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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. The topic has been the subject of theoretical analysis. Copper(I) hydroxide would also be expect to easily oxidise to copper(II) hydroxide:

4CuOH + 2 H₂O + O₂ → 4Cu(OH)₂

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.forapplications for use in solar cells.

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.

Cu(OH)−2 → CuOH + OH

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

Gaseous CuOH

Gaseous CuOH has been characterized spectroscopically using intracavity laser spectroscopy, single vibronic level emission, and microwave spectroscopic detection.

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.

Ligand-stabilized Cu(I) hydroxides

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. In addition to Cu(IPr)OH, the dimer [Cu(IPr)]₂OH] (as its BF−4 salt)) and the aquo complex [Cu(IPr)]OH₂] (as its SbF−6) have been characterized by X-ray crystallography.

References

1. Soroka, Inna L.; Shchukarev, Andrey; Jonsson, Mats; Tarakina, Nadezda V.; Korzhavyi, Pavel A. (2013). "Cuprous hydroxide in a solid form: does it exist?". Dalton Transactions. 42 (26): 9585–94. doi:10.1039/C3DT50351H. PMID 23673918.
2. Korzhavyi, P.A.; Soroka, I.; Boman, M.; Johansson, B. (2011). "Thermodynamics of stable and metastable Cu-OH compounds". Solid State Phenomena. 172: 973–78. doi:10.4028/www.scientific.net/SSP.172-174.973. S2CID 137644376.
3. ^ Illas, F.; Rubio, J.; Centellas, F.; Virgili, J. (1984). "Molecular Structure of Copper (I) Hydroxide and Copper Hydroxide (1-) (Cu (OH)₂). An ab initio Study". The Journal of Physical Chemistry. 88 (22): 5225–28. doi:10.1021/j150666a022.
4. "Thin film deposition of Cu₂O and Application for Solar Cells". Solar Energy. 1, 80 (6): 715–22. 2006. doi:10.1016/j.solener.2005.10.012.
5. Luo, K.; Li, W.; Lin, J.; Jin, Y. (2019). "Tandem Reaction of Heterocyclic Ketene Aminals with Diazoesters: Synthesis of Pyrimidopyrrolidone Derivatives". Tetrahedron Letters. 60 (41): 151136. doi:10.1016/j.tetlet.2019.151136. S2CID 203143147.
6. Harms, J.C.; O'Brien, L.C.; O'Brien, J.J. (2019). "Rotational Analysis of the A "–X~ 1A′ Transition of CuOH and CuOD Observed at High Resolution with Intracavity Laser Spectroscopy". Journal of Molecular Spectroscopy. 362: 8–13. doi:10.1016/j.jms.2019.05.013. S2CID 191158971.
7. Tao, C.; Mukarakate, C.; Reid, S.A. (2007). "Single Vibronic Level Emission Spectroscopy and Fluorescence Lifetime of the B~ 1A "→ X~ 1A′ System of CuOH and CuOD". Chemical Physics Letters. 449 (4–6): 282–85. doi:10.1016/j.cplett.2007.10.084.
8. Whitham, C.J.; Ozeki, H.; Saito, S. (1999). "Microwave spectroscopic detection of transition metal hydroxides: CuOH and AgOH". The Journal of Chemical Physics. 15, 110 (23): 11109–12. doi:10.1063/1.479051. hdl:10098/1528.
9. Fortman, George C.; Slawin, Alexandra M. Z.; Nolan, Steven P. (2010). "A Versatile Cuprous Synthon: [Cu(IPr)(OH)] (IPr = 1,3 Bis(diisopropylphenyl)imidazol-2-ylidene)". Organometallics. 29 (17): 3966–3972. doi:10.1021/om100733n.
10. Ibrahim, Houssein; Guillot, Régis; Cisnetti, Federico; Gautier, Arnaud (2014). "[{Cu(IPr)}2(μ-OH)][BF4]: Synthesis and Halide-Free CuAAC Catalysis". Chemical Communications. 50 (54): 7154–7156. doi:10.1039/C4CC03346A. PMID 24854111.
11. Muñoz-Castro, Alvaro; Wang, Guocang; Ponduru, Tharun Teja; Dias, H. V. Rasika (2021). "Synthesis and Characterization of N-Heterocyclic Carbene–M⋯OEt₂ Complexes (M = Cu, Ag, Au). Analysis of Solvated Auxiliary-Ligand Free [(NHC)M] Species". Physical Chemistry Chemical Physics. 23 (2): 1577–1583. doi:10.1039/D0CP05222A. PMID 33406199.

• Copper(I) compounds
• Hydroxides