Fachgruppe Chemie

Metal-like behavior of a 2D molecular catalyst enables redox-decoupled electrocatalysis

Tue, 20 May 2025 00:00:00 GMT

Metal-like behavior of a 2D molecular catalyst enables redox-decoupled electrocatalysis Wang, Yang; Zhang, Dongyu; Chen, Ting; Su, Caijie; Xie, Yi; Wu, Changzheng; Kornienko, Nikolay Molecular catalysts facilitate electrochemical conversion by changing their oxidation states to transfer electrons. However, this redox-mediated mechanism features stepwise electron transfer and substrate activation in separate elementary steps, thereby resulting in an inherent loss in efficiency. Here, we synthesize a two-dimensional (2D) iron phthalocyanine (FePc) material and uncover its non-mediated electron transfer behavior in electrocatalysis, which overcomes the conventional redox-mediated limitation in the oxygen reduction reaction (ORR) pathway that molecular catalysts face. The 2D geometry enables the FePc molecules to be positioned within the electrochemical double layer, enabling electrons to directly transfer to oxygen reactants, prior to the Fe(II/III) redox. This functions in a manner akin to a metal catalyst thereby opening a redox-decoupled ORR mechanism. As a result, the reported 2D FePc molecular catalyst exhibits unprecedented ORR half-wave potential at 0.945 V vs. the reversible hydrogen electrode, achieving efficient application in zinc-air batteries and H₂/O₂ fuel cells. These findings open new possibilities in voltage efficient, redox-decoupled molecular catalysis that integrates strengths of molecules and materials in one synergistic system.

Efficient Prediction of Mole Fraction Related Vibrational Frequency Shifts

Thu, 16 Nov 2023 00:00:00 GMT

Efficient Prediction of Mole Fraction Related Vibrational Frequency Shifts Blasius, Jan; Drysch, Katrin; Pilz, Frank Hendrik; Frömbgen, Tom; Kielb, Patrycja; Kirchner, Barbara While so far it has been possible to calculate vibrational spectra of mixtures at a particular composition, we present here a novel cluster approach for a fast and robust calculation of mole fraction dependent infrared and vibrational circular dichroism spectra at the example of acetonitrile/(R)-butan-2-ol mixtures. By assigning weights to a limited number of quantum chemically calculated clusters, vibrational spectra can be obtained at any desired composition by a weighted average of the single cluster spectra. In this way, peak positions carrying information about intermolecular interactions can be predicted. We show that mole fraction dependent peak shifts can be accurately modeled and, that experimentally recorded infrared spectra can be reproduced with high accuracy over the entire mixing range. Because only a very limited number of clusters is required, the presented approach is a valuable and computationally efficient tool to access mole fraction dependent spectra of mixtures on a routine basis.

A Quantum Cluster Equilibrium Theory for Multi-Component Liquids

Mon, 19 Feb 2024 00:00:00 GMT

A Quantum Cluster Equilibrium Theory for Multi-Component Liquids Frömbgen, Tom; Drysch, Katrin; Zaby, Paul; Dölz, Jürgen; Ingenmey, Johannes; Kirchner, Barbara In this work, we present a new theory to treat multi-component liquids based on quantum-chemically calculated clusters. The starting point is the binary quantum cluster equilibrium theory that is able to treat binary systems. The theory provides one equation with two unknowns. In order to obtain another linearly independent equation, conservation of mass is used. However, increasing the amount of components leads to more unknowns and this requires linearly independent equations. We address this challenge by introducing a generalization of the conservation of arbitrary quantities, accompanied by a comprehensive mathematical proof. Furthermore, a case study for the application of the new theory to ternary mixtures of chloroform, methanol and water is presented. Calculated enthalpies of vaporization for the whole composition range are given, and populations or weights of the different clusters are visualized.

Acid-Catalyzed Rearrangements of 3-Aryloxirane-2-Carboxamides: Novel DFT Mechanistic Insights

Wed, 01 Jul 2020 00:00:00 GMT

Acid-Catalyzed Rearrangements of 3-Aryloxirane-2-Carboxamides: Novel DFT Mechanistic Insights Qu, Zheng-Wang; Zhu, Hui; Katsyuba, Sergey; Mamedova, Vera L.; Mamedov, Vakhid A.; Grimme, Stefan Efficient synthesis of 3-arylquinolin-2(1H)-ones and N-(2-carboxyaryl)-oxalamides from protic acid-catalyzed rearrangements of 3-aryloxirane-2-carboxamides was achieved recently but not well understood. In contrast to the classical Meinwald rearrangement, extensive DFT calculations reveal that the proximal aryl and amide groups have strong synergetic effects to control the amide-aided and aryl-directed oxirane-opening and further rearrangement sequences. The ortho-nitro substituent of the proximal aryl is directly involved in a nucleophilic oxirane ring-opening, the amide C=O is an important proton shuttle for facile H-shifts, while the N-aryl may act as a potential ring-closing site via Friedel-Crafts alkylation. The mechanistic insights are useful for rational design of novel synthesis by changing the aryl and amide functional groups proximal to the oxirane ring.