CuH2O5OH

CuH2O5OH denotes a copper(II) aquo-hydroxo coordination complex. In many treatments it is represented as [Cu(H2O)5OH]+, a hydroxo-substituted form that arises when one water ligand of the hexaaqua copper(II) ion [Cu(H2O)6]2+ loses a proton. Thus the five remaining water ligands plus the hydroxide ligand give an octahedral coordination environment around the copper center, though Jahn-Teller distortion common to Cu(II) complexes often causes slight elongation along one axis.

The complex is typically formed in aqueous solution via hydrolysis of [Cu(H2O)6]2+ as the pH increases: [Cu(H2O)6]2+ ⇌ [Cu(H2O)5OH]+ + H+. Because this process is pH-dependent, CuH2O5OH+ is usually a transient species in dilute solutions and is more readily observed under conditions that stabilize intermediate hydroxo species, such as in the presence of certain ligands or in solid-state hydrates.

Properties of this species reflect those of copper(II) aquo-hydroxo complexes. It is paramagnetic due to Cu2+, and its electronic spectrum is influenced by ligand field changes from substituting one water ligand with hydroxide, often resulting in subtle shifts in visible coloration compared with [Cu(H2O)6]2+. The chemistry of CuH2O5OH+ is relevant to understanding hydrolysis equilibria of copper(II) salts and to the formation of copper hydroxide or oxide species in basic environments.

See also: copper(II) aqua complex, copper hydroxide, Jahn-Teller distortion in Cu(II) complexes.