Uranyl hydroxide

Uranyl hydroxide
Identifiers
CAS Number	211573-15-8 ;
3D model (JSmol)	Interactive image;
ChemSpider	4576989 ;
PubChem CID	5465112;
UN number	2909
CompTox Dashboard (EPA)	DTXSID201027718 ;
	InChI InChI=1S/2H2O.2O.U/h2*1H2;;;/q;;;;+2/p-2 Key: VWIQIIGYDAPONF-UHFFFAOYSA-L ;
	SMILES O=[U+2]=O.[OH-].[OH-];
Properties
Chemical formula	UH; 2O; 4
Molar mass	304.0424 g mol−1
Related compounds
Related compounds	Sulfuric acid; Chromic acid; Uranium trioxide
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Uranyl hydroxide is a hydroxide of uranium with the chemical formula UO₂(OH)₂ in the monomeric form and [(UO₂)₂(OH)₄]^2- in the dimeric; both forms may exist in normal aqueous media. In areobic conditions, up to 5 hydroxides can bind to Uranyl {[(UO₂)₂(OH)₅]^3-}. Uranyl hydroxide hydrate is precipitated as a colloidal yellowcake from oxidized uranium liquors near neutral pH.

Uranyl hydroxide was once used in glassmaking and ceramics in the colouring of the vitreous phases and the preparation of pigments for high temperature firing. The introduction of alkaline diuranates (like sodium diuranate) into glasses leads to yellow by transmission, green by reflection; moreover these glasses become dichroic and fluorescent under ultraviolet rays.

Uranyl hydroxide is teratogenic and radioactive.

Formation

The formation of uranyl hydroxide hydrate can occur via hydrated uranyl fluoride [(UO₂F₂)(H₂O)]₇·4H₂O which is not stable at an elevated water vapor pressure. A complete loss of fluorine is undergone and the formation of uranyl hydroxide hydrate ([(UO₂)₄O(OH)₆]·5H₂O) occurs. This uranyl hydroxide species is structurally similar to the uranyl hydroxide hydrate minerals schoepite and metaschoepite. X-ray diffraction data was gathered and found that this species has expanded interlayer spacing suggesting there may be additional water molecules in between uranyl layers. Unlike metaschoepite, however, this species does not form UO₂(OH)₂ upon dehydration.^[1]

Reactions

1) (UO₂(OH)⁺ + H₂O → [(UO₂(OH)(H₂O)]⁺

2) [(UO₂(OH)(H₂O)]⁺ + H₂O → [(UO₂(OH)(H₂O)₂]⁺

UO₂(OH)₂ reacts with water in a hydration reaction to form [(UO₂(OH)₂)(H₂O)]⁺ and the monohydrate form also reacted with water to form dihydrates [(UO₂OH)(H₂O)2]⁺ and trihydrates [(UO₂OH)(H₂O)₃]⁺. The hydration reaction to form the monohydrate was significantly slower than if the hydroxide were replaced with acetate or nitrate. This could be due to the strongly basic (OH)^- reducing the Lewis acidity of U or because the more complex acetate and nitrate anions provide more degrees of freedom. However, it was found that the formation of the dihydrate uranyl hydroxide hydrate (2) was nearly three times faster than the monohydrate (1).^[2]

Mechanisms

A mechanism for oxygen exchange between the UO₂²⁺ cations in a highly alkaline solution was proposed and investigated by Shamov et al. in the Journal of the American Chemical Society.^[3] An equilibrium between [UO₂(OH)₄]^2-] and [UO₂(OH)₅]^3-] was observed followed by the formation of the stable [UO₃(OH)₃·H₂O]³⁻] intermediate that formed from [UO₂(OH)₅]^3-] via intramolecular water elimination.

References

^ Kirkegaard, Marie C.; Spano, Tyler L.; Ambrogio, Michael W.; Niedziela, J. L.; Miskowiec, Andrew; Shields, Ashley E.; Anderson, Brian B. (2019). "Formation of a uranyl hydroxide hydrate via hydration of [(UO 2 F 2 )(H 2 O)] 7 ·4H 2 O". Dalton Transactions. 48 (36): 13685–13698. doi:10.1039/C9DT02835H. ISSN 1477-9226.
^ Chien, Winnie; Anbalagan, Victor; Zandler, Melvin; Van Stipdonk, Michael; Hanna, Dorothy; Gresham, Garold; Groenewold, Gary (2004-06-01). "Intrinsic hydration of monopositive uranyl hydroxide, nitrate, and acetate cations". Journal of the American Society for Mass Spectrometry. 15 (6): 777–783. doi:10.1016/j.jasms.2004.01.013. ISSN 1044-0305.
^ Shamov, Grigory A.; Schreckenbach, Georg (2008-10-15). "Theoretical Study of the Oxygen Exchange in Uranyl Hydroxide. An Old Riddle Solved?". Journal of the American Chemical Society. 130 (41): 13735–13744. doi:10.1021/ja804742f. ISSN 0002-7863.

The Structure of the a Form of Uranyl Hydroxide
Alexander, C.A. (2005) "Volatilization of urania under strongly oxidizing conditions," Journal of Nuclear Materials, 346, 312–318.

[1] Kirkegaard, Marie C.; Spano, Tyler L.; Ambrogio, Michael W.; Niedziela, J. L.; Miskowiec, Andrew; Shields, Ashley E.; Anderson, Brian B. (2019). "Formation of a uranyl hydroxide hydrate via hydration of [(UO 2 F 2 )(H 2 O)] 7 ·4H 2 O". Dalton Transactions. 48 (36): 13685–13698. doi:10.1039/C9DT02835H. ISSN 1477-9226.

[2] Chien, Winnie; Anbalagan, Victor; Zandler, Melvin; Van Stipdonk, Michael; Hanna, Dorothy; Gresham, Garold; Groenewold, Gary (2004-06-01). "Intrinsic hydration of monopositive uranyl hydroxide, nitrate, and acetate cations". Journal of the American Society for Mass Spectrometry. 15 (6): 777–783. doi:10.1016/j.jasms.2004.01.013. ISSN 1044-0305.

[3] Shamov, Grigory A.; Schreckenbach, Georg (2008-10-15). "Theoretical Study of the Oxygen Exchange in Uranyl Hydroxide. An Old Riddle Solved?". Journal of the American Chemical Society. 130 (41): 13735–13744. doi:10.1021/ja804742f. ISSN 0002-7863.

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