DFT Study of molecular and electronic structure of magnesium (II) tetra(1,2,5-chalcogenadiazolo) porphyrazines, [TXDPzMg] (X = O, S, Se, Te)
Abstract
The influence of the chalcogen atom (X) on the molecular and electronic structures for the series of MgII tetra(1,2,5-chalcogenadiazolo)porphyrazines [TXDPzMg] (X = O, S, Se, Te) and their monoaqua complexes [TXDPzMg(OH2)] was studied using DFT methods (B3LYP and PBE0 functionals) with cc-pVTZ basis sets. The chalcogen atom X changes strongly the geometry of the fused 1,2,5-chalcogenadiazole rings, but has only a weak influence on the dimensions of the coordination cavity of the porphyrazine macrocycle in [TXDPzMg] leading to its slight expansion in the sequence S < Se < Te < O. The electron density distribution was considered in terms of the natural bond order (NBO) and the natural population analysis (NPA). The frontier molecular orbitals are destabilzed along with the decrease of electronegativity of the chalcogen atoms. The a1u and e∗g orbitals (HOMO and LUMO) are mainly localized on atoms constituting the internal 16-membered macrocycle, while the chalcogen atoms have the strongest effect on the composition of the filled π-MOs having the a2u symmetry – 2a2u and lower lying 1a2u orbitals. The Gouterman type a2u orbital with predominant localization on the nitrogen atoms of the internal 16-membered macrocycle is 2a2u for the O- and S-containing complexes and for the Se- and Te-analogs it becomes 1a2u, while the higher lying 2a2u orbital resides mainly on the fused heterocycles (Se/Te and Cβ atoms). The lowest excited states have been calculated for [TXDPzMg] and used for the explanation of the peculiarities and tendencies observed in the experimental electronic absorption spectra available for the S, Se- and Te-containing MgII complexes.
Dedicated to Professor Claudio Ercolani on the occasion of his 80th Anniversary
Handbook of Porphyrin Science now available in 46 volumes
