An investigation of the solid-state reactions of some cobalt (III) ammine complexes

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1971

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In this investigation, the thermal properties, reaction stoichiometry, stereochemical changes, and reaction mechanisms of some tetramminecobalt(III)-complexes were studied by various thermoanalytical techniques. In Part I, the thermal properties of some anionoa-quotetramminecobalt(III) complexes were examined. Except for a few cases, the, deaquation of the aquo-complexes was accompanied by further deamination and/or reduction of the cobalt(III) ion. However, the themally stable dianionobis-(ethylenediamine)cobalt(III) complexes were obtained by deaquation of their aquo- or diaquo-complexes. Some interesting stereochemical changes were observed in the deaquation and anation reactions of bis(ethylenediamine)cobalt(III) complexes. A "cis-preferred" mechanism was introduced to explain most of the reactions. An example of such a "cis-preferred" reaction is: cis- or trans-[Co(en)[lowered 2](H[lowered 2]O)[lowered 2]]Cl[lowered 2][dot]2H[lowered 2]O ---> cis-[Co(en)[lowered 2]Cl[lowered 2]]Cl + 4H[lowered 2]O(g) The thermal dissociation of the dihalo-nitrate complexes with different degrees of chelation was also studied. The complexes containing both oxidizing and reducing groups exploded between 200-250[degrees]C, due to the strong oxidation-reduction reactions involved. In Part II, "trans-preferred" reactions were studied in detail in the following complexes: [Co(NH[lowered 3])[lowered 4]X[lowered 2]][raised n+], [Co(en)(NH[lowered 3])[lowered 2]X[lowered 2]][raised n+], and [Co(en)[lowered 2]X[lowered 2]][raised n+] . The trans-preferred or cis-trans-isomerization reaction can be described by the reaction: NH[lowered 4]+, No[lowered 3]- cis- [Co(A[lowered 4])X[lowered 2]] ---> trans-[Co(A[lowered 4])X[lowered 2]]+ NO[lowered 3]- where X is chloride or bromide. In Part III, the solid-state heterogeneous kinetics of the cis-trans isomerization of [Co(en)[lowered 2]Cl[lowered 2]]Cl was studied. An activation energy of 44 kcal/mole was obtained for the isomerization reaction. A reaction mechanism was postulated for the trans-preferred reactions.

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