Infrared Multiple Photon Dissociation Spectroscopy Confirms Reversible Water Activation in Mn+(H2O)n,n≤8

Controlled activation of water molecules is the key to efficient water splitting. Hydratedsingly charged manganese ions Mn+(H2O)nexhibit a size-dependent insertion reaction, which isprobed by infrared multiple photon dissociation spectroscopy (IRMPD) and FT-ICR massspectrometry. The noninserted isomer of Mn+(H2O)4is formed directly in the laser vaporizationion source, while its inserted counterpart HMnOH+(H2O)3is selectively prepared by gentle removal ofwater molecules from larger clusters. The IRMPD spectra in the O-H stretch region of both systemsare markedly different, and correlate very well with quantum chemical calculations of the respectivespecies at the CCSD(T)/aug-cc-pVDZ//BHandHLYP/aug-cc-pVDZ level of theory. The calculatedpotential energy surface for water loss from HMnOH+(H2O)3shows that this cluster ion is metastable.During IRMPD, the system rearranges back to the noninserted Mn+(H2O)3structure, indicating thatthe inserted structure requires stabilization by hydration. The studied system serves as an atomicallydefined single-atom redox-center for reversible metal insertion into the O-H bond, a key step in metal-centered water activation

Automated summary

Controlled activation of water molecules is crucial for efficient water splitting, as shown by studying the insertion reaction of hydrated singly charged manganese ions using IRMPD and mass spectrometry techniques. Comparison of IRMPD spectra and quantum chemical calculations reveal that the inserted structure requires stabilization through hydration.