Three unexpected cadmium(II)-based energetic metal–organic frameworks derived from 2-(dinitromethylene)-1,3-diazacyclopentane

Abstract

One cadmium–DNDZ [DNDZ = 2-(dinitromethylene)-1,3-diazacyclopentane] complex [Cd(NH3)4(DNDZ)2 (1)] and three unexpected cadmium–ADNA [ADNA = N-(2-aminoethyl)-2,2-dinitroacetamide] metal–organic frameworks (MOFs) {[Cd(NH3)2(ADNA)2]n (2), [Cd(CH3NH2)2(ADNA)2]n (3) and [Cd(CH3CH2NH2)2(ADNA)2]n (4)} were first synthesized by reactions of cadmium nitrate and DNDZ potassium salt in different aqueous amines. DNDZ molecules underwent a ring-opening reaction resulting in the formation of a new chain-like molecule ADNA, which is found for the first time and only in the cadmium(II) coordination environment compared with the previous other metal–DNDZ complexes, so the cadmium(II) ions should have special catalysis to the ring-opening reaction. The single crystal structures of complexes 1, 3 and 4 were obtained. The central cadmium(II) ion can form a distorted octahedral structure with six coordination atoms. Thermal behaviors and impact sensitivities of the four complexes were studied. Complex 1 presents one exothermic decomposition process (248.17 °C) after two consecutive endothermic processes, but the three MOFs present only one exothermic decomposition process and their peak temperatures are close to one another (about 168 °C). The impact sensitivities of the four complexes are tested to be >20 J for 1, >16 J for 2, >17 J for 3 and >11 J for 4, respectively.