GAS-PHASE COMPLEXATION OF MONOPOSITIVE ALKALINE-EARTH METAL-IONS WITHPOLYETHERS - COMPARISON WITH ALKALI-METAL ION AND ALUMINUM ION COMPLEXATIONS

The gas-phase reactions of the monopositive alkaline earth metal ions (Ca+ and Mg+) with a variety of crown ethers and their acyclic analogu es have been studied by laser desorption/quadrupole ion trap mass spec trometry. The initial monopositive Mg+ and Ca+ ions were generated dir ectly from laser desorption of a metal foil or salt and then reacted w ith a variety of neutral polyethers. Collisional activated dissociatio n (CAD) techniques were employed to evaluate the structures of these m etal/polyether adducts. The reactions of these initially monopositive ions (M(+)) are of special interest because the reactions with crown e thers or glymes involve incorporation of ''OH'', corresponding to form ation of (L + (M(2+)OH(-)))(+) ions, in which the metal ions attain th eir favored oxidation states. The alkaline earth metal ions apparently react with H2O, which may be loosely bound to a polyether ligand, by donation of the lone s electron to the oxygen atom in conjunction with elimination of H-.. The polyether ligand then solvates the (M(2+)OH(- )) species by formation of multiple electrostatic bonds between the et her oxygen atoms and the metal center. The reactions of the glycols wi th the metal ions are somewhat different in that the resulting product s may be assigned as (L + (M(2+)OH(-)) - H2O)(+), from unstable (L + ( M(2+)OH(-)))(+) complexes that spontaneously dehydrate, or as (L + M(2 +) - H-.)(+), in which the initial Mg+ ion reacts directly with a hydr oxyl terminus of the glycol molecule. Ligand-exchange methods used to measure the relative order of (Mg2+OH-) binding energies for the polye thers indicate that the relative binding energy increases with the siz e of the polyether. A comparison of the results with those for reactio ns of alkali metal ions and aluminum ions with polyethers in the gas p hase reveals further insight into the nature of the binding interactio ns.