Competitive interactions were investigated in M+(Acetone)(n)(H2O)(m) cluster ions for M = Na and K. Different [n,m] combinations were characterized by infrared predissociation spectroscopy. When n + m = 4 for Na+, shifts in the water O-H stretch modes demonstrate that the acetone weakens the ion-water interaction but does not alter the solvent configuration around the ion. For K+ at this size, the acetone weakens the ion-water interaction to the extent that hydrogen bonds are formed. When n + m = 5 for both ions, O-H frequency shifts indicate that hydrogen bonds in the immediate ionic environment are weakened by the presence of acetone. (c) 2005 Elsevier B.V. All rights reserved.