Acceptors cationic

B-Site Substitution Acceptor doping of the normally insulating per-ovskite structure SrTi03 has been widely explored for the purpose of fabricating mixed conductors. Replacement of part of the Ti4+ by a lower valence acceptor cation such as Fe3+ leads to enhanced total conductivity with greatly enhanced O2- migration. 

EA are the ionization potential and electron affinity of the donor anions and acceptor cations, respectively, in the gas phase and wp represents the ion-pair interaction. (Note the ionization potentials in the gas phase parallel the anodic potentials in solution for structurally related electron donors the same interrelationship applies to electron affinities and cathodic potentials.) Accordingly, these coloured crystals are also referred to as charge-transfer salts (Wei etal., 1992). 

Normally, the reaction partners in PET reactions are neutral molecules. That is why a donor radical cation—acceptor radical anion pair is obtained by the PET step. These highly reactive intermediates can be used for triggering interesting reactions. Since the PET is not restricted to neutral molecules PET reactions of donor anions and neutral acceptors or neutral donors and acceptor cations resulting in radical—radical anion (cation) pairs are known as well. These reactions are also called charge shift reactions due to the fact that the overall number of charged species is kept constant throughout the PET step. Finally, a PET process of a donor anion and a acceptor cation is possible as well (Scheme 2). 

Such a bond, in which the donor molecule (or anion) provides both bonding electrons and the acceptor cation provides the empty orbital, is called a coordinate or dative bond. The resulting aggregation is called a complex. Actually, any molecule with an empty orbital in its valence shell, such as the gas boron trifluoride, can in principle act as an electron pair acceptor, and indeed BF3 reacts with ammonia (which has a lone pair, NH3) to form a complex H3N ->BF3. Our concern here, however, is with metal cations, and these usually form complexes with from 2 to 12 donor molecules at once, depending on the sizes and electronic structures of the cation and donor molecules. The bound donor molecules are called ligands (from the Latin ligare, to bind), and the acceptor and donor species may be regarded as Lewis acids and Lewis bases, respectively. 

Fig. 1. Scheme for classification of materials prepared from a donor or donor cation, D+p, and acceptor or acceptor cation, A-q, (p, q = 0,1,. ..) with one or both components being a planar transition-metal complex... 

According to Mulliken charge-transfer theory (7), the separation of AhvCT = 0.61 eV for the two series represents the constant difference in the donor properties (ionization potential) of Co(CO)4- and I- in salt pairs with the same acceptor cation. The latter is a corollary of the Mulliken... 

Fig. 4. Limiting quantum yields for chaige-transfer photochemistry of Co(CO)4 salts of various acceptor cations at increasing concentrations of the additive L = PBu3 (27).

The presence of 1 equivalent of TPP1 OTf- with the chromium anion TpCr(CO)3- as the tetrabutylammonium salt in dichloromethane results in the loss of the carbonyl bands of the anion at 1890 and 1740 cm-1. Their complete replacement by the sharps, band at 2018 cm-1 and the broad E band (1898 and 1838 cm-1) of the 17-electron radical TpCr(CO)3- indicates that the ion-pair annihilation proceeds to completion. Variation of the pyrylium cation, by the replacement of TPP+ with a weaker acceptor such as tri-p-anisylpyrylium triflate (TAP+ OTf-), consistently results in lower conversions of the carbonylmetal anions. For example, the treatment of TpMo(CO)3 with the TAP+ salt leads to a light red solution of TAP (Am 560 nm) (92) and a greatly diminished concentration of TpMo(CO)3- as judged by the reduced carbonyl absorbances in comparison with that obtained from TPP+ at the same concentration. Even with this weaker acceptor cation, however, the strong chromium anionic donor TpCr(CO)3- is completely oxidized by 1 equivalent of TAP+ to form TpCr(CO)3- in essentially quantitative yields. 

Triorganostannates such as LiSnRs are sufficiently electron rich to be potential candidates for electron transfer to halides [52,126]. As for the silicon analogues MSiRa [115], the electron transfer mechanisms for the reduction by such at-complexes may be quite complicated because of the solvent-induced separation between the SiRJ donor anion and the a acceptor cation M. ... 

Donor anion Acceptor cation Solvent diss (m) Ref. 

Acidic catalysts AI2O3 Si02 dehydration electron pair acceptors (cations) predominate Mg(OH)2... 

The summation runs over all electron pairs L belonging to the electron donor-atom A of fragment A. The constant c is characteristic of the metal cation M, the occupation number of the electron pair N cc is multiplied by an integral I describing overlap of the donor lone pair and acceptor cation, and by the difference... 

M. Cheng, X. Yang, J. Zhao, C. Chen, Q. Tan, F. Zhang, L. Sun, Efficient Organic Dye-Sensitized Solar Cells Molecular Engineering of Donor-Acceptor-Acceptor Cationic Dyes. ChemSusChem 2013,6,2322-2329. 

These phenomena are attributed to competitive interactions between point defects and the formation of defect associates. The decrease in activation enthalpy in the dilute range is due to a decrease in association enthalpy as a result of electrostatic interactions between the associated pair and the unassociated acceptor cations. The ensuing decrease in conductivity and increase in activation energy with increasing dopant concentration is ascribed to the development of deep vacancy traps as a result of defect clustering and the formation of microdomains. For associated vacancies the activation energy consists of a migration and an association (dissociation) term Hi = H + H. ... 

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