Spherand complexes with Li and Na ions in the gas phase: encapsulation structure and characteristic unimolecular dissociation.

We investigated the complexes of Cram's hexa(-anisole) spherands (SPR, 1) with Li and Na ions (1·Li and 1·Na) isolated in the gas phase. Despite the small conformational difference between 1·Li and 1·Na owing to the rigid framework of 1, ultraviolet photodissociation (UVPD) spectroscopy under cryogenic (∼10 K) conditions yielded clearly distinguishable absorption edges: ∼34 000 and ∼34 500 cm for 1·Li and 1·Na, respectively. The spectral assignment and the preorganization characteristics of the host molecule were compared with those of dibenzo-18-crown-6-ether (DB18C6) complexes, which have more flexible frameworks. Furthermore, we revealed the characteristic unimolecular dissociation of the 1·Li complex using UVPD and collision-induced dissociation (CID); the formation of fragment ions with dibenzofuran moieties was detected. This dissociation pattern was ascribed to the efficient release of dimethyl ether molecule(s) from the 1·Li complex, which is characteristic of the cyclic skeleton formed with six methoxy groups in the SPR.