Constitutional Isomers or Stereoisomers? With regard to a trigonal bipyramidal molecule, such as $\ce{PIBrClF_2}$, can there be any constituional isomers? I'm thinking no, because constitutional isomers differ in the connectivity of their atoms. The molecule only has single bonds. All are bound to a single central atom. There is no way for the connectivity of the atoms to change versus something such as ethanol, $\ce{C_2H_6O}$. I can think of two constitutional isomers off the bat:

$\ce{H_3CCH_2OH}$ and $\ce{H_3COCH_3}$ in which the connectivity of the atoms differ; in the former, we have a hydroxyl group; in the latter, we are missing the hydroxyl group. 

Therefore, $\ce{PIBrClF_2}$ should not have any constitutional isomers but does have stereoisomers, correct?
Correct, no constitutional isomers, but there are stereoisomers (different substituents in the apical and equatorial positions).  Just for the record, what is your fifth substituent?