Mercury(II)- and nitrosyl-induced aquation of anionopenta-aminecobalt-(III) species. Reactions of the t-[Co{N(CH2CH2NH2)3}(NH3)X]2+ ions (X = Cl– or N3–) and the importance of ion pairs

Abstract

Evidence is presented which demonstrates that the Hg²⁺- and NO⁺-induced aquations of t-[Co(tren)(NH₃)Cl]²⁺,(1), and t-[Co(tren)(NH₃)(N₃)]²⁺, (2), respectively, follow different paths; i.e. that a common intermediate of the type [Co(tren)(NH₃)]³⁺ is not involved [tren = 2,2′,2″-triaminotriethylamine, N(CH₂CH₂NH₂)₃]. Saturation entry of NO₃^– to form t-[Co(tren)(NH₃)(NO₃)]²⁺(3) occurs as [NO₃^–] is raised to 1 mol dm^–3[48% for (1); 35% for (2)] and this limiting condition is interpreted in terms of pre-formed ion pairs (K_ipca. 5 dm³ mol^–1). Second-order rate constants for the Hg²⁺-induced reaction of p-[Co(tren)(NH₃)Cl]²⁺ and t-[Co(tren)(NH₃)Cl]²⁺, are 5.6 ± 0.2 and 9.7 ± 0.1 dm³ mol^–1s^–1 respectively.