Spectroscopic measurements on solutions of alkali metals in 1, 4, 7, 10, 13-pentaoxacyclopentadecane (15-crown-5)

Abstract

The alkali metals potassium, rubidium and caesium dissolve in the liquid crown ether 15-crown-5 to produce intensely coloured blue solutions. In this work we have employed a variety of spectroscopic techniques (optical spectroscopy, nuclear magnetic resonance (NMR) and electron spin resonance (ESR)) to investigate the nature of both the paramagnetic and diamagnetic solution species coexisting in equilibrium. The major paramagnetic species are the solvated electron, e - s , and the (metal-based) electron-cation complex M + s e - s . The diamagnetic species is the alkalimetal anion, M - . Comparisons in characteristic properties for the two liquid macrocyclic ionophores, 12-crown-4 and 15-crown-5, suggest that these two solvents both complex the alkali-metal cation and solvate excess electrons to quite different extents. For the alkali metals in the title solvent, the various equilibria appear to favour the formation of e - s and M + s e - s at the expense of the alkali anion.