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

Abstract: Reaction of tridentate ONS donor ligands H2L1, H2L2 and H2L3 (H2L1 =2-hydroxyacetophenone hexamethyleneimine-3-thiosemicarbazone; H2L2 =2-hydroxyacetophenone morpholine-3-thiosemicarbazone; H2L3 =2-hydroxyacetophenone N(4)-methyl, phenyl thiosemicarbazone) with Mn(OAc)2 ·4H2O afforded manganese(IV) complexes of the type [MnL2] in an ethanol–methanol mixture under air. The crystal structure of Mn(L2)2 ·0.25H2O reveals an octahedral geometry with the ligand coordinated in a meridional fashion. The molecule is packed in the crystal lattice with extended hydrogen bonding networks. EPR spectra of the complexes in frozen solution at 77K show a weak signal at g ≈4 and a strong sextet at g ≈2 consistent with manganese(IV) in an octahedral environment. Cyclic voltammetry in DMSO/ dichloromethane show quasi-reversible peaks corresponding to the Mn(IV)/Mn(III) redox couple. [Copyright &y& Elsevier]