New Investigations of Geometric, Electronic, and Spectroscopic Properties of Tetrapyrrolic Macrocycles by a TD−DFT Approach. Carbon, Nitrogen, and Chalcogen (O, S, Se) Peripheral Substitution Effects on Ni(II) Porphyrazinato Complexes

The electronic structure of five complexes [M(oXHpz)] [M = Ni2+; oXHpz2- = 2,3,7,8,12,13,17,18-octakis-substituted (X = CH2, NH, O, S, Se)-5,10,15,20-tetraazaporphyrinate dianion] has been investigated using a density functional approach. All the geometries have been obtained minimizing the total intramolecular energy using a nonlocal hybrid functional (B3LYP) at the 6-31g* level. The electronic configuration of Ni2+ is (dx2-y2)0(dxy)2(dxz,dyz)4(dz2)2. Optimized geometries exhibit a planar conformation and are all above the threshold for ruffling, which is described by a Ni−Np bond distance of 1.85−1.87 Å for sterically unhindered porphyrazines. Indeed, the smallest bond distance is 1.880 Å for Ni(oOHpz). Peripheral substituents yield modifications to the “core” of the macrocycle and to the energy levels, changing σ and π interactions. Furthermore, within a time-dependent density functional theory approach, excited states of Ni(oXHpz) [X = CH2, NH, O, S, Se,] complexes have been studied and compared with available experimental UV−vis spectra.