Beryllium borohydride

Beryllium borohydride is an inorganic compound with the chemical formula Be[BH₄]₂.^[2]

Beryllium borohydride

Beryllium   Boron   Hydrogen
Names
IUPAC name Beryllium borohydride
Other names Beryllium tetrahydroborate(1−), Beryllium tetrahydroborate(III)
Identifiers
CAS Number	17440-85-6 Y
3D model (JSmol)	Interactive image
ChemSpider	4809792
PubChem CID	6101896
UNII	4GV25JT031 Y
CompTox Dashboard (EPA)	DTXSID101030508
InChI InChI=1S/2BH4.Be/h2*1H4;/q2*-1;+2 Key: ONQXRAXVSQRPSX-UHFFFAOYSA-N
SMILES [Be+2].[BH4-].[BH4-]
Properties
Chemical formula	Be[BH4]2
Molar mass	38.70 g·mol−1
Appearance	white crystals
Density	0.604 g/cm3
Melting point	91.3 °C (196.3 °F; 364.4 K)
Boiling point	123 °C (253 °F; 396 K) decomposes
Solubility in water	reacts
Solubility	soluble in benzene, diethyl ether
Structure
Crystal structure	tetragonal
Space group	I41cd, No. 110
Thermochemistry
Std enthalpy of formation (ΔfH⦵298)	−108 kJ/mol
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)[1]
REL (Recommended)	Ca C 0.0005 mg/m3 (as Be)[1]
IDLH (Immediate danger)	Ca [4 mg/m3 (as Be)][1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Preparation

Beryllium borohydride is formed by the reaction of beryllium hydride with diborane in an ether solution.

It can also be formed by the reaction of beryllium chloride and lithium borohydride in a sealed tube at 120 °C:^[2]

BeCl₂ + 2 Li[BH₄] → Be[BH₄]₂ + 2 LiCl

Structure

The chemical formula of beryllium borohydride can be written as Be²⁺([BH₄]⁻)₂. The crystal structure is made up of a helical polymer of BH₄Be and BH₄ structure units.^[2][3] The borohydride ions, [BH₄]⁻, adopt a tetrahedral geometry.^[3] Beryllium is 6-coordinate and adopts a distorted trigonal prismatic geometry.^[2]

Application

The purest beryllium hydride is obtained by the reaction of triphenylphosphine, PPh₃, with beryllium borohydride, Be[BH₄]₂ at 180 °C:^[2]

Be[BH₄]₂ + 2 PPh₃ → 2 Ph₃P⁺−⁻BH₃ + BeH₂