DMSO complexes of Mg 2 + , [Mg(DMSO) n ] 2 + , have been created in the gas phase by electrospray ionization and have been interrogated by collisional activation. For n>4, ions shed DMSO ligands only, but the low energy reactions for n=2 are loss of first one and then a second methyl group with no loss of charge, giving [Mg(DMSO)(CH 3 SO)] 2 + and [Mg(CH 3 SO) 2 ] 2 + . [Mg(DMSO) 3 ] 2 + loses DMSO preferentially but also competitively loses one methyl. [Mg(DMSO) 4 ] 2 + shows only a trace of methyl loss. Structures computed at the B3LYP/6-31G * level show that the metal-ligand bonding in [Mg(DMSO) 2 ] 2 + is mainly electrostatic with the geometry of the ligand only changed slightly by complexation. However, in [Mg(DMSO)(CH 3 SO)] 2 + all atoms except the hydrogens are coplanar. Natural population analysis (NPA) shows that the DMSO sulfur has a significantly lower associated positive charge than it has in any other complex. [MgO(DMSO)(CH 3 SO)] + ions may be observed in the electrospray spectrum at high cone potential. These ions show a unique breakdown pattern involving first the loss of SO 2 and then competitive formation of MgCH 3 + and [Mg (DMSO)] + .