Exists in multiple polymeric forms, (BO)x. Prepn: E. Zintl et al., Z. Anorg. Allg. Chem. 245, 8 (1940); T. Wartik, E. F. Apple, J. Am. Chem. Soc. 77, 6400 (1955); and proposed structure: A. L. McCloskey et al., ibid. 83, 4750 (1961). VUV absorption spectrum: H. Bredohl et al., Mol. Phys. 101, 2145 (2003).