Intramolecular hydrogen bonding and electronic structure of thiadiazole annulated hemihexaphyrazine

Abstract

Different tautomeric structures of thiadiazole annelated hemihexaphyrazine (TDAHHp) were considered using DFT in B3LYP/pcseg-2 approximation. Energetics of the intramolecular hydrogen bonding was quantitatively estimated by means of NBO and AIM calculations and according to the NBO analysis results, the most energetically favorable tautomer of TDAHHp surprisingly turned out to possess the lowest total H-bond stabilization energy. The results are compared with that for the previously studied hemihexaphyrazine – 2,3,5,10,12,13,15,20,22,23,25,30-dodecaaza-hexaphyrin (C30 H15 N15 S3). Electronic absorption and infrared spectra were simulated for the most favorable tautomer of TDAHHp.