Donor-acceptor complexation

Bivalent tin compounds can act both as donors and as acceptors in the same molecule, as in FsB- S11X2 - - NMes (X = Cl, Br). The acceptor-donor complex (17) was obtained on treatment of the tin-nitrogen cage compound (18) with AI2CI6 (18) was produced from (5) and t-Bu2 NH (equation 3). Various other tin-nitrogen cages have been characterized, e.g. (19)-(22). ... 

Fig. 3. A switchable rotaxane based on acceptor-donor complexes [24]. Before oxidation, the electron acceptor (ring) interacts preferentially with the benzidine nucleus (donor). After electrochemical oxidation of the latter, the ring is shifted towards the biphenol group. The process is reversible...

Adsorption of SOC by activated carbon may involve various combinations of chemical, electrostatic, and physical (i.e. non-specific dispersion forces) interactions [59]. The overall adsorption interactions can be very complex for some SOCs. One good example is the adsorption of phenolic compounds, probably the most widely studied class of adsorbates in the activated carbon literature. Several possible mechanisms have been proposed for phenol adsorption [60-69]. These incluile (i) n-n dispersion interactions between the basal plane of activated carbon and the aromatic ring of the adsorbate, (ii) electrostatic attraction-repulsion interactions, (iii) hydrogen bonding between adsorbate and surface functional groups of activated carbons, (iv) electron acceptor-donor complex formation mechanisms between the carbonyl... 

Sainte-Catherine, J. Fraysse, J. Photovoltaic cells consisting of electron acceptor-donor complexes of carbon nanotubes, adsorbed dyes, and conjugated polymers. PCX Int. Appl. WO 2004112163, 2004 Chem. Abstr. 2004,142, 77596. 

A change in slope of the Arrhenius plot was found, and this was explained in terms of a mechanism which involved acceptor-donor complex formation. 

Phosphite triesters, P(OR)3, form donor complexes with transition metals and other acceptors and are oxidized to the respective phosphates under appropriate conditions. 

In this mechanism, a complexation of the electrophile with the 7t-electron system of the aromatic ring is the first step. This species, called the 7t-complex, m or ms not be involved directly in the substitution mechanism. 7t-Complex formation is, in general, rapidly reversible, and in many cases the equilibrium constant is small. The 7t-complex is a donor-acceptor type complex, with the n electrons of the aromatic ring donating electron density to the electrophile. No position selectivity is associated with the 7t-complex. 

In electron donor-acceptor (EDA) complexes, there is always a donor molecule and an acceptor. The donor may donate an unshared pair (an n donor) or a pair of electrons in a ti orbital of a double bond or aromatic system (a it donor). One test for the presence of an EDA complex is the electronic spectrum. These complexes generally exhibit a spectrum (called a charge-transfer spectrum) that is not the same as the sum of the spectra of the two individual molecules. Because the first excited state of the complex is relatively close in energy to the ground state, there is usually a... 

It has been shown that in certain cases (e.g., Me4Sn + I2) the reactants in an Se2 reaction, when mixed, give rise to an immediate charge-transfer spectrum (p. 102), showing that an electron donor-acceptor (EDA) complex has been formed. In these cases it is likely that the EDA complex is an intermediate in the reaction. 

In group transfer reactions, a group G is transferred from a donor D to an acceptor A, forming an acceptor group complex A-G ... 

The first example of a donor-acceptor molecular complex was noted in 1949 by Bensei and Hildebrand [137] in their studies involving charge transfer complexes between benzene and molecular iodine. Subsequently such complexes were studied by Mulliken [138] and now more recently have been used by Stoddart et al. [16,139] in designing novel self-assembling systems. 

This association has its counterpart that was also variously described as an encounter complex, a nonbonded electron donor-acceptor (EDA) complex, a precursor complex, and a contact charge-transfer complex.10 For electrically charged species such as anion/cation pairs (which are relevant to ion-pair annihilation), the pre-equilibrium association results in contact ion pairs (CIP)7 (equation 3)... 

In Chapter 8, Stavola and Pearton discuss the local vibrational modes of complexes in Si that contain hydrogen or deuterium. They also show how one can use applied stress and polarized light to determine the symmetry of the defects. In the case of the B-H complex, the bond-center location of H is confirmed by vibrational and other measurements, although there are some remaining questions on the stress dependence of the Raman spectrum. The motion of H in different acceptor-H complexes is discussed for the Be-H complex, the H can tunnel between bond-center sites, while for B-H the H must overcome a 0.2 eV barrier to move between equivalent sites about the B. In the case of the H-donor complexes, instead of bonding directly to the donor, H is in the antibonding site beyond the Si atom nearest to the donor. The main experimental evidence for this is that nearly the same vibrational frequency is obtained for the different donor atoms. There is also a discussion of the vibrational modes of H tied to crystal defects such as those introduced by implantation. The relationship of the experimental results to recent theoretical studies is discussed throughout. 

Characteristic infrared absorption lines have been identified for various hydrogen-acceptor and hydrogen-donor complexes (see Chapter 8), and the strength of such a line in any given specimen is a measure of the quantity of the complex present. However, depth resolution is crude, and masking by free-carrier absorption is sometimes a problem. Raman lines have also been seen (see Chapter 8) and in principle should be capable of detecting species that are not infrared active however, the sensitivity is low, and the most interesting and presumably abundant species, an H2 complex, has not yet been detected in this way. 

Germanium was the first crystalline semiconductor in which a number of shallow acceptor and donor complexes were discovered that were unambiguously proven to contain hydrogen. This series of discoveries began in the 1970s when several laboratories conducted research and development efforts with the aim of producing ultra-pure Ge single crystal for radiation... 

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