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

摘要

The electronic structure of five complexes [M(oXHpz)] [M = Ni2+; oXHpz(2-) = 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 (d(x)(-y)(2)2)(0)(d(xy))(2)(d(xz),d(yz))(4)(d(z)(2))(2). Optimized geometries exhibit a planar conformation and are all above the threshold for ruffling, which is described by a Ni-N-p bond distance of 1.85-1.87 A for sterically unhindered porphyrazines. Indeed, the smallest bond distance is 1.880 A for Ni(oOHpz). Peripheral substituents yield modifications to the "core" of the macrocycle and to the energy levels, changing sigma and pi 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.