User:Praseodymium-141/Rhenium oxides

Rhenium(IV) oxide (or rhenium dioxide) is an oxide of rhenium, with the formula ReO2. This gray to black crystalline solid is a laboratory reagent that can be used as a catalyst. It adopts the rutile structure. It forms via comproportionation:
 * 2 Re2O7 +  3 Re    →   7 ReO2

Single crystals are obtained by chemical transport, using iodine as the transporting agent. At high temperatures it undergoes disproportionation. It forms perrhenates with alkaline hydrogen peroxide and oxidizing acids. In molten sodium hydroxide it forms sodium rhenate.

Rhenium(VI) oxide, or rhenium trioxide, is another oxide of rhenium. It is the only stable group 7 trioxide. It has an appearance somewhat like copper. It can be formed by reducing rhenium(VII) oxide with carbon monoxide at 200 °C or elemental rhenium at 400 °C. Re2O7 can also be reduced with dioxane. Rhenium trioxide crystallizes with a primitive cubic unit cell, with a lattice parameter of 3.742 Å (374.2 pm). The structure of ReO3 is similar to that of perovskite (ABO3), without the large A cation at the centre of the unit cell. Each rhenium center is surrounded by an octahedron defined by six oxygen centers. These octahedra share corners to form the 3-dimensional structure. The coordination number of O is 2, because each oxygen atom has 2 neighbouring Re atoms.

Rhenium(VII) oxide, or rhenium heptoxide, is another oxide of rhenium. It is the anhydride form of perrhenic acid, and is the raw material for all rhenium compounds. Solid Re2O7 consists of alternating octahedral and tetrahedral Re centres. Upon heating, the polymer cracks to give molecular (nonpolymeric) Re2O7. This molecular species closely resembles manganese heptoxide, consisting of a pair of ReO4 tetrahedra that share a vertex, i.e., O3Re–O–ReO3.