Join us for a seminar by Professor Roland Fischer from Technical University of Munich on the "Living Libraries of Intermetallic Superatoms".

Abstract:

Intermetallics of metals of very different properties (M/E) can potentially substitute industrial catalysts based on rare and precious metals. To realize this opportunity, atom-precise/-efficient catalyst design is required at the size regime of £ 1 nm, where every metal atom ‘counts’. Such intermetallic clusters are molecular counterparts of the solid state M/E materials. Recently, we discovered a novel way to generate ‘living libraries’ of meta-stable, all-hydrocarbon ligated clusters [M_aE_b](R)_n. The electronic structure of the clusters’ “superatomic” valence shell controls stability and reactivity (Figure 1).

Figure 1. Living libraries of mixed metal clusters are obtained through organometallic precursor chemistry. The libraries are populated with interrelated clusters, including transient and highly reactive clusters, as well as more accessible but less reactive ones. Their evolutions are monitored by liquid injection field desorption mass spectroscopy (LIFDI-MS) and chemical information is gained without separation of the clusters.

To demonstrate our concept, we generated a rich library of all-hydrocarbon ligated Cu/Zn clusters, “embryonic brass”, characterized via LIFDI-MS using double labelling and varied collision energy experiments. A computational framework was developed, combining density functional theory (DFT) with a tight binding approach, suited to analyze the full compositional configuration space, that yields a set of structures for each cluster of the library. Through this methodology it is possible to efficiently characterize the clusters’ structure reactivity relationships for both weak and strong perturbations, highlighted by the formate containing species [Cu₁₁Zn₆](Cp*)₈(CO₂)₂(HCO₂) and the semi-hydrogenation catalyst [Cu₉Zn₇](Cp*)₆(3-hexene)₂(3-hexyne). The species were detected after stepwise perturbation of the initial library with carbon dioxide and dihydrogen and the later was identified after treatment with 3-hexyne and dihydrogen starting out either from the initial library or from the previously isolated cluster [Cu₄Zn₁₀](Cp*)₈.