Copper(I) hydroxide

Copper(I) hydroxide is the inorganic compound with the chemical formula of CuOH. Little evidence exists for its existence. A similar situation applies to the monohydroxides of gold(I) and silver(I). Solid CuOH has been claimed however as an unstable yellow-red solid.^[1] The topic has been the subject of theoretical analysis.^[2] Copper(I) hydroxide would also be expected to easily oxidise to copper(II) hydroxide:

4CuOH + 2 H₂O + O₂ → 4Cu(OH)₂

Copper(I) hydroxide

Names
Other names Cuprous hydroxide; Copper monohydroxide
Identifiers
CAS Number	19650-79-4
3D model (JSmol)	Interactive image
ChemSpider	8031144
PubChem CID	9855444
CompTox Dashboard (EPA)	DTXSID6034473
InChI InChI=1S/Cu.H2O/h;1H2/q+1;/p-1 Key: ZMHWUUMELDFBCZ-UHFFFAOYSA-M
SMILES [OH-].[Cu+]
Properties
Chemical formula	CuOH
Molar mass	80.55 g/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

It would also be expected to rapidly dehydrate:

2CuOH → Cu₂O + H₂O

Solid CuOH would be of interest as a possible intermediate in the formation of copper(I) oxide (Cu₂O), which has diverse applications, e.g. applications in solar cells.^[3][4]

Solid CuOH

Theoretical calculations predict that CuOH would be stable. Specifically, the dissociation of Cu(OH)₂⁻ leading to CuOH is subject to an energy of 62 ± 3 kcal/mol.^[3]

Cu(OH)−2 → CuOH + OH⁻

Without evidence for its existence, CuOH has been invoked as a catalyst in organic synthesis^[5]

Gaseous CuOH

Gaseous CuOH has been characterized spectroscopically using intracavity laser spectroscopy,^[6] single vibronic level emission,^[7] and microwave spectroscopic detection.^[8]

CuOH is calculated to be bent, with the point group C_s. In this case, the bond distance of the Cu-O bond was 1.818 Å and the bond distance of the O-H bond was 0.960 Å. The bond angle for this geometry was 131.9°. The compound is highly ionic in character, which is why this angle is not exactly 120°. Structural parameters for linear CuOH have also been examined computationally.^[3]

Ligand-stabilized Cu(I) hydroxides

Structure of a CuOH(IPr) complex. Color code: blue = N, copper = Cu, red = O, white = C, H.

Although simple CuOH compounds are fairly elusive or restricted to the gas-phase within spectrometers, some derivatives are well characterized.

Specifically cuprous hydroxides have been prepared using bulky NHC co-ligands.^[9] In addition to Cu(IPr)OH, the dimer [Cu(IPr)]₂OH]⁺ (as its BF−4 salt)^[10]) and the aquo complex [Cu(IPr)]OH₂]⁺ (as its SbF−6) have been characterized by X-ray crystallography.^[11]