The relative nucleophilic efficiency of water and the azide and thiocyanate ions in the aqueous substitution of chloropentacyanocobaltate(III)

Abstract

The kinetics of the substitution of Cl^– in [Co(CN)₅Cl]^3– by solvent H₂O and by X^–= NCS^– or N₃^– may be quantitatively interpreted by a stepwise mechanism, equations (i) and (ii). High-performance liquid chromatographic analysis confirms the absence of direct chloride substitution by reaction (iii). These results support the view that the substitution occurs by an I_d interchange mechanism. [Co(CN)₅Cl]^3–+ H₂O →[Co(CN)₅(OH₂)]^2–+ Cl^–(i)[Co(CN)₅(OH₂)]^2–+ X^–→[Co(CN)₅X]^3–+ H₂O (ii)[Co(CN)₅Cl]^3–+ X^–→[Co(CN)₅X]^3–+ Cl^–(iii)