UvA scientist Bas de Bruin in 'Nature Chemistry': atomic ‘nitridyl radical' detected for first time

21 May 2012

Scientists, including Dr Bas de Bruin of the University of Amsterdam's (UvA) Van 't Hoff Institute for Molecular Sciences, have for the first time detected a transition metal complex containing an atomic ‘nitridyl radical’ ligand. Such atomic nitrogen ligands play an important role in catalytic activation of molecular nitrogen (Haber-Bosch ammonia synthesis).

Using spectroscopic techniques a team of Dutch and German scientists has for the first time detected a transition metal complex containing an atomic ‘nitridyl radical’ ligand. Such atomic nitrogen ligands play an important role in catalytic activation of molecular nitrogen (Haber-Bosch ammonia synthesis), conversion of ammonia in ammonia-based fuel-cells and selective oxidation of ammonia (to N2O or N2) at heterogeneous catalysts.

The results were published in 'Nature Chemistry' by German chemists from the University of Erlangen and the Max-Planck Institute for Bio-Inorganic Chemistry in Mülheim together with dr. Bas de Bruin of the UvA's Van 't Hoff Institute for Molecular Sciences on 3 June 2012.

Until recently the {•N2‑} radical-ligands proved to be too reactive to detect spectroscopically. In 'Nature Chemistry' ,the researchers now describe a method for studying an iridium-nitridyl radical species which ‘lives’ long enough to measure its spectroscopic properties.

Characteristic reactivity

The unusual iridium-nitridyl species turns out to be stable enough to detect with IR (Erlangen) and EPR (UvA & Max Planck) spectroscopic techniques. Nonetheless it reacts in a characteristic manner with itself to form molecular nitrogen (N2) which is exactly the reverse reaction of the one occurring in the Haber-Bosch process.

Since the reverse process should (according to the principles of ‘microscopic reversibility’) occur via exactly the same transition state this confirms existing theories for N2-activation. Theoretical analysis by Bas de Bruin of the experimentally observed N2-formation process
(Erlangen) shows a reaction-pathway that involves a radical-radical coupling step between two {•N2‑} nitridyl radicals.

More efficient nitrogen fixation?

The obtained results clearly show that the redox-activity of the atomic nitrogen ligand in transition metal nitride complexes, and the radical character of the nitridyl ligands have an important influence on the reactivity of these species.

The results shed new light on the problems associated with nitrogen fixation via the current Haber-Bosch process (to synthesize ammonia, among others for the production of fertilizers). This is associated with an energy consumption corresponding roughly with 1% of
the total human energy consumption on earth. More efficient methods to convert dinitrogen are highly welcomed for sustainability reasons. They now may be within reach, building on the obtained new insights.

Part of Bas de Bruin's research has been funded through the prestigious Starting Grant he received from the European Research Council four years ago.

Full article

Closed-shell and open-shell square-planar iridium nitrido complexes Markus G. Scheibel, Bjorn Askevold, Frank W. Heinemann, Edward J. Reijerse, Bas de Bruin, Sven Schneider Nature Chemistry, 2012, advance online publication, DOI: 10.1038/NCHEM.1368

Published by  HIMS