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

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Abstract

Bond dissociation energies of Na+[O(CH3)2]x, x = 1−4; Na+[(CH2OCH3)2]x, x = 1 and 2; and Na+[c-(C2H4O)4] are reported. The bond dissociation energies 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 bond dissociation energies after accounting for the effects of multiple ion−molecule collisions, internal energy of the complexes, and unimolecular decay rates. Trends in the bond dissociation energies determined by experiment and recent theoretical ab initio calculations are in good agreement. Our best experimental values, which have an average uncertainty of ±7 kJ/mol, are lower than the theoretical values by 7 ± 5 kJ/mol per metal−oxygen interaction. These values are compared with bond dissociation energies for the comparable lithium cation−ether complexes. This comparison reveals the thermodynamic consequences of ligand−ligand repulsion.

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