Peculiar Covalent Bonds inα-Rhombohedral Boron

Abstract

A peculiar bonding feature of a-rhombohedral boron is found in the electron density distribution of the icosahedral B 12 cluster. The electron density distribution is obtained by using the maximum entropy method with synchrotron radiation powder data. It clearly shows the characteristic two-and three-center covalent bond network which threads through atoms on the cluster surface. Besides, two kinds of covalent bonds in intercluster space are also shown in detail: a three-center trilaterally formed bond among the three clusters and a two-center bond with a remarkable feature of a bent bond between the clusters. The obtained covalent bonding features indicate the cluster-based nature of this material.

Electronic structures and mechanical properties of boron and boron-rich crystals (Part I)

“…4. Related to this bond, experimentalists derived a peculiar charge distribution by the maximum entropy method for powder X-ray diffraction [84,85]. In all the DFT calculations, such a strange distribution is not obtained.…”

“…3. In this view, the basic building block becomes doublewalled icosahedron B 84 , that is, an endohedral B 60 with a B 12 inside it. When viewed from B 84 units, one sees multiple intericosahedral bonds (the middle of Fig.…”

“…The idea of the constraint theory is that the stiffness of crystals can be expressed by the number of the nearest neighbor bonds, which is successful for the classification of the stiffness among chalcogenides and amorphous semiconductors [151]. In the α-rhombohedral boron, B 12 units are connected to each other by a point contact, that is, a single bond, while in the β-rhombohedral boron, B 84 units are connected to each other by a face contact, that is, multiple bonds (see Fig. 3).…”

Evolution of Crystallographic Structures and Phases in Micropyretically Formed Boron Rich Boron Carbide – a New Material System

“…A variation in peak positions as observed for various rhombohedral boron carbides are explained to be the substitution of a carbon atom by a boron atom in the inter or intra icosahedrons [19,21,22,28].The phase detection has also been confirmed by a multiphase simulation programme and the results have been represented by Fig. 4.…”

ENIGMA: maximum-entropy method program package for huge systems

“…The method has been successfully applied to structural studies of oxide superconductors , manganite (Takata, Nishibori, Kato et al, 1999), metallofullerenes (Takata et al, 1997;Nishibori et al, 1998;, zeolite (Hasegawa et al, 1999;Iversen et al, 1999), -boron (Fujimori et al, 1999), and so on (Takata et al, 2001).…”