or Si(OH)₄. Other silicic acids such as metasilicic acid (H₂SiO₃), disilicic acid (H₂Si₂O₅), and pyrosilicic acid (H₆Si₂O₇) have been characterized. These acids also have hydroxide groups attached to the silicon; the formulas suggest that these acids are protonated forms of polyoxyanions.

Few hydroxo complexes of germanium have been characterized. Tin(II) hydroxide