Beryllium hydride

Beryllium hydride

Chembox new
Name = Beryllium hydride
ImageFile = Beryllium-hydride-3D-balls.png ImageSize = 230px
ImageName =
Section1 = Chembox Identifiers
CASNo = 7787-52-2

Section2 = Chembox Properties
Formula = BeH2
MolarMass = 11.03 g mol−1
Appearance = amorphous white solidGreenwood&Earnshaw, p. 115]
Density = 0.62-0.65 g cm−3, solid
Solubility =
MeltingPt = 250 °C with decomp.

Section3 = Chembox Structure
Structure =

Section8 = Chembox Related
OtherCations = lithium hydride, calcium hydride, boron hydrides
OtherCpds = beryllium fluoride

Beryllium hydride, BeH2, is a chemical compound of beryllium and hydrogen. Unlike the ionically bonded hydrides of the heavier Group 2 elements, beryllium hydride is covalently bonded.

Synthesis

BeH2 was first synthesised in 1951 by reacting dimethylberyllium, Be(CH3)2, with lithium aluminium hydride, LiAlH4 [ cite journal | author = Glenn D. Barbaras, Clyde Dillard, A. E. Finholt, Thomas Wartik, K. E. Wilzbach, and H. I. Schlesinger | year = 1951 | title = The Preparation of the Hydrides of Zinc, Cadmium, Beryllium, Magnesium and Lithium by the Use of Lithium Aluminum Hydride | journal = J. Am. Chem. Soc. | volume = 73 | issue = 10 | pages = 4585–4590 | doi = 10.1021/ja01154a025 ] .

Purer BeH2 forms from the pyrolysis of di-tert-butylberyllium, Be(C(CH3)3)2 at 210 °C [ cite journal | author = G. E. Coates and F. Glockling | year = 1954 | title = Di-tert.-butylberyllium and beryllium hydride | journal = J. Chem. Soc. | pages = 2526–2529 | doi = 10.1039/JR9540002526 ] .

The purest beryllium hydride is obtained by the reaction of triphenylphosphine, PPh3, with beryllium borohydride, Be(BH4)2:

:Be(BH4)2 + 2PPh3 → 2Ph3PBH3 + BeH2

Structure

BeH2 is usually formed as an amorphous white solid, but a hexagonal crystalline form with a higher density (~0.78 g cm−3) was reported cite journal | author = G. J. Brendel, E. M. Marlett, and L. M. Niebylski | year = 1978 | title = Crystalline beryllium hydride | journal = Inorg. Chem. | | volume = 17 | issue = 12 | pages = 3589–3592 | doi = 10.1021/ic50190a051 ] , prepared by heating amorphous BeH2 under pressure, with 0.5-2.5% LiH as a catalyst.

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 [ cite journal | author = Gordon S. Smith, Quintin C. Johnson, Deane K. Smith, D. E. Cox, Robert L. Snyder, Rong-Sheng Zhou and Allan Zalkin | 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 ] .

References


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