CUBANES: INTRA- AND SUPRA- MOLECULAR TRENDS. Richard Gilardi, Philip E. Eaton^* and Raymond J. Butcher⁺. Naval Research Laboratory, Washington, DC 20375-5341; ^*Univ. of Chicago, Chicago, IL; and ⁺Howard Univ., Washington, DC; all USA.

Large bond angle deformations in cubane make it a powerhouse of stored energy. Thus cubane might provide more powerful fuels, propellants, and explosives if its chemistry were mastered. The mere possibility of cubane itself was debated until it was made in 1964 and found to be a stable compound, with a shelf life of years. For ca. 20 years, few derivatives of cubane were known, but substitution methodology for cubanes has now been developed^1,2, and X-ray studies of many (>20) substituted cubanes have been reported & recently reviewed³. In 1994 and 1995, pentanitro-cubane, hexanitrocubane, and several octa-substituted cubanes were first made (at the Univ. of Chicago) and studied at NRL².

Surprisingly, the cubane framework is not rigid. Systematic deformations occur. Though saturated CC cube-edge bonds are usually longer (ave. 1.559A) than those in unstrained compounds, they are shortened, for no apparent reason, when eclipsed with a nitro group or when fused to an imidazolidone ring. Bond angles are also distorted; the interior angles at a cube corner are all larger than 90deg. at a nitro group site, while at other corners in the same cube they are smaller. Similar effects are seen in alkynylcubanes⁴.

A pseudo-HCP packing was reported for cubane. Poly-cubanes and alkynyl-cubanes⁴ show a tendency to assemble in simple, perhaps predict-able, patterns (like `stacked logs') that are hexagonal in one projection.

1. P.E. Eaton, et al, J. Am. Chem. Soc. 115, 10195-10202(1993).

2. R. Gilardi et al, Angewandte Chemie, (accepted, 1996).

3. R.J. Butcher, et al, J. Chem. Crystall. 25, 661-670(1995).

4. P.E. Eaton, et al, J. Am. Chem. Soc. 116, 7588-7596(1994).