Cation−Ether Complexes in the Gas Phase: Bond Dissociation Energies of K+(dimethyl ether)x, x = 1−4; K+(1,2-dimethoxyethane)x, x = 1 and 2; and K+(12-crown-4)

Abstract

Bond dissociation energies (BDEs) of K+[O(CH3)2]x, x = 1−4; K+[(CH2OCH3)2]x, x = 1 and 2; and K+[c-(C2H4O)4] are reported. The 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 and lowest energy 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. Trends in the BDEs determined by experiment and recent theoretical ab initio calculations are in good agreement, with experimental values being systematically lower than the theoretical values by 5 ± 3 kJ/mol per metal−oxygen interaction. Comparisons to trends in the BDEs for analogous Li+ and Na+ complexes reveal that Li+ is bound less strongly than expected when compared with analogous Na+ and K+ complexes.