BESSY II: Molecular orbitals determine stability
Molecular geometry structures of the trans- and cis-isomers fumarate and maleate (above, left to right) together with their hydrogenated molecule, succinate dianions (below). © HZB
Carboxylic acid dianions (fumarate, maleate and succinate) play a role in coordination chemistry and to some extent also in the biochemistry of body cells. An HZB team at BESSY II has now analysed their electronic structures using RIXS in combination with DFT simulations. The results provide information not only on electronic structures but also on the relative stability of these molecules which can influence an industry's choice of carboxylate dianions, optimizing both the stability and geometry of coordination polymers.
Carboxylic acid dianions of the type C4H2O4 or C4H4O4 (fumarate, maleate and succinate) can have different geometries (cis or trans) and different properties. Some variants are key in coordination chemistry, incorporating metallic elements into organic compounds, other variants play a role in biological processes. Fumarate and succinate, for example, are formed as intermediate products in the mitochondria of cells. Maleate, on the other hand, which is usually not formed in natural processes, is used in industrial applications that require durable materials. For environmental reasons, however, the question arises as to whether these compounds last forever or are biodegradable.
The stability of fumarate, maleate and succinate dianions is not only influenced by their molecular geometries, but also by the electronic structure of the molecules, in particular the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). However, the influence of the molecular orbitals on stability of these molecules has not been researched.
RIXS and XAS at BESSY II
Now, a team at HZB led by Prof. Alexander Föhlisch has elucidated the influence of the electronic structure on the stability of fumarate, maleate and succinate dianions. “We analysed these compounds at BESSY II with two different, very powerful methods,” says Dr Viktoriia Savchenko, first author of the study. X-ray absorption spectroscopy (XAS) can be used to investigate the unoccupied electronic states of a system, while resonant inelastic X-ray scattering (RIXS) provides information about the occupied highest orbitals and about interactions between the HOMO-LUMO orbitals. The results can be related to macroscopic properties, especially stability.
Maleate potentially less stable
The analysis of the spectral data shows that maleate is potentially less stable than fumarate and succinate. What’s more: The analysis also explains why: The electronic density in the HOMO orbital at the C=C bond between carboxylate groups could lead to weaker binding of maleate with molecules or ions. Fumarate and succinate, on the other hand, could be more stable, as their HOMO orbitals are equally delocalised.
“This means that there is a chance that maleate could be degraded by certain substances,” says Savchenko.
- AI agents deliver results – but do they reason scientifically?A research team co-led by Kevin Maik Jablonka from the Helmholtz Institute for Polymers in Energy Applications Jena (HIPOLE Jena) and N. M. Anoop Krishnan from the Indian Institute of Technology Delhi has developed Corral, a new benchmark for AI agents in science. The preprint “AI scientists produce results without reasoning scientifically” has been published on arXiv (https://doi.org/10.48550/arXiv.2604.18805). The analysis shows that current systems can execute scientific workflows and deliver results; however, they often do not follow the basic principles of scientific testing and reasoning.
- Magnetic field during catalyst synthesis triples ammonia yieldApplying an external magnetic field during the synthesis of CoFe₂O₄ electrocatalysts triples the ammonia yield during electrocatalytic conversion. The magnetic field alters the surface states of the spinel oxide thin films, making catalytically active sites more accessible. In the journal 'Advanced Functional Materials', a team led by Marcel Risch at HZB and Sanjay Mathur at University of Cologne demonstrates a scalable strategy for developing next-generation electrocatalysts for efficient and sustainable chemical production.
- Materials chemistry shapes the future of catalysisThe synthesis of materials can serve as a tool for developing smart, adaptive electrocatalysts. This rapidly evolving field of research involves in-situ analytics, data-driven discoveries and autonomous robotics. These new approaches could accelerate the discovery of long-lasting and efficient catalysts for future energy conversion and the decarbonisation of the chemical industry. A recent article by Dr Prashanth Menezes and his team in the renowned journal Angewandte Chemie provides an overview of this research.