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It was about two hundred years ago when Sir Humphrey Davy, a brilliant English scientist and poet whose fame is acknowledged for the discovery of alkaline metals (potassium, sodium, magnesium, barium), observed a surprising phenomenon: potassium metal exposed to ammonia vapours forms gold-blue coloured materials. About one hundred years later the American chemist Charles Kraus claimed, as possible explanation of this phenomenon, that potassium (K) atoms ionise (lose electrons) in liquid ammonia to form a cation K+ species, while the freed electrons are solvated (surrounded) by the ammonia (NH3) molecules. Several other alkaline metals such as lithium and sodium show similar behaviour when dissolved in amines and in ether solvents. The two phenomena of „electron solvation‟ and „cation complexation‟ linked to Davy‟s observation, are behind one of the most investigated and promising fields of chemical and materials science research in the last ten years: 'electrides'. |
