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 Mg[Formula: see text] tetra(1,2,5-chalcogenadiazolo)porphyrazines [TXDPzMg] (X [Formula: see text] O, S, Se, Te) and their monoaqua complexes [TXDPzMg(OH[Formula: see text]] 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 a[Formula: see text] and e[Formula: see text] 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 [Formula: see text]-MOs having the a[Formula: see text] symmetry – 2a[Formula: see text] and lower lying 1a[Formula: see text] orbitals. The Gouterman type a[Formula: see text] orbital with predominant localization on the nitrogen atoms of the internal 16-membered macrocycle is 2a[Formula: see text] for the O- and S-containing complexes and for the Se- and Te-analogs it becomes 1a[Formula: see text], while the higher lying 2a[Formula: see text] orbital resides mainly on the fused heterocycles (Se/Te and C[Formula: see text] 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 Mg[Formula: see text] complexes.