text: A number of organic compounds form charge-transfer complex, which are often described as electron-donor-acceptor complexes (EDA complexes).  Typical acceptors are nitrobenzenes or tetracyanoethylene (TCNE).  The strength of their interaction with electron donors correlates with the ionization potentials of the components.  For TCNE, the stability constants (L/mol) for its complexes with benzene derivatives correlates with the number of methyl groups: benzene (0.128), 1,3,5-trimethylbenzene (1.11), 1,2,4,5-tetramethylbenzene (3.4), and hexamethylbenzene (16.8).
  1,3,5-Trinitrobenzene and related polynitrated aromatic compounds, being electron-deficient, form charge-transfer complexes with many arenes.  Such complexes form upon crystallization, but often dissociate in solution to the components.  Characteristically, these CT salts crystallize in stacks of alternating donor and acceptor (nitro aromatic) molecules, i.e. A-B-A-B.