Anion-7t Interactions

Rosokha, Y. S., Lindeman, S. V., Rosokha, S. V., Kochi, J. K., Halide recognition through diagnostic anion-7t interactions Molecular complexes of C1-, Br-, and I- with olefinic and aromatic K receptors. Angew. Chem., Int. Ed. 2004, 43, 4650-4652. 

The authors state that a Cr- triazine complex due to electrostatic anion-7t interaction is present in the complex . Johnson, Hay et al. [45] have recently noticed that the role of the C - H groups of deficient arenes as potent hydrogen bonds should not be overlooked, in fact the structure of Meyer nicely illustrates this observation. The Cl(8) anion positioned above the center of the melamine is interacting with the C - H groups of the Cu(II)-coordinated pyridines. The hydrogen bonds formed may play a dominant role in determining the position of the anion within this cavity. 

Electropolymerized films of vinyl-substituted polypyridine complexes Synthesis, characterization, and appHcations 13CCR1357. Encapsulation of anions MacrocycHc receptors based on metal coordination and anion—7T interactions 13CCR1716. 

Non-covalent bonds include ionic and dipolar interactions, hydrogen bonds, aromatic interactions (7I—7I, cation k and anion 7t), closed shell interactions and van der Waals interactions. 

In a more recent study. Nelson and Yang [494] pre.sented a surface complex-ation model to describe the effect of pH on adsorption equilibria of chlorophe-nols, i.e., the electrostatic effect they also discussed the potential importance of 7t-7t interactions and donor-acceptor complex formation but could not distinguish between the two and concluded, somewhat vaguely, that [t]hese proposed mechanisms provide plausible explanations for the surface complexation reactions between chlorophenols (neutral or anionic forms) and the surface of activated carbon (acidic or basic sites). ... 

A two-dimensional sheetlike structure in [Ag2(L4e)(N03)-2] (138) is composed of bridging L46 and bridging nitrate anions coordinated to trigonal Ag(I) ions, forming six-membered rings of Ag(I) ions. The significant ff-7T interaction between two L46 molecules in the neighboring sheets (the shortest intermolecular distance of 3.34 A) indicates the formation of a Tr-Tx-interaction-assembled three-dimensional network structure. 

Anion-71 interaction is also recognized in halide associates with aromatic rings when the latter represents a part of the (positively charged) metal-ion complex and/or when 7t-bonding is supported by hydrogen bonding. 

In the 1,3-dipolar cycloaddition reactions of especially allyl anion type 1,3-dipoles with alkenes the formation of diastereomers has to be considered. In reactions of nitrones with a terminal alkene the nitrone can approach the alkene in an endo or an exo fashion giving rise to two different diastereomers. The nomenclature endo and exo is well known from the Diels-Alder reaction [3]. The endo isomer arises from the reaction in which the nitrogen atom of the dipole points in the same direction as the substituent of the alkene as outlined in Scheme 6.7. However, compared with the Diels-Alder reaction in which the endo transition state is stabilized by secondary 7t-orbital interactions, the actual interaction of the N-nitrone p -orbital with a vicinal p -orbital on the alkene, and thus the stabilization, is small [25]. The endojexo selectivity in the 1,3-dipolar cycloaddition reaction is therefore primarily controlled by the structure of the substrates or by a catalyst. 

Table 18 summarizes the interaction energies between the anions SbYsZ and the Lewis acids SbX5, In general, the formation of a conjugated anion proceeds exothermically (—0.7. .. —1.9 eV). This energy is clearly smaller than those for the interaction between a Lewis acid SbX5 and a halide ion 7T (—4.1. .. —6.3 eV). The interaction of Lewis acids with complex anions decreases in the rows respectively ... 

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