Hexanitrohexaazaisowurtzitane

Hexanitrohexaazaisowurtzitane, also called HNIW and CL 20, is a polycyclic nitroamine explosive with the formula |C6H6N12O12. In the 1980s, CL 20 was developed by the China Lake facility, primarily to be used in propellants. It has a better oxidizer to fuel ratio than conventional HMX or RDX. It releases 20% more energy than traditional HMX based propellants. While most development of CL 20 has been fielded by the Thiokol Corporation, the US Navy (through ONR) has also been interested in CL 20 for use in rocket propellants, such as for missiles, as it has lower observability characteristics such as less visible smoke. Thus far, CL 20 has only been used in the AeroVironment Switchblade 300 “kamikaze” drone, but is undergoing testing for use in the Lockheed Martin [LMT] AGM 158C Long Range Anti Ship Missile (LRASM) and AGM 158B Joint Air to Surface Standoff Missile Extended Range (JASSM ER). The Indian Armed Forces have also looked into CL 20.

First, benzylamine (1) is condensed with glyoxal (2) under acidic and dehydrating conditions to yield the first intermediate compound.(3). Four benzyl groups selectively undergo hydrogenolysis using palladium on carbon and hydrogen. The amino groups are then acetylated during the same step using acetic anhydride as the solvent. (4). Finally, compound 4 is reacted with nitronium tetrafluoroborate and nitrosonium tetrafluoroborate, resulting in HNIW.

In August 2012, Onas Bolton et al. published results showing that a cocrystal of 2 parts CL 20 and 1 part HMX had similar safety properties to HMX, but with a greater firing power closer to CL 20.

In August 2011, Adam Matzger and Onas Bolton published results showing that a cocrystal of CL 20 and TNT had twice the stability of CL 20—safe enough to transport, but when heated to the cocrystal may separate into liquid TNT and a crystal form of CL 20 with structural defects that is somewhat less stable than CL 20.

In 2017, K. P. Katin and M. M. Maslov designed one dimensional covalent chains based on the CL 20 molecules. Such chains were constructed using molecular bridges for the covalent bonding between the isolated CL 20 fragments. It was theoretically predicted that their stability increased with efficient length growth. A year later, M. A. Gimaldinova and colleagues demonstrated the versatility of molecular bridges. It is shown that the use of bridges is the universal technique to connect both CL 20 fragments in the chain and the chains together to make a network (linear or zigzag). It is confirmed that the increase of the effective sizes and dimensionality of the CL 20 covalent systems leads to their thermodynamic stability growth. Therefore, the formation of CL 20 crystalline covalent solids seems to be energetically favorable, and CL 20 molecules are capable of forming not only molecular crystals but bulk covalent structures as well. Numerical calculations of CL 20 chains and networks' electronic characteristics revealed that they were wide bandgap semiconductors.