Germanium dioxide

Germanium dioxide

tetragonal rutile form
Names
IUPAC name Germanium dioxide
Other names Germanium(IV) oxide Germania ACC10380 G-15 Germanium oxide Germanic oxide
Identifiers
CAS Number	1310-53-8
ChemSpider	14112
Jmol interactive 3D	Image
PubChem	14796
RTECS number	LY5240000
UNII	5O6CM4W76A
InChI InChI=1S/GeO2/c2-1-3 Key: YBMRDBCBODYGJE-UHFFFAOYSA-N InChI=1/GeO2/c2-1-3 Key: YBMRDBCBODYGJE-UHFFFAOYAG
SMILES O=[Ge]=O
Properties
Chemical formula	GeO2
Molar mass	104.6388 g/mol
Appearance	white powder or colourless crystals
Density	4.228 g/cm^3
Melting point	1,115 °C (2,039 °F; 1,388 K)
Solubility in water	4.47 g/L (25 °C) 10.7 g/L (100 °C)
Solubility	insoluble in HF, HCl soluble in other acid and alkali
Refractive index (nD)	1.650
Structure
Crystal structure	hexagonal
Hazards
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (Median dose)	3700 mg/kg (rat, oral)
Related compounds
Other anions	Germanium disulfide Germanium diselenide
Other cations	Carbon dioxide Silicon dioxide Tin dioxide Lead dioxide
Related compounds	Germanium monoxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Germanium dioxide, also called germanium oxide and germania, is an inorganic compound with the chemical formula GeO₂. It is the main commercial source of germanium. It also forms as a passivation layer on pure germanium in contact with atmospheric oxygen.

Structure

The two predominant polymorphs of GeO₂ are hexagonal and tetragonal. Hexagonal GeO₂ has the same structure as β-quartz, with germanium having coordination number 4. Tetragonal GeO₂ (the mineral argutite) has the rutile-like structure seen in stishovite. In this motif, germanium has the coordination number 6. An amorphous (glassy) form of GeO₂ is similar to fused silica.^[1]

Germanium dioxide can be prepared in both crystalline and amorphous forms. At ambient pressure the amorphous structure is formed by a network of GeO₄ tetrahedra. At elevated pressure up to approximately 9 GPa the germanium average coordination number steadily increases from 4 to around 5 with a corresponding increase in the Ge-O bond distance.^[2] At higher pressures, up to approximately 15 GPa, the germanium coordination number increases to 6 and the dense network structure is composed of GeO₆ octahedra.^[3] When the pressure is subsequently reduced, the structure reverts to the tetrahedral form.^[2][3] At high pressure, the rutile form converts to an orthorhombic CaCl₂ form.^[4]

Reactions

Heating germanium dioxide with powdered germanium at 1000 °C forms germanium monoxide (GeO).^[1]

The hexagonal (d = 4.29 g/cm3) form of germanium dioxide is more soluble than the rutile (d = 6.27 g/cm3) form and dissolves to form germanic acid, H₄GeO₄ or Ge(OH)₄.^[5] GeO₂ is only slightly soluble in acid but dissolves more readily in alkali to give germanates.^[5]

In contact with hydrochloric acid, it releases the volatile and corrosive germanium tetrachloride.

Uses

The refractive index (1.7) and optical dispersion properties of germanium dioxide makes it useful as an optical material for wide-angle lenses and in optical microscope objective lenses. It is transparent in infrared.

A mixture of silicon dioxide and germanium dioxide ("silica-germania") is used as an optical material for optical fibers and optical waveguides.^[6] Controlling the ratio of the elements allows precise control of refractive index. Silica-germania glasses have lower viscosity and higher refractive index than pure silica. Germania replaced titania as the silica dopant for silica fiber, eliminating the need for subsequent heat treatment, which made the fibers brittle.^[7]

Germanium dioxide is also used as a catalyst in production of polyethylene terephthalate resin,^[8] and for production of other germanium compounds. It is used as a feedstock for production of some phosphors and semiconductor materials.

Germanium dioxide is used in algaculture as an inhibitor of unwanted diatom growth in algal cultures, since contamination with the comparatively fast-growing diatoms often inhibits the growth of or outcompetes the original algae strains. GeO₂ is readily taken up by diatoms and leads to silicon being substituted by germanium in biochemical processes within the diatoms, causing a significant reduction of the diatoms' growth rate or even their complete elimination, with little effect on non-diatom algal species. For this application, the concentration of germanium dioxide typically used in the culture medium is between 1 and 10 mg/l, depending on the stage of the contamination and the species.^[9]

Toxicity and medical

Germanium dioxide has low toxicity, but in higher doses it is nephrotoxic.

Germanium dioxide is used as a germanium supplement in some questionable dietary supplements and "miracle cures".^[10] High doses of these resulted in several cases of germanium poisonings.

References

1. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9.
2. J W E Drewitt, P S Salmon, A C Barnes, S Klotz, H E Fischer, W A Crichton (2010). "Structure of GeO₂ glass at pressures up to 8.6 GPa". Physical Review B 81: 014202. Bibcode:2010PhRvB..81a4202D. doi:10.1103/PhysRevB.81.014202.
3. M Guthrie, C A Tulk, C J Benmore, J Xu, J L Yarger, D D Klug, J S Tse, H-k Mao, R J Hemley (2004). "Formation and Structure of a Dense Octahedral Glass". Physical Review Letters 93 (11): 115502. Bibcode:2004PhRvL..93k5502G. doi:10.1103/PhysRevLett.93.115502. PMID 15447351.
4. Structural evolution of rutile-type and CaCl₂-type germanium dioxide at high pressure, J. Haines, J. M.Léger, C.Chateau, A. S.Pereira, Physics and Chemistry of Minerals, 27, 8 ,(2000), 575–582,doi:10.1007/s002690000092
5. Egon Wiberg, Arnold Frederick Holleman, (2001) Inorganic Chemistry, Elsevier ISBN 0-12-352651-5
6. Robert D. Brown, Jr. (2000). "Germanium" (PDF). U.S. Geological Survey.
7. Chapter Iii: Optical Fiber For Communications
8. Thiele, Ulrich K. (2001). "The Current Status of Catalysis and Catalyst Development for the Industrial Process of Poly(ethylene terephthalate) Polycondensation". International Journal of Polymeric Materials 50 (3): 387–394. doi:10.1080/00914030108035115.
9. Robert Arthur Andersen (2005). Algal culturing techniques. Elsevier Academic Press.
10. Tao, S.H. and Bolger, P.M. (June 1997). "Hazard Assessment of Germanium Supplements". Regulatory Toxicology and Pharmacology 25 (3): 211–219. doi:10.1006/rtph.1997.1098. PMID 9237323.