why is tin(2) iodide a negligible product in the direct synthesis of tin(4)iodide?

Answer 1

By direct synthesis, do you mean the reaction of metalic tin with iodine?

Sn + 2I2 --> SnI4

This is usually done in CCl4 as a solvent. The reaction is an oxidation-reduction reaction. Tin is very easlity oxidized from the metal to the tin(4) ion, especially by the halogens, such as Iodine, which has a very strong oxidizing potential.

If you look at the first part of a possible reaction:

Sn + I2 --> (Sn)+2 + 2 I-

the (Sn)+2 is rapidly consumed by reacting with additional I2:

(Sn)+2 + I2 --> (Sn)+4 + 2I-

The Tin(II) ions are more easily oxidized than the Tin atoms.