Conformational Preference of the Torand Ligand in Its Complexes with Potassium and Rubidium Picrate

Despite the different sizes of the metal ions, torand 1 retains its staggered conformation in the complexes 1 · K+ (picrate−) and 1 · Rb+(picrate−), as established by X-ray structure determinations. In contrast, other macrocyclic ligands usually adjust their conformation according to the bonding demands of the metal ions. The exceptionally rigid cavity of 1 constructed from condensed ring systems is responsible for this behavior.