Question

What is the structure of `I_3^(-)`?

Answer 1

Do you want `I_2^(-)` or `I_3^-`?

Explanation:

`I_3^-` is a 22 valence electron system which gives 3 lone pairs around the central iodine atom...according to `"VSEPR"` the formal hybridization is `dsp^3`, which gives a trigonal bipyramidal structure with respect to the electron pairs.

However because we describe structure on the basis of bonding pairs of electrons, not non-bonding pairs, the structure is linear to a first approx., because the non-bonding pairs of electrons occupy the equatorial plane.......

And if we write Lewis structures of the ion we get.....

`I-stackrel(-)I-I` in which the CENTRAL iodine has 8 VALENCE electrons, and thus it is assigned the formal negative charge.

With `I_2^(-)` I don't know what you want..........