Binary hydrides of some group 14 elemets

   Silane, SiH₄, is formed when SiCl₄ or SiF₄ reacts with Li[AlH₄] and is a source of pure Si (equation 1.1) for semiconductors. Silanes Si_nH_2n+‏2 with straight or branched chains are known for 1 ≤ n ≤ 10, and Figure 1.1 compares the boiling points  of the first five straight-chain silanes with their hydrocarbon analogues. Silanes are explosively inflammable in air (equation 1.2).

             (1.1)

    (1.2)

     A mixture of SiH₄, Si₂H₆, Si₃H₈ and Si₄H₁₀ along with traces of higher silanes is obtained when Mg₂Si reacts with aqueous acid, but the non-specificity of this synthesis renders it of little practical value. By irradiating SiH₄ with a CO₂ laser, SiH₄ can be converted selectively into Si₂H₆. Silane is a colourless gas which is insoluble in water, reacts rapidly with alkalis (equation 1.3) and forms compounds of the type M[SiH₃] with Na, K (equation 1.4), Rb and Cs.The crystalline salt K[SiH₃] possesses an NaCl structure and is a valuable synthetic reagent, e.g. equation 1.5.

                                       (1.3)

                        (1.4)

           (1.5)

   Germanes Ge_nH_2n‏+2 (straight and branched chain isomers) are known for 1 ≤ n ≤ 9. GeH₄ is less reactive than SiH₄; it is a colourless gas (bp 184 K, dec 488 K), insoluble in water, and prepared by treating GeO₂ with Na[BH₄] although higher germanes are also formed. Discharges of various frequencies are finding increased use for this type of synthesis and have been used to convert GeH₄ into higher germanes, or mixtures of SiH₄ and GeH₄ into Ge₂H₆, GeSiH₆ and Si₂H₆. Mixed hydrides of Si and Ge, e.g. GeSiH₆ and GeSi₂H₈, are also formed when an intimate mixture of Mg₂Ge and Mg₂Si is treated with acid. Reactions between GeH₄ and alkali metals, M, in liquid NH₃ produce M[GeH₃], and, like [SiH₃]_, the [GeH₃]_ ion is synthetically useful. The reaction of SnCl₄ with Li[AlH₄] gives SnH₄ (bp 221 K) but this decomposes at 298K into Sn and H₂; note the variation in reactivities: SiH₄ > GeH₄ < SnH₄. Plumbane, PbH₄, is poorly characterized and may not actually have been isolated. Significantly, however, replacement of H atoms by alkyl or aryl substituents is accompanied by increased stability (see Section 18.5).

Silanes Si_nH_2n‏+2 with straight or branched chains are known for 1 ≤ n ≤ 10, and Figure 1.1 compares the boiling points of the first five straight-chain silanes with their hydrocarbon analogues. Silanes are explosively inflammable in air (equation1.2).

  A mixture of SiH₄, Si₂H₆, Si₃H₈ and Si₄H₁₀ along with traces of higher silanes is obtained when Mg₂Si reacts with aqueous acid, but the non-specificity of this synthesis renders it of little practical value. By irradiating SiH₄ with a CO₂ laser,SiH₄ can be converted selectively into Si₂H₆.

Fig. 1.1 Boiling points of the straight-chain silanes, Si_nH_2n‏+2, and hydrocarbons C_nH_2n‏+2.

Silane is a colourless gas which is insoluble in water, reacts rapidly with alkalis (equation 1.3) and forms compounds of the type M[SiH₃] with Na, K (equation 1.4), Rb and Cs. The crystalline salt K[SiH₃] possesses an NaCl structure and is a valuable synthetic reagent, e.g. equation 1.5.

Germanes Ge_nH_2n‏+2 (straight and branched chain isomers) are known for 1 ≤ n ≤ 9. GeH₄ is less reactive than SiH₄; it is a colourless gas (bp 184 K, dec 488 K), insoluble in water, and prepared by treating GeO₂ with Na[BH₄] although higher germanes are also formed. Discharges of various frequencies are finding increased use for this type of synthesis and have been used to convert GeH₄ into higher germanes, or mixtures of SiH₄ and GeH₄ into Ge₂H₆, GeSiH₆ and Si₂H₆. Mixed hydrides of Si and Ge, e.g. GeSiH₆ and GeSi₂H₈, are also formed when an intimate mixture of Mg₂Ge and Mg₂Si is treated with acid.

    Reactions between GeH₄ and alkali metals, M, in liquid NH₃ produce M[GeH₃], and, like [SiH₃]^-, the [GeH₃]^- ion is synthetically useful. The reaction of SnCl₄ with Li[AlH₄] gives SnH₄ (bp 221 K) but this decomposes at 298K into Sn and H₂; note the variation in reactivities: SiH₄ > GeH₄ < SnH₄. Plumbane, PbH₄, is poorly characterized and may not actually have been isolated. Significantly, however, replacement of H atoms by alkyl or aryl substituents is accompanied by increased stability.

Fig. 1.2 Representative reactions of SiH₃Cl. The structures of N(SiH₃)₃ (determined by Xray diffraction at 115 K) and (H₃Si)₂O (determined by electron diffraction).

مواضيع ذات صلة

كيمياء القصدير

تطبيقات الطبقات الثنائية الهيدروكسيد

تطبيقات عملية التبادل الأيوني

مواد التبادل الأيوني Ion exchanger

ظاهرة التبادل الايوني Ion Exchange

تاريخ التبادل الايوني Ion Exchange History

كيمياء البلاتين ومعقداته

كيمياء البلاديوم ومعقداته

طرائق تقدير النحاس

كيمياء النحاس ومعقداته

طرائق تقدير النيكل

كيمياء النيكل ومعقداته