Electron-donor molecule

Electron donor molecules are oxidized in solution easily. Eor example, for TTE is 0.33V vs SCE in acetonitrile. Similarly, electron acceptors such as TCNQ are reduced easily. TCNQ exhibits a reduction wave at — 0.06V vs SCE in acetonitrile. The redox potentials can be adjusted by derivatizing the donor and acceptor molecules, and this tuning of HOMO and LUMO levels can be used to tailor charge-transfer and conductivity properties of the material. Knowledge of HOMO and LUMO levels can also be used to choose materials for efficient charge injection from metallic electrodes. 

These two-step features, which will be further proved by the FTIR spectra of adsorbed CO, can be summarized as follows. The adsorption of CO, being accompanied by the increase of the coordination munber due to the formation of mono- and dicarbonyl species, causes a shift of the d - d transitions toward the values more typical of the octahedral coordination. Furthermore, in the presence of CO (electron donor molecule) more energy is required to transfer electrons from O to Cr as a consequence, the O Cr(II) CT transition shifts at higher frequencies (from 28000-30000 to 33 700cm ). At increasing CO pressure the CO Cr(II) CT transition also becomes visible (band at 33400 cm ). Analogous features have been reported in the past for NO adsorption on the reduced Cr/Si02 system [48,82]. 

For some strong electron donor molecules the polarization of the X2 molecule may be sufficient that the X atom not complexed to B serves as an electron donor to a second X2 molecule, i.e., the dihalogen is amphoteric , acting as a Lewis acid to Lewis base B, and as a Lewis base to the second X2 molecule, acting as a Lewis acid. For a 1 1 B X2 X2 ratio, an extended adduct (Fig. 1, mode AA) is formed, as illustrated in Fig. 2c for 4,5-bis(bromomethyl)-l,3-dithiole-2-thione-diiodine diiodine (HAMCAA) [58]. This is often referred to as an extended spoke structure. If the second X2 acts as Lewis acid acceptor at either end of the molecule, then a bridged amphoteric adduct (Fig. 1, mode BA) is formed, as illustrated for (acridine I2)2 I2 (QARGIZ) [31] in Fig. 2d. 

As for Erep, Ect is derived from an early simplified perturbation theory due to Murrel [46], Its formulation [47,48] also takes into account the Lrj lone pairs of the electron donor molecule (denoted molecule A). Indeed, they are the most exposed in this case of interaction (see Section 6.2.3) and have, with the n orbital, the lowest ionization potentials. The acceptor molecule is represented by bond involving an hydrogen (denoted BH) mimicking the set, denoted < > bh, of virtual bond orbitals involved in the interaction. 

Coming back to thermal homogeneous dissociative electron transfer reactions, the question arises whether the electron-donor molecule reacts as a single electron donor or as a nucleophile in an Sn2 reaction. We will review this long-debated question in Section 7, including the most recent developments. 

The electron-donor molecule most studied as a component of cation-radical salts is BEDT-TTF. Over 50 superconducting salts containing this molecule have been reported in the literature. Several distinct packing motifs [6-8] of the BEDT-TTF radical cations have yielded superconducting salts, but the most studied of these are... 

Scheme 1 Electron-donor molecules that have been utilized as components of cation radical salts with organometallic anions...

Fig. 2 Packing diagram of the layered structure of kl-(BEDT-TTF)2Cu(CF3)4(TCE) (top). The packing motif of the BEDT-TTF electron donor molecules (lower left). The anion layer contains both disordered [Cu(CF3)4] anions and neutral TCE solvent molecules (lower right). In all cases, hydrogen atoms have been omitted for clarity...

When the BETS donor replaces the BEDT-TTF electron donor molecule during the electrocrystallization process, crystals of KL-(BETS)2Ag(CF3)4(TCE) have been prepared [29] and structurally characterized. Replacement of the inner sulfur atoms of BEDT-TTF with selenium results in a slight expansion of the unit cell and prevents the stabilization of a superconducting state above 1.2 K. Disorder in one of the BETS ethylene endgroups has been offered as a possible explanation. 

The l,l -diferrocenyl-VT electron donor molecule is structurally similar to diferrocenyltetrathiafulvalene but with the TTF moiety replaced by bis(vinylene-dithio)tetrathiafulvalene (VT) [76]. It has currently not been possible to separate the cis- and trans-isomers. The 1 1 polyiodide complex of l,l -diferrocenyl-VT was obtained through reaction with iodine. EPR and Mossbauer spectra indicate that in this charge transfer salt the VT moiety is oxidized while the ferrocene... 

Knowledge of the gas-phase interactions between cations involving elements of group 14 and electron donor molecules has been used to create various basicity scales. In addition, the absolute methyl cation affinities (MCA) scale has been built by calculating the... 

In principle, aliphatic amines may interact as n electron donor molecules towards electron acceptor centres such as aromatic substrates, both homocyclic and heterocyclic, containing electron-withdrawing groups, usually nitro groups. These interactions are mainly electron donor-acceptor (EDA) interactions, in which aromatic amines are considered n or/and tt electron donors. 

One-electron oxidation of organoselenium and organotellurium compounds results in initial formation of a radical cation (equations (19) and (20)). The eventual fate of the radical cation depends on several variables, but is typically a Se(lV) or Te(lV) compound. The scope of this section will be the one-electron oxidation of selenides and tellurides that are not contained in a heteroaromatic compound, and ones in which the Se and Te are bonded to two carbons, rather than to other heteroatoms. Tellurium- and selenium-containing electron donor molecules have been reviewed. 

An explicit assumption in the preceding discussion was that, in the case of a stepwise process, the follow-up reaction is so fast that the electron-transfer step (59) is rate determining. A tacit additional assumption was that it is, however, not so fast that the decay of RX does not take place solely outside the diffusion layer surrounding the electron donor molecule. In other words, the reaction scheme (68) was assumed, where the parentheses represent a solvent cage. 

In this model the second (electron donor) molecule is represented by a pair of charges 2e separated by a distance 0 11 X lO- cm, this giving the correct component of the dipole moment (of a water molecule) along a tetrahedral direction. Taking a value of 1 8 x HH cm... 

The interaction between selective metal oxides and molecules to be oxidized is, of course, based on electron-accepting and electron-donating properties, respectively. In this way, Mo6+, Vs+, etc. act as electron acceptors and molecules with 7r-bonds as donors. Ai et al. [5—12] have drawn attention to the fact that this can also be described by acid—base properties. An electron donor molecule like butene is a basic entity interacting with acidic sites on the catalyst. Hence it follows that activity and selectivity depend on the relative acidity and basicity. Mo03, for example, is an acidic oxide, while Bi203 is a basic oxide. Different compositions Bi Mo have different acidities. The rate of oxidation depends on the number of acid sites (=acidity) and the acid strength, viz. 

Here AH2 is an oxidizable organic compound such as an alcohol or a pair of one-electron donor molecules. Catalases, which are found in almost all aerobic cells,194b may sometimes account for as much as 1% of the dry weight of bacteria. The enzyme catalyzes the breakdown of H202to water and oxygen by a mechanism similar to that employed by peroxidases. If Eq. 16-7 is rewritten with H202 for AH2 and 02 for A, we have the following equation ... 

The decay kinetics of excited electron donor molecules (the intensity of fluorescence is proportional to the concentration of excited molecules at any given time) can be interpreted in two ways. First, one may try to approxi-... 

For the non-heated sample, ESR signal (B in Fig. 5.5) characterized with a set of g-values (gi=l. 957, g2= 1.990, and g3= 1.990) appeared. This signal originates from the electrons trapped at the particle surface because the intensity increased in the presence of electron donor molecules while it decreased in the presence of electron acceptor molecules. Since this signal disappeared for the sample heated at 200 °C, this trapped electron may be stabilized by the hydroxyl groups of the Ti02 surface. This observation is consistent with the reported values of hydrated Ti3+, which shows g of gi=1.960, g2=1.990, and g3=1.990.18)... 

Ground state complex formation between t-1 and electron donor molecules has not been reported. The reduction potential of t-1 is substantially larger in absolute value than its oxidation potential (Table 5), thus providing an explanation for the observation of ground state complex formation between t-1 and electron acceptors but not electron donors. 

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