Germanate Explained

In chemistry, germanate is a compound containing an oxyanion of germanium. In the naming of inorganic compounds it is a suffix that indicates a polyatomic anion with a central germanium atom,^[1] for example potassium hexafluorogermanate, K₂GeF₆.^[2]

Germanate oxy compounds

Germanium is similar to silicon forming many compounds with tetrahedral ^[2] units although it can also exhibit 5^[3] and 6^[2] coordination. Analogues of all the major types of silicates and aluminosilicates have been prepared. For example, the compounds Mg₂GeO₄ (olivine and spinel forms), CaGeO₃(perovskite structure), Be₂GeO₄ (phenakite structure) show the resemblance to the silicates. BaGe₄O₉ has a complex structure containing 4 and 6 coordinate germanium. Germanates are important for geoscience as they possess similar structures to silicates and can be used as analogues for studying the behaviour of silicate minerals found in the Earth's mantle;^[4] for example, MnGeO₃ has a pyroxene type structure similar to that of MgSiO₃ which is a significant mineral in the mantle.^{[5] [6] [7]}

Germanates in aqueous solutions

The alkali metal orthogermanates, M₄GeO₄, containing discrete ions, form acidic solutions containing, and [(Ge(OH)₄)₈(OH)₃]³⁻.^[2] Neutral solutions of germanium dioxide contain Ge(OH)₄, but at high pH germanate ions such as, are present.^[8]

Germanate zeolites

Microporous germanate zeolites were first prepared in the 1990s.^{[9] [10]} A common method of preparation is hydrothermal synthesis using an organic amine as a template (structure determining agent).^[11] The frameworks are negatively charged due to extra oxide ions which leads to higher coordination numbers for germanium of 5 and 6. The negative charge is balanced by the positively charged amine molecules.

In addition to the ability of germanium to exhibit 4, 5 or 6 coordination, the greater length of the Ge–O bond in the tetrahedral unit compared to Si–O in and the narrower Ge–O–Ge angle (130°–140°) between corner shared tetrahedra allow for unusual framework structures.^[12] A zeolite reported in 2005^[13] has large pores – interconnected by channels defined by 30-membered rings (the naturally occurring zeolite faujasite with channels defined by 12-membered rings^[14]). Zeolites with frameworks containing silicon and germanium (silicogermanates), aluminium and germanium (aluminogermanates) and zirconium and germanium (zirconogermanates) are all known.^{[11] [15]}

See also

• Bismuth germanate (bismuth germanium oxide, BGO)
• Sodium germanate

Notes and References

1. http://old.iupac.org/publications/books/rbook/Red_Book_2005.pdf Nomenclature of Inorganic Chemistry IUPAC Recommendations 2005
2. Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier
3. Nguyen. Quang Bac. Lii. Kwang-Hwa. Cs₄UGe₈O₂₀: A Tetravalent Uranium Germanate Containing Four- and Five-Coordinate Germanium. Inorganic Chemistry. 50. 20. 2011. 9936–9938. 0020-1669. 10.1021/ic201789f. 21939186 .
4. Ringwood. A.E.. Phase transformations and the constitution of the mantle. Physics of the Earth and Planetary Interiors. 3. 1970. 109–155. 0031-9201. 10.1016/0031-9201(70)90047-6. 1970PEPI....3..109R.
5. Ringwood. A. E.. Seabrook. Merren. Some High-pressure Transformations in Pyroxenes. Nature. 196. 4857. 1962. 883–884. 0028-0836. 10.1038/196883a0. 1962Natur.196..883R. 4183493 .
6. Hirose. Kei. Nagaya. Yukio. Merkel. Sébastien. Ohishi. Yasuo. Deformation of MnGeO₃ post-perovskite at lower mantle pressure and temperature. Geophysical Research Letters. 37. 20. 2010. 0094-8276. 10.1029/2010GL044977. 2010GeoRL..3720302H. free.
7. Matsumura. Hisashi. Mamiya. Mikito. Takei. Humihiko. Growth of pyroxene-type MnGeO₃ and (Mn,Mg)GeO₃ crystals by the floating-zone method. Journal of Crystal Growth. 210. 4. 2000. 783–787. 0022-0248. 10.1016/S0022-0248(99)00850-7. 2000JCrGr.210..783M.
8. "Germanium: Inorganic Chemistry" F Glockling Encyclopedia of Inorganic Chemistry Editor R Bruce King (1994) John Wiley and Sons
9. Cheng. Jun. Xu. Ruren. Yang. Guangdi. Synthesis, structure and characterization of a novel germanium dioxide with occluded tetramethylammonium hydroxide. Journal of the Chemical Society, Dalton Transactions. 6. 1991. 1537. 0300-9246. 10.1039/dt9910001537.
10. Li. Hailian. Yaghi. O. M.. Transformation of Germanium Dioxide to Microporous Germanate 4-Connected Nets. Journal of the American Chemical Society. 120. 40. 1998. 10569–10570. 0002-7863. 10.1021/ja982384n.
11. Zeolites and Related Materials: Trends Targets and Challenges(SET), 1st Edition, 4th International FEZA Conference, 2008, Paris, France; Eds. Gedeon, Massiani, Babonneau; Elsevier Science;
12. Introduction to Zeolite Molecular Sieves, Jiri Cejka, Herman van Bekkum, A. Corma, F. Schueth, Elsevier, 2007
13. Zou. Xiaodong. Conradsson. Tony. Klingstedt. Miia. Dadachov. Mike S.. O'Keeffe. Michael. A mesoporous germanium oxide with crystalline pore walls and its chiral derivative. Nature. 437. 7059. 2005. 716–719. 0028-0836. 10.1038/nature04097. 16193048. 2005Natur.437..716Z. 4411828 .
14. Handbook Of Molecular Sieves: Structures, Rosemarie Szostak, 1992, Van Nostrand Reinhold,,
15. Plévert. Jacques. Sanchez-Smith. Rebeca. Gentz. Travis M.. Li. Hailian. Groy. Thomas L.. Yaghi. Omar M.. O'Keeffe. Michael. Synthesis and Characterization of Zirconogermanates. Inorganic Chemistry. 42. 19. 2003. 5954–5959. 0020-1669. 10.1021/ic034298g. 12971765 .