The infrared photodissociation spectra of mass-selected Mg+(CH3OH)(n) (n = 1-4) are measured and analyzed with the aid of density functional theory calculations. Hydrogen bonding between methanol molecules is found to be absent in Mg+(CH3OH)(3), but detected in Mg+(CH3OH)(4) through characteristic frequency shifts of the OH stretch of methanol. The maximum number of the methanol molecules that can be directly bonded to the Mg+ ion is limited to three and the fourth molecule starts to fill the second solvation shell. The vibrational spectroscopy provides clear evidence for the closure of the first shell at n = 3. (C) 2004 Published by Elsevier B.V.