Ring Size Effect on the Chemical Properties of Monovalent Nickel Complexes with Tetraazamacrocyclic Ligands in Aqueous Solutions

The chemical properties of the monovalent nickel complexes, NiLi⁺, where L₁ = 1,4,7,10 tetraazacyclotridecane and L₃ = 1,4,8,12 tetraazacyclopentadecane, in aqueous solutions were studied electrochemically and pulse‐radiolytically. The results are compared with those for L₂ = 1,4,8,11 tetraazacyclotetradecane which were earlier reported. The redox potentials for the NiLi²⁺/NiLi⁺ couples are < −1.70, −1.56 and −1.50 V vs. Ag/AgCl for L₁, L₂ and L₃ respectively. NiL⁺₂ has the longest half‐life in neutral solutions, ca 2 s and NiL₁ the shortest ca 100 μs. NiL⁺₁ and NiL⁺₂ react with N₂O to yield NiLi³⁺ in fast reactions; this reaction cannot be studied for NiL⁺₃. CO⁻₂ radicals reduce NiL²⁺₁ and NiL²⁺₂ in a reaction approaching the diffusion controlled limit via the bridged mechanism. No reaction between CO⁻₂ and NiL₃(H₂O)²⁺₂ is observed.