Donor-acceptor materials complexes

When the reaction of two compounds results in a product that contains all the mass of the two compounds, the product is called an addition compound. There are several kinds. In the rest of this chapter, we will discuss addition compounds in which the molecules of the starting materials remain more or less intact and weak bonds hold two or more molecules together. We can divide them into four broad classes electron donor-acceptor complexes, complexes formed by crown ethers and similar compounds, inclusion compounds, and catenanes. 

In analogy to its complexes with nitrosyl cation (as described above), benzene can form donor-acceptor adducts with a variety of metallic and non-metallic Lewis acids. These lead to materials with novel optical and electrical properties that can be tuned through substituents on the aromatic ring. 

The elimination reactions of /l-acetoxy sulfones 114 to give the donor-acceptor-substituted allenes 115 by a Julia-Lythgoe process are less conventional (Scheme 7.18) [157]. A new one-step synthesis of allene-l,3-dicarboxylates 118 from acetone derivatives 116 was developed by the use of 2-chloro-l,3-dimethylimidazolinium chloride 117 [158, 159]. This elimination of water follows also the general Scheme 7.17 if a derivative of the enol, resulting from 116, is assumed as an intermediate for an elimination step. More complex processes of starting materials 119 furnished allenyl ketones 120 in high yields [160-162]. 

Fig. 5. 75.4-MHz l3C cross-polarization spectra of the acetylium ion 1 on TaCl5 acquired at 298 K. The nonspinning spectrum shows a broad and axially symmetric powder pattern. The MAS spectrum shows that ca. 80% of the starting material (acetyl-f-13C chloride) was ionized to form the acetylium ion (<5lso = 153 ppm), and the rest formed the donor-acceptor complex with TaCls ( lso = 189 ppm). The nonspinning spectrum requires 20 times more scans to acquire than the MAS spectrum. The principal components of the l3C shift tensor of 1 were measured from both spectra, and the results are in very good agreement.

The terms co-ordination compound, dative covalent compound, complex, or donor-acceptor compound are used synonymously for those compounds formed by the interaction of a molecule containing an empty orbital with one that possesses a filled orbital. The term complex was used to distinguish materials such as CoBr33NH3 from simple salts such as CoBr3. Notice the use of a dot to indicate some kind of a dative covalent interaction. The molecule or ion with the filled orbital is termed the donor and that with the empty orbital is called the acceptor. Examples are known in which only main group compounds are involved (Fig. 1-1). 

In addition to the previously described donor-acceptor hybrid dyad systems, a few triads have also been considered and constructed. The fundamentals and principles for designing such triad systems are more complex, as there exist diverse arrangement options for their construction. Thus, the multiple electroactive units of a triad can be arranged in different ways giving rise to different materials [245]. 

Presumably, as in the case of Ca) fullerenes [230], donor-acceptor complexes are formed, as the curvature present in both materials classes lends acceptor character to the corresponding molecular carbon networks [231]. The stable aniline solutions of SWNTs can be diluted with other organic solvents without causing precipitation of the tubes. 

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