Synthesis, characterization, and comparison of explosive hexaamminecobalt(III) and nitropentamminecobalt(III) cyclopentazolate (cyclo-N-5-) salts

Metal pentazolate hydrates have attracted attention because of the unique stabilization mechanisms of cyclo-N-5(-) anions during crystal stacking. However, coordinated H2O molecules influence the stability of cyclo-N-5(-) 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(-) anions, a novel class of cyclo-N-5(-)-based materials, were prepared and characterized by infrared spectroscopy, elemental analysis, electrospray ionization mass spectrometry, and thermogravimetry with differential scanning calorimetry. The [Co(NH3)(5)(NO2)](2+) cation was also introduced via metathesis reactions to compare the intermolecular interactions in its intriguing structures. Single-crystal X-ray diffraction revealed extensive hydrogen bonding networks in hexaamminecobalt(III) and nitropentamminecobalt(III) cyclo-N-5(-) salts between cyclo-N-5(-) anions and NH3 ligands or nitro groups. In addition, [Co(NH3)(6)(N-5)(3)] (1) and [Co(NH3)(5)(NO2)](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.