BeO₆ Trigonal Prism with Ultralong Be–O Bonds Observed in a Deep Ultraviolet Optical Crystal Li₁₃BeBe₆B₉O₂₇

Abstract

Beryllium (Be) has high ionization energy (9.32 eV) with the greatest degree of covalency in the group IIA elements, and BeO₄ tetrahedra (and BeO₃ triangles) with covalent character are generally presented in beryllates. An unprecedented BeO₆ trigonal prism with ultralong Be-O bonds as well as a BeO₄ common tetrahedron is discovered in a new deep ultraviolet crystal Li₁₃BeBe₆B₉O₂₇ (LBeBBO) with a _∞²[Be₆B₉O₃₃] double-layer framework. The BeO₆ unit and its bond character are verified by an isostructural crystal Li₁₃(Mg_0.45Be_0.55)Be₆B₉O₂₇, while the orbital theory and charge density difference further clarify the ionic character of the BeO₆ unit. Phonon dispersion confirms the structural stability of LBeBBO.