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{{for|the monohydride|Beryllium monohydride}}
{{for|the monohydride|Beryllium monohydride}}
{{chembox
{{chembox
| Verifiedfields = changed
|Verifiedfields = changed
| Watchedfields = changed
|Watchedfields = changed
| verifiedrevid = 470456352
|verifiedrevid = 470456352
| Name = Beryllium hydride
|Name = Beryllium hydride
| ImageFile = Beryllium-hydride-3D-balls.png
|ImageFile = Beryllium-hydride-3D-balls.png
| ImageSize = 230px
|ImageSize = 230px
⚫
|OtherNames = Beryllium dihydride<br>Beryllium hydride<br>Beryllane
| ImageName =
⚫
| OtherNames = Beryllium dihydride<br>Beryllium hydride<br>Beryllane
|Section1={{Chembox Identifiers
|Section1={{Chembox Identifiers
| InChI = 1/Be.2H/rBeH2/h1H2
|InChI = 1/Be.2H/rBeH2/h1H2
| InChIKey = RWASOQSEFLDYLC-JICJMJRQAQ
|InChIKey = RWASOQSEFLDYLC-JICJMJRQAQ
| ChEBI_Ref = {{ebicite|correct|EBI}}
|ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 33787
|ChEBI = 33787
| SMILES = [BeH2]
|SMILES = [BeH2]
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
|StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/Be.2H
|StdInChI = 1S/Be.2H
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
|StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = RWASOQSEFLDYLC-UHFFFAOYSA-N
|StdInChIKey = RWASOQSEFLDYLC-UHFFFAOYSA-N
| CASNo_Ref = {{cascite|changed|??}}
|CASNo_Ref = {{cascite|correct|CAS}}
| CASNo = 7787-52-2
|CASNo = 7787-52-2
|UNII_Ref = {{fdacite|correct|FDA}}
⚫
| PubChem = 139073
|UNII = 5M7P3TK96I
⚫
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
⚫
|PubChem = 139073
⚫
| ChemSpiderID=17215712
⚫
|ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
⚫
}}
⚫
|ChemSpiderID=17215712
⚫
}}
|Section2={{Chembox Properties
|Section2={{Chembox Properties
| Formula = BeH<sub>2</sub>
|Formula = BeH{{sub|2}}
| MolarMass = 11.03 g mol<sup>−1</sup>
|MolarMass = 11.03 g mol{{sup|−1}}
| Appearance = amorphous white solid<ref name=G&E>{{Greenwood&Earnshaw}}, p. 115</ref>
|Appearance =white solid<ref name=G&E />
| Density = 0.65 g/cm<sup>3</sup>
|Density = 0.65 g/cm{{sup|3}}
| Solubility = decomposes
|Solubility = decomposes
| SolubleOther = insoluble in [[diethyl ether]], [[toluene]]
|SolubleOther = insoluble in [[diethyl ether]], [[toluene]]
| MeltingPtC = 250
|MeltingPtC = 250
| MeltingPt_notes = decomposes
|MeltingPt_notes = decomposes
}}
}}
|Section4={{Chembox Thermochemistry
|Section4={{Chembox Thermochemistry
| HeatCapacity = 30.124 J/mol K
|HeatCapacity = 30.124 J/mol K
}}
}}
|Section7={{Chembox Hazards
|Section7={{Chembox Hazards
| REL = Ca C 0.0005 mg/m<sup>3</sup> (as Be)<ref name=PGCH>{{PGCH|0054}}</ref>
|REL = Ca C 0.0005 mg/m{{sup|3}} (as Be)<ref name=PGCH>{{PGCH|0054}}</ref>
| PEL = TWA 0.002 mg/m<sup>3</sup><br/>C 0.005 mg/m<sup>3</sup> (30 minutes), with a maximum peak of 0.025 mg/m<sup>3</sup> (as Be)<ref name=PGCH/>
|PEL = TWA 0.002 mg/m{{sup|3}}<br/>C 0.005 mg/m{{sup|3}} (30 minutes), with a maximum peak of 0.025 mg/m{{sup|3}} (as Be)<ref name=PGCH/>
| IDLH = Ca [4 mg/m<sup>3</sup> (as Be)]<ref name=PGCH/>
|IDLH = Ca [4 mg/m{{sup|3}} (as Be)]<ref name=PGCH/>
}}
}}
|Section8={{Chembox Related
|Section8={{Chembox Related
| OtherCations = [[lithium hydride]], [[calcium hydride]], [[borane|boron hydrides]]
|OtherCations = [[lithium hydride]], [[sodium hydride]], [[magnesium hydride]], [[calcium hydride]], [[borane|boron hydrides]], [[aluminium hydride]]
| OtherCompounds = [[beryllium fluoride]]
|OtherCompounds = [[beryllium fluoride]]
}}
}}
}}
}}


'''Beryllium hydride''' (systematically named '''poly[beryllane(2)]''' and '''beryllium dihydride''') is an [[inorganic compound]] with the [[chemical formula]] ({{Chem|BeH|2|}})<sub>''n''</sub> (also written ({{Chem|[BeH|2|]}})<sub>''n''</sub> or {{Chem|BeH|2}}). This [[alkaline earth hydride]] is a colourless solid that is insoluble in solvents that do not decompose it.<ref>Pradyot Patnaik. ''Handbook of Inorganic Chemicals''. McGraw-Hill, 2002, {{ISBN|0-07-049439-8}}</ref> Unlike the [[ionic bond|ionically bonded]] [[hydride]]s of the heavier [[alkaline earth metal|Group 2]] elements, beryllium hydride is [[covalent bond|covalently bonded]]<ref name=G&E/> ([[three-center two-electron bond]]).
'''Beryllium hydride''' (systematically named '''poly[beryllane(2)]''' and '''beryllium dihydride''') is an [[inorganic compound]] with the [[chemical formula]] ({{Chem|BeH|2|}}){{sub|''n''}} (also written ({{Chem|[BeH|2|]}}){{sub|''n''}} or {{Chem|BeH|2}}). This [[alkaline earth hydride]] is a colourless solid that is insoluble in solvents that do not decompose it. Unlike the [[ionic bond|ionically bonded]] [[hydride]]s of the heavier [[alkaline earth metal|Group 2]] elements, beryllium hydride is [[covalent bond|covalently bonded]]<ref name=G&E>{{Greenwood&Earnshaw|p=115}}</ref> ([[three-center two-electron bond]]).


== Synthesis ==
== Synthesis ==
Unlike the other [[alkaline earth metal|group 2]] metals, beryllium does not react with hydrogen.<ref name = "Wiberg&Holleman">Egon Wiberg, Arnold Frederick Holleman (2001) ''Inorganic Chemistry'', Elsevier {{ISBN|0-12-352651-5}}, p. 1048</ref> Instead, BeH<sub>2</sub> is prepared from preformed beryllium(II) compounds. It was first synthesised in 1951 by treating dimethylberyllium, Be(CH<sub>3</sub>)<sub>2</sub>, with [[lithium aluminium hydride]], LiAlH<sub>4</sub>.<ref>{{cite journal |author1=Glenn D. Barbaras |author2=Clyde Dillard |author3=A. E. Finholt |author4=Thomas Wartik |author5=K. E. Wilzbach |author6=H. I. Schlesinger |last-author-amp=yes | year = 1951 | title = The Preparation of the Hydrides of Zinc, Cadmium, Beryllium, Magnesium and Lithium by the Use of Lithium Aluminum Hydride | journal = [[Journal of the American Chemical Society|J. Am. Chem. Soc.]] | volume = 73 | issue = 10 | pages = 4585–4590 | doi = 10.1021/ja01154a025 }}</ref>
Unlike the other [[alkaline earth metal|group 2]] metals, beryllium does not react with hydrogen.<ref name = "Wiberg&Holleman">Egon Wiberg, Arnold Frederick Holleman (2001) ''Inorganic Chemistry'', Elsevier {{ISBN|0-12-352651-5}}, p. 1048</ref> Instead, BeH{{sub|2}} is prepared from preformed beryllium(II) compounds. It was first synthesized in 1951 by treating [[dimethylberyllium]], Be(CH{{sub|3}}){{sub|2}}, with [[lithium aluminium hydride]], LiAlH{{sub|4}}.<ref>{{cite journal |author1=Glenn D. Barbaras |author2=Clyde Dillard |author3=A. E. Finholt |author4=Thomas Wartik |author5=K. E. Wilzbach |author6=H. I. Schlesinger |name-list-style=amp | year = 1951 | title = The Preparation of the Hydrides of Zinc, Cadmium, Beryllium, Magnesium and Lithium by the Use of Lithium Aluminum Hydride | journal = [[Journal of the American Chemical Society]] | volume = 73 | issue = 10 | pages = 4585–4590 | doi = 10.1021/ja01154a025 }}</ref>


Purer BeH<sub>2</sub> forms from the [[pyrolysis]] of di-tert-butylberyllium, Be(C(CH<sub>3</sub>)<sub>3</sub>)<sub>2</sub> at 210&nbsp;°C.<ref>{{cite journal |author1=G. E. Coates |author2=F. Glockling |lastauthoramp=yes | year = 1954 | title = Di-tert.-butylberyllium and beryllium hydride | journal = [[Journal of the Chemical Society|J. Chem. Soc.]] | pages = 2526–2529 | doi = 10.1039/JR9540002526 }}</ref>
Purer BeH{{sub|2}} forms from the [[pyrolysis]] of di-tert-butylberyllium, Be(C[CH{{sub|3}}]{{sub|3}}){{sub|2}} at 210°C.<ref>{{cite journal |author1=G. E. Coates |author2=F. Glockling |name-list-style=amp | year = 1954 | title = Di-tert.-butylberyllium and beryllium hydride | journal = [[Journal of the Chemical Society]] | pages = 2526–2529 | doi = 10.1039/JR9540002526}}</ref>


A route to highly pure samples involve the reaction of [[triphenylphosphine]], PPh<sub>3</sub>, with beryllium borohydride, Be(BH<sub>4</sub>)<sub>2</sub>:<ref name=G&E/>
A route to highly pure samples involves the reaction of [[triphenylphosphine]], PPh{{sub|3}}, with [[beryllium borohydride]], Be(BH{{sub|4}}){{sub|2}}:<ref name=G&E/>
:Be(BH<sub>4</sub>)<sub>2</sub> + 2 PPh<sub>3</sub> → 2 Ph<sub>3</sub>PBH<sub>3</sub> + BeH<sub>2</sub>
:Be(BH{{sub|4}}){{sub|2}} + 2 PPh{{sub|3}} → BeH{{sub|2}} + 2 Ph{{sub|3}}PBH{{sub|3}}


== Structure ==
== Structure ==
⚫
BeH<sub>2</sub> is usually formed as an amorphous white solid . To make up their electron deficiency Be or Mg forms four three centre two electron bonds or banana bonds hexagonal crystal system|hexagonal crystalline form]] with a higher density (~0.78 g cm<sup>−3</sup>) was reported,<ref name="Brendel">{{cite journal |author1=G. J. Brendel |author2=E. M. Marlett |author3=L. M. Niebylski |last-author-amp=yes | year = 1978 | title = Crystalline beryllium hydride | journal = [[Inorganic Chemistry (journal)|Inorg. Chem.]] | volume = 17 | issue = 12 | pages = 3589–3592 | doi = 10.1021/ic50190a051 }}</ref> prepared by heating amorphous BeH<sub>2</sub> under pressure, with 0.5-2.5% [[lithium hydride|LiH]] as a catalyst.


=== Gaseous form ===
⚫
A more recent investigation found that crystalline beryllium hydride has a body-centred [[orthorhombic crystal system|orthorhombic]] [[unit cell]], containing a network of corner-sharing BeH<sub>4</sub> tetrahedra, in contrast to the flat, hydrogen-bridged, infinite chains previously thought to exist in crystalline BeH<sub>2</sub>.<ref>{{cite journal | author = Gordon S. Smith | author2 = Quintin C. Johnson | author3 = Deane K. Smith| author4 = D. E. Cox | author5 = Robert L. Snyder | author6 = Rong-Sheng Zhou | author7 = Allan Zalkin | last-author-amp = yes | year = 1988 | title = The crystal and molecular structure of beryllium hydride | journal = [[Solid State Communications]] | volume = 67 | issue = 5 | pages = 491–494 | doi = 10.1016/0038-1098(84)90168-6 }}</ref>
⚫
[[File:Beryllium-hydride-molecule-IR-3D-balls.png|150px|thumb|left|Structure of gaseous BeH{{sub|2}}.]]
Isolated molecules of {{Chem|BeH|2}} (sometimes called dihydridoberyllium and written {{Chem|[BeH|2|]}} to emphasize the differences with the solid state) are only stable as a [[Concentration|dilute]] gas. When condensed, unsolvated {{Chem|BeH|2}} will spontaneously autopolymerise.


Studies of the amorphous form also find that it consists of a network of corner shared tetrahedra.<ref>{{cite journal |author1=Sujatha Sampath |author2=Kristina M. Lantzky |author3=Chris J. Benmore |author4=Jörg Neuefeind |author5=Joan E. Siewenie |last-author-amp=yes | year = 2003 | title = Structural quantum isotope effects in amorphous beryllium hydride | journal = J. Chem. Phys. | volume = 119 | issue = 23| pages = 12499 | doi = 10.1063/1.1626638}}</ref>
Free molecular BeH{{sub|2}} produced by high-temperature electrical discharge has been confirmed to have [[Linear molecular geometry|linear geometry]] with a Be-H bond length of 133.376 pm. Its hybridization is ''sp''.<ref>{{cite journal |author1=Peter F. Bernath |author2=Alireza Shayesteh |author3=Keith Tereszchuk |author4=Reginald Colin |year=2002 |title=The Vibration-Rotation Emission Spectrum of Free BeH<sub>2</sub> |journal=Science |volume=297 |issue=5585 |pages=1323–1324 |bibcode=2002Sci...297.1323B |doi=10.1126/science.1074580 |pmid=12193780 |s2cid=40961746}}</ref>

=== Condensed Beryllium hydride ===
⚫
BeH{{sub|2}} is usually formed as an amorphous white solid, but a [[hexagonal crystal system|hexagonal crystalline form]] with a higher density (~0.78 g/cm{{sup|3}}) was reported,<ref name="Brendel">{{cite journal |author1=G. J. Brendel |author2=E. M. Marlett |author3=L. M. Niebylski |name-list-style=amp | year = 1978 | title = Crystalline beryllium hydride | journal = [[Inorganic Chemistry (journal)|Inorganic Chemistry]] | volume = 17 | issue = 12 | pages = 3589–3592 | doi = 10.1021/ic50190a051}}</ref> prepared by heating amorphous BeH{{sub|2}} under pressure, with 0.5-2.5% [[lithium hydride|LiH]] as a catalyst.

[[File:BeH2 structure.svg|thumb|250px|Subunit of structure of BeH{{sub|2}}. Each Be is tetrahedral and each H is [[bridging ligand|doubly bridging]].<ref name="Smith" />|left]]
⚫
A more recent investigation found that crystalline beryllium hydride has a body-centred [[orthorhombic crystal system|orthorhombic]] [[unit cell]], containing a network of corner-sharing BeH{{sub|4}} tetrahedra, in contrast to the flat, hydrogen-bridged, infinite chains previously thought to exist in crystalline BeH{{sub|2}}.<ref name=Smith>{{cite journal | author = Gordon S. Smith | author2 = Quintin C. Johnson | author3 = Deane K. Smith| author4 = D. E. Cox | author5 = Robert L. Snyder | author6 = Rong-Sheng Zhou | author7 = Allan Zalkin | name-list-style = amp | year = 1988 | title = The crystal and molecular structure of beryllium hydride | journal = [[Solid State Communications]] | volume = 67 | issue = 5 | pages = 491–494 | doi = 10.1016/0038-1098(84)90168-6 | bibcode = 1988SSCom..67..491S }}</ref>

Studies of the amorphous form also find that it consists of a network of corner shared tetrahedra.<ref>{{cite journal |author1=Sujatha Sampath |author2=Kristina M. Lantzky |author3=Chris J. Benmore |author4=Jörg Neuefeind |author5=Joan E. Siewenie |name-list-style=amp | year = 2003 | title = Structural quantum isotope effects in amorphous beryllium hydride | journal = J. Chem. Phys. | volume = 119 | issue = 23| pages = 12499 | doi = 10.1063/1.1626638|bibcode=2003JChPh.11912499S }}</ref>


== Chemical properties ==
== Chemical properties ==
Line 71: Line 81:
Beryllium hydride reacts slowly with water but is rapidly hydrolysed by acid such as [[hydrogen chloride]] to form [[beryllium chloride]].<ref name = "Wiberg&Holleman"/>
Beryllium hydride reacts slowly with water but is rapidly hydrolysed by acid such as [[hydrogen chloride]] to form [[beryllium chloride]].<ref name = "Wiberg&Holleman"/>


:BeH{{sub|2}} + 2 H{{sub|2}}O → Be(OH){{sub|2}} + 2 H{{sub|2}}
===Reaction with Lewis bases===
⚫
Beryllium hydride reacts with [[trimethylamine]], N(CH<sub>3</sub>)<sub>3</sub> to form a dimeric adduct, with bridging hydrides.<ref name=Shepherd1969>{{Cite journal|last=Shepherd Jr.|first=Lawrence H. |author2=Ter Haar, G. L. |author3=Marlett, Everett M.|title=Amine complexes of beryllium hydride|journal=Inorganic Chemistry|date=April 1969|volume=8|issue=4|pages=976–979|doi=10.1021/ic50074a051|url=http://pubs.acs.org/doi/abs/10.1021/ic50074a051|accessdate=16 October 2013|publisher=American Chemical Society|format=PDF}}</ref> However, with [[dimethylamine]], HN(CH<sub>3</sub>)<sub>2</sub> it forms a trimeric beryllium diamide, [Be(N(CH<sub>3</sub>)<sub>2</sub>)<sub>2</sub>]<sub>3</sub> and hydrogen.<ref name = "Wiberg&Holleman"/>
⚫
The reaction with [[lithium hydride]] where the hydride ion is the Lewis base, forms sequentially LiBeH<sub>3</sub> and Li<sub>2</sub>BeH<sub>4</sub>.<ref name = "Wiberg&Holleman"/>


:BeH{{sub|2}} + 2 HCl → BeCl{{sub|2}} + 2 H{{sub|2}}
== Dihydridoberyllium ==
⚫
[[File:Beryllium-hydride-molecule-IR-3D-balls.png|150px|thumb|left|Structure of gaseous BeH<sub>2</sub>.]]
Dihydridoberyllium is a related compound with the chemical formula {{Chem|BeH|2}} (also written {{Chem|[BeH|2|]}}). It is a gas that cannot persist undiluted. Unsolvated dihydridoberyllium will spontaneously autopolymerise to oligomers. Free molecular BeH<sub>2</sub> produced by electrical discharge at high temperature has been confirmed as linear with a Be-H bond length of 133.376 pm. Its hybridisation is sp.
<ref>{{cite journal |author1=Peter F. Bernath |author2=Alireza Shayesteh |author3=Keith Tereszchuk |author4=Reginald Colin | year = 2002 | title = The Vibration-Rotation Emission Spectrum of Free BeH<sub>2</sub> | journal = Science | volume = 297 | issue = 5585| pages = 1323–1324 | doi = 10.1126/science.1074580 | pmid = 12193780 }}</ref>


=== Chemical properties ===
===Reaction with Lewis bases===
In theory, the two-coordinate hydridoberyllium group (-BeH) in hydridoberylliums such as dihydridoberyllium can accept an electron-pair donating ligand into the molecule by adduction:<ref name=Sharp2000>{{Cite journal|last1=Sharp|first1=Stephanie B.|last2=Gellene|first2=Gregory I.|title=σ Bond Activation by Cooperative Interaction with ''n''s<sup>2</sup> Atoms: Be + ''n'' {{Chem|H|2}}, ''n'' = 1−3|journal=The Journal of Physical Chemistry A|date=23 November 2000|volume=104|issue=46|pages=10951–10957|doi=10.1021/jp002313m|publisher=ACS Publications}}</ref>
The two-coordinate hydridoberyllium group can accept an electron-pair donating [[ligand]] (L) into the molecule by adduction:<ref name="Sharp2000">{{Cite journal |last1=Sharp |first1=Stephanie B. |last2=Gellene |first2=Gregory I. |date=23 November 2000 |title=σ Bond Activation by Cooperative Interaction with ''n''s{{sup|2}} Atoms: Be + ''n'' {{Chem|H|2}}, ''n'' = 1−3 |journal=The Journal of Physical Chemistry A |volume=104 |issue=46 |pages=10951–10957 |doi=10.1021/jp002313m}}</ref>
:{{Chem|[BeH|2|]}} + L → {{Chem|[BeH|2|L]}}
:{{Chem|[BeH|2|]}} + L → {{Chem|[BeH|2|L]}}
Because of this acceptance of the electron-pair donating [[ligand]] (L), dihydridoberyllium has [[lewis acids and bases|Lewis-acidic]]-acidic character. Dihydridoberyllium can accept two electron pairs from ligands, as in the case of the tetrahydridoberyllate(2-) anion ({{Chem|BeH|4|2-}}).
Because these reactions are energetically favored, beryllium hydride has [[lewis acids and bases|Lewis-acidic]] character.

⚫
The reaction with [[lithium hydride]] (in which the hydride ion is the Lewis base), forms sequentially LiBeH{{sub|3}} and [[Lithium beryllium hydride|Li{{sub|2}}BeH{{sub|4}}]].<ref name="Wiberg&Holleman" /> The latter contains the [[tetrahydridoberyllate(2-)]] anion {{Chem|BeH|4|2-}}.

⚫
Beryllium hydride reacts with [[trimethylamine]], N(CH{{sub|3}}){{sub|3}} to form a dimeric adduct with bridging hydrides.<ref name="Shepherd1969">{{Cite journal|last=Shepherd Jr.|first=Lawrence H. |author2=Ter Haar, G. L. |author3=Marlett, Everett M.|title=Amine complexes of beryllium hydride|journal=Inorganic Chemistry|date=April 1969|volume=8|issue=4|pages=976–979|doi=10.1021/ic50074a051}}</ref> However, with [[dimethylamine]], HN(CH{{sub|3}}){{sub|2}} it forms a trimeric beryllium diamide, [Be(N(CH{{sub|3}}){{sub|2}}){{sub|2}}]{{sub|3}}, and hydrogen.<ref name="Wiberg&Holleman" />


== References ==
== References ==
Line 91: Line 100:
{{Hydrides by group}}
{{Hydrides by group}}


{{DEFAULTSORT:beryllium hydride}}
[[Category:Beryllium compounds]]
[[Category:Beryllium compounds]]
[[Category:Metal hydrides]]
[[Category:Metal hydrides]]
[[Category:Substances discovered in the 1950s]]

Latest revision as of 18:43, 6 April 2024

For the monohydride, see Beryllium monohydride.
Beryllium hydride
Names
Other names
Beryllium dihydride
Beryllium hydride
Beryllane
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
UNII
  • InChI=1S/Be.2H checkY
    Key: RWASOQSEFLDYLC-UHFFFAOYSA-N checkY
  • InChI=1/Be.2H/rBeH2/h1H2
    Key: RWASOQSEFLDYLC-JICJMJRQAQ
  • [BeH2]
Properties
BeH2
Molar mass 11.03 g mol−1
Appearance white solid[1]
Density 0.65 g/cm3
Melting point 250 °C (482 °F; 523 K) decomposes
decomposes
Solubility insoluble in diethyl ether, toluene
Thermochemistry
30.124 J/mol K
Hazards
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 0.002 mg/m3
C 0.005 mg/m3 (30 minutes), with a maximum peak of 0.025 mg/m3 (as Be)[2]
REL (Recommended)
 Ca C 0.0005 mg/m3 (as Be)[2]
IDLH (Immediate danger)
 Ca [4 mg/m3 (as Be)][2]
Related compounds
Other cations
 lithium hydride, sodium hydride, magnesium hydride, calcium hydride, boron hydrides, aluminium hydride
Related compounds
 beryllium fluoride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Beryllium hydride (systematically named poly[beryllane(2)] and beryllium dihydride) is an inorganic compound with the chemical formula (BeH
2)n (also written ([BeH
2])n or BeH
2). This alkaline earth hydride is a colourless solid that is insoluble in solvents that do not decompose it. Unlike the ionically bonded hydrides of the heavier Group 2 elements, beryllium hydride is covalently bonded[1] (three-center two-electron bond).

Synthesis[edit]

Unlike the other group 2 metals, beryllium does not react with hydrogen.[3] Instead, BeH2 is prepared from preformed beryllium(II) compounds. It was first synthesized in 1951 by treating dimethylberyllium, Be(CH3)2, with lithium aluminium hydride, LiAlH4.[4]

Purer BeH2 forms from the pyrolysis of di-tert-butylberyllium, Be(C[CH3]3)2 at 210°C.[5]

A route to highly pure samples involves the reaction of triphenylphosphine, PPh3, with beryllium borohydride, Be(BH4)2:[1]

Be(BH4)2 + 2 PPh3 → BeH2 + 2 Ph3PBH3

Structure[edit]

Gaseous form[edit]

Structure of gaseous BeH2.

Isolated molecules of BeH
2 (sometimes called dihydridoberyllium and written [BeH
2] to emphasize the differences with the solid state) are only stable as a dilute gas. When condensed, unsolvated BeH
2 will spontaneously autopolymerise.

Free molecular BeH2 produced by high-temperature electrical discharge has been confirmed to have linear geometry with a Be-H bond length of 133.376 pm. Its hybridization is sp.[6]

Condensed Beryllium hydride[edit]

BeH2 is usually formed as an amorphous white solid, but a hexagonal crystalline form with a higher density (~0.78 g/cm3) was reported,[7] prepared by heating amorphous BeH2 under pressure, with 0.5-2.5% LiH as a catalyst.

Subunit of structure of BeH2. Each Be is tetrahedral and each H is doubly bridging.[8]

A more recent investigation found that crystalline beryllium hydride has a body-centred orthorhombic unit cell, containing a network of corner-sharing BeH4 tetrahedra, in contrast to the flat, hydrogen-bridged, infinite chains previously thought to exist in crystalline BeH2.[8]

Studies of the amorphous form also find that it consists of a network of corner shared tetrahedra.[9]

Chemical properties[edit]

Reaction with water and acids[edit]

Beryllium hydride reacts slowly with water but is rapidly hydrolysed by acid such as hydrogen chloride to form beryllium chloride.[3]

BeH2 + 2 H2O → Be(OH)2 + 2 H2
BeH2 + 2 HCl → BeCl2 + 2 H2

Reaction with Lewis bases[edit]

The two-coordinate hydridoberyllium group can accept an electron-pair donating ligand (L) into the molecule by adduction:[10]

[BeH
2] + L → [BeH
2L]

Because these reactions are energetically favored, beryllium hydride has Lewis-acidic character.

The reaction with lithium hydride (in which the hydride ion is the Lewis base), forms sequentially LiBeH3 and Li2BeH4.[3] The latter contains the tetrahydridoberyllate(2-) anion BeH2−
4.

Beryllium hydride reacts with trimethylamine, N(CH3)3 to form a dimeric adduct with bridging hydrides.[11] However, with dimethylamine, HN(CH3)2 it forms a trimeric beryllium diamide, [Be(N(CH3)2)2]3, and hydrogen.[3]

References[edit]

  1. ^ a b c Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 115. ISBN 978-0-08-037941-8.
  2. ^ a b c NIOSH Pocket Guide to Chemical Hazards. "#0054". National Institute for Occupational Safety and Health (NIOSH).
  3. ^ a b c d Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier ISBN 0-12-352651-5, p. 1048
  4. ^ Glenn D. Barbaras; Clyde Dillard; A. E. Finholt; Thomas Wartik; K. E. Wilzbach & H. I. Schlesinger (1951). "The Preparation of the Hydrides of Zinc, Cadmium, Beryllium, Magnesium and Lithium by the Use of Lithium Aluminum Hydride". Journal of the American Chemical Society. 73 (10): 4585–4590. doi:10.1021/ja01154a025.
  5. ^ G. E. Coates & F. Glockling (1954). "Di-tert.-butylberyllium and beryllium hydride". Journal of the Chemical Society: 2526–2529. doi:10.1039/JR9540002526.
  6. ^ Peter F. Bernath; Alireza Shayesteh; Keith Tereszchuk; Reginald Colin (2002). "The Vibration-Rotation Emission Spectrum of Free BeH2". Science. 297 (5585): 1323–1324. Bibcode:2002Sci...297.1323B. doi:10.1126/science.1074580. PMID 12193780. S2CID 40961746.
  7. ^ G. J. Brendel; E. M. Marlett & L. M. Niebylski (1978). "Crystalline beryllium hydride". Inorganic Chemistry. 17 (12): 3589–3592. doi:10.1021/ic50190a051.
  8. ^ a b Gordon S. Smith; Quintin C. Johnson; Deane K. Smith; D. E. Cox; Robert L. Snyder; Rong-Sheng Zhou & Allan Zalkin (1988). "The crystal and molecular structure of beryllium hydride". Solid State Communications. 67 (5): 491–494. Bibcode:1988SSCom..67..491S. doi:10.1016/0038-1098(84)90168-6.
  9. ^ Sujatha Sampath; Kristina M. Lantzky; Chris J. Benmore; Jörg Neuefeind & Joan E. Siewenie (2003). "Structural quantum isotope effects in amorphous beryllium hydride". J. Chem. Phys. 119 (23): 12499. Bibcode:2003JChPh.11912499S. doi:10.1063/1.1626638.
  10. ^ Sharp, Stephanie B.; Gellene, Gregory I. (23 November 2000). "σ Bond Activation by Cooperative Interaction with ns2 Atoms: Be + n H
    2    , n = 1−3". The Journal of Physical Chemistry A. 104 (46): 10951–10957. doi:10.1021/jp002313m.
  11. ^ Shepherd Jr., Lawrence H.; Ter Haar, G. L.; Marlett, Everett M. (April 1969). "Amine complexes of beryllium hydride". Inorganic Chemistry. 8 (4): 976–979. doi:10.1021/ic50074a051.
source: https://en.wikipedia.org/w/index.php?title=Beryllium_hydride&diff=1217588225&oldid=880261475

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