The Beryllium Group

Solutions of the halides of the beryllium group of elements can also be made by acting on the hydroxides or carbonates of the metals with the halogen acid. To take barium chlo-... 

Valency of Elements.—We may remark here the gradual increase of valency as we pass from left to right in the periodic table. Lithium is a monad, with its congeners the elements of the beryllium group are dyads boron a triad carbon a tetrad phosphorus acts as pentad as well as triad sulphur, as a pseudo-monad, a dyad, and a tetrad ... 

The properties of the head element of a main group in the periodic table resemble those of the second element in the next group. Discuss this diagonal relationship with particular reference to (a) lithium and magnesium, (b) beryllium and aluminium. 

Figure 5.4 The molecular structure of basic beryllium acetate showing (a) the regular tetrahedral arrangement of 4 Be about the central oxygen and the octahedral arrangement of the 6 bridging acetate groups, and (b) the detailed dimensions of one of the six non-planar 6-membeted heterocycles. (The Be atoms are 24 pm above and below the plane of the acetate group.) The 2 oxygen atoms in each acetate group are equivalent. The central Be-O distances (166.6 pm) are very close to that in BeO itself (165 pm).

Beryllium shows a hint of nonmetallic character, but the other Group 2 elements... 

THE STRUCTURE OF THE CARBOXYL GROUP. II. THE CRYSTAL STRUCTURE OF BASIC BERYLLIUM ACETATE... 

The arrangement of atoms in the molecule of Be40(CH3C00)6. Small circles represent carbon atoms, large circles oxygen atoms. The beryllium atoms occupy the centers of the four tetrahedra. One of the six acetate groups is not shown. 

Figure 8.26 The four-coordinated oxygen atom in basic beryllium acetate OBe4(CH3C02)6- Three of the acetate groups are shown as curved lines.

A polymeric structure is exhibited by "beryllium dimethyl," which is actually [Be(CH3)2] (see the structure of (BeCl2) shown earlier), and LiCH3 exists as a tetramer, (LiCH3)4. The structure of the tet-ramer involves a tetrahedron of Li atoms with a methyl group residing above each face of the tetrahedron. An orbital on the CH3 group forms multicentered bonds to four Li atoms. There are numerous compounds for which the electron-deficient nature of the molecules leads to aggregation. 

The structure of dimethylberyllium is similar to that of trimethylaluminum except for the fact that the beryllium compound forms chains, whereas the aluminum compound forms dimers. Dimethylberyllium has the structure shown in Figure 12.3. The bridges involve an orbital on the methyl groups overlapping an orbital (probably best regarded as sp3) on the beryllium atoms to give two-electron three-center bonds. Note, however, that the bond angle Be-C-Be is unusually small. Because beryllium is a Lewis acid, the polymeric [Be(CH3)2] is separated when a Lewis base is added and adducts form. For example, with phosphine the reaction is... 

Many of the results reported are of a dubious nature. For example, Perkins (219, 222) assumed that complexes of the type ML2 were formed and quoted log /32 values between 9.8 and 14.2. Not only was the possible formation of a simple complex of the type ML excluded (not to mention any other complexes), but the effects of hydrolysis (which, to be fair, were poorly understood at the time) were completely ignored. The high stability of amino acid complexes was put in doubt in successive publications (220, 229, 232, 233). It has even been suggested, on the basis of Raman spectra, that the amino group does not coordinate to the beryllium atom (232). Unfortunately the opposite conclusion was reached on the basis of IR measurements, namely that only the amino group was coordinated (234). 

The superior coordinating capacity of phosphonate over carboxylate is illustrated in the 9Be NMR spectra in Fig. 25 (260). The similarity of the spectra obtained by reaction of BeS04 and methylphosphonic acid or phosphonacetic acid indicates that the carboxylate group is not bound to the beryllium under these experimental conditions. It should be noted that substitution of a water molecule by a phosphonate ligand causes the 9Be resonance to move upfield when it co-ordinates, as does the fluoride ion (271), the only other monodenate ligand... 

Let s look at the ground state electron configuration and orbital diagram of the beryllium atom (4Be) which is the first element in group 2A. 

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