Substitution reactions of di-µ-cyano-bis[tetracyanoferrate(II)] in aqueous solution

Abstract

Data obtained in a kinetic investigation of the substitution reactions of the binuclear complex ion [Fe^II₂(CN)₁₀]^6–by X [X = HCN, pyridine (py), and 4-methylpyridine (Mepy)] support the stepwise mechanism in equations (i)–(v), [(NC)₄Fe^II(CN)(NC)Fe^II(CN)₄]^6–+ H₂O [graphic omitted] [(NC)₅Fe^II(NC)Fe^II(CN)₄(OH₂)]^6–(i),[Fe^II₂(CN)₁₀(OH₂)]^6–+ H₂O [graphic omitted] 2[Fe^II(CN)₅(OH₂)]^3–(ii), [Fe^II₂(CN)₁₀(OH₂)]^6–+ X [graphic omitted] [Fe^II₂(CN)₁₀X]+ H₂O (iii), [Fe^II₂(CN)₁₀X]+ H₂O [graphic omitted] [Fe^II(CN)₅X]+[Fe^II(CN)₅(OH₂)]^3–(iv),[Fe^II(CN)₅(OH₂)]^3–+ X [graphic omitted][Fe^II(CN)₅X](v), At 25 °C, k₃=(1.25 ± 0.5 )× 10^–3 s^–1, k_–3= 0.165 ± 0.035 s^–1, k_2HCN=(1.81 ± 0.07 )× 10^–3 s^–1, k_7HCN= 34 ± 8 dm³ mol^–1 s^–1, k_7py= 10 ± 3 dm³ mol^–1 s^–1, and k_7MepY= 9 ± 2 dm³ mol^–1 s^–1; ΔH^‡, ΔH_2HCN^‡,ΔS₃^‡, and ΔS_2HCN^‡ are 99 ± 4 kJ mol^–1, 92 ± 4 kJ mol^–1, 52 ± 16 J K^–1 mol^–1, and 31 + 12 J K^–1 mol^–1.