Formation and isomerisation of theO-sulphito complex of 1,4,7,10,13-penta-azacyclohexadecanecobalt(III)

Summary Dissolved SO₂ reacts rapidly with Co(16]aneN₅)OH]²⁺ to give Co(16]aneN₅OSO₂]⁺(16]aneN₅=1,4,7,10, 13-penta-azacyclohexadecane), which on immediate acidification loses SO₂ to give Co(16]aneN₅)OH₂]³⁺. The O-bonded sulphito complex (_max 526 nm) undergoes a slow linkage isomerisation to give the S-bonded species Co(16]aneN₅)SO₃]⁺ (_max 466 nm), rather than an internal redox reaction. The S-bonded complex has been isolated and characterised as the perchlorate salt Co(16]aneN₅) (SO₃H)](ClO₄)₂.