Zinc(II) and copper(II) complexes with benzothiadiazole Schiff-base ligands

Abstract

The ligand (2-[4-(2,1,3-benzothiadiazole)imino]methyl-phenol) HL1 containing the electron poor benzothiadiazole (BTD) unit, conveniently prepared by condensation of 4-amino-2,1,3-benzothiadiazole and salicylaldehyde, has been structurally characterized by single crystal X-ray diffraction. Two energy minima have been determined, by DFT calculations, for HL1 and for its ortho-vanillin analogue HL2, corresponding either to the conformer observed in the solid state or to the chelating tridentate form. TD-DFT calculations have been performed on HL1 and HL2 in order to assign their experimental UV–visible absorption bands. Reaction of HL1 and HL2 with copper (II) hexafluoroacetylacetonate (hfac), zinc (II) hexafluoroacetylacetonate or zinc (II) acetate provided the neutral complexes [Cu(L1)(hfac)] (1), [Zn(L1)2] (2), [Cu(L2)2] (3) and [Zn(L2)2] (4) which were structurally characterized, with a focus on the coordination sphere of the metal centre and on the intermolecular interactions. The UV–visible absorption properties of the Zn(II) complexes 2 and 4 have been experimentally and theoretically investigated and compared to those of the ligands. Finally, the cryomagnetic study of 1 and 3 in the temperature range 2.0–295.0 K reveals a Curie-Weiss law behaviour with very weak intermolecular antiferromagnetic interactions in the low temperature region.