Perrhenic acid 高铼酸
Perrhenic acid is the chemical compound with the formula Re
2O
7(OH
2)
2. It is obtained by evaporating aqueous solutions of Re
2O
7. Conventionally, perrhenic acid is considered to have the formula HReO
4, and a species of this formula forms when rhenium(VII) oxide sublimes in the presence of water or steam. When a solution of Re
2O
7 is kept for a period of months, it breaks down and crystals of HReO
4·H
2O are formed, which contain tetrahedral ReO−
4 For most purposes, perrhenic acid and rhenium(VII) oxide are used interchangeably. Rhenium can be dissolved in nitric or concentrated sulfuric acid to produce perrhenic acid.