Trisodium pentaborate

Trisodium pentaborate is a salt that can form as a monohydrate with formula Na3B5O8(OH)2*H2O, which contains the anion dihydroxydopentaborate [B5O8(OH)2](3-).

Its formula may be incorrectly given as Na3B5O8*2H2O, or as 3Na2O5B2O3*4H2O. It may also be called simply sodium pentaborate, but this name is more properly reserved for the compound with elemental formula Na2O*5B2O3*nH2O.

Structure
Trisodium pentaborate monohydrate crystallizes as thin plates in the orthorhombic crystal system, with symmetry group Pbca and cell parameters a = 880.4 pm, b = 1837.1 pm, c = 1092.4 pm, formulas per cell Z = 8.