Abstract

A theoretical study of the electronic structure, UV-Vis absorption spectra, reactivity and EPR parameters using density functional theory (DFT) and its extension time dependent-density functional theory (TD-DFT) was performed for a family of paramagnetic Ni(II)-Porphyrazines dimers connected by Ni(III)-dithiolene, with general formula [Ni(II)PzR(6)Ni(III)S(4)PzR(6)Ni(II)](1-) where the peripheral substituents R are -NH2 (1), -OH (2), -CH3 (3), -H (4), -C6H5 (5), -Cl (6), -CO2H (7) and -NO2 (8)). The simulated UV-Vis absorption spectra exhibit the usual B or Soret and Q bands. The energies of the electronic transitions, the g-tensors and the simulated EPR spectrum are in good agreement with previously reported experimental data. The results show that the odd electron in complexes with R being electron donor are delocalized over the bridge fragment and the systems with R being electron withdrawing are delocalized over the macrocycles Pz. Thus, along with the frontier MOs analysis and reactivity indexes, it was possible to conclude that the character of the peripheral substituents R affect the reactivity of this kind of systems where the most reactive are those with R being electron donor. In addition, the effect of the R groups on the frontier MOs energies is showed by the correlation of HOMO, LUMO and HOMO-LUMO gap energies with the Hammett constants. On the other hand, charge transfer from the ligands to the Ni atoms and back-donation from the Ni atoms to the ligands is observed in the charge transfer analysis. (C) 2012 Elsevier Ltd. All rights reserved.