ICOSAHEDRAL PACKING OF B-12 ICOSAHEDRA IN BORON SUBOXIDE (B6O)

Objects with icosahedral symmetry (I-h) bear a special fascination; na tural examples are rare, but include radiolaria(1) and virus particles (virions)(2). The discovery(3) of C-60, a molecule in the shape of a truncated icosahedron with a symmetry, has aroused widespread interest . In 1962, Mackay(4) described a radiating packing of spheres in I-h s ymmetry, in which the centres of successive shells of spheres lie on t he surfaces of icosahedra. There has been extensive investigation of t he conditions under which such packing might be realized in assemblies of atoms or of molecules such as C-60 (ref. 5). Here we report the pr eparation, at high temperatures and pressures, of boron suboxide (B6O) in which the preferred form of the material is as macroscopic, near-p erfect, regular icosahedra, similar to the multiply-twinned particles observed in some cubic materials. A major difference is that B6O has a rhombohedral structure that nearly exactly fits the geometrical requi rements needed to obtain icosahedral twins. These icosahedral particle s have a structure that can be described as a Mackay packing of icosah edral B-12 units, and thus has long-ranged order without translational symmetry.