* Inorganic compounds generally lack carbon-hydrogen bonds (C-H).

* Diamond is a crystalline form of pure carbon where each carbon atom is bonded to four other carbon atoms in a tetrahedral arrangement. This structure lacks C-H bonds, making it inorganic.

Other examples of inorganic forms of carbon include:

* Graphite: Another crystalline form of carbon with a layered structure.

* Fullerene: A molecule composed of carbon atoms that form a hollow sphere, ellipsoid, or tube.

* Carbon nanotubes: One-dimensional cylindrical structures of carbon atoms.

* Carbon nanofoam: An ultralight, porous form of carbon with a sponge-like structure.

While all these are composed of carbon, their structures and lack of C-H bonds classify them as inorganic compounds.