Wikipedia
Sodium perborate
Sodium perborate (PBS) is a white, odorless, water-soluble chemical compound with the chemical formula . It crystallizes as the monohydrate, NaBO·HO, trihydrate, NaBO·3HO and tetrahydrate, NaBO·4HO. The monohydrate and tetrahydrate are the commercially important forms. The elementary structural unit of sodium perborates is a dimer anion BO(OH), in which two boron atoms are joined by two peroxo bridges in a chair-shaped 6-membered ring, and the simplistic NaBO·nHO-type formulas are just a convenient way to express the average chemical composition.