Double-armed and tetra-armed cyclen-based cryptands

<p>Double-armed and tetra-armed cyclen-based cryptands (<b>1a</b>–<b>1d</b> and <b>2</b>) that bridge two aromatic rings by diethyleneoxy and triethyleneoxy units were prepared. The CSI-MS of 1:1 mixtures ([Ag<sup>+</sup>]/[ligand]) indicated that these new cryptands form 1:1 complexes with Ag<sup>+</sup>. The log <i>K</i> values for the interaction between Ag<sup>+</sup> and <b>2</b> was greater than those of <b>1a</b>–<b>1d</b>, double-armed cyclens (<b>3a</b>–<b>3c</b> and <b>4</b>), and tetra-armed cyclen (<b>5</b>). The Ag<sup>+</sup>-ion-induced <sup>1</sup>H NMR spectral changes suggest that the Ag<sup>+</sup>–<i>π</i> interactions of the Ag<sup>+</sup> complexes with the cryptands (<b>1a</b>–<b>1d</b> and <b>2</b>) are stronger than those in Ag<sup>+</sup>/double-armed and tetra-armed cyclens. To visualise the Ag<sup>+</sup>−<i>π</i> interactions, the isosurfaces of the LUMO and HOMOs of the Ag<sup>+</sup> complexes were calculated at the B3LYP/3–21G(*) theoretical level. The LUMO of the Ag<sup>+</sup> ion is distorted by interaction with the HOMOs of the aromatic side arms. The calculations reveal Ag<sup>+</sup>−<i>π</i> interactions between the Ag<sup>+</sup> ion and the aromatic side arms, and these are shown graphically.</p>