Article by Dr Cina Foroutan-Nejad in Journal of the American Chemical Society

15 July 2022

In ordinary matter electrons and protons are closely bound together and make united entities called atoms and molecules. However, in a bizarre group of molecules called electrides this unity changes in a way that an electron stands alone, far from any other nucleus around it, and acts like an anion to balance the positive charge of the rest of the molecule. Electrides, in particular inorganic electrides, are interesting for their unique conductivity and their application as the source of the electron beam. Organic electrides are known as strong reducing reagents owing to their freely available electrons. The first organic electrides were identified in complexes between alkali metals, such as Cs, Rb and K with cryptands. In these complexes often a free electron is trapped in the empty space between several cryptands that tightly embrace metallic cations. However, despite their interesting properties, organic electrides have not found their niche in materials science because electrons in their structures are often too loosely connected to the rest of the structure. Therefore, in temperatures way below room temperature they decompose. Until very recently only one room-temperature-stable organic electride was known.

In a recent contribution published in the Journal of the American Chemical Society dr. Cina Foroutan-Nejad from the Institute of Organic Chemisry PAS in collaboration with the researchers of the Institute of Chemical Research of Catalonia, ICIQ, in Spain, and UiT the Arctic University of Norway synthesized and characterized an organic electride that is unique from several perspectives. This electride is the second example of a room-temperature-stable electride and the first known electride that is formed by magnesium and an acyclic ligand, bipyridine. Another unique aspect of this electride is that apart from the theoretical characterization, the free electron was identified by the presence of an unusual electron accumulation in the center of the molecule via X-ray crystallography. This species is further characterized via EPR and NMR but interestingly because of the non-interacting nature of electride’s electron with the rest of the molecule, no hyperfine coupling in EPR or peak broadening in NMR was observed. This electride can be a potential candidate for a qubit because of its specific structure in which an electron is encaged in a topological cage.

Bonus fact about this work: The paper was 5 times reviewed by 9 referees until we could convince everyone that there is a free electron in the middle of an Mg4 ring!