Fixation of Sulphur Dioxide by Manganese(II)-Schiff Base Complexes: Thermal Stability of these Adducts and the Possible Conversion of the Coordinated SO2 to Sulphate

A series of manganese(II) complexes of general formula MnLn(H2O)m (where H2Ln are substituted N,N′‐bis(salicylidene)‐1,2‐diimino‐2,2‐dimethylethane) have been prepared by electrochemical synthesis and characterized by analytical and spectroscopic techniques, magnetism and by studying their redox reversibility character by cyclic and normal pulse voltammetry. The reactivity of these complexes with sulphur dioxide has been investigated in the solid state and in toluene slurries at room temperature. The studies of the reversibility of the reaction (desorption studies) by thermogravimetrical analysis (TGD) have shown a different behaviour among the SO2‐adducts (from irreversible to totally reversible fixing), pointing to different SO2 binding modes. Thus, adducts 10, 12 and 14, kept the SO2 after TGD, signifying S–bridged SO2 binding mode, while TGD for 8, 9 and 13 revealed the lability of their SO2, attributable to ligand bound SO2 coordination. The manganese(II) precursor 4 is that one which has the ability of reversily fixing a major quantity of SO2 and undergoes the sulphato reaction to form 11 also.