Stabilization of Octahedral Thorium Clusters by Interstitial Hydrogen

The synthesis, structure, and characterization of the cluster compounds Th₆ H_x Br₁₅ (x = 5 and 7) are reported. The compounds can be prepared by a reversible hydrogenation/dehydrogenation process; their structures have been determined by X-ray and neutron diffraction methods. Both compounds form a body-centered cubic structure of octahedral cluster units with five or seven hydrogen atoms in eight disordered positions above the faces of the octahedron. The chemical bonding in these diamagnetic compounds has been analyzed: the simple counting rules for octahedral cluster compounds are fulfilled, and MO and band structure calculations confirm the hydridic nature of the bonding.