Aggregation of a Zn(II)-salen complex: Theoretical study of structure and spectra

A theoretical study of the dimerization of amphiphilic Schiff-base bis(salicylaldiminato)Zinc(II) complex (1) in dichloromethane with and without pyridine, is reported in this paper. A comparative investigation between experimental and calculated H-1 NMR and UV-vis spectra was performed to evaluate the percentage contribute of each conformer in non-coordinating solvent. DFT calculations and a detailed analysis of the rotational barrier were carried out to study various dimer aggregate. Gibbs free energy related to the dimerization process, in presence of pyridine, was also estimated. Results highlight that in solution of non-coordinating solvent are mainly present three different conformers (D1, D2 and D3) which can convert each other at room temperature. Moreover, it was confirmed that dimerization is a favored process in the non-coordinating solvent. Without a doubt, best fit procedure demonstrates that the greater contribute to the dimers distribution in solution, is due to conformer D3. UV-vis bands were also assigned to the corresponding electronic transitions. Finally the dimerization process is, thermodynamically, not favored in presence of pyridine. In this case the stable complex monomer pyridine is formed. (C) 2015 Elsevier B.V. All rights reserved.