predicted.

Several structures have been obtained for Ru₃(CO)₁₂ at pressures of 0-8 GPa. Single crystal intensity data were collected on a Xcalibur diffractometer equipped with both a point detector and a CCD detector. High pressures were generated with transmission-geometry diamond anvil cells of ETH-design with 4:1 methanol:ethanol mixture as hydrostatic pressure medium. Cell volume compressed more than 20% over the 8 GPa range. This compression manifest itself primarily in shortening of the intermolecular interactions, with the molecules sliding past each other and adopting a herring bone type structure. There is no indication of change in molecular geometry.

1) Lauher, J.W. J. Am. Chem. Soc. 1986, 108, 1521-31.

2) Johnson, B. F. G. J. Chem. Soc. Chem. Commun. 1976, 211-3.