Complexation of Organic Cations

Gradually, the binding of metallic cations gave way to the complexation of organic cations and then to salts, dications, some anions, and even molecules. Lehn offered the term supramolecular chemistry to describe chemistry beyond the molecule, which is to say assemblies organized by noncovalent interactions [6]. 

Importantly, the purple color is completely restored upon recooling the solution. Thus, the thermal electron-transfer equilibrium depicted in equation (35) is completely reversible over multiple cooling/warming cycles. On the other hand, the isolation of the pure cation-radical salt in quantitative yield is readily achieved by in vacuo removal of the gaseous nitric oxide and precipitation of the MA+ BF4 salt with diethyl ether. This methodology has been employed for the isolation of a variety of organic cation radicals from aromatic, olefinic and heteroatom-centered donors.174 However, competitive donor/acceptor complexation complicates the isolation process in some cases.175... 

Recent results obtained by the authors and their co-workers in the field of organic cationic complexes generated under stable ion conditions are discussed. Complexes with C- and N-centered electrophiles are considered. 

By employing modem physical methods and quantum-chemical calculations, a significant body of data concerning the structure and reactivity of organic cationic complexes has been accumulated during the past decade and further studies on this dynamic area of organic chemistry are currently underway in our laboratoiy. 

Longevialle, P. Ion-Neutral Complexes in the Unimolecular Reactivity of Organic Cations in the Gas Phase. Mass Spectrom. Rev. 1992,11, 157-192. 

Complexation of metal cations and transport in ore-forming solutions derived from sedimentary basins by organic acid anionic complexes present in oil field brines... 

Large cations, such as the afore mentioned ammine complexes or organic cations like tetraphenylarsonium or tetrabutylammonium, have practically no influence on the internal vibrations of the anion. On the one hand the classical polarizing effect of the cation would be decreased because of the greater radius on the other hand, the large volume of the cation screens the anion so that all the lattice interactions would be decreased. Usually, in such cases, sharp and very clear anion bands are found, indicating screening (110, 115). 

In view of the compensatory enthalpy-entropy relationship observed for a wide variety of ionophore types, we may conclude that the cation-binding behavior, where the weak ion-dipole and dipole-dipole interaction is the major driving force for complexation, can be quantitatively analyzed and characterized by the slope and intercept of the AH-TAS plot without any exception. In this context, it is stimulating to extend the scope of this theory to the inclusion complexation of organic guests with molecular hosts. 

Solov ev, V.P., Kireeva, N.V., Tsivadze, A.Yu., Varnek, A. 2006. Structure-property modeling of complexation of strontium cation by organic ligands. J. Struct. Chem. 47 311-325. 

Complexation of inorganic cations such as alkaline or alkaline earth metals by macrocyclic polyethers produces large, lipophilic cationic metal-macrocycle complexes that are readily soluble in nonpolar solvents such as benzene, toluene and haloalkanes. In order to maintain charge balance, the cationic complex has an associated counter anion. In an immiscible two-phase liquid system, such as a mixture of chloroform and water, the anion is necessarily pulled into the organic phase as the cationic complex crosses the phase boundary. A simple illustration of this principle is obtained by addition of a chloroform solution of [18]crown-6 to an aqueous solution of potassium picrate (potassium 2,4,6-trinitrophenolate). The yellow colour of the picrate anion is transported rapidly into the contiguous (physically in contact) chloroform phase upon agitation (Figure 3.43). 

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