Bond length determination

F H, O Kennard, D G Watson, L Brammer, A G Orpen and R Taylor 1987.1 ables of Bond Lengths determined by X-ray and Neutron Diffraction. 1. Bond Lengths in Organic Compounds. Journal of he Chemical Society Perkin Transactions 11 51-519. 

TABLE 2 Bond lengths estimation from DQ solid state NMR of rhodopsin and bond length determined by X-ray diffraction on model compound (pm)69... 

The average bond lengths determined for some transition metal dichlorides by electron diffraction the length of the vertical bar indicates experimental uncertainty the line connect the data points for CaQ2> MnQ2 and ZnQj... 

Scheme 10.1 Syntheses and proposed structures of the supported Ru complex 3 and the unsaturated active complexes 4 and 5 on SI02, following exoergonic (energy-gaining) routes, together with bond lengths determined by XRD (for ligands) and EXAFS (for Oy)...

The first use of the CSD was the determination of average intramolecular bond lengths. These are now coded for all types of chemical bond [21], and such reference values are so well established that any bond length determination at variance with them is presumably wrong. Intramolecular geometry is hardly a frontier topic any more. 

It is unwise to trust any bond length determined by X-ray diffraction to better than 0.01 A, and sometimes errors are much greater. A very detached and realistic discussion of error limits has been given previously (72pmh(5)174). 

When a single crystal of a solid can be produced. X-ray diffraction provides an accurate, definitive structure, with bond lengths determined to tenths of a picometre. In recent years, the technique has been transformed from a very slow method reserved only for the most special structures, to a method of almost routine analysis with modern machines, suites of computer programs and fast computers are used to solve several crystal structures per week. 

Note that because of the different scattering mechanisms, the bond lengths determined by X-ray and neutron studies will be different. The neutron determination will give the true distance between the nuclei, whereas the X-ray values are distorted by the size of the electron cloud and so are shorter. 

Wu and Farges (1999) have made use of eqn (9.17) relating bond valence to the coefficient of thermal expansion to confirm that it is possible to resolve the different thermal expansions of the long and short Th-O bonds in thorite (o -ThSi04) from XAFS spectra measured between room temperature and 1700K. They also use this relation to estimate the anharmonic corrections needed for the bond lengths determined from XAFS (Brown et al. 1995, pp. 358-9). 

Table V. Compilation of M-H Bond Lengths Determined by Single-Crystal Neutron Diffraction0...

The P-B bond length determined crystallographically for the (CH2)3-bridged compound 41d (2.092(7) A) is noticeably shorter than that predicted computationally for the related (CH2)2-bridged system 40a (2.21 A). This further substantiates the influence of ring strain on the magnitude of intramolecular P-B interactions. 

Allen, F. H., Kennard, 0., Watson, D. G., Brammer, L., Orpen, A. G., Taylor, R., Tables of bond lengths determined by X-ray and neutron-diffraction. 1. Bond lengths in organic-compounds. J. Chem. Soc., Perkin Trans. 21987, S1-S19. 

The inspection of bond lengths determined by absolute structure methods or ab initio calculations for compounds with homonuclear multiple bonds reveals that a similar relationship is valid only for boron and the heavier members of group 15 and 16. Nitrogen and oxygen display a much stronger shortening of about 30 and 27 pm, respectively,... 

Table 4 Bond lengths determined using x-ray crystallography.

It did not show properties of typical unsaturated compounds, suggesting that ordinary -C=C- double bonds were not present. The bond lengths determined by X-ray analysis showed that all the carbon-to-carbon bonds in the ring were the same length. The chemical reactions normally undergone by double-bonded compounds were not shown by benzene. This was explained by assuming that six of the electrons in the benzene, one from each carbon atom, are able to move freely around the ring. They form new orbitals where electrons circulate freely, not... 

Covalent and metallic bondings suppose a strong overlap of the outermost atomic orbitals and so the atomic radii will be approximately the radii of the outermost orbitals. The atomic radii are empirically obtained from interatomic distances [59], For example, the length of the bond C-C is 154 pm in diamond, Si-Si is 234 pm in disilane, and so on. The consistency of this approach is shown by the agreement between the Si-C bond lengths determined experimentally and calculated from the corresponding atomic radii. The interatomic distances appreciably depend on the coordination. With decreasing coordination number, the bonds usually get shorter. For coordinations 8, 6, and 4, the bonds get shorter by about 2, 4, and 12%, respectively, as compared with the coordination number of 12. 

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