Higher Diamondoids: A New Class Of 3-D Diamond Molecules 1 To 2 nm in Size

Hydrogen-terminated diamonds form a continuous series of molecules ranging in size from macroscopic diamonds, to micron-sized diamonds (including CVD diamonds), to ultra-nanocrystalline diamonds (including ion implant and detonation diamonds as small as 2 to 3 nm), to higher diamondoids (recently isolated for the first time by us, and having sizes from ~1 to 2 nm), finally ending with the lower diamondoids of which, adamantane, consisting of one C10 diamond crystal lattice cage, is the smallest. Except for the higher diamondoids, which have not been available until now, all of these forms have been studied, characterized and used in a variety of applications. We have identified and isolated higher diamondoids (C22 and higher polymantanes) including tetramantanes, pentamantanes, hexamantanes, heptamantanes, octamantanes, nonamantanes, a decamantane and an undecamantane from petroleum. These molecules contain from four to eleven diamond crystal cages face-fused in a variety of ways to give a variety of geometries. Exceptional thermal stability and diverse geometries make possible their isolation from petroleum. Structures were proven by single crystal X-ray crystallography for selected members of three families of higher diamondoids. As members of the H-terminated diamond series, these molecules have great strength and rigidity, but they also show a remarkable variety of 3-dimensional shapes, including resolvable chiral forms (some with unusual primary helical structures, where the helicity is built into the backbone of the molecule, rather than arising from steric effects, such as in the helicenes). Properties of higher diamondoids can be tuned by the attachment of various functional groups, allowing customized mechanical, electronic and biomedical properties. The combination of diamond structure and versatile derivative chemistries, gives these 3-D, 1-2 nm size, chiral/achiral higher diamondoids potential for applications in a wide range of fields, including pharmaceuticals, microelectronics, optics, lubricants, and specialty chemicals. They are useful molecular building blocks that may find applications in nanotechnology and new nanostructured materials. Research quantities of higher diamondoids will be produced this year and larger quantities in the future.