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, experimental evidence as well as 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 ab initio
calculations, which also reveal the structures of the various hydrated cation complexes.