Abstract
<p>Part I. A new redox switching mechanism was investigated by Electron Spin Resonance (ESR) Spectroscopy. The concept involves the attachment of an electron deficient group to a macrocyclic polyether or podand to control the compound's binding properties.Two reducible moieties were studied: nitrobenzene and anthraquinone. When the nitrobenzene was appended to a crown ether, cation selectivity and metal hyperfine were observed for the more flexible nitrogen-pivot lariat ethers due to a strong intramolecular ion-pairing interaction. N-(2-nitrobenzyl)aza-15-crown-5 (1 and 26) showed Na$\sp+$ cation selectivity over Li$\sp+$ or K$\sp+$ and a metal splitting of 2.50 G was observed. This is the largest metal splitting ever reported for this type of compound. It was generally observed that the strength and specificity of the interaction was related to the cation radius and the cavity size of macroring. This dependence is the result of increased coulombic interaction which confers added rigidity to the complex.For the more flexible anthraquinone podands, the cation effect follows the order Li$\sp+ >$ Na$\sp+ >$ K$\sp+$, and the degree of interaction was interpreted in terms of geometric and electronic effects. Structurally rigid compound 21 shows selectivity for the sodium cation due to rigidity of the reduced ligand.Part II. The spin distribution of a series of COT derivative compounds was investigated by ESR. The Bis-COT-phenyl derivatives (32-34) showed preferred localization of the unpaired electron in one of the COT moieties but 33 showed an opposite spin distribution to that of 32 upon further reduction. Thus the substituent acts as an electron-releasing group towards COT due to the excess of charge in the trianion radical.</p>