Zintl ions containing Si, Ge, Sn and Pb

There are nine Sn atoms and each provides two valence electrons, assuming that each atom carries a lone pair of electrons. 

Total number of cage-bonding electrons available = (9 X 2) -I- 4 = 22 electrons = 11 pairs 

[Sng] has 11 pairs of electrons with which to bond nine Sn atoms. 

Rationalize why Sis) adopts the same cluster structure as C2B3HJ. Hint Look back to worked example 13.9) 

Worked example 14.4 Structures of Zintl ions Rationalize the structure of [Sn9] shown in Fig. 14.13a. 

Total number of cage-bonding electrons available 

This means that there are (n + 2) pairs of electrons for n vertices, and so [Sng] is a nido-cage, based on a 10-vertex deltahedron (see Fig. 13.30) with otic vertex vacant. This corresponds to the observed structure of a monocapped square-antiprism. 

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