TH6BR15H7-STABILIZATION OF A TH6BR12 CLUSTER BY 7 HYDROGEN-ATOMS

Vertices, edges, and faces-in other words, the whole periphery of the Th6 octahedron in the title compound-are covered with Br and H atoms. The structure is novel in that the H atoms are not bonded interstitially but rather from ''outside'' to the cluster core, as shown by neutron diffraction of the perdeuterated compound (see the picture on the right; o = Th, O = Br, o = D). If the metal-metal bonds in the cluster are described qualitatively by eight closed three-center two-electron bonds directed toward the middle of the faces of the octahedron, it is clearly seen that seven of these bonds are stabilized by the additional electrons of the H atoms at the centers of the faces.