Beryllium hydride (systematically named poly eryllane(2)'' and beryllium dihydride) is an

inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...

with the

chemical formula A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as pare ...

() (also written () or ). This alkaline earth hydride is a colourless solid that is insoluble in solvents that do not decompose it. Unlike the ionically bonded

hydride In chemistry, a hydride is formally the anion of hydrogen (H−), a hydrogen ion with two electrons. In modern usage, this is typically only used for ionic bonds, but it is sometimes (and has been more frequently in the past) applied to all che ...

s of the heavier

Group 2 The term Group 2 may refer to: * Alkaline earth metal The alkaline earth metals are six chemical elements in group (periodic table), group 2 of the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (B ...

elements, beryllium hydride is

covalently bonded A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atoms ...

(

three-center two-electron bond A three-center two-electron (3c–2e) bond is an electron-deficient chemical bond where three atoms share two electrons. The combination of three atomic orbitals form three molecular orbitals: one bonding, one ''non''-bonding, and one ''anti''- ...

Synthesis

Unlike the other

group 2 The term Group 2 may refer to: * Alkaline earth metal The alkaline earth metals are six chemical elements in group (periodic table), group 2 of the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (B ...

metals, beryllium does not react with hydrogen.Egon Wiberg, Arnold Frederick Holleman (2001) ''Inorganic Chemistry'', Elsevier , p. 1048 Instead, BeH is prepared from preformed beryllium(II) compounds. It was first synthesized in 1951 by treating

dimethylberyllium Organoberyllium chemistry involves the synthesis and properties of organometallic compounds featuring the group 2 alkaline earth metal beryllium (Be). The area remains less developed relative to the chemistry of other main-group elements, because ...

, Be(CH), with

lithium aluminium hydride Lithium aluminium hydride, commonly abbreviated to LAH, is an inorganic compound with the chemical formula or . It is a white solid, discovered by Finholt, Bond and Schlesinger in 1947. This compound is used as a reducing agent in organic synthe ...

, LiAlH. Purer BeH forms from the

pyrolysis Pyrolysis is a process involving the Bond cleavage, separation of covalent bonds in organic matter by thermal decomposition within an Chemically inert, inert environment without oxygen. Etymology The word ''pyrolysis'' is coined from the Gree ...

of di-tert-butylberyllium, Be(C H at 210°C. A route to highly pure samples involves the reaction of

triphenylphosphine Triphenylphosphine (IUPAC name: triphenylphosphane) is a common organophosphorus compound with the formula P(C6H5)3 and often abbreviated to P Ph3 or Ph3P. It is versatile compound that is widely used as a reagent in organic synthesis and as a l ...

, PPh, with beryllium borohydride, Be(BH): :Be(BH) + 2 PPh → BeH + 2 PhPBH

Structure

Gaseous form

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

Condensed Beryllium hydride

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

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

orthorhombic In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic Lattice (group), lattices result from stretching a cubic crystal system, cubic lattice along two of its orthogonal pairs by two different factors, res ...

unit cell In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector In mathematics, a unit vector i ...

, containing a network of corner-sharing BeH tetrahedra, in contrast to the flat, hydrogen-bridged, infinite chains previously thought to exist in crystalline BeH. Studies of the amorphous form also find that it consists of a network of corner shared tetrahedra.

Chemical properties

Reaction with water and acids

Beryllium hydride reacts slowly with water but is rapidly hydrolysed by acid such as

hydrogen chloride The Chemical compound, compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hyd ...

to form

beryllium chloride Beryllium chloride is an inorganic compound with the formula BeCl2. It is a colourless, hygroscopic solid that dissolves well in many polar solvents. Its properties are similar to those of aluminium chloride, due to beryllium's diagonal relations ...

. :BeH + 2 HO → Be(OH) + 2 H :BeH + 2 HCl → BeCl + 2 H

Reaction with Lewis bases

The two-coordinate hydridoberyllium group can accept an electron-pair donating

ligand In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...

(L) into the molecule by adduction: : + L → Because these reactions are energetically favored, beryllium hydride has Lewis-acidic character. The reaction with

lithium hydride Lithium hydride is an inorganic compound with the formula Li H. This alkali metal hydride is a colorless solid, although commercial samples are grey. Characteristic of a salt-like (ionic) hydride, it has a high melting point, and it is not solub ...

(in which the hydride ion is the Lewis base), forms sequentially LiBeH and LiBeH. The latter contains the tetrahydridoberyllate(2-) anion . Beryllium hydride reacts with

trimethylamine Trimethylamine (TMA) is an organic compound with the formula N(CH3)3. It is a trimethylated derivative of ammonia. TMA is widely used in industry. At higher concentrations it has an ammonia-like odor, and can cause necrosis of mucous membranes ...

, N(CH) to form a dimeric adduct with bridging hydrides. However, with

dimethylamine Dimethylamine is an organic compound with the formula (CH3)2NH. This secondary amine is a colorless, flammable gas with an ammonia-like odor. Dimethylamine is commonly encountered commercially as a solution in water at concentrations up to around ...

, HN(CH) it forms a trimeric beryllium diamide, e(N(CH)) and hydrogen.

References

{{Hydrides by group Beryllium compounds Metal hydrides Substances discovered in the 1950s