A Gas-Phase Ca Mn O Cluster Model for the Oxygen-Evolving Complex of Photosystem II.

One of the fundamental processes in nature, the oxidation of water, is catalyzed by a small CaMn O ⋅MnO cluster located in photosystem II (PS II). Now, the first successful preparation of a series of isolated ligand-free tetrameric Ca Mn O (n=0-4) cluster ions is reported, which are employed as structural models for the catalytically active site of PS II. Gas-phase reactivity experiments with D O and H O in an ion trap reveal the facile deprotonation of multiple water molecules via hydroxylation of the cluster oxo bridges for all investigated clusters.

Size-dependent self-limiting oxidation of free palladium clusters.

Temperature-dependent gas phase ion trap experiments performed under multicollision conditions reveal a strongly size-dependent reactivity of Pd(x)(+) (x = 2-7) in the reaction with molecular oxygen. Yet, a particular stability and resistance to further oxidation is generally observed for reaction products with two oxygen molecules, Pd(x)O4(+). Complementary first-principles density functional theory simulations elucidate the details of the size-dependent bonding of oxygen to the small palladium clusters and are able to assign the pronounced occurrence of Pd(x)O4(+) complexes to a dissociatively chemisorbed bridging oxygen atomic structure which impedes the chemisorption of further oxygen molecules.

Dimensionality dependent water splitting mechanisms on free manganese oxide clusters.

The interaction of ligand-free manganese oxide nanoclusters with water is investigated, aiming at uncovering phenomena which could aid the design of artificial water-splitting molecular catalysts. Gas phase measurements in an ion trap in conjunction with first-principles calculations provide new mechanistic insight into the water splitting process mediated by bi- and tetra-nuclear singly charged manganese oxide clusters, Mn2O2(+) and Mn4O4(+). In particular, a water-induced dimensionality change of Mn4O4(+) is predicted, entailing transformation from a two-dimensional ring-like ground state structure of the bare cluster to a cuboidal octa-hydroxy-complex for the hydrated one.

Pd6O4+: an oxidation resistant yet highly catalytically active nano-oxide cluster.

The palladium oxide cluster Pd(6)O(4)(+) is formed as the sole product upon reaction of a bare palladium cluster Pd(6)(+) with molecular oxygen in an octopole ion trap under multicollision conditions. This oxide cluster is found to be resistant to further oxidation over a large temperature range, and further O(2) molecules merely physisorb on it at cryogenic temperatures. The particular stability of Pd(6)O(4)(+) is confirmed by the observation that the reaction of Pd(7)(+) with O(2) leads to fragmentation resulting in the formation of Pd(6)O(4)(+).