Structural Characterization of 1,2-Bis(4-cyanophenyl)diazene Oxide and Its Cyclotrimerization to a Triazine-Linked Polymer

Abstract

Azoxybenzenes have been widely studied due to their diverse applications, but reports on their detailed structural characterization are rare. It is often the case that even when the structure is obtained, the azoxy group is disordered, which makes it difficult to determine its geometrical parameters correctly and, in some cases, even its chemical identity (due to oxygen disorder at both nitrogen sites). Here, the molecular structure of a nitrile-substituted azoxybenzene derivative, 1,2-bis(4-cyanophenyl)diazene oxide (1), was accurately determined by single-crystal X-ray diffraction (SCXRD) performed by using crystals of a dichloromethane solvate (1a), which displays channels that propagate along the a-axis. SCXRD measurements showed no significant changes in the unit cell parameters of 1a, even at 127 °C. TG measurements reveal that 1a remains stable up to ∼190 °C, at which point dichloromethane molecules start to leave the structure, and a disordered structure (1b) forms. Compound 1 was used for the synthesis of azoxy-linked triazine-based polymer (2) by a trifluoromethanesulfonic acid-catalyzed trimerization reaction under microwave conditions. The obtained polymer 2 is an amorphous solid with good thermal stability, which exhibits a rather low BET surface area of 10.2 m2 g–1 and shows no affinity for CO2 adsorption. The preliminary investigation revealed that polymer 2 has a band gap of 2.69 eV, rendering it a wide-bandgap semiconductor.