Interstitial boron

Fig. 10-1.—Structure of tetragonal boron as viewed in the direction of the c axis. One unit cell is shown. Two of the icosahedral groups (light lines) are centered at z , and the other two (heavy lines) at. The interstitial boron atoms (open circles) are at (0, 0, 0) and (j, ). Numbers identify...

The basic structural feature is boron icosahedra. In the unit cell, there are 50 boron atoms, with 150 valence electrons and 148 boron-boron nearest neighbors (bond positions). These 50 boron atoms form four nearly regular icosahedra plus two interstitial boron atoms in the unit cell. Within each B12 icosahedron, each B atom has five adjacent atoms at the distance 1.797 0.015 A. Each icosahedral B atom has an interstitial B atom lying 1.62 0.02 A from it. Furthermore, each of the interstitial B atoms has four nearest neighbors (icosahedral B atoms). This implies that the icosahedral B atoms have ligancy 6, and the interstitial B atoms have ligancy 4. 

Metal Borides Interstitial Boron at the Molecular Level... 

This article reviews strategies that we have used to link transition metal boride clusters of types 1 (semi-interstitial boron, M4B cage) and 2 (fully interstitial boron, M5B cage), and addresses some of the problems of competing reactions. 

Figure 2. Semi- and fully-interstitial boron environments in M4, M5 and Me cages having butterfly, square-based pyramidal, octahedral, and trigonal prismatic structures respectively.

Hwu, S.-J. Corbett, J. D. (1986). Metal-Metal-Bonded Scandium Cluster (SC7CI12Z) and Infinite Chain (Sc4ClgZ) Phases Stabilized by Interstitial Boron or Nitrogen (Z), J. Solid State Chem. 64, 331 -346. 

The thermolysis of [Os3H3(CO)9(BCO)] in toluene has been reinvestigated and a new hexanuclear cluster [Os6(p-H)3( i6-B)(CO)i6] isolated. The 86 c.v.e. cluster adopts a geometry based on a pentagonal bipyramid with a vertex removed and containing an interstitial boride, a geometry unlike that previously seen for 86 c.v.e. hexaosmium clusters, but duplicating instead that observed for the 84 c.v.e. Os6(CO)i8 with the additional interstitial boron. ... 

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