Cations chromium

Functionally, as shown in Figure 4.10, the protection layer is intended first to serve as a mass barrier to both chromium cation outward and oxygen inward transport... 

Fig. 8 a The crystal is formed of columns of methoxychromate anions and of columns of bis-benzene chromium cations extending parallel to the c-axis. b The anions are apparently linked along the column via a short C-H O interaction (H O 2.381 A, C-H O 173°) between a methyl hydrogen and a chromate oxygen... 

However, consider the corresponding situation for a closely related complex in which, instead of an iodide ion bound to pentaaquo chromium, there is an aliphatic fragment such as an alkyl group. As one example, we may consider the hydroxyiso-propyl chromium cation. Here the possibility for both homolytic and heterolytic substitution exists (Scheme II). With proper experiments, one can evaluate separately the rate constant values for cleavage by each of these pathways. 

Chromium in the trivalent state forms a variety of salts, the most important and the simplest being the violet salts, which liberate in aqueous solution chromium cation Cr" A green series of chromic salts, isomeric with the violet salts, liberate in aqueous solution some chromium cation, whilst part of the chromium is present as a complex ion. With weak acids, sulphurous, hydrocyanic, or thiocyanic acids, the chromic ion forms complex ions of great stability. Finally, a very large group of salts exists where chromium associated with ammonia forms the complex ion, the chromi-ammines. 

The rate constants of this bimolecular reaction for a given organo-chromium cation change in order of the driving force, with fis increasing in the series Ig- < SCNg- < Br. ... 

In contrast, Kim et al. (13) found that the amount of aluminum removed from the zeolite lattice during ion-exchange with solutions of metal chlorides was directly related to the pH of the solution and that the presence of the metal cation played no part in the dealumination. Our work more closely mirrors that of Bailar and coworkers (14-16) who found that solutions of CrCl3 under reflux conditions could dealuminate a variety of zeolites to a much greater extent than the pH of the CrCl3 solutions would predict. To explain their results, they proposed that the chromium cations could complex with hydrolyzed aluminum ions in the zeolite through the formation of "ol bridges" which then diffused out of the zeolite. Therefore,... 

Zinc(II) and chromium(IV) cations are smaller (0.88 and 0.69 A respectively) than oxygen(II) anions (1.24 A), so one way to view this reaction is through cation migration. The zinc cations need to extract themselves from their oxide octahedral hole and move to the chromium compound to find an available tetrahedral hole. Simultaneously, chromium cations are moving in the direction of the zinc compound. After a few exchanges of cations, the two crystallites look as shown in Figure 5.2. 

Organochromium species containing tt-bonded ligands were first prepared by Hein as early as 1919, but were not definitively characterized for another 35 years. Hein reported on the reaction of PhMgBr with CrCb to give Chromorganoverbindungen this synthesis was reproduced by Zeiss and Tsutsui in 1954, at which time they identified the products as bis(arene)chromium cations. Shortly thereafter, Fischer and Haftier published their route to neutral bis(benzene)chromium. This early work has been chronicled, most recently by Seyferth. ... 

The aforementioned requirements on surface stability are typical for all exposed areas of the metallic interconnect, as well as other metallic components in a SOFC stack (e.g., some designs use metallic frames to support the ceramic cell). In addition, the protection layer for the interconnect, or in particular the active areas that interface with electrodes and are in the path of electric current, must be electrically conductive. This conductivity requirement differentiates the interconnect protection layer from many traditional surface modifications as well as nonactive areas of interconnects and other components in SOFC stacks, where only surface stability is emphasized. While the electrical conductivity is usually dominated by their electronic conductivity, conductive oxides for protection layer applications often demonstrate a nonnegligible oxygen ion conductivity as well, which leads to scale growth beneath the protection layer. With this in mind, a high electrical conductivity is always desirable for the protection layers, along with low chromium cation and oxygen anion diffusivity. 

Bisarene chromium compounds have been shown to undergo reversible exchange with aromatic hydrocarbons in the presence of aluminum trihalides (207). The exchange reaction has been used to improve the preparation of the bisbenzene chromium cation via the more readily prepared bismesitylene chromium cation 157b). 

Bisbenzene chromium reacts with good 77-acceptor Lewis acids to form complexes (CgHg)2Cr L" (L = tetracyanoethylene, trinitrobenzene, -quinone, chloranil) in which electron transfer from the (CgHg)2Cr to the Lewis acid has taken place. The complexes are best described as bisbenzene chromium cation salts of radical anions (765). The crystal structure of one such compound [(MeCgHg)2Cr] (TCNQ) (TCNQ = 7,7,8,8-tetracyanoquinodimethane) has been determined and consists of Stacks of TCNQ anions and bisbenzene chromium cations with interplanar spacings of 3.42 A (577). 

The reaction can be made catalytic by addition of NaaS204 which reduces the bisarene chromium cation formed back to the neutral species 192). 

Disproportionation of the bis (biphenyl) chromium cation is observed in the photoreaction with dipyridyl (Dipy.) in water or methanol 223> ... 

The high initial activity of the fresh alumocopperchromium catalyst in the oxidation of carbon monoxide is due to Cufll) cations within the copper chromite and in CuO surface clusters (Fig 1) Centres with chromium cations in the highest oxidation degrees are bound to the support surface and solid solutions of the aluminate type. These contain cations of bivalent copper and are less active in the CO oxidation reaction. It was shown by IRS and XPS that during the use of this catalyst in CHG, as well as during the unsteady-state oxidation reaction/ a partial reduction of Cu(II) to Cu I occurs (Fig, 2), which leads to a decrease in catalyst activity in the oxidation of the carbon monoxide. In the fresh alumomagnesiumchromium catalyst, the activity for carbon monoxide is determined by the centres containing chromium cations in... 

In each case, the coordination number of the chromium cation is 6. 

A less accurate value for of -l-0-74(7) had been derived previously from the spectra at 80 K of CuCraTe, which is a ferromagnetic spinel [66]. The apparent doublet spectrum corresponds to an unresolved magnetic splitting of 148(5) kG. Again the field is produced by spin polarisation, this time by the magnetic chromium cations. 

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