Oxides, of Ge, Sn and

Another study on the electrosynthesis of (alkyl) M compounds (M = Ge, Pb, Sn n = 2, 4) provides illustrative examples37. Sacrificial cathodes of Cd, Zn and Mg were used to produce the corresponding metal alkyls which are subsequently oxidized on sacrificial anodes of Ge, Sn and Pb. The cells are of very simple construction, with the proper metal electrodes. Diethylcadmium is utilized in this way for the manufacture of tetraethyllead from lead acetate and triethylaluminum in the following reaction sequence ... 

A second important characteristic of the mass spectra of Ge-, Sn- and Pb-containing compounds is the tendency to display abundant peaks corresponding to the M(IV) and M(II) oxidation states of these elements. 

Trends in ionization energies have been illustrated previously but other examples are of particular interest. The halides of Ge, Sn and Pb can be singled out because they have been extensively characterized for both the (IV) and (II) oxidation states. As in the case of C and Si, the tetrafluoro derivatives display very high ionization energies, and the observed trends in Ge demonstrate the decrease in IE in going from F to I, and the decrease in going from the (IV) to the (II) oxidation state, i.e. 

Herrmann and coworkers183 reported a series of Cp-manganese carbonyl complexes which bind Ge, Sn and Pb as central atoms linearly coordinated in clusters, to two Mn atoms in one series and trigonal-planar coordinated to three Mn atoms in another series 8 and 9. The group 14 atoms are double-bonded to two Mn atoms in these compounds, or carry one double bond and two single bonds to three Mn atoms. Potentiometric measurements of these compounds show irreversible reductions and oxidation by CV. No products could be isolated from either reduction or oxidation. The exceptionally high oxidation potential of (/i-Pb) r/ -CsHs )Mn(CO)2]2 as compared to the apparently similar Sn compound is noteworthy (Table 15). 

Although the majority of these complexes contain phosphines as supporting ligands, compounds of platinum(IV) with Pt—Ge and Pt—Sn bonds have been formed by oxidative addition of Ge—X and Sn—X bonds to complexes PtMe2(L—L) (L—L = bipy, phen). Trace... 

The thermal and chemical stability of C—M bonds (M = Si, Ge, Sn, Pb), and therefore of all organic compounds of the silicon subgroup elements, decreases, both in homolytic and in heterolytic processes, when the atomic number of the M element increases. For example, the thermal stability of tetraalkyl derivatives R4M diminishes essentially when M is changed consecutively from Si to Pb151 l52. The ease of oxidation of R4M compounds and the ease of cleavage of C—M bonds by halogens, protic and aprotic acids, etc.,... 

Most decaphenylmetailocenes also exhibit an unsurpassed thermal stability for sandwich complexes. The decaphenyl Ge, Sn, and Pb derivatives do not decompose until above 350°C (under nitrogen) (39), in contrast with around 100°C for the decabenzyl analogs (106). For sym-penta- and decaphenylferrocene and -ruthenocene an extraordinary degree of thermal and oxidative stability is noted (40) they are unchanged in air ( ) at 315°C and volatilize only at 250-300° C in the mass spectrometer. 

The elements Si, Ge, Sn, and Pb all exhibit the oxidation states of +2 and +4. However, the +2 state for Si is rare. One reason is that SiO is not stable and the halides SiF2 and SiCl2 are polymeric solids. A few Ge(II) compounds are known (e.g., GeO, GeS, and Gel2). The +2 and +4 oxidation states are about equally common for Sn and Pb. For example, Sn02 is the most common ore of Sn, and numerous compounds contain Sn(II) (stannous compounds). As we will see later, there are also numerous common compounds of both Pb(II) and Pb(IV). 

Many ionic compounds of AX2 stoichiometry possess the CaF2 (fluorite), or Na20 (antifluorite) structures shown in Figure 3.15. Fluorite is similar to CsCl, but with every other eight coordinate cation removed. Each fluoride anion is tetrahedrally coordinated by calcium ions. This structure is adopted by several fluorides and oxides. In the antifluorite structure, the coordination numbers are the inverse. Most oxides and other chalcogenides of the alkali metals (e.g. Na2Se, K2Se) possess the antifluorite structure, but so do some more covalent compounds, such as the silicides of Mg, Ge, Sn, and Pb. 

Azides of the lower oxidation state are less stable but nonetheless several have been reported, including HB(3,5-Me2-pz)3]Ge(N3) (pz = pyrazolyl), (Kl)Gc(N3) (Kl = Klaui s ligand) (amino-tropinimate)M(N)3 (M = Ge, Sn), and (A,A -mes2-l,5-diazapentadienyl)M(N3) (M = Ge, Sn). These complexes all exhibit geometries consistent with stereochemically active lone pairs and... 

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