Regulation of the structure and density of KN5 frameworks with CH3COOK and CF3COOK

Abstract

Two novel potassium pentazolate frameworks KN₅·1.5CH₃COOK (1) and KN₅·3CF₃COOK (2) were achieved by changing the content and type of K-carboxylates. All the compounds were characterized via infrared (IR), single-crystal X-ray diffraction, thermogravimetric analysis, and differential scanning calorimetry. 1 exhibited two unique nanocages featuring KN₅ and CH₃COOK. 2 with a high density (2.097 g cm⁻³) was constructed by replacing the H atoms of 1 with the most electronegative F atoms. The F atoms of 2 form channels that constituted a peculiar porous structure. The electronegativity, atomic charge, and electrostatic potential were further analyzed for the differences between the two frameworks and explained the reasons for the constitution. This work demonstrates that it is possible to regulate the crystal structure and density through appropriate additives.