Germanates

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Germanates are compounds of germanium that are derived from its oxide . In almost all minerals containing germanium, germanium is present as germanate.

Since the properties of germanium are similar to those of silicon , the acidic character of germanium dioxide (GeO 2 ) predominates . The latter therefore reacts with alkali lye to form the germanates. Germanates are also obtained by reacting germanium dioxide with various metal oxides during melting or sintering .

Classification

Germanates of different compositions are known (M: singly charged metal cation; X: halide):

  • Orthogermanate, M 4 GeO 4
  • Metagermanate, (M 2 GeO 3 ) n
  • Meta- digermanate, (M 2 Ge 2 O 5 ) n
  • Hexahydroxogermanate, M 2 Ge (OH) 6
  • Hexahalogenogermanates, M 2 GeX 6

Metagermanate and Meta-digermanate are available in polymeric form. The germanic acids on which the germanates are based are, similar to carbonic acid and silicon oxyacids , not stable in anhydrous form, but only in dilute solutions. Of the halogenogermanates, for example, potassium hexafluorogermanate (K 2 GeF 6 ) is known, which can be obtained from potassium fluoride and germanium tetrafluoride . A cesium hexachlorogermanate (IV) Cs 2 [GeCl 6 ] is also known.

Substance class

Germanates are a class of substances with very diverse properties. Many analogies can be observed between the oxygen compounds of germanium and the corresponding silicon compounds. Silicates and germanates are often isotypic . Zeolite- like structures and the tendency to form glass are also known from germanium . Because of their high refractive indices , they are sometimes used for optical elements such as wide-angle lenses in photography . Many doped germanates show luminescence when irradiated with UV light: (Sr, Ba) 2 (Mg, Zn) Ge 2 O 7 : Pb (blue-violet), Zn 2 GeO 4 : Mn (yellow-green), MgGeO 3 : Mn (deep red) .

Admixtures of lead germanate in ceramics generate a material that has semiconductor properties.

Sodium and ammonium germanates can be used as catalysts in polyester synthesis.

Bismuth germanate is used in scintillation counters .

Individual evidence

  1. ↑ Gmelin's Handbook of Inorganic Chemistry: Germanium, System Number 45, supplementary volume, Verlag Chemie GmbH Weinheim / Berchtesgaden, 1958. 8th ed., Page 569.
  2. ↑ Andrea Pfeifer: Chemical transport of Germanates . Hannover 2001, DNB  963909304 , p. 11 , urn : nbn: de: gbv: 089-3381596652 (dissertation, University of Hanover).
  3. ↑ B. Xu, J. Evans, V. Petricevic, SP Guo, O. Maksimov, MC Tamargo, RR Alfano: Continuous-wave and passively mode-locked operation of a cunyite (Cr 4+ : Ca 2 GeO 4 ) laser . In: Applied Optics . tape 39 , no. 27 , 2000, pp. 4975-4978 , doi : 10.1364 / AO.39.004975 .
  4. ↑ T. Kimura, M. Watanabe, S. Kobayashi, T. Sugita, K. (Mitsubishi Chemical Industries Co., Ltd., Japan). Japan. 1975, JP 50031199, October 8, 1975, Appl. JP 69-67393, August 26, 1969.

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