beryllium hydride

Unlike the other group 2 metals, beryllium does not react with hydrogen.Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier {{ISBN|0-12-352651-5}}, p. 1048 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}}.{{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 }}

Purer BeH{{sub|2}} forms from the pyrolysis of di-tert-butylberyllium, Be(C[CH{{sub|3}}]{{sub|3}}){{sub|2}} at 210°C.{{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}}

A route to highly pure samples involves the reaction of triphenylphosphine, PPh{{sub|3}}, with beryllium borohydride, Be(BH{{sub|4}}){{sub|2}}:

:Be(BH{{sub|4}}){{sub|2}} + 2 PPh{{sub|3}} → BeH{{sub|2}} + 2 Ph{{sub|3}}PBH{{sub|3}}

File:Beryllium-hydride-molecule-IR-3D-balls.png

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 dilute gas. When condensed, unsolvated {{Chem|BeH|2}} will spontaneously autopolymerise.

Free molecular BeH{{sub|2}} 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.{{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 BeH₂ |journal=Science |volume=297 |issue=5585 |pages=1323–1324 |bibcode=2002Sci...297.1323B |doi=10.1126/science.1074580 |pmid=12193780 |s2cid=40961746}}

BeH{{sub|2}} is usually formed as an amorphous white solid, but a hexagonal crystalline form with a higher density (~0.78 g/cm{{sup|3}}) was reported,{{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 | volume = 17 | issue = 12 | pages = 3589–3592 | doi = 10.1021/ic50190a051}} prepared by heating amorphous BeH{{sub|2}} under pressure, with 0.5-2.5% LiH as a catalyst.

File:BeH2 structure.svg.|left]]

A more recent investigation found that crystalline beryllium hydride has a body-centred 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}}.{{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 }}

Studies of the amorphous form also find that it consists of a network of corner shared tetrahedra.{{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 }}

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

:BeH{{sub|2}} + 2 H{{sub|2}}O → Be(OH){{sub|2}} + 2 H{{sub|2}}

:BeH{{sub|2}} + 2 HCl → BeCl{{sub|2}} + 2 H{{sub|2}}

The two-coordinate hydridoberyllium group can accept an electron-pair donating ligand (L) into the molecule by adduction:{{Cite journal |last1=Sharp |first1=Stephanie B. |last2=Gellene |first2=Gregory I. |date=23 November 2000 |title=σ Bond Activation by Cooperative Interaction with ns{{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}}

:{{Chem|[BeH|2|]}} + L → {{Chem|[BeH|2|L]}}

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 LiBeH{{sub|3}} and Lithium beryllium hydride. 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.{{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}} 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.

{{Reflist|2}}

{{Beryllium compounds}}

{{Hydrides by group}}

Category:Beryllium compounds

Category:Metal hydrides

Category:Substances discovered in the 1950s