Species Formed on Fluorination of Phosphorus Pentachloride

To determine the species formed upon the fluorination of phosphorus pentachloride ($\text{PCl}_5$) in a polar organic solvent, we analyze the structure and reactivity of $\text{PCl}_5$ during the substitution reaction:

1. Ionic Nature in Polar Media: In polar solvents (as well as in the solid state), phosphorus pentachloride auto-ionizes and exists in an ionic structure as: $2\text{PCl}_5 \rightleftharpoons [\text{PCl}_4]^+[\text{PCl}_6]^-$

2. Fluorination Mechanism: When a fluorinating agent (such as $\text{AsF}_3$ or $\text{SbF}_5$) is added in a polar solvent, chloride ions are progressively substituted by fluoride ions.

   • Partial Fluorination: The octahedral anion $[\text{PCl}_6]^-$ undergoes fluorination more readily than the tetrahedral cation $[\text{PCl}_4]^+$ due to higher nucleophilic susceptibility. This yields the stable hexafluorophosphate species $[\text{PCl}_4]^+[\text{PF}_6]^-$: $3[\text{PCl}_4]^+[\text{PCl}_6]^- + 2\text{AsF}_3 \rightarrow 3[\text{PCl}_4]^+[\text{PF}_6]^- + 2\text{AsCl}_3$

   • Complete Fluorination: Upon further fluorination, the chlorine atoms on the tetrachlorophosphonium cation $[\text{PCl}_4]^+$ are also replaced by fluorine atoms, forming the tetrafluorophosphonium cation $[\text{PF}_4]^+$. This yields the ionic compound $[\text{PF}_4]^+[\text{PF}_6]^-$: $[\text{PCl}_4]^+[\text{PF}_6]^- + \text{fluorinating agent} \rightarrow [\text{PF}_4]^+[\text{PF}_6]^-$

Therefore, the species formed on fluorination of phosphorus pentachloride in a polar organic solvent are $[\text{PF}_4]^+[\text{PF}_6]^-$ and $[\text{PCl}_4]^+[\text{PF}_6]^-$.

Correct Option: A