Inorganics, Volume 8, Issue 11 (November 2020) – 6 articles

The decrease of total amount of atmospheric CO₂ is an important societal challenge in which CO₂ reduction has an important role to play. Electrocatalytic CO₂ reduction with homogeneous catalysts is based on highly tunable catalyst design and exploits an abundant C₁ source to make valuable products such as fuels and fuel precursors. These methods can also take advantage of renewable electricity as a green reductant. Mn-based catalysts offer these benefits while incorporating a relatively cheap and abundant first-row transition metal. Historically, interest in this field started with Mn(bpy-R)(CO)₃X, whose performance matched that of its Re counterparts while achieving substantially lower overpotentials. This review examines an emerging class of homogeneous Mn-based electrocatalysts for CO₂ reduction, Mn complexes with meridional tridentate coordination also known as Mn pincers, most of which contain redox-active ligands that enable multi-electron catalysis. Although there are relatively few examples in the literature thus far, these catalysts bring forth new catalytic mechanisms not observed for the well-established Mn(bpy-R)(CO)₃X catalysts, and show promising reactivity for future studies. Full article

This paper describes the catalytic activity of air stable and easy to handle manganese complexes towards the hydrosilylation of aldehydes. These catalysts incorporate a bulky diazabutadiene ligand and exhibit good functional group tolerance and chemoselectivity in the hydrosilylation of aldehydes, utilizing primary silanes as the reducing agent. The reactions proceed with turnover frequencies approaching 150 h⁻¹ in some instances, similar to those observed for other manganese-based catalysts. The conversion of aromatic aldehydes to the corresponding alcohols was found to be more efficient than that for the analogous aliphatic systems. Full article

The new coordination polymers (CPs) [Zn(tr₂ad)Cl₂]_n, {[Cu(tr₂ad)Cl]Cl∙4H₂O}_n, [Cd₂(tr₂ad)Cl₄]_n, {[Cu(tr₂ad)(NO₃)](NO₃)}_n and {[Cd(tr₂ad)(NO₃)](NO₃)∙H₂O}_n were obtained in the form of air- and moisture-stable microcrystalline powders by the solvothermal reactions of zinc(II), copper(II) and cadmium(II) chlorides or nitrates with the ligand 1,3-bis(1,2,4-triazol-4-yl)adamantane (tr₂ad). Investigation of the thermal behaviour assessed the thermal stability of these CPs, with [Cd₂(tr₂ad)Cl₄]_n starting to decompose only around 365 °C. As retrieved by powder X-ray diffraction, while [Zn(tr₂ad)Cl₂]_n features 1-D chains along which the metal centre shows a tetrahedral geometry and the spacer is exo-bidentate, the other CPs contain 2-D double-layers in which the metal ions possess an octahedral stereochemistry and the linker is exo-tetradentate. A comparative structural analysis involving known coordination compounds containing the tr₂ad ligand enabled us to disclose (i) the versatility of the ligand, as far as the coordination modes are concerned; (ii) the variability in crystal structure dimensionality, ranging from 1-D to 3-D; (iii) the fact that, to the best of our knowledge, [Zn(tr₂ad)Cl₂]_n is the first Zn^II-based CP containing the tr₂ad spacer. Full article

Precious metal nanoparticles, in particular palladium nanomaterials, show excellent catalytic properties and are key in the development of energy systems. For instance, ethanol fuel cells are promising devices for sustainable energy conversion, where Pd-based catalysts are key catalysts for the related ethanol oxidation reaction (EOR). Pd is a limited resource; thus, a remaining challenge is the development of efficient and stable Pd-based catalysts. This calls for a deeper understanding of the Pd properties at the nanoscale. This knowledge can be gained in comparative studies of different Pd nanomaterials. However, such studies remain challenging to perform and interpret due to the lack of cross-studies using the same Pd nanomaterials as a reference. Here, as-prepared sub 3 nm diameter surfactant-free Pd nanoparticles supported on carbon are obtained by a simple approach. The as-prepared catalysts with Pd loading 10 and 30 wt % show higher activity and stability compared to commercially available counterparts for the EOR. Upon electrochemical testing, a significant size increase and loss of electrochemical active surface are observed for the as-prepared catalysts, whereas the commercial samples show an increase in the electrochemically active surface area and moderate size increase. This study shines light on the challenging comparison of different catalysts across the literature. Further advancement in Pd (electro)catalyst design will gain from including self-prepared catalysts. The simple synthesis detailed easily leads to suitable nanoparticles to be used as a reference for more systematic comparative studies of Pd catalysts across the literature. Full article

Following the E-MRS (European Materials Research Society) fall meeting 2019, Symposium L, this Special Issue of Inorganics, entitled “Beyond Hydrogen Storage—Metal Hydrides as Multifunctional Materials for Energy Storage and Conversion”, is dedicated to the wide range of emerging energy-related inorganic hydrogen-containing materials [...] Full article