CH-anion interactions

This type of receptor is represented by compounds 16a,b bearing ruthenium ) bipyridine moieties. Both calixarenes [18] exhibit 1 1 binding of chloride and bromide anions (DMSO-d6), and they are especially suitable for the complexation of H2POj (X16a=2.8-104 M-1 K16b=5.2 103 M"1). On the other hand, if we compare these results with those for similar non-calixarene receptors, where the bipyridine unit is substituted by alkyl, aryl or ethylene glycol substituents, the introduction of calixarene does not bring any substantially new features into the complexation abilities of these derivatives. As shown by X-ray analysis, the anion is encapsulated within the cavity formed by amidic functions with the contributions of CH...anion interactions from the bipyridine unit. 

This kind of concept has been extended to imidazolium-based ligands, in which three 2,2 -bipyridyl substituents bind an Fe(II) center resulting in the formation of an anion-binding pocket capable of complexing Cl" and Br" in acetonitrile solution with log K >1. The X-ray crystal structure of the metaUocryptand shows that halides are bound solely by CH- anion interactions. Figure 17. ... 

Scheme 14 A sensor that combines a boronic acid receptor with CH-anion interaction 95.

In 2008, three groups independently observed strong 1,2,3-triazole CH anion interactions within aryl-triazole-based receptors. Li and Flood synthesized a shape-persistent macrocychc receptor, triazolophane [16, 17] (Fig. 2), with an unexpectedly high affinity for chloride that rivaled many synthetic receptors with NH and OH hydrogen bond donors. At the time, the binding constant was evaluated at ATa = 130,000 (CH2CI2), but it has since been reevaluated first to... 

Fig. 11 a Side view of an anion layer sandwiched between cation layers viewed down along the crystallographic n-axis. b CH/n interactions between the aromatic groups in the ammonium cation layers for 1-naphthylmethylammonium ( , )-sorbate [82]... 

Lastly, it is conceivable that the size of the anion may have an influence over coordination polymer structure. Such an effect can be difficult to assess, and in particular, de-convolute from other factors, most noticeably from weak interactions with the polymer structure such as CH acceptor interactions. If the size of an anion is influencing a structure, it is likely that it is in close contact with the polymer and therefore the formation of hydrogen bonds, or other supramolecular interactions, could be the main factor in affecting the structure. 

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