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

摘要

Reaction of tridentate ONS donor ligands H2L1, H2L2 and H2L (3) (H2L1 = 2-hydroxyacetophenone hexamethylencimine-3-thiosemicarbazone; H2L2 = 2-hydroxyacetophenone morpholine-3-thiosemicarbazone; H2L3 = 2-hydroxyacetophenone N(4)-methyl, phenyl thiosemicarbazone) with Mn(OAC)(2) center dot 4H(2)O afforded manganese(IV) complexes of the type [MnL2] in an ethanol-methanol mixture under air. The crystal structure of Mn(L-2)(2) center dot 0.25H(2)O 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 77 K show a weak signal at g approximate to 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. (c) 2005 Elsevier Ltd. All rights reserved.