Anionic complexes macrocycles

Following the discovery of the above solid-state fluoride anion complex, the authors succeeded in crystallizing the bishydrochloride salt of this same system, 3. The X-ray structure of this derivative revealed the presence of two chloride counterions bound via hydrogen bonds to the diprotonated macrocycle (Figure 2). In contrast to what was seen in the case of the fluoride anion structure, in this instance neither of the counteranions is located in the plane of the sapphyrin macrocycle. Rather, they are found in near symmetric fashion ca. 1.8 A above and below the mean Nj plane. This out-of-plane binding reflects, presumably, the fact... 

Recently, two related bis-tren type macrocycles, 21 and 22 have been shown to complex CIO4 and SiF anions in the solid state, highlighting the potential of these types of hosts for inorganic anion complexation. ... 

While anion complexation might more appropriately be divided according to the complexity of the anion, the format followed in the preceding two subsections will be maintained for this section, i.e. subdivision according to the dimensionality of the macrocycles (mono-, bi- and tri-cyclic systems). A brief overview of anion complexation will, however, be presented in this introductory subsection. The types of anions which undergo complexation with macrocyclic ligands are categorized below. 

Multidentate polyaza and mixed polyaza-polyoxa macrocycles in their polyammonium form complex a variety of anions. Complexation ability is, as anticipated, related to macrocyclic ring size, macrocyclic topology and the relation of these factors to the substrate to be complexed. Polyammonium macromonocydes of various ring sizes and binding subunits complex polycarboxylate... 

The complexation of various molecular anions by other types of macrocyclic ligands has been reported [3.1-3.4] in particular with cyclophane-type compounds. Two such receptors are represented by the protonated forms of the macropolycycles 40 [3.29] and 41 [3.30]. Quaternary polybipyridinium compounds also bind anionic substrates [3.31]. Progress is also being made towards the developments of neutral anion receptor molecules [3.32]. The thermodynamic and kinetic data for anion complexation by macrocyclic receptors have been reviewed [2.18c]. 

Kimura, E. and Koike, T. (1998) Dynamic anion recognition by macrocyclic polyamines in neutral pH aqueous solution development from static anion complexes to an enolate complex, Chem. Commun. 15, 1495-1500. 

The solid state structure of the pyridinium-chloride pseudorotaxane Figure 8) reveals the interpenetrative nature of the components and provides evidence for anion complexation by the macrocycle s isophthalamide motif, n-n donor-acceptor interactions between the electron rich hydroquinone units of the macrocycle and... 

Oxaazamacrocycles are molecules with combined crown ether and amino group properties for example, in dependence on the size of macrocyclic ring and the position of heteroatoms stable complexes with various metals can be formed [32]. Furthermore, when protonated, these compounds are excellent anion binders. In fully protonated polyammonium macrocycles, the coulom-bic attractions and hydrogen bond formation play a dominant role in the anion complexation. The receptors (R,R)-5 and (S,S,S,S)-6 were designed to bind dicarboxylates [33]. 

The principle of geometric correspondence, formulated by Nobel laureate Pedersen [561], is the basis for explaining the crown-ether complexes formation. Their selectivity depends on the correspondence of the size and form of the ion complex-former to the size of cavity of the macrocycle. However, it was established later that this principle does not have an absolute dependability [571]. Such factors as type of anion, complex composition, and the nature of solvent used during synthesis also have considerable influence [571],... 

The addition of stoichiometric amounts of tetrabutylammonium bromide to electrochemical solutions of (84) led to gradual cathodic shifts in the reversible reduction wave of the host. A maximum shift of 45 mV was observed after 4 equivalents had been added. No cathodic shifts were observed with (87), which implies that bromide anion complex-ation within the macrocyclic cavity of (84) is essential for electrochemical detection. 

These systems exhibit considerable affinity for halide anions. X-ray analysis ascertained the formation of an anionic 2 1 chloride adduct of (1) where the chloride is simultaneously bound by four mercury atoms. In the crystal structures of (2) Cl and (2) l2, the anions are located within the macrocycle and complexed cooperatively by the four mercury(II) centers. Several anionic complexes of (3), including bromide, iodide, and thiocyanide salts, have been isolated. The compounds adopt multidecker stmctures with the hexacoordinated anions effectively sandwiched between two successive molecules of (3). The Lewis acidity of perfluoro-ortAo-phenylenemercury (3) has also been substantiated by its ability to form stable adducts with neutral substrates (HMPA, DMSO, ethyl acetate, and acetonitrile) and arenes. The (3) -CeHe adduct exists as extended stacks of nearly parallel, staggered molecules of (3), which sandwich benzene molecules. Similar structures have been reported for the corresponding adducts with biphenyl, naphthalene, pyrene, and triphenylene. 

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