Stabilization of pentazolate anions in the high-pressure compounds Na2N5and NaN5and in the sodium pentazolate framework NaN5·N2

Abstract

Synthesis and characterization of nitrogen-rich materials is important for the design of novel high energy density materials due to extremely energetic low-order nitrogen-nitrogen bonds. The balance between the energy output and stability may be achieved if polynitrogen units are stabilized by resonance as incyclo-N5−pentazolate salts. Here we demonstrate the synthesis of three oxygen-free pentazolate salts Na2N5, NaN5and NaN5·N2from sodium azide NaN3and molecular nitrogen N2at ∼50 GPa. NaN5·N2is a metal-pentazolate framework (MPF) obtainedviaa self-templated synthesis method with nitrogen molecules being incorporated into the nanochannels of the MPF. Such self-assembled MPFs may be common in a variety of ionic pentazolate compounds. The formation of Na2N5demonstrates that thecyclo-N5group can accommodate more than one electron and indicates the great accessible compositional diversity of pentazolate salts.