Novel ultrahigh-energy materials

This paper reviews the recent work carried out in the field of modern high-energy materials (HEMs) with the emphasis on homoleptic polynitrogen compounds. A large volume of quantum-chemical investigations have predicted the possibility of existence of polynitrogen compounds not only as short-lived transient species but also in the form of isolable discrete molecules. Despite the theoretical speculations, only a few polynitrogen ions are known today in addition to well-entrenched N$_3^{1-}$ – discovered almost 100 year ago. Extraordinary potential of these green molecules to deliver high amounts of energy in comparison with today’s and tomorrow’s most powerful HEMs, namely, hexanitrohexaazaisowurtzitane (CL-20) and octanitrocubane (ONC), has fuelled the imagination of propellant and explosive engineers and technologists. Research activities are in progress in many quantum-chemical schools to explore the possibility of other promising polynitrogen compounds. After the recent discovery of key synthons/building blocks Mg(N$_5$)$_2$, N$_5^{1+}$SbF$_6^{1-}$, N$_5^{1+}$SbF$_{11}$, N$_5^{1+}$, N$_5^{1+}$SnF$_6$, and N$_5^{1+}$Sn(CF$_3$)$_4$, the wealth of polynitrogen compounds is just waiting to be harvested by the HEMs community. There are ambitious plans all over the globe to realize N$_{60}$, which only prove a eco-friendly dense powerhouse of energy.