A diamondoid, in the context of building materials for nanotechnology components, most generally refers to structures that resemble diamond in a broad sense: namely, strong, stiff structures containing dense, 3-D networks of covalent bonds, formed chiefly from first and second row atoms with a valence of three or more. Examples of diamondoid structures would include crystalline diamond, sapphire, and other stiff structures similar to diamond but with various atom substitutions which might include N, O, Si, S, and so forth. Sp²-hybridized carbon structures that – in contrast to sp³-hybridized carbon in diamond – arrange in planar sheets ("graphene" sheets) are sometimes also included in the class of diamondoid materials for nanotechnology, e.g., graphite, carbon nanotubes consisting of sheets of carbon atoms rolled into tubes, spherical buckyballs and other graphene structures.
In the context of classical chemistry, "diamondoid" refers to variants of the carbon cage molecule known as adamantane (C10H16), the smallest unit cage structure of the diamond crystal lattice. Diamondoids also known as nanodiamonds or condensed adamantanes may include one or more cages (adamantane, diamantane, triamantane, and higher polymantanes) as well as numerous isomeric and structural variants of adamantanes and polymantanes. These diamondoids occur naturally in petroleum deposits and have been extracted and purified into large pure crystals of polymantane molecules having more than a dozen adamantane cages per molecule . These species are of interest as molecular approximations of the cubic diamond framework, terminated with C-H bonds. Cyclohexamantane may be thought of as a nanometer-sized diamond of approximately 5.6 * 10-22 grams. 
- Adamantane (C10H16)
- Iceane (C12H18)
- BC-8 (C14H20)
- Diamantane (C14H20) also diadamantane, two face-fused cages
- Triamantane (C18H24), also triadamantane. Diamantane has 4 identical faces available for anchoring a new C4H4 unit.
- Isotetramantane (C22H28). Triamantane has 8 faces on to which a new C4H4 unit can be added resulting in 4 isomers. One of these isomers displays a helical twist and is therefore prochiral. The P and M enantiomers have been separated.
- Pentamantane has 9 isomers with chemical formula C26H32 and one more pentamantane exists with chemical formula C25H30
- Cyclohexamantane (C26H30)
- Super-adamantane (C35H36)
- Basic beryllium acetate Be4O(O2CCH3)6
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