On the Possibility of Using Aza-Cryptands to Design Superalkalis

The possibility to design new superalkali species by encapsulating main-group s-block metals (alkali metal and alkaline earth metal) into aza-cryptands has been examined under density functional theory in this work. Utilizing 36adamanzane (36adz) as an example, a series of M@36adz (M = Li, Na, K, Be, Mg, and Ca) complexes have been constructed and investigated in detail. It is interesting to find that these complexes possess much lower IE values (1.94–2.34 eV) than that of 3.89 eV for the Cs atom due to the repulsion between the valence electron of embedded M atoms and lone pairs of N atoms in the complexant. Therefore, these complexes can be regarded as a new kind of superalkalis. However, only the Li@36adz and Be@36adz complexes are found to be thermodynamically stable with negative interaction energies and positive dissociation energies because 36adz is not large enough to wrap Na, K, Mg, and Ca atoms. Thus, a larger cryptand tri-pip-aza222 was further used to construct the M@tri-pip-aza222 (M = Na and K) complexes with higher stability and better reducing ability than M@36adz (M = Na and K). We, therefore, hope that experimental chemists could synthesize such metal complexes, as novel superalkali species by choosing proper cryptands for specific metal atoms.