Chromium structural data

Structural data confirm that the Daniphos ligands are readily adaptable to most ligand environments. A major advantage of the chromium system is the commercial availability of phenylethylamine and its derivatives in both enantiomeric forms. In contrast to the cyclopentadienyl ring, arenes have an almost unlimited potential for controlled substitutional variation, accessible through standard reaction protocols. 

The insertion of various isocyanates into chromium(lll) alkoxide M—O bonds has been reported.737 The complexes are prepared by refluxing the isocyanates with a suspension of the alkoxide in benzene. No structural data were given for the products. Unusual bimetallic alkoxides have recently been prepared738 by the reaction of Cr[Al(OPr )4]3 with alcohols and acetylacetone (166). A wide range of spectroscopic methods were used to study them. In general, the results were in accord with a monomeric formulation similar to (166) below Cr[Al(OMe)4]3 was grossly insoluble the small size of the methyl groups may permit extensive polymerization. 

Fig. 34. Influence of a (/ -coordinated chromium atom on the geometry of [2.2]paracyclophanes (the structural data of the uncomplexed phane are given in brackets)...

Iron polycations are not as well known as chromium or aluminum polycations because of the lability of ferric complexes. Only a few polycations (dimers, trimers) have been characterized in acidic solutions (pH < 1.5) [39]. [Fe2(OH)2] and [Fc20] dimers are present in organic complexes such as L3(H20)Fe(OH>2-Fc(OH2)L3 and LjFeOFeLs, where the L3 ligand is a tridentate picolinate and L5 a tridentate amine [16,40,41]. Other polydentate ligands, such as proteins, are able to stabilize many polynuclear iron complexes [42-45]. The existence of lire aquo complexes [(H20)4Fe2(0H)2(0H2)4] " and [(H20)5Fe20(0H2)s] is very probable in spite of the lack of structural data. 

UV irradiation. Indeed, thermal reaction of 1-phenyl-3,4-dimethylphosphole with (C5HloNH)Mo(CO)4 leads to 155 (M = Mo) and not to 154 (M = Mo, R = Ph). Complex 155 (M = Mo) converts into 154 (M = Mo, R = Ph) under UV irradiation. This route was confirmed by a photochemical reaction between 3,4-dimethyl-l-phenylphosphole and Mo(CO)6 when both 146 (M = Mo, R = Ph, R = R = H, R = R" = Me) and 155 (M = Mo) resulted (89IC4536). In excess phosphole, the product was 156. A similar chromium complex is known [82JCS(CC)667]. Complex 146 (M = Mo, R = Ph, r2 = R = H, R = R = Me) enters [4 -H 2] Diels-Alder cycloaddition with diphenylvinylphosphine to give 157. However, from the viewpoint of Woodward-Hoffmann rules and on the basis of the study of UV irradiation of 1,2,5-trimethylphosphole, it is highly probable that [2 - - 2] dimers are the initial products of dimerization, and [4 - - 2] dimers are the final results of thermally allowed intramolecular rearrangement of [2 - - 2] dimers. This hypothesis was confirmed by the data obtained from the reaction of 1-phenylphosphole with molybdenum hexacarbonyl under UV irradiation the head-to-tail structure of the complex 158. 

It is clear that an ah initio calculation of the ground state of AF Cr, based on actual experimental data on the magnetic structure, would be at the moment absolutely unfeasible. That is why most calculations are performed for a vector Q = 2ir/a (1,0,0). In this case Cr has a CsCl unit cell. The local magnetic moments at different atoms are equal in magnitude but opposite in direction. Such an approach is used, in particular, in papers [2, 3, 4], in which the electronic structure of Cr is calculated within the framework of spin density functional theory. Our paper [6] is devoted to the study of the influence of relativistic effects on the electronic structure of chromium. The results of calculations demonstrate that the relativistic effects completely change the structure of the Or electron spectrum, which leads to its anisotropy for the directions being identical in the non-relativistic approach. 

The structure and composition of diffusion coatings depends of necessity on the metal or alloy from which the article is made. Thus, for example, it is not possible to speak of chromised coatings generally the material into which chromium is diffused must be specified. Some data on methods of application and properties of commercially chromised irons and steels are given in Table 12.4. 

Calculate the atomic radius of each of the following elements from the data given (a) silver, fee structure, density 10.500 g-cm 3 (b) chromium, bcc structure, density 7.190 g-cm-3. 

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,... 

The reactivity of chromium(V) and chromium(IV) species is uncertain since there are no reliable thermodynamic data, and not much can be said at present about the structure of these species. With respect to the latter some hints can be obtained from the fact that the changeover from chromium(V) to chromium(IV) or vice versa in all cases was found to be rate determining, which seems to correlate well with the conclusion of Tong and King d that Cr(VI) and Cr(V) have coordination number four, whereas Cr(IV) and Cr(III) have six. 

Figure 2 shows the SEM image of the flake at a magnification of 350 x, as it was mounted on the conductive carbon tape. If there is a polymeric film covering the sample, the SEM will only show the surface topography of the film, not the structure residing below the polymeric film. EDS was conducted on two areas on the sample as indicated in Figure 2. The EDS analysis was conducted in square spot mode, approximately 1 pm by 1 pm in size. The elemental results are shown in Table 2. Based on these data sets it is apparent that the Type A defect is an iron-rich particle. Based on the lack of chromium or nickel the Type A defect is a particle of steel, not stainless steel.

X-ray powder diagrams obtained by the Guinier method show the tris (O-ethyl dithiocarbonato) complexes of chro-mium(III), indium(III), cobalt(III), iron(III), arsenic(III), and antimony(III) to be isomorphous. Carrai and Gottardi have determined the structure of the arsenic(III)18 and anti-mony(III)19 complexes. Crystallographic data for the cobalt(III) and chromium(III) ethylxanthate complexes are given by Derenzini20 and Franzini and Schiaffino,21 respectively. 

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