Self-assembled energetic coordination polymers based on multidentate pentazole cyclo-N5−

Abstract

Coordination to form polymer is emerging as a new technology for modifying or enhancing the properties of the existed energetic substances in energetic materials area. In this work, guanidine cation CN3H6+ (Gu) and 3-amino-1,2,4-triazole C2H4N4 (ATz) were crystallized into NaN5 and two novel energetic coordination polymers (CPs), (NaN5)5[(CH6-N3)N5](N5)3– ( 1 ) and (NaN5)2(C2H4N4) ( 2 ) were prepared respectively via a self-assembly process. The crystal structure reveals the co-existence of the chelating pentazole anion and organic component in the solid state. In polymer 1 , Na+ and N5– were coordinated to form a cage structure in which guanidine cation [C(NH2)3]+ was trapped; for polymer 2 , a mixed-ligand system was observed; N5– and ATz coordinate separately with Na+ and form two independent but interweaved nets. In this way, coordination polymer has been successfully utilized to modify specific properties of energetic materials through crystallization. Benefiting from the coordination and weak interactions, the decomposition temperatures of both polymers increase from 111°C (1D structure [Na(H2O)(N5)]∙2H2O) to 118.4 and 126.5°C respectively. Moreover, no crystallized H2O was generated in products to afford the anhydrous compounds of pentazole salts with high heats of formation (> 800 kJ mol–1). Compared to traditional energetic materials, the advantage in heats of formation is still obvious for the cyclo -N5– based CPs, which highlights cyclo -N5– as a promising energetic precursor for high energy density materials (HEDMs).