Editing Hydroxide (section)

==Basic salts containing hydroxide==
In some cases, the products of partial hydrolysis of metal ion, described above, can be found in crystalline compounds. A striking example is found with [[zirconium]](IV). Because of the high oxidation state, salts of Zr<sup>4+</sup> are extensively hydrolyzed in water even at low pH. The compound originally formulated as ZrOCl<sub>2</sub>·8H<sub>2</sub>O was found to be the chloride salt of a [[tetrameric]] cation [Zr<sub>4</sub>(OH)<sub>8</sub>(H<sub>2</sub>O)<sub>16</sub>]<sup>8+</sup> in which there is a square of Zr<sup>4+</sup> ions with two hydroxide groups bridging between Zr atoms on each side of the square and with four water molecules attached to each Zr atom.<ref name=wells561>Wells, p.&nbsp;561</ref>

The mineral [[malachite]] is a typical example of a basic carbonate. The formula, Cu<sub>2</sub>CO<sub>3</sub>(OH)<sub>2</sub> shows that it is halfway between [[basic copper carbonate|copper carbonate]] and [[copper hydroxide]]. Indeed, in the past the formula was written as CuCO<sub>3</sub>·Cu(OH)<sub>2</sub>. The [[crystal structure]] is made up of copper, carbonate and hydroxide ions.<ref name=wells561/> The mineral [[atacamite]] is an example of a basic chloride. It has the formula Cu<sub>2</sub>Cl(OH)<sub>3</sub>. In this case the composition is nearer to that of the hydroxide than that of the chloride: CuCl<sub>2</sub>·3Cu(OH)<sub>2</sub>.<ref>Wells, p.&nbsp;393</ref> Copper forms hydroxyphosphate ([[libethenite]]), arsenate ([[olivenite]]), sulfate ([[brochantite]]), and nitrate compounds. [[White lead]] is a basic [[lead]] carbonate, (PbCO<sub>3</sub>)<sub>2</sub>·Pb(OH)<sub>2</sub>, which has been used as a white [[pigment]] because of its opaque quality, though its use is now restricted because it can be a source for [[lead poisoning]].<ref name=wells561/>