Oxides of germanium, tin, and lead

Key point: The 2 oxide becomes more stable on going down the group from Ge to Pb. Germanium (II) oxide, GeO, is a reducing agent and disproportionates to Ge and GeO₂. The structure of germanium (IV) oxide, GeO₂, is based on tetrahedral four-coordinate GeO4 units. It also exists in a six-coordinate crystalline form with a rutile-like structure and in a vitreous form that resembles fused silica. Germanium analogues of silicates and aluminosilicates are also known (Section 14.15). In the blue-black form of SnO the Sn (II) ions are four-coordinate (Fig. 14.11), but the O₂ ions around the Sn (II) lie in a square to one side with the lone pair on Sn pointing away from the square. This structure can be rationalized by the presence of a stereochemically active lone pair on the Sn atom and can be described as a fluorite structure (Section 3.9) with alternate layers of anions missing. The red form of SnO has a similar

Figure 14.11 The structure of blue black SnO showing parallel layers of square-based pyramidal SnO₄ units.structure and can be converted to the blue-black form by heat, pressure, and treatment with alkali. When heated in the absence of air, SnO disproportionates into Sn and SnO₂. The latter occurs naturally as the mineral cassiterite and has a rutile structure (Section 3.9). It has low solubility in glasses and glazes, and is used in large quantities as an opacifier and pigment carrier in ceramic glazes to make them less transparent. The oxides of lead are very interesting from both fundamental and technological standpoints. The red form of PbO has the same structure as blue black SnO with a stereochemically active lone pair (Fig. 14.11). Lead also forms mixed oxidation state oxides. The best known is ‘red lead’, Pb₃ O₄, which contains Pb (IV) in an octahedral environment and Pb (II) in an irregular six-coordinate environment. The assignment of different oxidation numbers to the lead in these two sites is based on the shorter PbO distances for the atom identified as Pb (IV). The maroon form of lead (IV) oxide, PbO₂, crystallizes in the rutile structure. This oxide is a component of the cathode of a lead acid battery.

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مواضيع ذات صلة

Phosphine, arsane, and stibine

Hydrazine and hydroxylamine

Ammonia

Phosphides

Azides

Nitrides

Nitrogen activation

Microporous solids

Aluminosilicates

Compounds with nitrogen

Compounds of carbon with oxygen and sulfur

Tin and lead halides