By Reduction of Potassium Perrhenate

Metallic rhenium prepared by this method is generally between 99.0 and 99.8 per cent pure. The chief impurity is potassium, probably as potassium hydroxide. The product is a dense gray-black powder. The yield is between 85 per cent and 95 per cent based upon the potassium per-rhenate used. 

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Potassium hexahalorhenate(IV) complexes have been prepared by reduction of potassium perrhenate in concentrated hydrohalic acid media. Among the reducing agents which have been employed are iodide ion, chromium(II), ... 

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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