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