Micro-hydration of the MgNO3+ cation in the gas phase

Coordination complexes of the magnesium nitrate cation with water [MgNO3(H2O)(n)](+) up to n = 7 are investigated by experiment and theory. The fragmentation patterns of [MgNO3(H2O)(n)](+) clusters generated via electrospray ionization indicate a considerable change in stability between n = 3 and 4. Further, ion-molecule reactions of mass-selected [MgNO3(H2O)(n)](+) cations with D2O reveal the occurrence of consecutive replacement of water ligands by heavy water, and in this respect the complexes with n = 4 and 5 are somewhat more reactive than their smaller homologs with n = 1-3 as well as the larger clusters with n = 6 and 7. For the latter two ions, the theory suggests the existence of isomers, such as complexes with monodentate nitrato ligands as well as solvent-separated ion pairs with a common solvation shell. The reactions observed and the ion thermochemistry are discussed in the context of ob initio calculations, which also reveal the structures of the various hydrated cation complexes.