Don Bruce Sullenger’s favorite structure is:

beta-rhombohedral boron

beta-rhombohedral boron

Source: Source of photo: Monsanto Research Corp., Mound Laboratory, Miamisburg, OH. (A now closed and environmentally restored DOE laboratory).

Why?

Why this is my favorite X-ray crystal structure: The beautiful, strikingly unique structure of B-rhombohedral boron has successfully withstood numerous challenges of its correctness and has for a half century experienced nearly constant investigations of its structurally implied material characteristics. Arguably the most important of the several known phases of elemental boron, this form has been found to be experimentally stable from absolute zero to its melting point. Detailed consideration of the 5-foldness of its numerous discrete and merged 12-atom regular icosahedral motifs and their extended 84-atom truncated icosahedral arrays has forced a significant modification of chemical bonding theory in attempts to explain the low density, high strength, high melting, semiconducting and other notable properties of this low atomic number element. Even the observed partial occupancy of one of its 6-fold Wyckoff sets of atoms within the structure appears to be correct and to imply intriguing electronic possibilities. As one affected colleague has remarked: "You never fully recover from a bite of the boron bug." This structure illustrates some of the allure.—Don Bruce Sullenger

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