Cluster size dependent coordination of formate to free manganese oxide clusters
Abstract
The interaction of free manganese oxide clusters, MnxOy+ (x = 1–9, y = 0–12), with formic acid was studied via infrared multiple-photon dissociation (IR-MPD) spectroscopy together with calculations using density functional theory (DFT). Clusters containing only one Mn atom, such as MnO2+ and MnO4+, bind formic acid as an intact molecule in both the cis- and trans-configuration. In contrast, all clusters containing two or more manganese atoms deprotonate the acid's hydroxyl group. The coordination of the resulting formate group is strongly cluster-size-dependent according to supporting DFT calculations for selected model systems. For Mn2O2+ the co-existence of two isomers with the formate bound in a bidentate bridging and chelating configurations, respectively, is found, whereas for Mn2O4+ the bidentate chelating configuration is preferred. In contrast, the bidentate bridging structure is energetically considerably more favorable for Mn4O4+. This binding motif stabilizes the 2D ring structure of the core of the Mn4O4+ cluster with respect to the 3D cubic geometry of the Mn4O4+ cluster core.
- This article is part of the themed collection: Size effects in chemistry & physics of atomic & molecular clusters, nanoparticles & nanostructures
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