Liquid Ammonia—Revisiting an Old Friend with New Purpose

Liquid ammonia was investigated extensively as a solvent in the 20th century and was invaluable in the reduction of elements. Its recent fame lies in its great potential for green energy, particularly for hydrogen storage. Herein, a brief overview of this unique solvent, highlighting its promising properties toward the isolation of novel species, especially in unusually low oxidation states, is provided.

Ammonia was first discovered as a chemical solvent in the 19th century. Extensive investigations during the 20th century toward its physical and chemical properties have yielded substantial knowledge regarding the compound. Historically, its merit was mainly seen in chemical synthesis and its ability to accommodate syntheses that could not be pursued in aqueous solvents. With a growing demand for low-emission energy systems, the scientific focus on ammonia shifted toward its potential for efficient hydrogen storage and transportation, as well as for direct combustion. Herein, a brief overview of the development of the role of ammonia, with the goal of highlighting its unique properties as a solvent, is provided, in particular, in the chemical syntheses of unprecedented species and reactive compounds.

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