Reactions of µ-hydroxo-dicobalt(III) complexes. Part VIII. Kinetic studies of the bridge cleavage of the µ-hydroxo-bis[penta-amminecobalt(III)] complex
Wharton, R. K.; Sykes, A. G.
Журнал:
Journal of the Chemical Society, Dalton Transactions
Дата:
1973
Аннотация:
The kinetics of bridge cleavage of the µ-hydroxo-bis[penta-amminecobalt(III)] complex, (NH3)5Co·OH·Co(NH3)5 <sup>5+</sup>[equation (i)] have been studied in aqueous perchloric acid solutions, I= 2·0M(LiClO4), at 15â 30 °C. (NH3)5Co·OH·Co(NH3)5 <sup>5+</sup>+ H<sup>+</sup>+ H2O â 2Co(NH3)5H2O<sup>3+</sup>(i) For the range of hydrogen-ion concentration investigated (10<sup>â 4</sup>â 2·0M), first-order rate constants, k obs, show the dependdence (ii) on [H<sup>+</sup>]. k obs=k 1[H<sup>+</sup>]+k 2(ii) At 25 ° C: k 1=(5·37 ± 0·07)à 10<sup>â 3</sup> l mol<sup>â 1</sup> s<sup>â 1</sup>, Î H 1 <sup>â ¡</sup>= 12·0 ± 0·8 kcal mol<sup>â 1</sup>, Î S 1 <sup>â ¡</sup>=â 28·7 ± 2·7 cal K<sup>â 1</sup> mol<sup>â 1</sup>; and k 2=(7·58 ± 0·10)à 10<sup>â 3</sup> s<sup>â 1</sup>, Î H 2 <sup>â ¡</sup>= 20·1 ± 0·70 kcal mol<sup>â 1</sup>, Î S 2 <sup>â ¡</sup>=â 1·0 ± 2·2 cal K<sup>â 1</sup> mol<sup>â 1</sup>. In the presence of thiocyanate ions (0·06â 0·80M), K obs, can be expressed as in (iii), where a and bare ca. 15% smaller than k 1 and k 2 due to ion-pairing. k obs=a[H<sup>+</sup>]+b+c[H<sup>+</sup>][NCS<sup>â </sup>](iii) At 25 °C and I= 2·0M(LiClO4) : c= 0·137 ± 0·003 I<sup>2</sup> mol<sup>â 2</sup> s<sup>â 1</sup>, Î H c <sup>â ¡</sup>= 10·9 ± 0·6 kcal mol<sup>â 1</sup>, and Î Sc <sup>â ¡</sup>=â 25·8 ± 2·2 cal K<sup>â 1</sup> mol<sup>â 1</sup>. The thiocyanate-dependent path yields equal amounts of the complexes Co(NH3)5NCS<sup>2+</sup> and Co(NH3)5H2O<sup>3+</sup> as primary products.
825.2Кб