 Some compounds termed orthoborates do not necessarily contain the trigonal planar ion, for example, gadolinium orthoborate GdBO3 contains the polyborate [B3O9]9− ion, whereas the high-temperature form contains planar [BO3]3−.All borates can be considered derivatives of boric acid, B(OH)3.Boric acid is a weak proton donor (p"K"a ~ 9) in the sense of Brønsted acid, but is a Lewis acid, i.e., it can accept an electron pair.