Hydroxo-bridge cleavage in dicobalt(III) complexes

Ellis, John; Scott, Keith L.; Wharton, Roland K.; Sykes, A. G.

doi:10.1021/ic50116a061

Cited by 12 publications

(3 citation statements)

References 3 publications

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“…Role of Oxygen in the Solutions. The first type of event corresponds to the oxidation of Co(II)−en complexes by oxygen dissolved in solution, , in line with the influence of Co environment on Co(III)/Co(II) redox potential . The oxidation of [Co(en) 2 (H 2 O) 2 ] 2+ leads to [Co(en) 2 (H 2 O) 2 ] 3+ or to one of its deprotonated or dimeric forms, which our data do not allow to identify.…”

Section: Discussionmentioning

confidence: 65%

A Study of Cobalt Speciation in Co/Al₂O₃ Catalysts Prepared from Solutions of Cobalt−Ethylenediamine Complexes

2007

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The thermal reduction of Co/Al2O3 catalysts prepared by impregnation of Co(II) nitrate generally leads to migration of cobalt ions into alumina with formation of cobalt aluminate. In order to prevent the latter, it is attempted to reduce cobalt by decomposition of supported precursor salts containing ethylenediamine (en), a procedure successfully applied earlier to nickel. Alumina is impregnated with an aqueous solution containing Co(II) nitrate and two or three equivalents of en. After drying, several cobalt compounds are detected on the support by X-ray diffraction, diffuse reflectance UV−vis spectroscopy and X-ray absorption spectroscopy: crystals of [Co(III)(en)3](NO3)3 whatever the initial en/Co stoichiometry, Co(II) and Co(III)−en complexes, grafted or not, as well as a Co(II)(OH)2-like phase. The composition of these phases reveals that dramatic evolutions in cobalt speciation have taken place in the impregnating solution, driven by the oxidation of complexed cobalt by dissolved oxygen and by the precipitation of the Co(III) salt. Decomposition of these phases in an inert gas atmosphere does not lead to metal particles exclusively, as is the case of nickel, but to a mixture of oxidic and metallic phases. A treatment in hydrogen at 500 °C completes cobalt reduction, leading to 6−20 nm metal particles. This rather broad size distribution is linked to the wide range of cobalt species on the support, which stems itself from the coordination chemistry of cobalt bonded to ethylenediamine in aqueous solutions.

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Section: Discussionmentioning

confidence: 65%

A Study of Cobalt Speciation in Co/Al₂O₃ Catalysts Prepared from Solutions of Cobalt−Ethylenediamine Complexes

2007

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“…Several mechanisms have been proposed to account for such results, as summarized in the paper by El-Awady and Hugus18 and further discussed by Sykes and his co-workers. 26 It turns out that one can readily develop alternatives for the acid catalysis which combine protonation of one of the hydroxo bridges with subsequent rate-determining bridge cleavage, and this latter process may or may not be acid catalyzed. A particularly simple and appealing mechanism is one involving the reactions of (3), in which R symbolizes the various types k,…”

Section: Resultsmentioning

confidence: 99%

Preparation, structure, and interconversion kinetics of mono- and binuclear aquo(nitrilotriacetato)cobaltate(III) complexes

Meloon¹,

Harris²

1977

Inorg. Chem.

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“…Unklar ist weiter die pH-Abhangigkeit der Geschwindigkeit der beiden Schritte I + I1 und I1 --f 111. Die erstmalige Synthese eines Kobalt(II1)-mono-ols, namlich IV [ 5 ] , dessen Saurespaltung eine besonders einfache pH-Abhangigkeit zeigt [6], analog wie die Aufspaltung von p-Amido-p-hydroxo-bis[tetramminkobalt (111)] V zum saurestabilen VI [7l (Reaktion Z), hat die Diskussion um den Mechanismus des Vorganges (1) von neuem angeregt [8]. …”

Section: IVunclassified

Die Kinetik der Spaltung dinuklearer Tri‐μ‐hydroxo‐kobalt(III)‐Komplexe N₃Co(Oh)₃CoN₃³⁺ (triole) mit Säure

Kähler¹,

Geier²,

Schwarzenbach³

1974

Helvetica Chimica Acta

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ging OH with half life of 0,2, 0,03 and 0,025 sec. respectively (perchlorate medium p = I N , ZOO, pH = 0). The rate of the back reaction could also be determined, yielding ratios of the two rate constants corresponding to pK-values between 0 and 1,5. Whereas Tach-Trio1 is protonated to the di-p-hydroxo-p-quo complex at about p H 1, it is deprotonated to the di-p-hydroxo-p-oxo complex a t about pH 14 (Siroky [16]). The second step of (l), the aquation of the di-p-hydroxo-paquo species to the di-p-hydroxo-diaquo complex (Diol) takes place with half lives between 4 and 9 sec.The final cleavage to the mononuclear triaquo complex needs many hours to go half way and is again initiated by protonation of one of the remaining two OH-bridges. Neither the p-aquo complex produced thereby, nor the Mono-ol [mono-p-hydroxo-tetraaquo complex] formed as an intermediate cause any observable changes of the spectrum. The Mono-ol aquates at a rate which is inverse in [H+] because of the labilisation brought about by deprotonation of its aquo ligands. b 2 t c !-w I 3 ' Q 0

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Hydroxo-bridge cleavage in dicobalt(III) complexes

Cited by 12 publications

References 3 publications

A Study of Cobalt Speciation in Co/Al₂O₃ Catalysts Prepared from Solutions of Cobalt−Ethylenediamine Complexes

A Study of Cobalt Speciation in Co/Al₂O₃ Catalysts Prepared from Solutions of Cobalt−Ethylenediamine Complexes

Preparation, structure, and interconversion kinetics of mono- and binuclear aquo(nitrilotriacetato)cobaltate(III) complexes

Die Kinetik der Spaltung dinuklearer Tri‐μ‐hydroxo‐kobalt(III)‐Komplexe N₃Co(Oh)₃CoN₃³⁺ (triole) mit Säure

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Hydroxo-bridge cleavage in dicobalt(III) complexes

Cited by 12 publications

References 3 publications

A Study of Cobalt Speciation in Co/Al2O3 Catalysts Prepared from Solutions of Cobalt−Ethylenediamine Complexes

A Study of Cobalt Speciation in Co/Al2O3 Catalysts Prepared from Solutions of Cobalt−Ethylenediamine Complexes

Preparation, structure, and interconversion kinetics of mono- and binuclear aquo(nitrilotriacetato)cobaltate(III) complexes

Die Kinetik der Spaltung dinuklearer Tri‐μ‐hydroxo‐kobalt(III)‐Komplexe N3Co(Oh)3CoN33+ (triole) mit Säure

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A Study of Cobalt Speciation in Co/Al₂O₃ Catalysts Prepared from Solutions of Cobalt−Ethylenediamine Complexes

A Study of Cobalt Speciation in Co/Al₂O₃ Catalysts Prepared from Solutions of Cobalt−Ethylenediamine Complexes

Die Kinetik der Spaltung dinuklearer Tri‐μ‐hydroxo‐kobalt(III)‐Komplexe N₃Co(Oh)₃CoN₃³⁺ (triole) mit Säure