Abstract
Investigating metal-ion solvation—in particular, the fundamental binding interactions—enhances the understanding of many processes, including hydrogen production via catalysis at metal centers and metal corrosion. Infrared spectra of the hydrated zinc dimer (Zn2+(H2O)n; n = 1–20) were measured in the O–H stretching region, using infrared multiple photon dissociation (IRMPD) spectroscopy. These spectra were then compared with those calculated by using density functional theory. For all cluster sizes, calculated structures adopting asymmetric solvation to one Zn atom in the dimer were found to lie lower in energy than structures adopting symmetric solvation to both Zn atoms. Combining experiment and theory, the spectra show that water molecules preferentially bind to one Zn atom, adopting water binding motifs similar to the Zn+(H2O)n complexes studied previously. A lower coordination number of 2 was observed for Zn2+(H2O)3, evident from the highly red-shifted band in the hydrogen bonding region. Photodissociation leading to loss of a neutral Zn atom was observed only for n = 3, attributed to a particularly low calculated Zn binding energy for this cluster size.
Highlights
Metal–metal bonds have received much interest over the years; homonuclear metal bonds have received particular attention
Infrared spectra of size-selected clusters were recorded via action spectroscopy, Reaction (1): Zn2+ (H2 O)n + m hν → Zn2+ (H2 O)n− x + x (H2 O)
For n = 3, a competing fragmentation channel was observed; photodissociation of the neutral zinc atom is represented by Reaction (2): Zn2+ (H2 O)3 + m hν → Zn+ (H2 O)3 + Zn
Summary
Metal–metal bonds have received much interest over the years; homonuclear metal bonds have received particular attention. Computed electronic and geometrical structures of homonuclear 3d neutral metal dimers, as well as the cations and anions [7]. Their results confirmed the suggestion of a 4s–4s bond in Zn2 + , reporting a bond length of 2.60 Å and a value for the dissociation energy. We recently published a study investigating hydrated zinc monomer ions Zn+ (H2 O)n with up to 35 water molecules, [70] where we found evidence for surface solvation of Zn+ , which was previously established by Duncan and co-workers for n ≤ 4 [71]. We investigate the solvation evolution of the zinc dimer cation up to 20 water molecules utilizing infrared multiple photon dissociation (IRMPD) spectroscopy. Going to large cluster sizes up to 20 water molecules, the evolution of infrared spectra with increasing cluster size is a first step towards understanding metal dimer solvation
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