Zinc (II) Imidoyl Azide Coordination Polymer, an Unexpected Compound with Insensitive Explosive Properties

Abstract A wide interest has recently been shown for the use of the tetrazole ring structures in the preparation of insensitive high‐energy materials. Tetrazoles provide a perfect balance between insensitivity and explosive performances and several synthetic routes are available to generate such compounds in high yields. When studying the two‐step synthesis of N,N’‐bis((1H‐tetrazol‐5‐yl)methyl)nitramide (BTMNA), suggested by Shreeve et al ., an unexpected intermediate structure was observed. This stable intermediate in aqueous conditions, reacted with hydrochloric acid to generate the desired tetrazole heterocycle suggesting the existence of a scarce organozinc imidoyl azide compound, also coined “open tetrazole” . This unusually stable structure is exceptionally isolated as a solid. Furthermore, the possibility of zinc ions coordinating several organic imidoyl azide molecules at the same time, creates a sparse and unprecedented coordination polymer. This new polymeric intermediate is revealed in the synthesis of BTMNA when the starting material, the iminodiacetonitrile (IDA), reacts with sodium azide in water with the assistance of zinc chloride. The intermediate was characterized by Infrared spectroscopy (IR), Differential Scanning Calorimetry (DSC), Thermogravimetric analysis (TGA), and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP‐OES). The observation of such unprecedented intermediates shows the mechanism complexity of the Demko‐Sharpless [3+2] cycloaddition and broadens the understanding of the formation and potential use of organic zinc imidoyl azide coordination polymers as insensitive explosives.