Question

why in solid state PCl5 behaves as ionic species??

Answer 1

PCl5 exists in ionic state in solids. The reason being that it does not exists simply as a PCl5 molecule. Rather it forms two complex compounds:-

1. PCl4+  

2. PCl6-

So it exists as an ionic compound with formula [PCl4]+[PCl6]-.

I hope you will find my answer helpful!

Answer 2

PCL5 exist as pcl4 plus and PCL 6 - in its solid state so daring the solid state PCL5 behaves as a ionic species