Interatomic bond length

A similarly distorted tetrahedral arrangement around the silicon atom is found in the intermolecular HMPA-stabilized acyclic heterobutadiene 3 (Fig. 4). Compound 3 crystallizes in the orthorhombic space group / i2. The Crl-Sil, Sil-Cll, and Sil-06 interatomic bond lengths of 3 are comparable with the distances found in other silanediyl compounds of type [R2Si=Cr(CO)5] HMPA [9]. 

Fig. 1. Interatomic bond lengths and bond angles for glycine (Marsh, 1958) L-proline (Mathieson and Welsh, 1952), and L-hydroxyproline (Donahue and True-blood, 1952).

Fig. 2. Interatomic bond lengths and bond angles for a-glyclglycine (Hughes and Moore, 1949) and /3-glycylglycine (Hughes, et al., 1964).

The deviation of nitrogen atoms from the equatorial plane of Np coordination polyhedron in the crystal structure of the compound [Np02(Re04)(Phen)(H20)2] (18) (Fig. 18) is less than in two structures with Bipy and does not exceed 0.135 A [95]. However, the planar phenanthroline molecule is inclined significantly with respect to the equatorial plane at an angle of 12.9. The equatorial interatomic bond lengths are unexceptional and equal to 2.641(9), 2.592(8) A, and 2.445(8)-2.532(8) A for Np-N and Np-0 bonds, respectively. In contrast, the axial Np-0 distances display unusually high values, 1.902(9) and 1.907(10)... 

The kind of accuracy possible in solving the Schrodinger equation today can be clearly seen by the impressive agreement of many ab initio results with experimental data. As an example, Figure I gives a number of results comparing ab initio interatomic bond lengths with experimental values. There is no question that with the present capabilities we can tap into the actual potential... 

Table 1 Selected interatomic bond lengths (Aj and angles (°) in complexes 1, 2 and 3...

Another parameter of importance in metal nanoparticles is the change in interatomic bond length. Extended X-Ray absorption fine structure (EXAFS) showed this on many transition metal nanoparticles with diameters less than 5 nm [89, 90]. On Pd particles with a diameter 1.4 nm, the interatomic distance reduction was about 3%. Note that this is again in hne with surface observation. More generally, surfaces are submitted to tensile stress and ah initio calculations on 2D Pt models show a strong interatomic distance reduction by 6.6% and 9.1% for the (111) and (100) structures, respectively [91]. Of course, in nanopartides, the structure is not purely 2D and the coordination lowering is not as strong. 

As the distances between neighboring protrusions are typical for interatomic bond lengths, one is inclined to interpret the images in Figure 19.10 as real-space images of the distribution of the atoms at the surface of these amorphous glasses. 

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