Reactivity of [Ba(H2O)n⩽2]2+ with neutral molecules in the gas-phase: An experimental and DFT study

A combination of multistage mass spectrometry experiments and DFT calculations are used to examine reactivity of [Ba(H2O)n⩽2]2+ with neutral molecules in the gas-phase. Under collision-induced dissociation conditions Ba2+ reacts with neutral molecules of collision gas (wet nitrogen), by three different pathways: addition of either N2 or H2O, dissociative proton transfer to form [Ba(OH)]+, and charge reduction to yield Ba+. Generation of Ba+ is calculated to be endothermic by 58 kcal mol−1 when water acts as the source of the electron. For complexes of [Ba(H2O)n⩾2]2+, as n increases, water elimination is calculated to become increasingly favorable over proton transfer pathway. Failure to detect adducts of [Ba(H2O)n⩾1]+ by mass spectrometer indicates that electron transfer from neutral molecules to [Ba(H2O)n⩾1]2+ does not occur; our DFT calculations show that all the electron transfer reactions have large endothermicities and the endothermic value increases with the number of water molecules. Ion Ba2+ was observed to form adducts with dinitrogen and water but not with dioxygen; by contrast, the only adduct observed for Ba+ was with dioxygen. Comparison of binding energies indicates that strong binding of Ba+ with dioxygen originates not only from electrostatic interaction, but also from formation of a partial ionic bond.