The quest for beryllium peroxides

There is no experimental proof documented in the literature for the existen ce of any beryllium peroxide compound. All recent pertinent preparative att empts described in this work, using a range of beryllium salts with various peroxides as reagents under mild conditions, were equally unsuccessful. H- 1 and Be-9 NMR investigations of aqueous solutions containing beryllium sal ts and hydrogen peroxide in a broad pH range also gave no definite evidence for the presence of peroxoberyllates as components of the manifold equilib ria in such solutions. Quantum chemical calculations have therefore been ca rried out to delineate the energetics and structures of various beryllium p eroxide model compounds. Standard Hartree-Fock and density functional metho ds were employed at various levels of sophistication. The series of prototy pes considered consists of [BeOH](+), Be(OH)(2), Be(OH)(OOH), Be(OOH)(2), [ Be(O-2)(2)](2-), [BeO2(OH2)(2)], and [Be-2(O-2)(2)(OH2)(4)] (all in the gas phase). Surprisingly, the triatomic cation [BeOH](+) has been found to hav e a linear structure. All the Be-O(peroxide) bonds are found to be rather l ong, suggesting weaker bonding compared to the Be-O bonds in aquo, hydroxo, or oxo complexes. Hydrogen peroxide or anions derived therefrom are theref ore not able to compete successfully with water (hydroxide anions) in aqueo us solution. In the mononuclear beryllium peroxide molecules, the peroxide groups form chelating units at tetrahedrally 4-coordinate metal atoms. The binuclear compound [Be-2(O-2)(2)(OH2)(4)] has a puckered six-membered-ring structure, close to the standard chair conformation. A significant lengthen ing of the O-O bonds upon coordination to the Be2+ centers has been calcula ted, but it is unlikely that the polarization of the peroxide group by the high positive charge density at Be2+ is significant to cause an intrinsic i nstability of beryllium peroxides. Ail structures represent distinct local minima on the potential energy surface and are predicted to be (meta)stable species in nonaqueous media. The field of aluminum peroxides is a similar gray area on the map of metal and metalloid peroxides and is reminiscent of the well-established "diagonal-relation'' of Be and Al in the periodic tab le of the elements.