Chromium interatomic distance

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. " ...

It is indicated by the observed interatomic distances and shown by magnetic data that there occurs some deviation from this simple and attractive scheme in the middle region of the sequence. From chromium to cobalt the interatomic distances do not continue to decrease in value, as expected with increase in the number of bonds instead they remain nearly constant Cr, A2, 2.49A Mn, no simple structure Fe, A2, 2.48A, Al, 2.52A Co, Al, A3, 2.50-2.51A Ni,... 

These maxima in the Fourier transform data, which correspond to the different chromium coordination shells, were isolated using a filter window function. The inverse transform of each peak was generated and fitted using a non-linear least squares program. The amplitude and phase functions were obtained from the theoretical curves reported by Teo and Lee (2 ). The parameters which were refined included a scale factor, the Debye-Waller factor, the interatomic distance, and the threshold energy difference. This process led to refined distances of 1.97(2) and 2.73(2) A which were attributed to Cr-0 and Cr-Cr distances, respectively. Our inability to resolve second nearest neighbor Cr-Cr distances may be a consequence of the limited domain size of the pillars. 

Complexes with S-Donor, Se-Donor, or Te-Donor Ligands. The interatomic distances and valence distributions in the chromium thiospinels have been reviewed.151 Several mixed-metal sulphides, selenides, and tellurides containing chromium(m) have been reported this year, as detailed in Table 2. 

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. 

We may well expect that the strongest bonds would have the shortest interatomic distances, and it is accordingly not surprising that the large interatomic distances shown in Figure 17-2 are those for soft metals, such as potassium the smallest ones, for chromium, iron, nickel, and others, refer to the strong, hard metals. 

Intermolecular interactions may cause a difference between the structure of a free molectile and the molecule in a crystal. However, the results reported in electron diffraction and in X-ray diffraction investigations may also deviate because of a difference in the definition of interatomic distances. To the author s knowledge no accurate formulae exist for correcting the distances obtained by the two methods to the same distance type. Table 7 shows the results reported in two studies of dibenzene chromium. The X-ray data were recorded at 100 K. When these results have been corrected for thermal motion, the agreement with the electron diffraction value is quite satisfactory. 

Chromium (Cr) forms a body-centered cubic lattice. Its density is 7.19 g cm. Find the unit cell dimension and the interatomic distance. 

Figure I. Experimental dependences of the unit cell volume (a) and the interatomic Mn-O distance (b) ofLag ySrQ jMni jCrfDjij i samples on the chromium content (points) and theoretical curves calculated in supposition of the different charge compensation mechanisms...

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