Germanium bond type

Compare and contrast the chemistry of silicon, germanium, tin and lead by referring to the properties and bond types of their oxides and chlorides. 

Recently, Schleyer and co-workers reported a theoretical study on the stabilities and geometries of a series of carbonyl type compounds, R2M=0 (M = C, Si, Ge, Sn, Pb R = H, CH3), and those of carbene type isomers [R(RO)M ] as shown in Table II.15 These results show that in (CH3)2 M=0 series the carbene type structure is more stable than the double bond type structure in the case of germanium, tin, and lead, unlike the case of carbon in which the double bond structure is preferred. 

The bonds formed between germanium and elements of Group VA can be divided into two categories those in which the element is bonded via a covalent bond and others in which a Lewis acid-Lewis base interaction between the two elements results in coordinate bond formation. The same classification of bond types is also appropriate when discussing organogermanium derivatives of Groups VIA and VII A. 

SCHEME 1. Synthesis of a germanium axial-bonding -type hybrid trimer. Reprinted with permission from Reference 5. Copyright 1999 American Chemical Society... 

Yield and absolute hardness, 72 Y-sialon glass density, 229 Knoop hardness, 229 Modulus, 229 Young s modulus of AljOj, 241, 259-261 anisotropy in /3-AI2O3, 281 of B4C, 228, 241 and bond type, 172 and crack depth, 155 and cracking, 147 of CrjCj, 302 of germanium, 252 of glass, 238 and hardness, 72 hardness ratio, 179 from Knoop indents, 180 mismatch stress, 273 of MgO, 241, 269 and penetration depth, 47, 240 and plasticity parameter, 241 and residual impression parameter, 240... 

Thus we have shown that when s and p orbitals are available and s—p quantization is broken an atom can form four (or fewer) equivalent bonds which are directed towards tetrahedron corners. To the approximation involved in these calculations the strength of a bond is independent of the nature of other bonds. This result gives us at once the justification for the tetrahedral carbon atom and other tetrahedral atoms, such as silicon, germanium, and tin in the diamond-type crystals of the elements and, in general, all atoms in tetrahedral structures. 

The catenation abihty of lead being considerably lower than that of germanium or tin, plumbanes with Pb—Pb bonds are quite difficult to prepare, even though a number of such compounds have been synthesized. As already pointed out, the main method for the preparation of this type of compound is the reaction of an appropriate Grignard reagent with PbCl2159, e.g. 

The germabenzene species 15 reacts in two different fashions with a variety of substrates to give cylcoaddition products (Scheme 7).30 With MesCNO and 2,3-dimethylbutadiene, 15 behaves similarly to a compound with a single Ge-C double bond, whereas in reactions with styrene and phenylacetylene, 15 behaves as a 1-germabuta-l,3-diene to give Diels-Alder-type adducts. The germanium-carbon doubly bonded species 23 reacts with nitriles in several different ways, including as a 1,2-dipolar species with Bu CN, as a 1,4-dipolar species with PhCN, and as a base with various /3-functionalized nitriles (Scheme 8). 

Refined X-ray methods have also been applied to other types of crystal [7—9). In some metals, for example, the inter-ionic electron minimum density corresponds to some few electrons spread over the lattice (2 for Mg, 3 for A1 for example). And in covalent crystals like diamond there are non-spherical interatomic concentrations corresponding to the chemists covalent bonds, although such effects are small even for germanium (7). 

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