Infrared Spectroscopy of Multiply Charged Metal Ions: Methanol-Solvated Divalent Manganese 18-Crown-6 Ether Systems

We have developed an electrosonic spray ionization source to successfully generate divalent Mn2+(18-crown-6)(CH3OH)1−3 complexes in the gas phase. These complexes have been investigated using infrared predissociation spectroscopy in both the CH and OH stretching regions and with density functional theory calculations. To resolve complications from overlapping bands in the CH stretching region due to CH3OH and 18-crown-6 CH stretching modes along with strongly perturbed OH stretching modes, we have used d1 and d4 methanol substitution. For n = 1, the Mn2+···18-crown-6 geometry is highly distorted from its gas-phase neutral configuration in order to maximize favorable electrostatic interactions between the 18-crown-6 macrocyclic oxygens and Mn2+. For n = 2 and 3, CH3OH···CH3OH and CH3OH···18-crown-6 interactions compete with the Mn2+···18-crown-6 interaction, as evidenced by intense hydrogen-bonded OH stretching modes shifted over 500 cm−1 to lower frequency.