Uranyl/12-crown‑4 Ether Complexes and Derivatives: Structural Characterization and Isomeric Differentiation

The following gas-phase uranyl/12-crown-4 (12C4) complexes were synthesized by electrospray ionization: [UO₂(12C4)₂]²⁺ and [UO₂(12C4)₂(OH)]⁺. Collision-induced dissociation (CID) of the dication resulted in [UO₂(12C4-H)]⁺ (12C4-H is a 12C4 that has lost one H), which spontaneously adds water to yield [UO₂(12C4-H)­(H₂O)]⁺. The latter has the same composition as complex [UO₂(12C4)­(OH)]⁺ produced by CID of [UO₂(12C4)₂(OH)]⁺ but exhibits different reactivity with water. The postulated structures as isomeric [UO₂(12C4-H)­(H₂O)]⁺ and [UO₂(12C4)­(OH)]⁺ were confirmed by comparison of infrared multiphoton dissociation (IRMPD) spectra with computed spectra. The structure of [UO₂(12C4-H)]⁺ corresponds to cleavage of a C–O bond in the 12C4 ring, with formation of a discrete U–O_eq bond and equatorial coordination by three intact ether moieties. Comparison of IRMPD and computed IR spectra furthermore enabled assignment of the structures of the other complexes. Theoretical studies of the chemical bonding features of the complexes provide an understanding of their stabilities and reactivities. The results reveal bonding and structures of the uranyl/12C4 complexes and demonstrate the synthesis and identification of two different isomers of gas-phase uranyl coordination complexes.