Tag: oxidation states

A new series of [M(B11H11)2] 3-anions with metals in their highest known oxidation states

A new series of [M(B11H11)2] 3-anions with metals in their highest known oxidation states

In collaboration with Prof. Finze’s research group (University of Würzburg) and Dr. Alexey Maximenko (SOLARIS National Synchrotron Radiation Centre at Jagiellonian University) Prof. Adam Slabon’s research group has successfully synthesized and comprehensively characterized a new series of anions of the type [M(B11H11)2]3- (M = Cu, Ag, Au). The nido-[B11H11]4- ligand coordinates to copper, silver, and gold stabilizing them in the exceptionally high formal oxidation state +V. This is the highest oxidation state known to date for these metals. XANES analysis, carried out by Dr. Alexey Maximenko, additionally confirmed the unusually high oxidation state of copper in K3[Cu(B11H11)2]·5H2O.

DFT calculations showed the relative stability of different structural isomers, while experimental investigations revealed an unusual property of the silver complex. X-ray structural analyses of single crystals revealed that [Ag(B11H11)2]3⁻exists in equilibrium between two coordination forms: a kinetically stable η5 species with Ag(V) and a labile η2species with Ag(I). When cooled below 130 K, a reversible phase transition occurs in which the ligand coordination changes from η5 na η2 and reverts back when heated. This is the first observation of such low-temperature isomerization in this class of compounds.

Read more on the SOLARIS website

Image: Reversible transition between (n-Bu4N)3[Ag+V(η5 – B11H11)2] and (n-Bu4N)3[Ag+I (η2-B11H11)2]

Electrocatalysis – Iron and Cobalt Oxyhydroxides examined

Electrocatalysis – Iron and Cobalt Oxyhydroxides examined

A team led by Dr. Prashanth W. Menezes (HZB/TU-Berlin) has now gained insights into the chemistry of one of the most active anode catalysts for green hydrogen production. They examined a series of Cobalt-Iron Oxyhydroxides at BESSY II and were able to determine the oxidation states of the active elements in different configurations as well as to unveil the geometrical structure of the active sites. Their results might contribute to the knowledge based design of new highly efficient and low cost catalytical active materials.

Very soon, we need to become fossil free, not only in the energy sector, but as well in industry. Hydrocarbons or other raw chemicals can be produced in principle using renewable energy and abundant molecules such as water and carbon dioxide with the help of electrocatalytically active materials. But at the moment, those catalyst materials either consist of expensive and rare materials or lack efficiency.

Key reaction in water splitting

A team led by Dr. Prashanth W. Menezes (HZB/TU-Berlin) has now gained insights into the chemistry of one of the most active catalysts for the anodic oxygen evolution reaction (OER), which is a key reaction to supply electrons for the hydrogen evolution reaction (HER) in water splitting. The hydrogen can then be processed into further chemical compounds, e.g., hydrocarbons. Additionally, in the direct electrocatalytic carbon dioxide reduction to alcohols or hydrocarbons, the OER also plays a central role.

Read more on the HZB website

Image: LiFex-1Cox Borophosphates have been used as inexpensive anodes for the production of green hydrogen. Their dynamic restructuring during OER as well as their catalytically active structure, have been elucidated via  X-ray absorption spectroscopy.

Credit: © P. Menezes / HZB /TU Berlin

Third-highest oxidation state secures rhodium a place on the podium

Third-highest oxidation state secures rhodium a place on the podium

Oxidation states of transition metals describe how many electrons of an element are already engaged in bonding, and how many are still available for further reactions. Scientists from Berlin and Freiburg have now discovered the highest oxidation state of rhodium, indicating that rhodium can involve more of its valence electrons in chemical bonding than previously thought. This finding might be relevant for the understanding of catalytic reactions involving highly-oxidized rhodium. The result was recognized as a „very important paper“ in Angewandte Chemie.

Transition metals in high or unusual oxidation states might play an important role as catalysts or reaction intermediates in chemical reactions. Because transition metals are already well characterized in most cases, the discovery of a new oxidation state of rhodium came as a real surprise. The identification of rhodium(VII) was made possible by PhD student Mayara da Silva Santos and co-workers, who were able to isolate the species from any reactant in a low-temperature ion trap, and perform x-ray absorption spectroscopy for its characterization. 

BESSY II was essential for the discovery

These kinds of experiments are highly demanding, and can, at present, only be carried out at BESSY II. „The combination of advanced sample preparation, low-temperature ion trapping, and x-ray spectroscopy is unique. Because these essential tools can even be applied to more complex systems, we anticipate further insight into exotic transition metal oxides“, says Vicente Zamudio-Bayer, head of the ion trap group at beamline UE52-PGM, who develops and operates the ion trap endstation at BESSY II. „What was important for us was that our surprising experimental findings could be substantiated by Sebastian Riedel‘s group at FU Berlin, who performed state-of-the-art calculations on the species in question“, explains Zamudio-Bayer. “Even rhodium in oxidation state +6 is very rare, so we had to be extremely careful about +7. New oxidation states are not discovered every day”, says Mayara da Silva Santos.

Read more on the HZB website

Image: For the first time, a team has detected rhodium in the +7 oxidation state, the third highest oxidation state experimentally among all elements in the periodic table. © https://doi.org/10.1002/anie.202207688