Cation-ether complexes in the gas phase: Bond dissociation energies of M+(dimethyl ether)(x), x = 1-3, M+(1,2-dimethoxyethane)(x), x = 1 and 2, and M+(12-crown-4) where M = Rb and Cs

Bond dissociation energies of M+[O(CH3)(2)](x), x=1-3; M+[(CH2OCH3)(2)](x), x=1 and 2; and M+[c-(C2H4O)(4)], where M=Rb and Cs are reported. The bond dissociation energies (BDEs) are determined experimentally by analysis of the thresholds for collision-induced dissociation of the cation-ether complexes by xenon (measured using guided ion beam mass spectrometry). In all cases, the primary dissociation channel observed experimentally is endothermic loss of one ligand molecule. The cross section thresholds are interpreted to yield 0 and 298 K BDEs after accounting for the effects of multiple ion-molecule collisions, internal energy of the complexes, and unimolecular decay rates. The experimentally determined BDEs for the monodentate ligand complexes are in good agreement with conventional ideas of electrostatic ligation of gas-phase ions and with recent ab initio calculations by Feller et al. (average discrepancy of 5 +/- 6 kJ/mol). The experimentally determined BDEs for the multidentate ligand complexes do not agree well with conventional ideas of electrostatic ligation of gas-phase ions or with recent ab initio calculations by Feller et al. (average discrepancy of 15 +/- 5 kJ/mol per metal oxygen interaction). The presence of multiple conformers of the multidentate ligand complexes in the experimental apparatus is the likely cause of these large discrepancies.