Pb-catalyzed transformation of aromatic nitriles to heptanitrogen anions sodium azide: a combined experimental and theoretical study.

Under hydrothermal conditions, an open-chain N anion stabilized in a metal-organic framework (MOF) was achieved for the first time the reaction of 4-fluorobenzonitrile and sodium azide with Pb ion as catalyst. The anion with symmetry in the MOF was studied by FT-IR, single-crystal XRD and theoretical calculations. Thermal analysis results demonstrated the stability of the anion in the MOF below 430 °C and a high energy content of 8.61 kJ g. The anion is also a good reducing agent. It can easily react with basic KMnO solution. Moreover, the present study indicates that the Pb ion activates the azide rather than nitrile in the reaction of nitriles with azides to form polynitrogen and this mechanism is a distinct contradiction with the previous results in which the nitrile reacts with azide in the presence of transition metal ions. Our findings may open a new avenue towards the synthesis and capture of polynitrogen compounds.