CRYSTAL STRUCTURE OF RHENIUM (7) OXIDE

The crystal structure of rhenium(VII)oxide, Re2O7, has been determined from three-dimensional single-crystal X-ray data collected by film techniques. The least-squares refinement converges to a conventional R factor of 0.053 for 1126 nonzero reflections. The compound crystallizes in the orthorhombic system, space group P212121, with a = 12.508, b = 15.196, c = 5.448 Å, and V = 1035.5 Å3. The unit cell contains 8 formula units. Measured and calculated densities are 6.14 and6.214 g/cm3, respectively.The structure consists of strongly distorted ReO6 octahedra andfairly regular ReO4 tetrahedra which are connected through corners to form polymeric double layers in the ac plane. The double layers have only van der Waals contacts to neighboring ones. Parallel zigzag chains of octahedra, every other chain beingpart of the upper or lower half of the double layer, are linked through corners of the tetrahedra in such a waythat rings (o-t-o-t) (o, octahedron, t, tetrahedron) within the layers areformed. The octahedra contain three short (1.65-1.75 Å) and three long (2.06-2.16 Å) Re-O bonds, while in the tetrahedra the bond distances range from 1.68 to 1.80 Å. The structure is one of the relatively few known examples where metal atoms of the same oxidation number occur with coordination numbers 4 and 6 in the same structure. From the crystal structure the mechanisms of evaporation (to form O3ReOReO3 molecules) and of hydrolysis (where Re2O7(OH2)2 is formed) can be derived. In its structural and bond properties, rhenium(VII) oxide represents an intermediate between the polymeric oxides MoO3 and WO3and the more covalently bonded OsO4, which forms a molecular structure. © 1969, American Chemical Society. All rights reserved.