Si-O bond length

Stishovite is a high-pressure modification of Si02 having the rutile structure. Should it have longer or shorter Si-O bond lengths than quartz ... 

Figure 4. The Correlation between the M-N bond length (x-Axis) and the Si-N and Si-O bond lengths (y-Axis) in [Me2(tBuO)Si]->N)2M, M = Zn, Fe, Mn, Ca, Ba.

The structures of these oxidation products were confirmed by X-ray crystallography (Fig. 11). The oxygen atom of 8 connects two bridgehead silicon atoms with a Si-O bond length of 1.683(4) A and a Si-O-Si bond angle of 120.2(4)°. The Si-O bond length is somewhat longer than those of... 

With the compound (2-Me2NCH2C6H4)PhSi(H)(03SCF3) 786, it was demonstrated that more than one built-in ligand is needed for the stabilization of trivalent silicon cations as, in this structure, the triflate anion is involved in the coordination to the silicon atoms.810 The related Si-O bond distance of 1.951(1) A is longer than the standard Si-O bond length (approx. 1.6 A) and therefore compound 786 might be best described as contact ion pairs (Figure 5). 

Baur W. H. (1978). Variation of mean Si-O bond lengths in silicon-oxygen tetrahedra. Acta Cryst, B34 1754-1756. 

Some of the diversity that characterizes the properties and compositions of the silicate minerals stems from the ability of the aluminum ion (Al ) to substitute for silicon in the tetrahedral unit. When silicate tetrahedra in a mineral are replaced by aluminum-containing tetrahedra, concomitant changes occur in the size of the tetrahedron (usual Si—O bond length = 0.160 nm. A1—O bond length = 0.178 nm) and in the cations or protons that balance the tetrahedral unit charge. Regular substitutions with distinct chemistries and structures lead to the formation of groups of discrete minerals called aluminosilicates. 

The presence of a silicon atom in the tether strongly influences the cyclization mode. The 6-endo mode and even the 1-endo are favored over the 5-exo because of the greater Si-O bond length, compared with that of C-O [94,97]. 

A C6Si2 O-skeleton with a C3SiOSiC3 sequence should also lead to a similar N—N distance. Only a little shortening is expected because of the Si—O bond length and SiOSi bond angle. According to this concept, the disiloxanes 213—215 should also exhibit curare-like activity. 

FIGURE 8. A scatter diagram of the minimum energy Si—O bond length, R(Si—O), calculated for a number of hydroxyacid molecules vs the value of the electron density, p(rc), evaluated at (3,-1) critical points. The geometries of the hydroxyacid molecules used to prepare the plot were those of minimum energy at the Hartree-Fock 6-31++G level... 

At that time the calculated Si—O bond length was 1.64(3) A. In 1989, Sheldrick15 indicated in his review that the additional data available at the time he wrote his review confirmed this finding. This value is smaller than the Stevenson-Schomaker corrected sum of the covalent radii of silicon and oxygen (1.76 A). The large amount of XRD structural data available today enables more accurate statistical analysis and the ability to verify it by theoretical calculation. 

The 3276 bond lengths obtained by XRD have been used to calculate the average Si—O bond length in compounds containing tetracoordinate silicon atom bonded to a dicoordinate oxygen atom. The average Si—O bond length is 1.629 A (s.d. 0.03 A, s.m. 

FIGURE 15. Histograms of Si—O bond lengths (left) and Si—O—X (X / Si) (right) in compounds with tetracoordinate silicon and dicoordinate oxygen atoms... 

Most of the exceptional bond lengths were obtained for compounds that were found to be disordered in their crystalline state. Shorter bond lengths have been found to belong to similar systems as presented by 174-176. The average Si—O bond lengths in these compounds are 1.552, 1.551 and 1.503 A in 174183, 175184 and 176185, respectively. The attachment of an electronegative sulphur atom to the silicon atom increases the Si—O bond ionicity and therefore the bond tends to become shorter. 

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