Tori and Dumbbells

>
> Making nanotubes requires atoms that can take three neighbors to
form
> graphitic-like sheets. C, B, and N can happily bond with only three
> neighbors, but Si cannot. Si only forms covalent bonds in a
tetrahedral
> geometry. Therefor, Si nanotubes cannot be one atom thick as C, N,
and B
> nanotubes can.

But SiO2, can for three covalent bonds, so SiO2 nanotubes should be
possible. Also SiCl3H2 has the same property. The sp2 orbital is the
dominant structure in SiN so that should be able to form nanotubes.

Once you go into molecules instead of elements, Silicon becomes a
contender. After silicon, Germanium, and phosphorus, should also for
nanotubes.

Now is it absolutely necessary to have an sp2 bond structure for
nanotubes?

How small a radius does the helix need before it is called a nanotube?
This is not a acedemic question since most protiens form helices one
molecule thick, but the helices is hundreds of molecules in diameter.

Bill