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 synthesised 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]
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 hybridisation is sp.[6]
Condensed Beryllium hydride
Subunit of structure of BeH2. Each Be is tetrahedral and each H is doubly bridging.[7]
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,[8] 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 orthorhombicunit 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.[7]
Studies of the amorphous form also find that it consists of a network of corner shared tetrahedra.[9]
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]
^ abcdEgon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier ISBN0-12-352651-5, p. 1048
^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.
^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.
^Sharp, Stephanie B.; Gellene, Gregory I. (23 November 2000). "σ Bond Activation by Cooperative Interaction with ns2 Atoms: Be + nH 2, n = 1−3". The Journal of Physical Chemistry A. 104 (46): 10951–10957. doi:10.1021/jp002313m.
^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.
