{"title":"Influence of Di-n-butyl Phosphoric Acid on Cerium Redox and Speciation in Tri-n-butyl Phosphate","authors":"Joshua R. Dunbar, and , Mark P. Jensen*, ","doi":"10.1021/acs.inorgchem.4c01309","DOIUrl":null,"url":null,"abstract":"<p >The effects of simulated radiolytic degradation of tri-<i>n-</i>butyl phosphate (TBP) on the chemical speciation of cerium were studied by spectrophotometry and electrochemistry of TBP solutions containing increasing amounts of di-<i>n</i>-butyl phosphoric acid (HDBP), a common degradation product of TBP. Tetravalent cerium was found to exchange coordinated nitrate for the dibutyl phosphate anion, forming dinuclear complexes of the formula (CeOCe)(NO<sub>3</sub>)<sub>(6-<i>d</i>)</sub>(DBP)<sub><i>d</i></sub>·3TBP (<i>d</i> = 0–3). Compared to Ce(IV), Ce(III) was complexed less strongly by HDBP in TBP, but HDBP displaced both nitrate and TBP to form the series of mononuclear complexes Ce(NO<sub>3</sub>)<sub>(3-<i>d</i>)</sub>(HDBP·DBP)<sub><i>d</i></sub>·(3-<i>d</i>)TBP (<i>d</i> = 0–3). Dibutyl phosphate coordination caused large negative shifts in the Ce(IV/III) reduction potential in TBP, indicating a strong stabilization of the tetravalent state. Electrochemical investigation of the reduction of Ce(IV) in TBP revealed it to be a two-electron process in accordance with the dinuclear nature of the organic-phase Ce(IV) complexes. The diffusion coefficients of the <i>d</i> = 0 dinuclear Ce(IV)-nitrate-TBP complex and mononuclear Ce(III)-nitrate-TBP complex in TBP equilibrated with 7 M HNO<sub>3</sub> were determined to be (1.16 ± 0.06) × 10<sup>–7</sup> cm<sup>2</sup>/s and (1.9 ± 0.4) × 10<sup>–7</sup> cm<sup>2</sup>/s, respectively, which also is consistent with the larger molecular volume of the dinuclear Ce(IV) complexes.</p>","PeriodicalId":40,"journal":{"name":"Inorganic Chemistry","volume":null,"pages":null},"PeriodicalIF":4.3000,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Inorganic Chemistry","FirstCategoryId":"92","ListUrlMain":"https://pubs.acs.org/doi/10.1021/acs.inorgchem.4c01309","RegionNum":2,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"CHEMISTRY, INORGANIC & NUCLEAR","Score":null,"Total":0}
引用次数: 0
Abstract
The effects of simulated radiolytic degradation of tri-n-butyl phosphate (TBP) on the chemical speciation of cerium were studied by spectrophotometry and electrochemistry of TBP solutions containing increasing amounts of di-n-butyl phosphoric acid (HDBP), a common degradation product of TBP. Tetravalent cerium was found to exchange coordinated nitrate for the dibutyl phosphate anion, forming dinuclear complexes of the formula (CeOCe)(NO3)(6-d)(DBP)d·3TBP (d = 0–3). Compared to Ce(IV), Ce(III) was complexed less strongly by HDBP in TBP, but HDBP displaced both nitrate and TBP to form the series of mononuclear complexes Ce(NO3)(3-d)(HDBP·DBP)d·(3-d)TBP (d = 0–3). Dibutyl phosphate coordination caused large negative shifts in the Ce(IV/III) reduction potential in TBP, indicating a strong stabilization of the tetravalent state. Electrochemical investigation of the reduction of Ce(IV) in TBP revealed it to be a two-electron process in accordance with the dinuclear nature of the organic-phase Ce(IV) complexes. The diffusion coefficients of the d = 0 dinuclear Ce(IV)-nitrate-TBP complex and mononuclear Ce(III)-nitrate-TBP complex in TBP equilibrated with 7 M HNO3 were determined to be (1.16 ± 0.06) × 10–7 cm2/s and (1.9 ± 0.4) × 10–7 cm2/s, respectively, which also is consistent with the larger molecular volume of the dinuclear Ce(IV) complexes.
期刊介绍:
Inorganic Chemistry publishes fundamental studies in all phases of inorganic chemistry. Coverage includes experimental and theoretical reports on quantitative studies of structure and thermodynamics, kinetics, mechanisms of inorganic reactions, bioinorganic chemistry, and relevant aspects of organometallic chemistry, solid-state phenomena, and chemical bonding theory. Emphasis is placed on the synthesis, structure, thermodynamics, reactivity, spectroscopy, and bonding properties of significant new and known compounds.