In chemistry, germanate is a compound containing an

oxyanion An oxyanion, or oxoanion, is an ion with the generic formula (where A represents a chemical element and O represents an oxygen atom). Oxyanions are formed by a large majority of the chemical elements. The formulae of simple oxyanions are determine ...

germanium Germanium is a chemical element; it has Symbol (chemistry), symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid or a nonmetal in the carbon group that is chemically ...

. In the naming of inorganic compounds it is a suffix that indicates a

polyatomic anion A polyatomic ion (also known as a molecular ion) is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that usually has a net charge that is not zero, or in special case ...

with a central germanium atom, for example potassium hexafluorogermanate, K₂GeF₆.Egon Wiberg, Arnold Frederick Holleman (2001) ''Inorganic Chemistry'', Elsevier

Germanate oxy compounds

Germanium is similar to silicon forming many compounds with tetrahedral units although it can also exhibit 5 and 6 coordination. Analogues of all the major types of

silicate A silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is also used ...

s and

aluminosilicate Aluminosilicate refers to materials containing anionic Si-O-Al linkages. Commonly, the associate cations are sodium (Na+), potassium (K+) and protons (H+). Such materials occur as minerals, coal combustion products and as synthetic materials, of ...

s have been prepared. For example, the compounds Mg₂GeO₄ (

olivine The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...

and

spinel Spinel () is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula in the cubic crystal system. Its name comes from the Latin word , a diminutive form of ''spine,'' in reference to its pointed crystals. Prop ...

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; for example, MnGeO₃ has a

pyroxene The pyroxenes (commonly abbreviated Px) are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents ions of calcium (Ca), sodium (Na), iron ( ...

type structure similar to that of MgSiO₃ which is a significant mineral in the mantle.

Germanates in aqueous solutions

The

alkali metal The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K),The symbols Na and K for sodium and potassium are derived from their Latin names, ''natrium'' and ''kalium''; these are still the origins of the names ...

orthogermanates, M₄GeO₄, containing discrete ions, form acidic solutions containing , and Ge(OH)₄)₈(OH)₃sup>3−. Neutral solutions of germanium dioxide contain Ge(OH)₄, but at high pH germanate ions such as , are present.

Germanate zeolites

Microporous germanate

zeolite Zeolites are a group of several microporous, crystalline aluminosilicate minerals commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ･y where is either a meta ...

s were first prepared in the 1990s. A common method of preparation is

hydrothermal synthesis Hydrothermal synthesis includes the various techniques of synthesizing substances from high-temperature aqueous solutions at high pressures; also termed "hydrothermal method". The term "hydrothermal" is of geologic origin. Geochemists and mine ...

using an organic

amine In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...

as a template (structure determining agent).Zeolites and Related Materials: Trends Targets and Challenges(SET), 1st Edition, 4th International FEZA Conference, 2008, Paris, France; Eds. Gedeon, Massiani, Babonneau; Elsevier Science; The frameworks are negatively charged due to extra

oxide An oxide () is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion (anion bearing a net charge of −2) of oxygen, an O2− ion with oxygen in the oxidation st ...

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. A zeolite reported in 2005 has large pores – interconnected by channels defined by 30-membered rings (the naturally occurring

faujasite Faujasite (FAU-type zeolite) is a mineral group in the zeolite family of silicate minerals. The group consists of faujasite-Na, faujasite-Mg and faujasite-Ca. They all share the same basic formula by varying the amounts of sodium, magnesium and ...

with channels defined by 12-membered ringsHandbook Of Molecular Sieves: Structures, Rosemarie Szostak, 1992, Van Nostrand Reinhold, , ). Zeolites with frameworks containing silicon and germanium (silicogermanates), aluminium and germanium (aluminogermanates) and zirconium and germanium (zirconogermanates) are all known.

References

{{Authority control Oxometallates

Germanate oxy compounds

Germanates in aqueous solutions

Germanate zeolites

See also

References