The Structure of Boron Monoxide

Boron monoxide (BO), prepared by the thermal condensationof tetrahydroxydiboron,was first reported in 1955; however, its structure could not be determined.With the recent attention on boron-based two-dimensional materials,such as borophene and hexagonal boron nitride, there is renewed interestin BO. A large number of stable BO structures have been computationallyidentified, but none are supported by experiments. The consensus isthat the material likely forms a boroxine-based two-dimensional material.Herein, we apply advanced B-11 NMR experiments to determinethe relative orientations of B(B)O-2 centers in BO. We findthat the material is composed of D (2h )-symmetric O2B-BO2 units thatorganize to form larger B4O2 rings. Further,powder diffraction experiments additionally reveal that these unitsorganize to form two-dimensional layers with a random stacking pattern.This observation is in agreement with earlier density functional theory(DFT) studies that showed B4O2-based structuresto be the most stable.