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Australian Journal of Chemistry Australian Journal of Chemistry Society
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RESEARCH ARTICLE

Octahedral cobalt(III) complexes in dipolar aprotic solvents. IV. Solvolysis and isomerization of dibromobisethylenediaminecobalt(III) ions inanhydrous NN-dimethylformamide and NN-dimethylacetamide

WR Fitzgerald and DW Watts

Australian Journal of Chemistry 19(6) 935 - 947
Published: 1966

Abstract

The equilibrium system (SOL)+Br-+cis-[CoBr2 em]+ = cis-[CoBr(SOL) en2]2++2Br-   =trans[CoBr2en2]2++Br-+SOL where SOL represents either of the solvents NN-dimethylformamide (DMF) or NN-dimethylacetamide (DMA), has been studied. The compounds cis- [CoBr(DMF) en2](ClO4)2, and cis-[CoBr(DMA) en2]XO3,ClO4, have been isolated and thus it has been possible to study these equilibria using as starting materials both the cis- and trans-dibromo complexes (cis- and trans-[CoBr2 en2]+) and the solvento complexes (cis-[CoBr(DXA) en2]2+ and cis-[CoBr(DMF) en2]2+). The mechanism of the bromide entry reactions cis-[CoBr(SOL) en2]2+ +Br- = cis- and trans-[CoBr2 en2]++SOL is bimolecular in DMA while in DMF the reaction is dissociative: the rate showing bromide concentration dependence only in the concentration range where ion association is not complete. In both systems the isomerization proceeds mainly through the solvento complex; in dimethylacetamide there is evidence for a seven-coordinated intermediate. The isomerization equilibria are found to be bromide concentration dependent, cis-[CoBr2 en2]+ being favoured by high bromide concentrations. This is consistent with the lower stability of the trans-[CoBr2 en2]- ion pair with bromide ion.

https://doi.org/10.1071/CH9660935

© CSIRO 1966

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