Assignment of individual structures from intermetalloid nickel gallium cluster ensembles.

Poorly selective mixed-metal cluster synthesis and separation yield reaction solutions of inseparable intermetalloid cluster mixtures, which are often discarded. High-resolution mass spectrometry, however, can provide precise compositional data of such product mixtures. Structure assignments can be achieved by advanced computational screening and consideration of the complete structural space. Here, we experimentally verify structure and composition of a whole cluster ensemble by combining a set of spectroscopic techniques. Our study case are the very similar nickel/gallium clusters of M12, M13 and M14 core composition Ni6+xGa6+y (x + y ≤ 2). The rationalization of structure, bonding and reactivity is built upon the organometallic superatom cluster [Ni6Ga6](Cp*)6 = [Ga6](NiCp*)6 (1; Cp* = C5Me5). The structural conclusions are validated by reactivity tests using carbon monoxide, which selectively binds to Ni sites, whereas (triisopropylsilyl)acetylene selectively binds to Ga sites.

Understanding and Controlling Molecular Compositions and Properties in Mixed-Linker Porphyrin Metal-Organic Frameworks.

Porphyrin-based metal-organic frameworks (MOFs) are attractive materials for photo- and thermally activated catalysis due to their unique structural features related to the porphyrin moiety, guest-accessible porosity, and high chemical tunability. In this study, we report the synthetic incorporation of nonplanar ß-ethyl-functionalized porphyrin linkers into the framework structure of PCN-222, obtaining a solid-solution series of materials with different modified linker contents. Comprehensive analysis by a combination of characterization techniques, such as NMR, UV-vis and IR spectroscopy, powder X-ray diffraction, and N2 sorption analysis, allows for the confirmation of linker incorporation. A detailed structural analysis of intrinsic material properties, such as the thermal response of the different materials, underlines the complexity of synthesizing and understanding such materials. This study presents a blueprint for synthesizing and analyzing porphyrin-based mixed-linker MOF systems and highlights the hurdles of characterizing such materials.

Topology- and wavelength-governed CO2 reduction photocatalysis in molecular catalyst-metal-organic framework assemblies.

Optimising catalyst materials for visible light-driven fuel production requires understanding complex and intertwined processes including light absorption and catalyst stability, as well as mass, charge, and energy transport. These phenomena can be uniquely combined (and ideally controlled) in porous host-guest systems. Towards this goal we designed model systems consisting of molecular complexes as catalysts and porphyrin metal-organic frameworks (MOFs) as light-harvesting and hosting porous matrices. Two MOF-rhenium molecule hybrids with identical building units but differing topologies (PCN-222 and PCN-224) were prepared including photosensitiser-catalyst dyad-like systems integrated via self-assembled molecular recognition. This allowed us to investigate the impact of MOF topology on solar fuel production, with PCN-222 assemblies yielding a 9-fold turnover number enhancement for solar CO2-to-CO reduction over PCN-224 hybrids as well as a 10-fold increase compared to the homogeneous catalyst-porphyrin dyad. Catalytic, spectroscopic and computational investigations identified larger pores and efficient exciton hopping as performance boosters, and further unveiled a MOF-specific, wavelength-dependent catalytic behaviour. Accordingly, CO2 reduction product selectivity is governed by selective activation of two independent, circumscribed or delocalised, energy/electron transfer channels from the porphyrin excited state to either formate-producing MOF nodes or the CO-producing molecular catalysts.