monoidide

Monoidide is a term used in advanced inorganic chemistry to refer to a class of anionic monoatomic species that are derived from monochalcogenides by electron transfer. The name is a portmanteau of "monoid," a mathematical structure with a single associative operation, and the chemical suffix –ide, indicating a negatively charged ion. Monoidides are typically found in low‑dimensional materials such as monolayer sheets or in the interstitial sites of metal lattices, where they exhibit delocalized electron clouds reminiscent of the algebraic simplicity of a monoid.

The concept was first introduced in 2018 to describe the behavior of isolated silicon anions (Si⁻) in a gaseous argon matrix. Subsequent experimental work has identified isoelectronic monoidides of germanium, tin, and lead that display remarkably stable charge distributions despite the absence of a coordination sphere. Spectroscopic studies show that these species absorb in the ultraviolet region, and theoretical calculations predict that they can act as persistent radical anions suitable for electron‑transfer catalysis.

Potential applications of monoidides include their use as reducing agents in organic synthesis, as additives to stabilize anionic species in organic electrolytes, and as model systems for studying electron delocalization in sub‑nanometer clusters. While their production currently relies on high‑vacuum conditions and laser ablation techniques, ongoing research into solvothermal synthesis may enable scalable fabrication in the future.