Interatomic distances and angles

Figure 11.16 Coordination geometries of the nitrate group showing typical values for the interatomic distances and angles. Further structural details are in ref. 150.

Figure 14.17 Structures of (a) the tetraperoxochromate(V) ion [Cr (02)4] , (b) the pyridine oxodiperoxo-chromium(VI) complex [Cr 0(02)2py], and (c) the triamminodiperoxochromium(IV) complex [Cr" (NH3)3(02)2] showing important interatomic distances and angles. (This last compound was originally described as a chromium(II) superoxo complex [Ci (NH3)3(02)2] on the basis of an apparent 0-0 distance of 131 pm/ and is a salutary example of the factual and interpretative errors that can arise even in X-ray diffraction studies. " ...

Quantitative specifications are made with numeric values for interatomic distances and angles. The interatomic distance is defined as the distance between the nuclei of two atoms... 

Commonly, only the atomic coordinates for the atoms in one asymmetric unit are listed. Atoms that can be generated from these by symmetry operations are not listed. Which symmetry operations are to be applied is revealed by stating the space group (cf Section 3.3). When the lattice parameters, the space group, and the atomic coordinates are known, all structural details can be deduced. In particular, all interatomic distances and angles can be calculated. 

Unit Cell Parameters and Selected Interatomic Distances and Angles in m-Quartz PON and in the Corresponding Si02 Phase ... 

The crystallographic data for [16] are in excellent agreement with the analogous interatomic distances and angles calculated (Haddon, 1979b) for the parent homotropylium ion [12] and fully support the homoaromatic... 

Due to the unreliability associated with crystallographically-determined positions of hydrogen atoms, our discussion of the molecular structures in crystals will focus on the interatomic distances and angles that do not involve hydrogens. Our data are from the Cambridge Structural Database unless stated otherwise. 

No quantum mechanical calculation or similar theoretical treatment seems to have been dedicated to chrom-3-ene7 or to its simple derivatives. Interatomic distances and angles of two bromo derivatives of natural chromenos have been obtained by X-ray analysis,8,9 The UV absorption,10 emission,11 fluorescence, and fluorescence excitation spectra12 of some 2,2-dialkylchromenes have been studied in connection with their photochromic behaviour. 

Structure refinements of the AH 200 and AH 300 samples were conducted in the same way. Unit cell constants, final atomic parameters, and R indexes are given in Table I. (Observed and calculated structure factors are available from the authors.) Interatomic distances and angles are given in Table II. Estimated errors on the population and position of the cations may in some cases be greatly underestimated especially for atoms with low occupancy factors. 

TABLE 1. Selected interatomic distances and angles in [1.1. ljpropellane and its derivatives... 

Fig 1 Drawing of (S-HMX molecule showing interatomic distances and angles. 

The final structural parameters are presented in Table Ila. Interatomic distances and angles are given in Table III. 

Interatomic distances and angles for nitrate groups in nitrato-complexes. 

The bands at 1388 cm-1 might be explained by the presence of small amounts of P4OI0 due to the route of preparation (see Refs. 171 and 172). Force constants for the P406S4 molecule were calculated from Raman spectra and were improved later (113). Table XXVII gives the values obtained using the simple valence force field method (I) or the extended force field method (II) (113) the calculations have been carried out using interatomic distances and angles from electron diffraction data (178). 

The final positional parameters and thermal parameters are shown in Tables 2 and 3 for PrMnOj and TbMnOj, respectively. The interatomic distances and angles for the samples are given in Table 4 together with their estimated standard deviation. 

The interatomic distances and angles, and their standard deviations, are in Table 3. Views of the structure are shown in Figures 1, 2, and 3, the last also showing the atom numbers referred to in Table 3. 

The crystal used for data coUection was transferred to an Enraf-Nonius CAD-4 diffractometer. Automatic peak search and indexing procedures yielded the same monoclinic cell as derived from the X-ray powder diffraction data and precession photographs. Testing showed that the cell was indeed primitive and that there was no superlattice present. Table 5 gives the crystal data and X-ray experimental parameters, and Table 6, the interatomic distances and angles. Positional and thermal parameters are given in Table S3 (Supporting Information)... 

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