Bipyridinium cations

The influence of the organocation structure on the exchange adsorption becomes evident from the data in table V. 4,4 Bipyridinium cations adsorb two times more energetically (AH s 2j2 kJ Eq ) than do 2,2 bipyridinium cations (AH° = 11 f5 Eq ). The former adapt a planar orientation (dnm = f 26 nm) in contrast to the inclined position of the latter ( qq = 1.4 nm), despite the fact that sufficient surface is available for adsorption in a flat configuration. Smaller enthalpy terms are consistent with smaller electrostatic interaction energies. The reason for the tilting is unknown however. 

The phosphorescence spectra of 2,2 -bipyridine the sterically hindered 3,3 -dimethyl-2,2 -bipyridine, 4,4 -bipyri-and the monoprotonated 4,4 -bipyridinium cation ... 

The far IR spectra of the [Znd4]2- anion in salts with the 1,10-phenanthrolinium and 2,2-bipyridinium cations have been reported.1039 The anion in the former salt appears to be tetrahedral, while that in the latter is believed to be halogen-bridged. 

Since the photoreduction of viologen is induced by electron abstraction (oxidation) by the excited bipyridinium cation from the counteranion, it is difficult to relate the photoelectron transfer to the dark redox potential. However, the photosensitivity for the same skeleton is almost proportional to the first dark reduction potential, as mentioned in the previous section. The degree of solvation... 

The thiophene-bridged 4,4 -bipyridinium salts 149 and 150 can be prepared by alkylation of bis-bipyridinium cations <1999T4709>. The order of alkylation is crucial. Whereas in the thiophene derivative the xylene core is introduced in the last step, it is not possible to obtain the benzothiophene derivative in the same way due to the less stable bis-cation. Therefore, the benzothiophene unit is introduced in the last ring-closing step. 

Bipyridinium cation 9 [58], phosphonium [59-62], guanidinium [63], and vina-midinium [64] cations were used to form thermotropic ionic liquid crystals. For example, the mixture of diheptyl and dioctyl viologens 9 (20 80 by wt%) with TFSI anion forms a smectic A phase between 22° and 132°C. It was reported that the viologens show fluorescence in both non-polar and polar organic solvents, which can be useful for the development of biological and chemical sensors [65]. 

The self-assembly of a hybrid rotaxane (and related pseudocatenanes) incorporating both ammonium and bipyridinium cationic units in the linear components is known. The switchable [2]-rotaxane 46 incorporates one of each of these... 

Figure 38. Biocatalyzed photosynthetic systems mediated by photochemically generated N.N -dimethyl- 4,4 -bipyridinium cation radical.

Quenching of [ Ru(bipy)3] by [MV] (methylviologen, [MV] = N,N -dimethyl-4,4 -bipyridinium cation) proceeds with a rate constant of 1.4 x 10 M s, and flash-photolysis studies show that [Ru(bipy),] and [MV]" " are produced . Thus oxidative quenching of [ Ru(bipy)3] by is implicated ... 

Hayes, M.H.B., M.E. Pick, and B.A. Thoms. 1978a. The influence of organocation structure on the adsorption of mono- and of bipyridinium cations by expanding lattice clay minerals. I. Adsorption by Na+-montmorillonite. J. Colloid Interface Sci. 65 254-265. 

The halide salts of the dipositive iV7V -dimethyl-4,4 -bipyridinium cation react with indium monohalides to give the first reported examples of salts containing the InXg" anion, [Me2bipy] +jlnX3] (X = Cl, Br, or I). These were characterized by elemental analysis, conductivity measurements, and vibrational spectroscopy. The last technique revealed that the anions possessed symmetry, e.g. for InClg, v- 252, 102, 185, and 97 an. ... 

Typically, the CDs were shown to form inclusion complexes with some ionic polymers, with both a-CD and /3-CD complexing with ionene polymers, cationic polymers containing a polymethylene chain, and bipyridinium cation groups in aqueous solution (Figure 36.11) [81]. In these cases, the complexes proved to be water-soluble, which enabled spectroscopic methods to be used for their characterization. The NMR spectrum of the polymer in the presence of a-CD demonstrated a splitting of each peak, in addition to two sets of peaks for both methylene protons and aromatic protons this indicated that the polymer had formed a stable complex with a-CD. In contrast, the NMR spectrum showed that all the protons had broadened on the addition of /3-CD this indicated that the polymer had formed dynamic complexes with /S-CD. Notably, y-CD failed to cause any changes in the H NMR spectrum of the polymer. 

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