Alkali and alkaline earth metal salts of 2,2′,4,4′,6,6′-hexanitrodiphenylamine (HND) were extracted into nitrobenzene in the absence or presence of several crown ethers or cryptands which differ from one another in hole size. The quantity of water transferred to the nitrobenzene phase was determined by means of the Karl-Fischer method. The NMR and near-infrared spectra show that the coextraction of water is caused by the hydration of the cations. The number of water molecules attached to the cations increases upon going from Cs+ (0.6) to Li+ (5.6) and from Ba2+ (10.5) to Ca2+ (13.0). The complexation between these cations and the crown ethers causes a clear decrease in the hydration number; e.g., in the 1:1 metal–crown ether complexes, more than half of the water molecules are removed, and in the 1:1 metal–cryptand complexes, less than one water molecule remains unremoved. The complexes of a 1:2 stoichiometry are also found; some are stable and carry virtually no water molecules. The number and type of donor atoms have no significant effect on the coextraction of water. The presence of fused benzo rings on the crown ether also has no influence on the number of water molecules.

The hydration numbers of alkali metal cations and their complex

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