Charge-transfer complexes interactions

Masaguer, J.R., Sousa-Alonso, A., Garcia-Vazquez, J.A. and Sueiras, J. (1976) Molecular charge-transfer complexes. Interaction of molecular iodine with methyl derivatives of pyridine V-oxide. Acta dent. Compostelana, 13, 3-21. 

Although most nonionic organic chemicals are subject to low energy bonding mechanisms, sorption of phenyl- and other substituted-urea pesticides such as diuron to sod or sod components has been attributed to a variety of mechanisms, depending on the sorbent. The mechanisms include hydrophobic interactions, cation bridging, van der Waals forces, and charge-transfer complexes. 

Interaction of PCSs with electron acceptors and donors results in molecular complexes with partial or complete charge transfer. In particular, detailed investigations involved charge transfer complexes (CTC) of poly (schiff base), polyazines, products of thermal transformations of PAN and a number of other PCSs129, 238, 241 243, 267. ... 

Equilibrium constants for complex formation (A") have been measured for many donor-acceptor pairs. Donor-acceptor interaction can lead to formation of highly colored charge-transfer complexes and the appearance of new absorption bands in the UV-visible spectrum may be observed. More often spectroscopic evidence for complex formation takes the font) of small chemical shift differences in NMR spectra or shifts in the positions of the UV absorption maxima. In analyzing these systems it is important to take into account that some solvents might also interact with donor or acceptor monomers. 

The interaction of the template with monomer and/or the propagating radical may involve solely Van der Waals forces or it may involve charge transfer complexation, hydrogen bonding, or ionic forces (Section 8.3.5.1). In other cases, the monomer is attached to the template through formal covalent bonds (Section 8.3.5.2). 

Zollinger and coworkers (Nakazumi et al., 1983) therefore supposed that the diazonium ion and the crown ether are in a rapid equilibrium with two complexes as in Scheme 11-2. One of these is the charge-transfer complex (CT), whose stability is based on the interaction between the acceptor (ArNj) and donor components (Crown). The acceptor center of the diazonium ion is either the (3-nitrogen atom or the combined 7r-electron system of the aryl part and the diazonio group, while the donor centers are one or more of the ether oxygen atoms. The other partner in the equilibrium is the insertion complex (IC), as shown in structure 11.5. Scheme 11-2 is intended to leave the question open as to whether the CT and IC complexes are formed competitively or consecutively from the components. ... 

The proton is not the only entity that can dissociate from a substrate or bond to it. We can enumerate other interactions, such as metal-ligand complexation, ion-pair formation, charge-transfer complex formation, etc. For the sake of brevity, we treat all of these as... 

More recently, Kim et al. synthesized dendritic [n] pseudorotaxane based on the stable charge-transfer complex formation inside cucurbit[8]uril (CB[8j) (Fig. 17) [59]. Reaction of triply branched molecule 47 containing an electron deficient bipyridinium unit on each branch, and three equiv of CB[8] forms branched [4] pseudorotaxane 48 which has been characterized by NMR and ESI mass spectrometry. Addition of three equivalents of electron-rich dihydrox-ynaphthalene 49 produces branched [4]rotaxane 50, which is stabilized by charge-transfer interactions between the bipyridinium unit and dihydroxy-naphthalene inside CB[8]. No dethreading of CB[8] is observed in solution. Reaction of [4] pseudorotaxane 48 with three equiv of triply branched molecule 51 having an electron donor unit on one arm and CB[6] threaded on a diaminobutane unit on each of two remaining arms produced dendritic [ 10] pseudorotaxane 52 which may be considered to be a second generation dendritic pseudorotaxane. 

The authors [33] have elucidated the linear dependence of Ao0 (z-dep) on E for the polyanions by a quantum chemical consideration. A model Hamiltonian approach to the charge transfer (CT) interaction between a polyanion and solvents has been made on the basis of the Mulliken s CT complex theory [34]. 

Fig. 20 Log EM for interaction of end-groups on polymer chains with average polymerisation degree 3c (i) pyridine-catalysed hydrolysis of the p-nitrophenyl ester group of [27] ( ) and [28] ( ) in aqueous solution (data from Sisido et at., 1976, 1978), (f i) intramolecular charge-transfer complexes of [29] in chloroform ( ) and in ethanol (O). (Data from Sisido et at., 1977 Takagi et at., 1977)...

Figure 5.41 The optimized structure and one of three equivalent leading n-+o donor-acceptor interactions oftheCgHg- -B charge-transfer complex. (The scale in (b) is 9 A along each edge, 50% larger than in other such plots in this book.)...

Figure 5.42 The optimized structure (a) and leading nN-7TNO donor-acceptor interaction (b) of the H3N NO+ charge-transfer complex.

Figure 5.46 Optimized structure views, (a) and (b), and leading donor-acceptor interactions, (c) and (d), in the C3H6- NO+ charge-transfer complex. The contour plane of (c) and (d) corresponds approximately to view (a).

Let us briefly mention some other binary A- B charge-transfer complexes involving neutral monomers A and B chosen rather arbitrarily from the large number of possible species of this type. These examples serve to illustrate interesting aspects of the general CT phenomenon and exhibit the strong commonality with donor-acceptor interactions considered elsewhere in this book. 

Figure 5.50 The optimized structure (a) and leading 7i

---