would Fe3+ react with Br- ?

FeBr3 is existed in the world. However, as defined in Wikilpedia, Fe3+ + Br- to form FeBr3 may not be classfied as reaction.

In Wikipedia,

"Classically, chemical reactions encompass changes that strictly involve the motion of electrons in the forming and breaking of chemical bonds, although the general concept of a chemical reaction, in particular the notion of a chemical equation, is applicable to transformations of elementary particles, as well as nuclear reactions."

So I will not say that "Fe3+ react with Br-". For example, there are H3O+ and OH- in water. H3O+ and OH- can form H2O, but we will not say there is a reaction occurred in water itself.