DFT computational correlations on conformational barriers of Zn²⁺ and Ni²⁺ chiral meso-(α,β-unsaturated)- porphyrins

Abstract

Correlations between DFT and experimental measurements on Zn²⁺ and Ni²⁺ chiral meso-(α,β-unsaturated)- porphyrins were performed using Kohn-Sham methodology. The exchange-correlation Becke88–Perdew86 functional was used in conjunction with double-zeta Slater basis sets. An accurate description of the electronic processes depending on the metal ion (Zn, Ni) or ligand (perilaldehyde and myrtenal) was made, confirming experimental results in terms of structural and electronic modifications. Moreover, this theoretical study provides a stronger knowledge and interpretation of the dynamical conformational features of the free base, Zn and Ni structures. Fundamental links between the central metallic atom and distortions of the porphyrinic core and ligands were demonstrated, in agreement with experimental data. We observed that the core in ZnPeriP and ZnMyrtP species is almost flat, in comparison with the Ni porphyrinic core, which appeared much more distorted. The type of distortion differs between PeriP and MyrtP ligands, with a combined saddled-ruffled characteristic with the former and a pronounced ruffled twisting for the latter. Finally, conformational energy barriers were extracted by spinning one of the arms in steps of 20° in a 360° dihedral angle. The resulted conformational barriers for NiPeriP or NiMyrtP are lower in energy than for ZnPeriP or ZnMyrtP, in agreement with experimental data.