Germanium-stabilized

The oxidation state -1-4 is predominantly covalent and the stability of compounds with this oxidation state generally decreases with increasing atomic size (Figure 8.1). It is the most stable oxidation state for silicon, germanium and tin, but for lead the oxidation state +4 is found to be less stable than oxidation state +2 and hence lead(IV) compounds have oxidising properties (for example, see p. 194). 

The yellow hydrated oxide is slightly acidic and forms germanates(II) (germanites). The increased stability of germanium(II) oxide compared to silicon(II) oxide clearly indicates the more metallic nature of germanium. 

Mujica A and R J Needs 1993. First-principles Calculations of the Structural Properties, Stability, aind Band Structure of Complex Tetrahedral Phases of Germanium ST12 and BC8. Physical Review B48 17010-17017. 

The state of the synthetic art in this area, in 1979, is much more satisfactory. During the past decade, several new synthetic developments have occurred such that we are closer to the point where the limitations upon synthesis of trifluoromethyl compounds are related more to stability problems in isolated cases, and are not nearly so much due to lack of widely applicable synthetic techniques. We find ourselves, for example, in a position in 1979 where the germanium compound, Ge(CF3)4, which in the past decade, was considered by many workers to be of insufficient stability to permit isolation, has been prepared by four independent methods and is known to be stable to over 100°C. Many of these new synthetic techniques have emerged from studies conducted in our laboratory at the University of Texas and previously... 

Tris(trifluoromethyl)germanium iodide is unstable in 3M base, however, and yields fluoroform quantitatively. All of the compounds showed good thermal stability (15). 

Ni [182], V [183], and A1 [184]. SU-M [185] is a mesoporous germanium oxide with crystalline pore walls, possessing one of the largest primitive cells and the lowest framework density of any inorganic material. The channels are defined by 30-rings. Structural and thermal information show that there exists a mismatch between framework stability and template decomposition. The latter requires temperatures higher than 450 °C, while the structure is preserved only until 300 °C. 

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. 

Until recently, there have been only two examples of stable Ge-S double bond compounds and one each for Ge-Se and GE-Te double bond compounds, but both of them are stabilized by the intramolecular coordination of a nitrogen ligand to the germanium center. 

Meanwhile, Parkin and his co-workers have also reportedthe synthesis of a series of terminal chalcogenido complexes of germanium 66, 67, and 68 (Scheme 20).42 X-ray structural analyses of 66, 67, and 68 revealed that they have unique germa-chalcogenourea structures stabilized by the intramolecular coordination of nitrogen atoms. The central Ge-X (X = S, Se, Te) bond of 66, 67, and 68 should be represented by a resonance structure, Ge+ - X- —>- Ge=X, because their bond... 

A variety of preparation methods are known for transient germanium-chalcogen double bond species some of them seemed to be useful also for the synthesis of kinetically stabilized systems. Indeed, the reaction of a germylene with an appropriate chalcogen source was found to be one of the most versatile and general methods for the synthesis of stable germanium-containing heavy ketones (Scheme 21). 

In view of these situations, synthesis and isolation of a kinetically stabilized germanetellone are significant not only for clarifying the character of the Ge-Te double bond by itself but also for elucidating the properties of germanium-containing heavy ketones systematically. 

In contrast to the considerable thermal stability of the isolated heavy ketones of silicon, germanium, and tin, a plumbanethione behaves differently. When stable... 

X-ray diffraction (XRD) patterns for the materials were recorded on a X-ray diffractometer using nickel-filtered CuKa (0.154 nm) radiation and a liquid nitrogen-cooled germanium solid-state detector. Thermal stability of the materials was performed using a thermogravimetric analyser. The acidity of calcined samples were determined... 

The low-temperature thermometers based on heavily doped compensated germanium (see Section 9.6.2.1) show high stability, good reproducibility, low noise and low specific heat. Ge used for cryogenic sensors is heavily doped (1016 - 1019 atoms/cm3), with T0 of Mott s law ranging between 2 and 70K (see formula 9.6). 

Hexamethylcyclotrigermathiane (22) and hexamethylcyclotristannathiane (23) also react easily with Et3P=CHMe, which enabled us to obtain the first betaines with the thiolate center in the germanium (24) and tin (25) series (Scheme 12).60,61 Both betaines are solid finely crystalline white substances, whose solubility and stability in the solid state and in solutions are similar to those of the silicon analog 20n. 

In contrast to silicon, germanium has a well-established though limited chemistry of inorganic compounds in the +11 state which are of reasonable thermal stability though usually air-sensitive. Divalent organogermanium(II) species known at present fall into three groups ... 

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