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From monomers to π stacks, from nonconductive to conductive: Syntheses, characterization, and crystal structures of benzidine radical cations

Journal Article


Abstract


  • Salts that contain radical cations of benzidine (BZ), 3,3',5,5'- tetramethylbenzidine (TMB), 2,2',6,6'-tetraisopropylbenzidine (TPB), and 4,4'-terphenyldiamine (DATP) have been isolated with weakly coordinating anions [Al(ORF)4]- (ORF=OC(CF 3)3) or SbF6-. They were prepared by reaction of the respective silver(I) salts with stoichiometric amounts of benzidine or its alkyl-substituted derivatives in CH2Cl2. The salts were characterized by UV absorption and EPR spectroscopy as well as by their single-crystal X-ray structures. Variable-temperature UV/Vis absorption spectra of BZ.+[Al(ORF)4] - and TMB.+[Al(ORF) 4]- in acetonitrile indicate an equilibrium between monomeric free radical cations and a radical-cation dimer. In contrast, the absorption spectrum of TPB.+SbF6- in acetonitrile indicates that the oxidation of TPB only resulted in a monomeric radical cation. Single-crystal X-ray diffraction studies show that in the solid state BZ and its methylation derivative (TMB) form radical-cation π dimers upon oxidation, whereas that modified with isopropyl groups (TPB) becomes a monomeric free radical cation. By increasing the chain length, π stacks of π dimers are obtained for the radical cation of DATP. The single-crystal conductivity measurements show that monomerized or π-dimerized radicals (BZ.+, TMB.+, and TPB .+) are nonconductive, whereas the π-stacked radical (DATP.+) is conductive. A conduction mechanism between chains through π stacks is proposed.

Authors


  •   Chen, Xiaoyu (external author)
  •   Ma, Binbin (external author)
  •   Wang, Xingyong
  •   Yao, Shengxin (external author)
  •   Ni, Lichen (external author)
  •   Zhou, Zhaoyi (external author)
  •   Li, Yizhi (external author)
  •   Huang, Wei (external author)
  •   Ma, Jing (external author)
  •   Zuo, Jing-Lin (external author)
  •   Wang, Xinping (external author)

Publication Date


  • 2012

Citation


  • Chen, X., Ma, B., Wang, X., Yao, S., Ni, L., Zhou, Z., Li, Y., Huang, W., Ma, J., Zuo, J. & Wang, X. (2012). From monomers to π stacks, from nonconductive to conductive: Syntheses, characterization, and crystal structures of benzidine radical cations. Chemistry: A European Journal, 18 (37), 11828-11836.

Scopus Eid


  • 2-s2.0-84865747528

Ro Metadata Url


  • http://ro.uow.edu.au/smhpapers/3926

Has Global Citation Frequency


Number Of Pages


  • 8

Start Page


  • 11828

End Page


  • 11836

Volume


  • 18

Issue


  • 37

Place Of Publication


  • Germany

Abstract


  • Salts that contain radical cations of benzidine (BZ), 3,3',5,5'- tetramethylbenzidine (TMB), 2,2',6,6'-tetraisopropylbenzidine (TPB), and 4,4'-terphenyldiamine (DATP) have been isolated with weakly coordinating anions [Al(ORF)4]- (ORF=OC(CF 3)3) or SbF6-. They were prepared by reaction of the respective silver(I) salts with stoichiometric amounts of benzidine or its alkyl-substituted derivatives in CH2Cl2. The salts were characterized by UV absorption and EPR spectroscopy as well as by their single-crystal X-ray structures. Variable-temperature UV/Vis absorption spectra of BZ.+[Al(ORF)4] - and TMB.+[Al(ORF) 4]- in acetonitrile indicate an equilibrium between monomeric free radical cations and a radical-cation dimer. In contrast, the absorption spectrum of TPB.+SbF6- in acetonitrile indicates that the oxidation of TPB only resulted in a monomeric radical cation. Single-crystal X-ray diffraction studies show that in the solid state BZ and its methylation derivative (TMB) form radical-cation π dimers upon oxidation, whereas that modified with isopropyl groups (TPB) becomes a monomeric free radical cation. By increasing the chain length, π stacks of π dimers are obtained for the radical cation of DATP. The single-crystal conductivity measurements show that monomerized or π-dimerized radicals (BZ.+, TMB.+, and TPB .+) are nonconductive, whereas the π-stacked radical (DATP.+) is conductive. A conduction mechanism between chains through π stacks is proposed.

Authors


  •   Chen, Xiaoyu (external author)
  •   Ma, Binbin (external author)
  •   Wang, Xingyong
  •   Yao, Shengxin (external author)
  •   Ni, Lichen (external author)
  •   Zhou, Zhaoyi (external author)
  •   Li, Yizhi (external author)
  •   Huang, Wei (external author)
  •   Ma, Jing (external author)
  •   Zuo, Jing-Lin (external author)
  •   Wang, Xinping (external author)

Publication Date


  • 2012

Citation


  • Chen, X., Ma, B., Wang, X., Yao, S., Ni, L., Zhou, Z., Li, Y., Huang, W., Ma, J., Zuo, J. & Wang, X. (2012). From monomers to π stacks, from nonconductive to conductive: Syntheses, characterization, and crystal structures of benzidine radical cations. Chemistry: A European Journal, 18 (37), 11828-11836.

Scopus Eid


  • 2-s2.0-84865747528

Ro Metadata Url


  • http://ro.uow.edu.au/smhpapers/3926

Has Global Citation Frequency


Number Of Pages


  • 8

Start Page


  • 11828

End Page


  • 11836

Volume


  • 18

Issue


  • 37

Place Of Publication


  • Germany