:Germanate

Germanium is similar to silicon forming many compounds with tetrahedral {GeO₄} units although it can also exhibit 5{{cite journal|last1=Nguyen|first1=Quang Bac|last2=Lii|first2=Kwang-Hwa|title=Cs₄UGe₈O₂₀: A Tetravalent Uranium Germanate Containing Four- and Five-Coordinate Germanium|journal=Inorganic Chemistry|volume=50|issue=20|year=2011|pages=9936–9938|issn=0020-1669|doi=10.1021/ic201789f|pmid=21939186 }} and 6 coordination. Analogues of all the major types of silicates and aluminosilicates have been prepared.{{Greenwood&Earnshaw}} 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.{{cn|date=September 2023}} 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;{{cite journal|last1=Ringwood|first1=A.E.|title=Phase transformations and the constitution of the mantle|journal=Physics of the Earth and Planetary Interiors|volume=3|year=1970|pages=109–155|issn=0031-9201|doi=10.1016/0031-9201(70)90047-6|bibcode=1970PEPI....3..109R}} for example, MnGeO₃ has a pyroxene type structure similar to that of MgSiO₃ which is a significant mineral in the mantle.{{cite journal|last1=Ringwood|first1=A. E.|last2=Seabrook|first2=Merren|title=Some High-pressure Transformations in Pyroxenes|journal=Nature|volume=196|issue=4857|year=1962|pages=883–884|issn=0028-0836|doi=10.1038/196883a0|bibcode=1962Natur.196..883R|s2cid=4183493 }}{{cite journal|last1=Hirose|first1=Kei|last2=Nagaya|first2=Yukio|last3=Merkel|first3=Sébastien|last4=Ohishi|first4=Yasuo|title=Deformation of MnGeO₃ post-perovskite at lower mantle pressure and temperature|journal=Geophysical Research Letters|volume=37|issue=20|year=2010|issn=0094-8276|doi=10.1029/2010GL044977|bibcode=2010GeoRL..3720302H|doi-access=free}}{{cite journal|last1=Matsumura|first1=Hisashi|last2=Mamiya|first2=Mikito|last3=Takei|first3=Humihiko|title=Growth of pyroxene-type MnGeO₃ and (Mn,Mg)GeO₃ crystals by the floating-zone method|journal=Journal of Crystal Growth|volume=210|issue=4|year=2000|pages=783–787|issn=0022-0248|doi=10.1016/S0022-0248(99)00850-7|bibcode=2000JCrGr.210..783M}}

The alkali metal orthogermanates, M₄GeO₄, containing discrete {{chem|GeO|4|4−}} ions, form acidic solutions containing {{chem|GeO(OH)|3|−}}, {{chem|GeO|2|(OH)|2|2−}} and [(Ge(OH)₄)₈(OH)₃]³⁻. Neutral solutions of germanium dioxide contain Ge(OH)₄, but at high pH germanate ions such as {{chem|GeO(OH)|3|−}}, {{chem|GeO|2|(OH)|2|2−}} are present."Germanium: Inorganic Chemistry" F Glockling Encyclopedia of Inorganic Chemistry Editor R Bruce King (1994) John Wiley and Sons {{ISBN|0-471-93620-0}}

Microporous germanate zeolites were first prepared in the 1990s.{{cite journal|last1=Cheng|first1=Jun|last2=Xu|first2=Ruren|last3=Yang|first3=Guangdi|title=Synthesis, structure and characterization of a novel germanium dioxide with occluded tetramethylammonium hydroxide|journal=Journal of the Chemical Society, Dalton Transactions|issue=6|year=1991|pages=1537|issn=0300-9246|doi=10.1039/dt9910001537}}{{cite journal|last1=Li|first1=Hailian|last2=Yaghi|first2=O. M.|title=Transformation of Germanium Dioxide to Microporous Germanate 4-Connected Nets|journal=Journal of the American Chemical Society|volume=120|issue=40|year=1998|pages=10569–10570|issn=0002-7863|doi=10.1021/ja982384n}}

A common method of preparation is hydrothermal synthesis using an organic amine 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; {{ISBN|9780444532961}}

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.Introduction to Zeolite Molecular Sieves, Jiri Cejka, Herman van Bekkum, A. Corma, F. Schueth, Elsevier, 2007 A zeolite reported in 2005{{cite journal|last1=Zou|first1=Xiaodong|last2=Conradsson|first2=Tony|last3=Klingstedt|first3=Miia|last4=Dadachov|first4=Mike S.|last5=O'Keeffe|first5=Michael|title=A mesoporous germanium oxide with crystalline pore walls and its chiral derivative|journal=Nature|volume=437|issue=7059|year=2005|pages=716–719|issn=0028-0836|doi=10.1038/nature04097|pmid=16193048|bibcode=2005Natur.437..716Z|s2cid=4411828 }} has large pores – {{nowrap|18.6 × 26.2 Å}} interconnected by channels defined by 30-membered rings (the naturally occurring zeolite faujasite with channels defined by 12-membered ringsHandbook Of Molecular Sieves: Structures, Rosemarie Szostak, 1992, Van Nostrand Reinhold, {{ISBN|0442318995}}, {{ISBN|978-0442318994}}). Zeolites with frameworks containing silicon and germanium (silicogermanates), aluminium and germanium (aluminogermanates) and zirconium and germanium (zirconogermanates) are all known.{{cite journal|last1=Plévert|first1=Jacques|last2=Sanchez-Smith|first2=Rebeca|last3=Gentz|first3=Travis M.|last4=Li|first4=Hailian|last5=Groy|first5=Thomas L.|last6=Yaghi|first6=Omar M.|last7=O'Keeffe|first7=Michael|title=Synthesis and Characterization of Zirconogermanates|journal=Inorganic Chemistry|volume=42|issue=19|year=2003|pages=5954–5959|issn=0020-1669|doi=10.1021/ic034298g|pmid=12971765 }}

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

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Category:Oxometallates