title: From monomers to π stacks, from nonconductive to conductive: syntheses, characterization, and crystal structures of benzidine radical cations.
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(OR(F))(4)](-) (OR(F) = OC(CF(3))(3)) or SbF(6)(-). They were prepared by reaction of the respective silver(I) salts with stoichiometric amounts of benzidine or its alkyl-substituted derivatives in CH(2)Cl(2). 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(OR(F))(4)](-) and TMB(·)(+)[Al(OR(F))(4)](-) in acetonitrile indicate an equilibrium between monomeric free radical cations and a radical-cation dimer. In contrast, the absorption spectrum of TPB(·)(+)SbF(6)(-) 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: State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, PR China.
authors: Xiaoyu
authors: X
authors: Chen
authors: Binbin
authors: B
authors: Ma
authors: Xingyong
authors: X
authors: Wang
authors: Shengxin
authors: S
authors: Yao
authors: Lichen
authors: L
authors: Ni
authors: Zhaoyi
authors: Z
authors: Zhou
authors: Yizhi
authors: Y
authors: Li
authors: Wei
authors: W
authors: Huang
authors: Jing
authors: J
authors: Ma
authors: Jinglin
authors: J
authors: Zuo
authors: Xinping
authors: X
authors: Wang
mesh_terms: D001560:Benzidines / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D018360:Crystallography, X-Ray; D004553:Electric Conductivity; D005609:Free Radicals / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry
chemical_list: D001560:Benzidines; D002412:Cations; D005609:Free Radicals; D009942:Organometallic Compounds; C029876:benzidine