Structure
BeO crystallizes in the hexagonal wurtzite structure, featuring tetrahedral Be2+ and O2- centres, like lonsdaleite and w-BN (both of which it is isoelectronic with). In contrast, the oxides of the larger group 2 metals, i.e., MgO, CaO, SrO, BaO, crystallize in the cubic rock salt motif with octahedral geometry about the dications and dianions. At high temperature the structure transforms to a tetragonal form.
In the vapour phase, beryllium oxide is present as discrete diatomic molecules. In the language of valence bond theory, these molecules can be described as adopting sp orbital hybridisation, featuring two sigma and two pi bonds. The corresponding ground state is .. (2sσ)2(2sσ*)2(2pπ)4, where both degenerate π orbitals can be considered as dative bonds from oxygen towards beryllium.
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