Electron structure, Zintl ions

In an effort to make the distannyne, Ar Sn=SnAr (Ar = 2,6-(2,4,6-Pr 3C6H2)2C6H3), Ar SnH was heated in toluene hydrogen was eliminated but SnC bonds also were cleaved, and gave the paramagnetic cluster Ar 3Sn9 59 (g= ca. 2.031), with a structure that is based on the 21-electron [Sng]3- cage that is known as a Zintl ion.478... 

The first transition metal derivatives of a Zintl ion was prepared by Teixidor et al. in 1983 in reactions between Pt(PPli4)4 and en solutions of the Eg (E = Sn, Pb) [25, 26]. Despite being the first examples in this important class of clusters, the complexes have yet to be isolated and their structures and compositions remain unknown. The authors propose that complexes have a (PPh3)2PtSng stoichiometry and a nido-ty structure. Based on comparisons with NMR parameters from the past 30 years and the stoichiometry of the reactions described by Teixidor et al., we believe that the Rudolph compounds are most likely 22-electron cZos )-Pf E9Pt (PPh3) complexes. Our rationale is given below. 

If electrons are added into the crystal structure, they lead to the breaking of the Sn-Sn bonds, each atom carrying an unshared electron pair, and ultimately to the formation of isolated anionic clusters with triangular faces (deltahedra), known as Zintl ions (e.g. 1 and 2 see Chapter 1.6). These compounds are diamagnetic and poor conductors. They can be prepared either by reduction of tin with an alkali metal or electrochemically, and are soluble in polar, basic solvents. For example, [Na+]4 [Sng]" " can be prepared from the reaction of tin with sodium in ethylenediamine, or in the presence of a crown ether to associate with the sodium cations. The most common structure is a nine-atom cluster 2. ... 

Arsenides and antimonides containing the [Asy] and [Sby] ions can be prepared by, for example, reactions 15.54 and 15.55. These Zintl ions are structurally related to (15.18) and their bonding can be described in terms of localized 2-centre 2-electron interactions. 

Correlations between structure and electron counting for homo and heteronuclear Zintl ions are described in Table 4.19. 

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