SYNTHESIS AND STRUCTURAL STUDIES ON ZINC(II) MACROCYCLIC AND HETROCYCLIC COMPLEXES DERIVED FROM SCHIFF BASE AND MIXED LIGANDS OF 1,4-DIHYDROQUINOXALINE-2,3-DIONE, ORTHOPHENYLENE DIAMINE AND HYDROQUINONE.

In this study two new zinc(II) complexes involving oxygen and nitrogen donor sequences derived from 1,4-dihydroquinoxaline-2,3-dione (QXD), o-phenylenediamine (OPD) and hydroquinone (HQ) were synthesized through a template procedure. The structural elucidation of these complexes was carried out using measurement of molar conductance in 1x10-3 M solution of DMSO and various spectral techniques; 1H and 13C NMR, FT-IR, UV-VIS and AAS. The results showed that the zinc(II) ion coordinates with the Schiff base ligands in octahedral geometry, leading to the formation of stable macrocyclic and heterocyclic structures. The cyclic ligand (L) was found to coordinate as NNNN donor, through four imine nitrogen atoms which were formed up on condensation of the -NH2 groups on o-phenylenediamine with C=O group on quinoxaline dione in a 2:2 mole ratio, in the presence of one mole equivalent of ZnCl2 in ethanol medium. It also indicates the formation of a new mixed ligand zinc(II) complex with an OO OO O O coordination around zinc(II). The study contributes to the understanding of the coordination chemistry of zinc(II) with Schiff bases and provides insights into the development of novel zinc-based complex compounds. [ABSTRACT FROM AUTHOR]