Mixed C-heteroatom hosts

The allyl lariat ether (Section 3.3) 3.132 forms complexes with both K+ and Ag+ (which are of similar ionic radins. Table 3.5). In the case of the complex, as may be expected, the potassium ion is too large to ht snngly within the aza[15]crown-5 ring and lies somewhat above the donor atom plane. The exposed face of the metal atom is occupied by a PFg anion. Similar coordination to the crown is exhibited by Ag+ bnt instead of an anion, the exposed face of the metal ion is coordinated to the allyl side chain of an adjacent molecnle to give an infinite polymer in the solid state (Fignre 3.91). 

A study of the selectivity of lariat aza[15]crown-5 (3.133) and BiBLE (bi-brachial lariat ether) diaza[18]crown-6 derived ligands (3.134) containing variously substituted arene rings showed that the Ag complex stability decreased as a function of the electron-withdrawing ability of the substituents, R, as measured by the substituents Taft 0° inductive constant (a parameter measuring the electron-withdrawing 

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