Question

Explain relationship between size of crown ether and radius of corresponding alkali metal cation.

Answer 1

Answer:

Explanation:

Numerous alkali metal cations with heavy group 14 anions have been observed as Zintl phases in the form of homoatomic clusters.241,241a The following is a brief glimpse of this emerging area of Zintl chemistry. Among the homoatomic clusters involving group 14 anions, the E9M4 (M = alkali metal; E = Si, Ge, Sn, Pb) clusters are most prominent; selected examples include Ge17K12 232,242 Si17Rb12 233,243 Ge9M4 (M = K 234, Cs 235),244,244a as well as Pb9K4 236.245 The listing of the 17 : 12 clusters as examples for E9M4 geometry is not a mistake, since E9M4 clusters coordinate with additional E44− units.

Use of sequestering agents such as crown ethers or cryptands to dissolve the alkali metals led to the isolation of a larger variety of discrete En clusters, an example being Ge92− 237.246,246a–246c Other selected examples include [2,2,2-crypt-K]3[KSn9] 238,247 the dicationic [Ge9enK(18-crown-6)2] 239,248 or the tin analogs [K(18-crown-6)]3[KSn9(en)] 240 and [Sn9[K(18-crown-6)]4] 241.249 In all species, alkali metal group 14 contacts are present.

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