Theoretical spectroscopic study of seven zinc(II) complex with macrocyclic Schiff-base ligand

• The agreement is found between experimental and theoretical results.
• The optimized structures of zinc complexes are demonstrated by using structural parameters, IR and NMR spectra.
• The UV–VIS spectrum of mentioned complexes are predicted and explained by using orbital character and transition character analysis.
• Ranking of biological activity of relevant zinc complexes is predicted by using quantum chemical descriptors.

Seven zinc complexes, which are [ZnL1]2+, [ZnL2]2+, [ZnL3]2+, [ZnL4]2+, [ZnL5]2+, [ZnL6]2+ and [ZnL7]2+, are studied as theoretically. Structural parameters, vibration frequencies, electronic absorption spectra and 1H and 13C NMR spectra are obtained for Zn(II) complexes of macrocyclic penta and heptaaza Schiff-base ligand. Vibration spectra of Zn(II) complexes are studied by using Density Functional Theory (DFT) calculations at the B3LYP/LANL2DZ. The UV–VIS and NMR spectra of the zinc complexes are obtained by using Time Dependent-Density Functional Theory (TD-DFT) method and Giao method, respectively. The agreements are found between experimental data of [ZnL5]2+, [ZnL6]2+ and [ZnL7]2+ complex ions and their calculated results. The geometries of complexes are found as distorted pentagonal planar for [ZnL1]2+, [ZnL2]2+ and [ZnL3]2+ complex ions, distorted tetrahedral for [ZnL4]2+ complex ion and distorted pentagonal bipyramidal for [ZnL5]2+, [ZnL6]2+ and [ZnL7]2+ complex ions. Ranking of biological activity is determined by using quantum chemical parameters and this ranking is found as: [ZnL7]2+ > [ZnL6]2+ > [ZnL5]2+ > [ZnL3]2+ > [ZnL2]2+ > [ZnL1]2+.

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