A study on the aromaticity and magnetic properties of triazolephorphyrazines

Abstract

The aromaticity of porphyrazine (PA) and its three triazoleporphyrazine (TAP) tautomers as well as their metal complex compounds was examined using the TRE (topological resonance energy) and the MRE (magnetic resonance energy) methods. Their local aromaticity was studied using the BRE (bond resonance energy) and the CRE (circuit resonance energy) methods. The relationship between the global and local aromaticity of TAPs and the position of the substituted nitrogen atom is discussed. The results of these calculations are compared with those provided by other aromaticity indices. Our TRE and MRE results indicate that PA and TAPs possess lower global aromaticity than porphyrin. Our BRE and CRE results show that global aromaticity is closely associated primarily with the five-membered rings which contain the –NH– pyrrolic rings, and the [18]-annulene-like conjugation pathway is not crucial for determining the aromaticity of the entire π-system. Moreover, the circuit-current susceptibility (χ_i) and ring current (RC) were obtained using the graph-theoretical method. The χ_i and RC results show that all the compounds sustain a diatropic current along the macrocycle and this current is bifurcated when it passes through every five-membered ring. Ring current maps reveal that in the five-membered rings, the ring current prefers to pass through the C–C bond when the ring contains an –NH– group, and through the C–N bond when the ring does not contain an –NH– group.