Hemihexaphyrazine and Thiadiazole Annulated Hemihexaphyrazine: A Theoretical Insight into Aromaticity and Energetics of Hydrogen Bonding

Abstract

Seventeen tautomeric structures of hemihexaphyrazine were considered using DFT in B3LYP/pcseg-2 approximation. The tautomer of D 3h symmetry was found to be the most energetically favorable, and transformations into other tautomers are practically forbidden by high energy barriers (more than 50 kJ·mol-1). The energetics of hydrogen bonding was estimated by NBO and QTAIM calculations and the preferable D 3h tautomer turned out to possess the lowest total hydrogen bond stabilization energy, according to the results of the NBO-analysis. Aromaticity of the D 3h and C 3h tautomers of hemihexaphyrazine and its thiadiazole annulated analogue was described with use of three popular descriptors: NICS, HOMA and FLU. Tautomeric preference and structural features of the both molecules were found to be very similar.

Vaporization Processes and Accurate Molecular Structure of a Number of Organic and Inorganic Compounds Promising for Use in Technologies Involving the Gas Phase

“…Структуры свободных молекул H2hp и H2dchp были определены методом газовой электронографии [19] Строение и энергетика гемигексафиразина, его металлокомплексов и тиадиазол-аннелированного гемигексафиразина Исследование строения молекул гемигексафиразина и его металлокомплексов, а также тиадиазол-аннелированного гемигексафиразина представлено в работах [21][22][23][24][25][26][27][28]. Эффузионным методом Кнудсена с масс-спектрометрическим контролем состава пара определена энтальпия сублимации незамещенного гемигексафиразина, которая составила 252(2) кДж/моль [21].…”

“…Методом газовой электронографии и с помощью квантовохимических расчетов определена молекулярная структура незамещенного гемигексафиразина [22]. В работе [24] было изучено полное таутомерное многообразие гемигексафиразина и тиадиазол-аннелированного гемигексафиразина. Обе структуры обладают симметрией D3h.…”

Dianionic States of Trithiadodecaazahexaphyrin Complexes with Homotrinuclear MII3O Clusters (M = Ni and Cu): Crystal Structures, Metal- Or Macrocycle-Centered Reduction, and Doublet–Quartet Transitions in the Dianions

“…The nonaromatic character of H 3 Hhp was the subject of a number of the articles. 4a,5c, 18 Recently, the appearance of the aromatic character of the macrocycles at complex formation of some substituted Hhps has been described. 19 The NICS values (fragments a 1 −f 3 , Figure S13) are negative for all local fragments of the {Ni 3 O(Hhp)} 2− and {Cu 3 O(Hhp)} 2− dianions (from approximately −2.2 to −13.4 ppm, Table S2), indicating their aromatic character.…”