BeH2

Beryllium Hydride. BeryUium hydride [13597-97-2] is an amorphous, colorless, highly toxic polymeric soHd (H = 18.3%) that is stable to water but hydroly2ed by acid (8). It is insoluble in organic solvents but reacts with tertiary amines at 160°C to form stable adducts, eg, (R3N-BeH2 )2 (9). It is prepared by continuous thermal decomposition of a di-/-butylberylhum-ethyl ether complex in a boiling hydrocarbon (10). 

Only H2, BeH2, and Be(BH 2 have higher heats of combustion. When diborane is pyroly2ed above 100°C ia a sealed tube, it is decomposed to higher boron hydrides and hydrogen gas ia a complex sequence of reactions. This reaction has been investigated ia considerable detail (65). 

Therefore we should expect in the gaseous state to find molecules such as BeH2 and BeF2. These molecules have been detected. On the other hand, beryllium has the trouble boron has, only in a double dose. It has two vacant valence orbitals. As a result, BeH2 and BeF2 molecules, as such, are obtained only at extremely high temperatures (say, above 1000°K). At lower temperatures these vacant valence orbitals cause a condensation to a solid in which these orbitals can participate in bonding. We shall discuss these solids in the next chapter. 

Kinetic data for the decompositions of several metal hydrides are summarized in Table 12 to which the following information can be added. The acceleratory period in the decomposition of BeH2 (a < 0.35) is ascribed [673] to the random formation of metal nuclei followed by linear growth. The increase in rate consequent upon exposure to X-irradia-tion is attributed to enhanced nucleation. Grinding similarly increased the... 

BeH2 (129a) and M2BeH4 (M = Li, Na) (129b) are polymeric materials. 

Fig. 4. The quantum reaction probability for BeH + H2 —> BeH2 +H at J = 0 is shown as a function of the relative translational energy. The PES was evaluated using the simple weight function of Eq. (49) with a data set of 926 ( ) and 1110 (—) data points.

Figure 8.5 Contour maps of the electron density distribution of LiH, BeH2, BH3, and CH4...

Beryllium atoms generated under similar conditions react in an acetylene/argon matrix at 10 K to produce HBeCCH (//,Be-Hi = 2,119cm-1).10 The observation of BeH, BeH2, -CCH, and HCC-CCH as co-products indicates that some fraction of the beryllium atoms abstracts hydrogen from HCCH (Equation (2)) ... 

One of the most important factors when describing molecules that have only single bonds is the repulsion that exists between electrons. Repulsion is related to the number of electron pairs both shared and unshared around the central atom. When only two pairs of electrons surround the central atom (as in BeH2), the structure is almost always linear because that gives the configuration of lowest energy. 

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