Synthesis, spectroscopic and thermal studies of the reactions of the donors piperazine and N,N′-dimethylpiperazine with σ- and π-acceptors

The interactions of the electron donors piperazine (PIP) and N,N′-dimethylpiperazine (DMPIP) with the σ-acceptor iodine and the π-acceptors tetracyanoethylene (TCNE) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) were studied spectrophotometrically in chloroform at 25 °C. The electronic and infrared spectra of the resulting charge-transfer complexes were recorded, in addition to thermal analysis. The results obtained showed that the stoichiometries of the reactions are not fixed and depend on the nature of both the donor and the acceptor. The formed CT-complexes have the formulas of [(PIP)2I]+I3-, [(PIP)(TCNE)2], [(PIP)(DDQ)2], [(DMPIP)4I]+I3-, [(DMPIP)(TCNE)2] and [(DMPIP)(DDQ)2]. A general mechanism explaining the formation of triiodide complexes was suggested.