Beryllium complex compounds, anions

Polyalcohols do not generally interact noticeably with beryllium, probably on account of the low acidity of the alkyl-OH group. Two exceptions are known where solid compounds have been isolated. The complex anion [bis(meso-oxolane-3,4-diolato)Be]2 has been shown to contain two anionic diolato ligands (258). 

An operational description is that one reactant (the more ionic compound with the more electropositive metal) transfers alkyl anions to the other. Thus the four methyl groups in Li2BeMe4 form a distorted tetrahedron around the beryllium, with longer distances to the lithium ions. However, this description is oversimplified. The low-temperature nuclear magnetic resonance (NMR) spectrum of Li3MgMe5 has three different methyl resonances, suggesting structure (14), related to the MeLi tetramer. Ate complexes with zinc and aluminum compounds also form. Electron-deficient bridge-bonded structures, exemplified by the X-ray structure of... 

Beryllium (Be, at. mass 9.012) forms cations Be ". In its chemical properties, beryllium resembles magnesium and aluminium. Beryllium hydroxide is precipitated at pH 6, and dissolves in alkali hydroxides. Freshly precipitated Be(OH)2 dissolves in NaaCOs solution to form a rather unstable carbonate complex. Beryllium also forms weak complexes with citrate, tartrate, and fluoride anions. Beryllium and its compounds are highly toxic. 

For these s-block elements, the stability of complexes is often affected by the difference in the size of the ionic radii relative to the cation and anion pair. Large anions are generally better stabilized by large cations for example, barium peroxide is more stable than beryllium peroxide. In fact, the barium peroxide compound is so stable that it forms spontaneously in air. 

All beta-ditetone compounds exist in the enol form and readily form stable anions with electron delocalization over the O—C—CH—C—O chain, which chelates the cations via the two oxygen atoms. The "oxygen-loving" metals whose cations are hard acids form stable chelate complexes of the form [M(n)(ACAC)J(Figure 4). Beryllium is particularly well extracted as the neutral [) ACAC)2] complex because the combination of the tetrahedral [BeO I coordination geometry and the small radius of the ion results in a v y stable and compact molecule. 

The reaction of beryllium metal with aqueous acids yields hydrogen and ionic compounds, such as BeCl2 4 H2O. In BeCl2 4 H2O, water molecules are covalently bonded to Be ions, producing the complex cations [Be(OH2)4] that, together with the anions d , form the crystal lattice. In covalent compounds, Be atoms appear to use hybrid orbitals—sp orbitals in BeCl2(g) and sp orbitals in BeCl2(s) (Fig. 21-12). 

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