Question

Pcl5 is known by PI5 is not known . explain why?

Answer 1

There are two main reasons which determine the non-stability of PI5.
The first one is the large radius for I, which doesn’t allow to place five Iodine around phosphorus at proper distances. At the same time, as iodine is in the bottom of the group, the stability of P-I bonds are lower than for P-Cl. This is also conditioned by its large radius, which can’t promote the sufficient stabilization of bonding electrons upon bond formation.