CATION-ETHER COMPLEXES IN THE GAS-PHASE - BOND-DISSOCIATION ENERGIES AND EQUILIBRIUM STRUCTURES OF LI-DIMETHOXYETHANE)(X), X=1 AND 2, AND LI+(12-CROWN-4)((1,2)

Bond dissociation energies, equilibrium structures, and harmonic vibra tional frequencies are reported for Li+(DXE), where DXE = CH3O(CH2)(2) OCH3, Li+(DXE)(2), and Li+(12-crown-4). The bond dissociation energies are determined experimentally by analysis of the thresholds for colli sion-induced dissociation of the cation-ether complexes by xenon (meas ured using guided ion beam mass spectrometry) and computationally by a b initio electronic structure calculations. For Li+(DXE)(x); x = 1 and 2, the primary and lowest energy dissociation channel observed experi mentally is endothermic loss of one dimethoxyethane molecule. For Li+( 12-crown-4), the primary dissociation channel is endothermic loss of t he intact crown ether, although ligand fragmentation is also observed. The cross section thresholds are interpreted to yield 0 and 298 K bon d energies after accounting for the effects of multiple ion-molecule c ollisions, internal energy of the complexes, and unimolecular decay ra tes. The calculated and experimentally-derived bond energies are in go od agreement for Li+(DXE), are in reasonable agreement for Li+(12-crow n-4), and differ by 32 +/- 12 kJ/mol for Li+(DXE)(2). On average, the experimental bond dissociation energies differ from theory by 9 +/- 6 kJ/mol per metal-oxygen interaction. The equilibrium structures are de termined primarily by strong electrostatic and polarization interactio ns between Li+ and the ligands. Charge transfer interactions are also important, as indicated by a natural energy decomposition analysis. Co rrelations between the bond dissociation energies and the equilibrium structures demonstrate that the orientation of the C-O-C subunits in t he ethers relative to the metal cation is more important than the Li+. .. O bond length in determining the stability of the complexes as pred icted by Hay ct al.(1,2)