2004 Volume 77 Issue 4 Pages 681-686
Charge-transfer complexes of 1,2,4-triazole (1T), 3-amino-1,2,4-triazole (2T), 4-amino-4H-1,2,4-triazole (3T), and guanazole (3,5-diamino-1,2,4-triazole) (4T) with iodine as a typical σ-type acceptor and with typical π-type acceptors (tetracyanoethene (TCNE) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)) have been synthesized and characterized. The spectral characteristics and thermodynamic properties of such CT complexes were investigated. The system triazoles/iodine is characterized by the formation of triiodide ions (I3−), which is proposed to occur via the initial formation of outer-sphere charge-transfer complexes. The systems (1T–4T)/TCNE and (1T–4T)/DDQ produced the corresponding anion radicals, TCNE•− and DDQ•−, respectively. The time dependency of the spectral bands due to the 4T/TCNE system is discussed in terms of the scope of transformation from outer-sphere CT complexes to inner-sphere ones. Meanwhile, for the system 4T/DDQ the time dependency is accounted for by the stepwise reduction of DDQ to its anion radicals, and then to the corresponding hydroquinone (2,3-dichloro-5,6-dicyanohydroquinone), DDQH2. However, because the resulting in situ (DDQH2) was an unconventional new acceptor, it formed a CT complex with the donor (4T). The results show that the formed complexes are strong kinds of n–σ and n–π types in a 1:2 and 1:1 stoichiometry for the complexes of triazoles donors with iodine and DDQ, respectively.
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