Tricapped trigonal prisms metal complexes

Although some transition-metal complexes containing only the hydride ligand are known—an example is the 9-coordinate [ReHg] ion (Figure 9.35), the classic example of a tricapped trigonal prism —we are principally concerned with complexes containing... 

Potassium nonahydridorhenate(VII) K2[ReH9] was prepared by reduction of potassium perrhenate in aqueous ethylenediamine with potassium or lithium metal. Neutron diffraction analysis established unequivocally the correct composition and molecular structure of this polyhydride complex. The diffraction study was performed within an evacuated cryostat maintained at room temperature, since the crystals are unstable in moist air. The Re atom hes at the center of a trigonal prism of H atoms, with three H atoms beyond the centers of the prism faces. Thus, the structure is a tricapped trigonal prism of symmetry. The average Re—H distance is 1.68(1) A and the average H—Re—H angle between hydrogens in the same vertical mirror plane is 93.6(6)°. 

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