Structure and Interactions in 1:2 K⁺–Crown Ether Complexes via Gas-Phase Cold UV and IR Spectroscopy

We obtained gas-phase UV and IR spectra of 1:2 potassium ion-crown ether (CE) complexes (benzo-15-crown-5 (B15C5), benzo-18-crown-6 (B18C6), dibenzo-18-crown-6 (DB18C6), and 18-crown-6 (18C6)) at approximately 10 K and determined the structure and intermolecular interactions between K+ and the two CEs, supported by quantum chemical calculations. The vibronic features of K+(B15C5)2 revealed two conformers in the UV photodissociation spectrum, and the K+ ion was held equally by both B15C5 moieties. For K+(B18C6)2 and K+(DB18C6)2, the K+ ions were not equally shared between the two CEs. For K+(B18C6)(18C6) and K+(DB18C6)(18C6), the K+ ion mainly interacted with 18C6, and the interaction between K+ and B18C6 or DB18C6 was very weak. In contrast, K+(B18C6)(18C6) produced photofragment K+(B18C6) ion exclusively, whereas K+(DB18C6)(18C6) produced K+(18C6). The photodissociation of K+(B18C6)(18C6) indicates that K+ transfer from 18C6 to B18C6 occurs upon UV excitation, probably in the electronically excited states.