Halide anion discrimination by a tripodal hydroxylamine ligand in gas and condensed phases

Abstract

Electrospray ionization of solutions containing a tripodal hydroxylamine ligand, H₃TriNOx ([((2-^tBuNOH)C₆H₄CH₂)₃N]) denoted as L, and a hydrogen halide HX: HCl, HBr and/or HI, yielded gas-phase anion complexes [L(X)]⁻ and [L(HX₂)]⁻. Collision induced dissociation (CID) of mixed-halide complexes, [L(HX_aX_b)]⁻, indicated highest affinity for I⁻ and lowest for Cl⁻. Structures and energetics computed by density functional theory are in accord with the CID results, and indicate that the gas-phase binding preference is a manifestation of differing stabilities of the HX molecules. A high halide affinity of [L(H)]⁺ in solution was also demonstrated, though with a highest preference for Cl⁻ and lowest for I⁻, the opposite observation of, but not in conflict with, what is observed in gas phase. The results suggest a connection between gas- and condensed-phase chemistry and computational approaches, and shed light on the aggregation and anion recognition properties of hydroxylamine receptors.