Estudo da estrutura eletrônica de possíveis tautômeros de valência com diferentes metais de transição: uma análise teórica via DFT

Abstract

In the present work, a study was conducted using Density Functional Theory (DFT) on novel coordination complexes, synthesized and experimentally characterized, based on phenanthroline- and bipyridine-type ligands, with the potential occurrence of the valence tautomerism phenomenon. This phenomenon involves a reversible intramolecular electronic transition, induced by external stimuli such as photoirradiation or temperature variation. The investigated systems are classified as molecular solids containing transition metals, including experimental data for complexes with Zn and Co, as well as theoretical studies involving metal substitutions with Cr, Mn, Fe, Cu, and Ni. The analysis focused on the electronic properties of the complexes, with emphasis on the density of states (DOS), projected density of states (PDOS), band structure, spin density distribution, and magnetic dipole moment. Additionally, the influence of metal–nitrogen bond distances on the system’s unpaired electronic charge was examined. The role of solvents in the structural arrangement was also investigated, along with the effects of positional and substitutional disorders arising from experimental inaccuracies. An analysis of the formation enthalpy was performed to understand the stability of the complexes upon solvation and the resulting impact on their electronic properties. The results indicate significant changes in the electronic properties depending on the different ligands, metals, and solvents involved. These findings highlight the systems' sensitivity to their chemical environment, thus reinforcing the possibility of valence tautomerism occurrence. However, further theoretical and experimental studies are still required for a more comprehensive understanding of the phenomenon in the studied compounds.