Microhydrated cobalt-nitrate cations [Co(NO3)(H2O)n]+ (n = 2, 3) studied by infrared spectroscopy in the gas phase

The microhydrated cations [Co(NO3)(H2O)n]+ (n = 2, 3) generated via electrospray ionization of aqueous cobalt(II) nitrate are studied by means of infrared-multiphoton dissociation (IRMPD) spectroscopy in an ion-trap mass spectrometer (IT-MS) at the free electron laser CLIO. While [Co(NO3)(H2O)3]+ shows a simple photo-induced fragmentation upon IRMPD, the situation is more complex for [Co(NO3)(H2O)2]+ because during storage in the IT-MS the ion associates with background water to afford [Co(NO3)(H2O)3]+, and both species adsorb IR photons in the same range. By means of kinetic modeling, it is demonstrated that also in such a more complicated situation useful insights can be achieved. For all [Co(NO3)(H2O)n]+ cations studied (n = 0–3) in parallel theoretical studies, a bidentate coordination of the nitrato ligand is preferred, and this conclusion finds support by a comparison of the computed and experimental IR spectra. In addition, the binuclear cluster [Co2(NO3)3(H2O)3]+ is probed by means of IRMPD.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (144 K)Download as PowerPoint slideHighlights► IRMPD spectra of mass-selected [Co(NO3)(H2O)2]+ and [Co(NO3)(H2O)3]+. ► Computed structures and IR spectra of [Co(NO3)(H2O)n]+ cations. ► Kinetic modeling of association/dissociation equilibria in an ion-trap mass spectrometer.