Chelating behavior of 2-hydroxyacetophenone N(4)-disubstituted thiosemicarbazones: Facile formation of Mn(IV) complexes - X-ray structure, EPR and cyclic voltammetric studies

Facile formation of three manganese(IV) complexes (MnL2) occur when 2-hydroxyacetophenone N(4)-disubstituted thiosemicarbazones (H2L) were treated with manganese(II) acetate tetrahydrate in ethanol-methanol medium under aerobic condition. The crystal structure of Mn(L2)2 · 0.25H2O reveals an octahedral geometry with a skewed arrangement of the ligand about the metal ion. EPR spectra at 77 K shows a weak g ≈ 4 signal and a strong sextet at g ≈ 2 consistent with manganese(IV) with marginally distorted octahedral environment. Cyclic voltammetry in DMSO/dichloromethane show reversible and quasi-reversible peaks corresponding to Mn(IV)/Mn(III) redox couple.