Silicon interatomic distance

COMPUTED DISPLACEMENTS AND INTERATOMIC DISTANCES (A) FOR THE H—B PAIR IN SILICON WHEN IN THE BC GEOMETRY. AN X-ORIGIN DISPLACEMENT IS POSITIVE WHEN AWAY FROM THE BC SITE. 

This disilaborane was an unexpected co-product in the synthesis of decaborane-alkylamine polymers. The Si2Bio cluster core consists of a distorted icosahedron in which the two silicon atoms occupy adjacent positions. The Si-Si interatomic distance is 2.308(2) A, which is slightly less than the Si-Si distance in organodisilanes (2.35 A) and the Si-B distances [2.017(3) to 2.116(3) A] are very close to the sum of the covalent radii of the two atoms (2.07 A). Further derivatives with disilaborane cluster geometry are known for the phenyl substituted compounds l,2-Ph2-doso-l,2-Si2B1oH1o and l-Me-2-Ph-doso-l,2-Si2BioHi0 [6, 7]. In addition to these disila-doso-dodecaborane clusters one example with two different group 14 elements as a part of the cluster core is known. In Scheme 3.3-2 the synthesis of this sila-stanna-doso-dodecaborate is shown. The structure of this heteroborate was determined in the solid state and the Si-Sn distance is 2.608(4) A (Scheme 3.3-2) [8]. 

In contrast to cyclotetrasilenylium ion 70, the four-membered ring of cyclotetrasilenyl radical 72 is almost planar with a dihedral angle of 4.7°.43 The distances between unsaturated silicon atoms of 72 (2.226(1) and 2.263(1) A) are also intermediate between the Si = Si double bond and the Si Si single bond in 49. In contrast to cation 70, radical 72 has a long interatomic distance between terminal unsaturated silicon atoms [3.225(2) A] indicating no significant 1,3-orbital interaction in 72.27... 

We performed structural optimization using ideal B6, B12-co, and B12-ico clusters (shown in Figure 8.1) with a 64-silicon-atom supercell. Table 8.1 shows the interatomic distances of these clusters and nearest-neighbor distances between boron and silicon atoms. The B6 cluster kept its octahedral symmetry during optimization, and the structure of the B12-co cluster was not altered appreciably its symmetry was lowered from Oh to Ta following that of the bulk. In contrast, the B12-ico cluster underwent distortion and its symmetry was reduced drastically from Ih to C3. 

It is impossible to tell at this time whether the spacings and configuration of the polyorganosiloxanes follow those of silicon dioxide or silicon disulfide, or neither of them. Such comparisons must await X-ray analysis of the polymeric structure. Once the interatomic distances and the approximate bond angles are known for several organo-siloxane chains, it tnay become possible to plan stronger and better polymeric structures instead of continuing to seek them on a purely empirical basis. 

Compound 7 crystallizes in the monoclinic space group P2 ln, and shows a pseudo-tetrahedral geometry around the silicon atom. One notable feature of 7 is the short Crl-Sil interatomic distance of 2.385(1) A, which corresponds to those found in other chromium-silicon multiple bond systems [9, 12]. In addition, the Sil-Nl interatomic distance of 1.954(2) A is shorter than that found in hypervalent DMBA- substituted aryl- [12], alkyl-, and vinyl-dichlorosilanes [13]. This is in agreement with the high electrophilicity of the silicon atom in 7. 

Silicon also has the diamond structure, the interatomic distance being... 

The fact that Na is the ratio of the molar volume to the atomic volume of any element provides a route to measuring its value, and several methods have been nsed to determine this ratio. A new method to refine the valne cnrrently is under development. Nearly perfectly smooth spheres of highly crystalline silicon (Si) can be prepared and characterized. The surface roughness of these spheres (which affects the determination of their volume) is 1 silicon atom. The molar volnme is determined by carefnlly measnring the mass and volume of the sphere, and the atomic volume is determined by measuring the interatomic distances directly nsing x-ray diffraction. (X-ray diffraction from solids is described in Chapter 21.) Avogadro s nnmber is the ratio of these two quantities. 

Fig. 5.14 Side view of a slab model of the surface of amorphous silica [55]. The top surface consists only of Si and O atoms the bottom one is fully hydroxylated. Black, light grey and white spheres are silicon, oxygen and hydrogen atoms, respectively. The large spherical oxygen and all the silicon atoms are to scale with the interatomic distances.

Further experimental support has been provided by the results of structure determinations of surfaces cleaned by ion bombardment and the annealing method (i5). They show that the surface atoms are rearranged from bulk positions especially for the diamond structures of the semiconductors Ge and Si. At a clean cleavage plane of silicon the Si-tetrahedra are distorted to such an extent that the interatomic distances between surface Si-atoms are 260 pm as compared to 384 pm within the crystal lattice (ij). 

Fig. 7. Perspective view of the structure of rare-earth silicate oxyapatites (RE3.88 Qo.67)REe(Si04)a02 along [OOl] and [lOO], Interatomic distances from data on the Gd analogue (47) with e. s. d. s ranging from 0.002 A to 0.008 A. Black balls rare earths in the special positions (4/) and (6A), white balls free , not silicon-bonded oxygen, solid (Si04) tetrahedra...

X-ray diffraction studies on single crystals of NdFe oSiCo 5 have established its structure with the space group I4i/amd and Z = 4 formula units per unit cell. The positions of the neodymium, iron and silicon atoms correspond to the BaCdn structure. The positional and thermal parameters for NdFejoSiCo s of BaCdj, type structure have been given by Le Roy et al. (1987), as well as the interatomic distances in this compound. This structure is a disordered version of LaMnnC, 52 (Ross et al. 1981). Each neodymium atom is surrounded by a polyhedron of 26 atoms, i.e. 18 iron atoms, four carbon atoms and four atoms which may be iron or silicon. Fe(l) is surrounded by 14 atoms, Fe(2) by 13 atoms, and the (Fe-Si) site by 12 atoms. As has been pointed out, the carbon atoms fill octahedral voids formed by four iron atoms and two neodymium atoms, with an occupancy of 25%. 

In Fig. 1 the space structure, the interatomic distance and coordination number distribution function for the most regular diamond-like silicon dioxide structure is presented. This cluster was constructed as 3x3x3 extended crystobalite cells and it containings 708 atoms. This cluster has been used as a reference for highly regular structures. 

Fig. 1. The space structure, the interatomic distance and coordination number distribution function for the most regular diamond-like silicon dioxide structure.

The shortest interatomic distances in the structure of Mn4Si7 are shown in Table 2. The distances between the manganese and silicon atoms are accurate to 0.002 A, and between the silicon atoms to 0.003 A. 

---