Type 14 complexes include electrophilic haloenium ion or carbenium ion reagents with non-electrophilic counter ions.
Lobe-LUMO Lewis acids have a strong symbiotic affinity for halogen anion ligands, close in type to those they already possess. Thus:
• AlCl3 has a high affinity for Cl– to give [AlCl4]–
• FeBr3 has a high affinity for Br– to give [FeBr4]–
Type 14 complexes are not prepared from the cation plus anion, but from the dihalogen, organic halide or acyl halide plus halophilic Lewis acid:
Cl2 + AlCl3 Cl+ [AlCl4]–
R–Cl + AlCl3 R+ [AlCl4]–
The resulting Type 14 complexes act as sources of "naked" electrophilic Cl+, Br+ and R3C+, etc. that are able to undergo electrophilic aromatic substitution with benzene and other aromatics: