The Group 14 Elements Si, Ge, Sn, Pb

There is no more striking example of an enormous discontinuity in general properties between the first- and the second-row elements followed by a relatively smooth change toward more metallic character thereafter than in Group 14. Little of the chemistry of silicon can be inferred from that of carbon. Carbon is strictly nonmetal-lic silicon is essentially nonmetallic germanium is metalloid tin and especially lead are metallic. Some properties of the elements are given in Table 8-1. 

However, there is a general if not entirely smooth decrease in the tendency to catenation in the order C Si Ge Sn Pb, which may be ascribed partly to diminishing strength of the C—C, Si—Si, Ge—Ge, Sn—Sn, and Pb—Pb bonds (Table 8-2). 

It may be noted also that (a) there is a steady decrease in E—C and E—H bond energies and (b) E—H bonds are stronger than E—C bonds. 

However, the divalent state becomes increasingly stable down the group and is dominant for lead. 

Inspection of Table 8-1 clearly shows that this trend cannot be explained exclusively in terms of ionization enthalpies, since these are essentially the same for all the elements Si—Pb. The inert pair concept probably holds only for the lead ion Pbaq where there could be a 6s2 configuration. In more covalent Pbn compounds and most Sn11 compounds there are stereochemically active lone pairs—indeed some EX2 and ER2 compounds of Ge and Sn can act as donor ligands. 

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Of the group 14 elements (Si, Ge, Sn and Pb), only tin is known to form a variety of poly(pyrazoIyl)borato alkyl derivatives. For example, the reactions between K[pzTp] and the silicon derivatives Me SiCl4 (n = 1-3) have not given tractable products (115). Similarly, the reaction between K[pzTp] and Me2GeCl2 gives a complex that has been spectroscopically characterized as [pzTp]2GeMe2, but which readily decomposes. 

Fig. 42 Sublimation enthalpies of the group 14 elements Si, Ge, Sn, and Pb from the literature and the extrapolated sublimation enthalpy of FI (Z = 114) (from Ref. [145] and using the correlation depicted in Fig. 38)...

The tetrasulfides R R MS4 with M=Si, Ge, Sn, or Pb bearing bulky substituents on the group 14 element were synthesized by the reaction of the corresponding divalent species R R M, which are heavier analogues of the carbenes, with elemental sulfur (see Scheme 1) [11-20]. The divalent species... 

The most fundamental issues of the structures of heavier group 14 element-centered anionic derivatives R3EM (R = alkyl, aryl, silyl E = Si, Ge, Sn, Pb M = alkali or alkaline earth metals) turned out to be the questions of their aggregation states (monomeric, dimeric, or oligomeric), nature of the E-M bond (covalent or ionic), and configuration of the anionic centers E (tetrahedral, pyramidal, or planar). The most important experimental techniques that are widely used to clarify these questions are NMR spectroscopy and X-ray diffraction analysis. 

Although some review articles are now available on the synthesis of heavy ketones," they are restricted to dealing with some selected elements, especially silicon and germanium. We delineate here a more general account of the whole chemistry of stable double bonds between heavier Group 14 and Group 16 elements [i.e., RR M=X (M = Si, Ge, Sn, Pb X = O, S, Se, Te)]. 

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