Regulating of pore environment is an efficient way to improve the performance of covalent organic frameworks (COFs) for specific application requirements. Herein, the design and synthesis of two pyrene‐based 2D COFs with ‐H or ‐Me substituents, TFFPy‐PPD‐COF and TFFPy‐TMPD‐COF are reported. Both of them show long order structure and high porosity, in which TFFPy‐PPD‐COF displays a larger pore volume and bigger BET surface area (2587 m2 g−1, 1.17 cm3 g−1). Interestingly, TFPPy‐TMPD‐COF exhibits a much higher vapor iodine capacity (4.8 g g−1) than TFPPy‐PPD‐COF (2.9 g g−1), in contrast to their pore volume size. By using multiple techniques, the better performance of TFPPy‐TMPD‐COF in iodine capture is ascribed to the altered pore environment by introducing methyl groups, which contributes to the formation of polyiodide anions and enhances the interactions between the frameworks and iodine. These results will be helpful for understanding the effect of pore environment in COFs for iodine uptake and constructing novel structure with high iodine capture performance.
Metal pentazolate hydrates have attracted attention because of the unique stabilization mechanisms of cyclo-N 5 À anions during crystal stacking. However, coordinated H 2 O molecules influence the stability of cyclo-N 5 À anion-containing salts, and the structure-property relationship of high-valent cobalt pentazolate salts has not been previously reported. Werner-type cobalt(III) cations that trap cyclo-N 5 À anions, a novel class of cyclo-N 5 À -based materials, were prepared and characterized by infrared spectroscopy, elemental analysis, electrospray ionization mass spectrometry, and thermogravimetry with differential scanning calorimetry. The [Co(NH 3 ) 5 (NO 2 )] 2 + cation was also introduced via metathesis reactions to compare the intermolecular interactions in its intriguing structures. Single-crystal Xray diffraction revealed extensive hydrogen bonding networks in hexaamminecobalt(III) and nitropentamminecobalt(III) cyclo-N 5À salts between cyclo-N 5 À anions and NH 3 ligands or nitro groups. In addition, [Co(NH 3 ) 6 (N 5 ) 3 ] (1) and [Co(NH 3 ) 5 (NO 2 )](N 5 ) 2 (2) exhibited relatively high nitrogen contents of 79.2 % and 67.9 %, respectively, and the impact sensitivities of 1 (IS = 5 J) and 2 (IS = 4 J) are comparable to that of lead azide.
Herein, we present the synthesis and characterization of three novel energetic compounds based on 2,5dinitroiminooctahydroimidazo [4,5-d]imidazole (DNII). The tetrazole groups were linked to DNII through an ethylene bridge (3), a methylene bridge (5), or direct connection (6). These compounds were fully characterized and their detonation properties were well determined by quantum chemical calculations. Among them, compound 5 exhibited two crystal forms (U-5 and T-5) in methanol and water. Compared to U-5, T-5 increased in density, formation enthalpy, detonation velocity, and pressure by 0.04 g/cm 3 (2.3%), 0.22 kJ/g (8.1%), 0.34 km/s (4.2%), and 2.6 GPa (10.8%), respectively, owing to the tighter packing model. More importantly, with the gradual shortening of the linkages between imidazole and tetrazole, the performance of these compounds was gradually improved. Moreover, compound 6 showed the best detonation properties (D = 9.08 km/s, P = 33.1 GPa), which was better than TNT and close to HMX, while its sensitivity toward external forces (impact sensitivity (IS) = 40 J, friction sensitivity (FS) = 360 N) was much lower, making it safer. This work aims to prepare high-energy, low-sensitivity materials and hope to be helpful for the development of future energetic materials.
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