Germanate
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
[edit | edit source]Germanium is similar to silicon forming many compounds with tetrahedral {GeO4}[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.[4] For example, the compounds Mg2GeO4 (olivine and spinel forms), CaGeO3(perovskite structure), Be2GeO4 (phenakite structure) show the resemblance to the silicates.[4] BaGe4O9 has a complex structure containing 4 and 6 coordinate germanium.[citation needed] 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;[5] for example, MnGeO3 has a pyroxene type structure similar to that of MgSiO3 which is a significant mineral in the mantle.[6][7][8]
Germanates in aqueous solutions
[edit | edit source]The alkali metal orthogermanates, M4GeO4, containing discrete GeO4−
4 ions, form acidic solutions containing GeO(OH)−
3, GeO
2(OH)2−
2 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 GeO(OH)−
3, GeO
2(OH)2−
2 are present.[9]
Germanate zeolites
[edit | edit source]Microporous germanate zeolites were first prepared in the 1990s.[10][11] A common method of preparation is hydrothermal synthesis using an organic amine as a template (structure determining agent).[12] 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 {GeO4} tetrahedral unit compared to Si–O in {SiO4} and the narrower Ge–O–Ge angle (130°–140°) between corner shared tetrahedra allow for unusual framework structures.[13] A zeolite reported in 2005[14] has large pores – 18.6 × 26.2 Å interconnected by channels defined by 30-membered rings (the naturally occurring zeolite faujasite with channels defined by 12-membered rings[15]). Zeolites with frameworks containing silicon and germanium (silicogermanates), aluminium and germanium (aluminogermanates) and zirconium and germanium (zirconogermanates) are all known.[12][16]
See also
[edit | edit source]- Bismuth germanate (bismuth germanium oxide, BGO)
- Sodium germanate
References
[edit | edit source]- ^ Nomenclature of Inorganic Chemistry IUPAC Recommendations 2005 – Full text (PDF)
- ^ a b c d Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
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- ^ "Germanium: Inorganic Chemistry" F Glockling Encyclopedia of Inorganic Chemistry Editor R Bruce King (1994) John Wiley and Sons Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
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- ^ a b Zeolites and Related Materials: Trends Targets and Challenges(SET), 1st Edition, 4th International FEZA Conference, 2008, Paris, France; Eds. Gedeon, Massiani, Babonneau; Elsevier Science; Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
- ^ Introduction to Zeolite Molecular Sieves, Jiri Cejka, Herman van Bekkum, A. Corma, F. Schueth, Elsevier, 2007
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- ^ Handbook Of Molecular Sieves: Structures, Rosemarie Szostak, 1992, Van Nostrand Reinhold, Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value)., Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
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