Unique Eu^II Coordination Environments with a Janus Cryptand

Two new Eu^II-containing cryptates were prepared with a new nitrogenous cryptand functionalized with three benzo groups. The introduction of three aromatic rings into the ligand backbone imparts lopsided geometrical features on the resulting Eu^II coordination environments. In both complexes, the interactions between Eu and the amines on the aromatic side of the molecule are weaker than those on the nonaromatic side, resulting in one discrete unit with two distinct faces. One of the new complexes is, to the best of our knowledge, the first direct observation of a bis-aquo Eu^II-containing cryptate with two nonadjacent inner-sphere water molecules. In addition to solid-phase structure, the electronic UV–visible and emission spectra of the new complexes were studied in acetonitrile. Experimental results show that the decreased Lewis basicity of the aromatic face hypsochromically shifts absorbances and emissions from a structurally related compound without the benzo groups.