Reaktionen von koordinierten S22?-Liganden.I Reaktion von [Mo2(S2)6]2? mit Nucleophilen und einfache Darstellung des Bis-Disulfido-Komplexes [Mo2O2S2(S2)2]2?

Rearrangement and decomposition pathways of bare and hydrogenated molybdenum oxysulfides in the gas phase

Molybdenum sulfides and molybdenum oxysulfides are considered a promising and cheap alternative to platinum as a catalyst for the hydrogen evolution reaction (HER). To better understand possible rearrangements during catalyst activation, we perform collision induced dissociation experiments in the gas phase with eight different molybdenum oxysulfides, namely [Mo₂O₂S₆]^2-, [Mo₂O₂S₆]^-, [Mo₂O₂S₅]^2-, [Mo₂O₂S₅]^-, [Mo₂O₂S₄]^-, [HMo₂O₂S₆]^-, [HMo₂O₂S₅]^- and [HMo₂O₂S₄]^-, on a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. We identify fragmentation channels of the molybdenum oxysulfides and their interconnections. Together with quantum chemical calculations, the results show that [Mo₂O₂S₄]^- is a particularly stable species against further dissociation, which is reached from all starting species with relatively low collision energies. Most interestingly, H atom loss is the only fragmentation channel observed for [HMo₂O₂S₄]^- at low collision energies, which relates to potential HER activity, since two such H atom binding sites on a surface may act together to release H₂. The calculations reveal that multiple isomers are often very close in energy, especially for the hydrogenated species, i.e., atomic hydrogen can bind at various sites of the clusters. S₂ groups play a decisive role in hydrogen adsorption. These are further features with potential relevance for HER catalysis.

Tuning and mechanistic insights of metal chalcogenide molecular catalysts for the hydrogen-evolution reaction

The production of hydrogen through water splitting using earth-abundant metal catalysts is a promising pathway for converting solar energy into chemical fuels. However, existing approaches for fine stoichiometric control, structural and catalytic modification of materials by appropriate choice of earth abundant elements are either limited or challenging. Here we explore the tuning of redox active immobilised molecular metal-chalcoxide electrocatalysts by controlling the chalcogen or metal stoichiometry and explore critical aspects of the hydrogen evolution reaction (HER). Linear sweep voltammetry (LSV) shows that stoichiometric and structural control leads to the evolution of hydrogen at low overpotential with no catalyst degradation over 1000 cycles. Density functional calculations reveal the effect of the electronic and structural features and confer plausibility to the existence of a unimolecular mechanism in the HER process based on the tested hypotheses. We anticipate these findings to be a starting point for further exploration of molecular catalytic systems.

Cyclic molecular materials based on [M2O2S2]2+ cores (M = Mo or W)

The purpose of this article is to illustrate how conventional precursors can serve, when used with a drop of imagination, to the synthesis of sophisticated inorganic rings and wheels. The self-condensation of the [M2O2S2]2+ fragments under acido-basic process produces, in the presence or absence of guest species, linear enchainment restricted to discrete cyclic entities. This approach was revealed to be a highly fruitful strategy for developing an extended family of compounds, differing in their nuclearity, size and shape, and the nature of the encapsulated guest molecule. Indeed, the resulting cycles delimit a cationic open cavity, which can be filled by neutral polar molecules such as aquo ligands or anionic molecules such as phosphates, polycarboxylates and even metalates. The flexibility of the rings is at the origin of interesting host-guest properties: the deformation (symmetry) and the adaptation (nuclearity) of the inorganic cycle are directly related to the size and the coordination requirements of the encapsulated substrate. The versatility of the metal coordination, octahedral or square pyramidal, confers dynamic properties to the ring. In the solid state, molecular rings assemble in striking 3-D networks based on direct cation-anion connections. Alkali cations are arranged in pillars or layers for anchoring the anionic rings.