| Abstract
| - A set of substituted (sulfonate, amino) nickel porphyrin derivatives such as phthalocyanine and phenylporphyrinwas studied by spectroscopic (UV−vis, FTIR, XPS) and quantum-chemical methods. The Q and Soret bandswere identified in the UV−vis spectra of aquo solutions of the tetrasulfo-substituted complexes and in DMFand ACN solutions of the amino-substituted phenylporphyrin and phthalocyanine Ni(II) complexes, respectively.In all the complexes the frontier molecular orbitals predict that the oxidation and reduction sites are localizedon the ligand rather than in the metal atom. A natural bonding orbital (NBO) analysis of all the complexesshowed that a two-center bond NBO between the pyrrolic nitrogens (Npyrr) and the nickel atom does notexist, the Npyrr···Ni interaction occurring instead by a delocalization from one lone pair of each Npyrr towardone lone pair of the nickel atom, as estimated by second-order perturbation theory. The calculated values ofelectronic transitions between the frontier molecular orbitals are in good agreeement with the UV−vis data.At the theoretical level, we found that while the ligand effect is more important in the Q-band (∼16 kcal/mol), the substituent effect is more significant in the Soret band (∼9 kcal/mol). A good agreement was alsofound between the experimental and calculated infrared spectra, which allowed the assignment of manyexperimental bands. The XPS results indicate that the Ni(II) present in the phenylporphyrin structure is notaffected by a change of the substituent (sulfonate or amino).
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