Strontium cryptate

H. Kagenow, A. Jensen, Differential kinetic analysis and flow injection analysis, Part 3. The (2.2.2) cryptates of magnesium, calcium and strontium, Anal. Chim. Acta 114 (1980) 227. 

The Crowns were found in the U.S.A. The Cryptates , a more recent French discovery, are mixed ether-amine macrocycles that not merely encircle the salts of inorganic cations, as Crowns do, but actually surround them in all directions, leading to somewhat tighter binding (Lehn, Sauvage, and Dietrich, 1970), and to very strong binding of strontium vts d vis calcium. Of the alkali metals, potassium is often preferred to sodium and lithium. 

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