Why sulphur hexaiodide does not exist?

Question

Why sulphur hexaiodide does not exist?

Answer 1

Interesting.  There's just not much on the web for compounds of sulfur and iodine.

You can find a mention of S2I2, but no SI6.

And this one on S2I4^2+ is interesting:

http://pubs.acs.org/cen/science/83/i12/8...

But even this is a loose alignment of S2 and two I2 units.

The two elements have almost the same electronegativity, so iodine has no tendency to attract the electrons of sulfur.  

Sulfur would have to hybridize as sp3d2 to accommodate six iodine atoms.  Perhaps there is a size issue, so that it is difficult to get six iodine atoms around a single sulfur atom.  The iodines would be more stable as I2 than in a compound with sulfur.

============ Follow up =============

I suggested earlier that there might be an issue with the relative sizes, so I checked them.

Atomic radius S = 0.104 nm

Atomic radius I = 0.128 nm

By way of comparison SF6 does indeed exist.  A fluorine atom has an atomic radius of 0.072 nm.  Then we can conclude that fluorine is small enough to fit six around the sulfur;   Also, fluorine is much more electronegative than is iodine, and will produce much more polar bonds.

Answer 2

The iodine atom is just too big for 6 of them to fit around the sulfur atom