Effective Na⁺-Binding Ability and Molecular Assembly of an Alkylamide-Substituted Penta(ethylene)glycol Derivative

A new amphiphilic penta(ethylene glycol) derivative (1) bearing two hydrogen-bonding -CONHC14H29 chains was prepared. Compound 1 exhibited ion-recognition abilities for Na+ and K+, and its properties were compared with those of the macrocyclic [18]crown-6. Although both compound 1 and [18]crown-6 have six ether oxygen atoms (-OC2H2-), the Na+-binding ability of the former was much higher than that of the latter. K+-binding ability of cyclic [18]crown-6 was much higher than its Na+-binding ability, while the reverse was true for acyclic compound 1. Single-crystal X-ray structural analysis of Na+·1·B(Ph)4-·(hexane)2 at 100 K revealed the existence of a wrapped Na+-coordination by six ether and one carbonyl oxygen atoms of 1, which was further stabilized by intramolecular N-H···O= hydrogen-bonding interactions. The complex phase transition during glass (G) formation and recrystallization was confirmed in the thermal cycle of Na+·1·B(Ph)4-, whose molten state showed two kinds of liquid phases, Na+-complexed (Na+·1) + B(Ph)4- and completely dissociated Na+ + 1 + B(Ph)4-. The Na+ conductivity of the molten state was 2 orders of magnitude higher than that of the G phase.