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).

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.

 

arö

  • Copy link

You might also be interested in

  • Hydrogen: Breakthrough in alkaline membrane electrolysers
    Science Highlight
    28.10.2024
    Hydrogen: Breakthrough in alkaline membrane electrolysers
    A team from the Technical University of Berlin, HZB, IMTEK (University of Freiburg) and Siemens Energy has developed a highly efficient alkaline membrane electrolyser that approaches the performance of established PEM electrolysers. What makes this achievement remarkable is the use of inexpensive nickel compounds for the anode catalyst, replacing costly and rare iridium. At BESSY II, the team was able to elucidate the catalytic processes in detail using operando measurements, and a theory team (USA, Singapore) provided a consistent molecular description. In Freiburg, prototype cells were built using a new coating process and tested in operation. The results have been published in the prestigious journal Nature Catalysis.
  • HZB patent for semiconductor characterisation goes into serial production
    News
    10.10.2024
    HZB patent for semiconductor characterisation goes into serial production
    An HZB team has developed together with Freiberg Instruments an innovative monochromator that is now being produced and marketed. The device makes it possible to quickly and continuously measure the optoelectronic properties of semiconductor materials with high precision over a broad spectral range from the near infrared to the deep ultraviolet. Stray light is efficiently suppressed. This innovation is of interest for the development of new materials and can also be used to better control industrial processes.
  • Alternating currents for alternative computing with magnets
    Science Highlight
    26.09.2024
    Alternating currents for alternative computing with magnets
    A new study conducted at the University of Vienna, the Max Planck Institute for Intelligent Systems in Stuttgart, and the Helmholtz Centers in Berlin and Dresden takes an important step in the challenge to miniaturize computing devices and to make them more energy-efficient. The work published in the renowned scientific journal Science Advances opens up new possibilities for creating reprogrammable magnonic circuits by exciting spin waves by alternating currents and redirecting these waves on demand. The experiments were carried out at the Maxymus beamline at BESSY II.