The hydration shell of Na+ ion in the gas phase (similar to4) is smaller than that in solution (6). The energetics of various solvated Na+ clusters indicate that lowering the pairwise interaction between the ligand and the ion can increase the coordination number in the gas phase. We report here the first hexa-coordinated Na+ cluster ion in the gas phase, which can be formed by substituting H2O with 1,4-difluorobenzene. Infrared-photodissociation spectroscopy of the O-H stretch was used to infer the structure. (C) 2003 American Institute of Physics.