Chromium complexes with chloride bridges

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,... 

Complexes 7-10 are dimerized through bridging of the terphenyl bound chromiums by the chlorides. For 9 and 10, the bridging chloride positions are contaminated with iodide due to its inclusion as a Lil impurity in the ArLi salt. The structures... 

Binuclear difluoro-bridged chromium complexes are rare and the only well-characterized previous example is the multidentate Cr(in) derivative [A, A"-(2-0-3, 5- Bu2-C6H2-CH2)2-1,2-NHCH2CH2NH]Cr(p,-F) 2 [25]. The terphenyl stabilized chromium fluoride 4-CF3-Ar Cr(p,-F) 2 (11) was obtained by decomposition during the reduction of 4-CF3-Ar Cr(p,-Cl) 2 with KCg in THF. Unlike the generally blue color observed for the chlorides, 11 has a pale purple color. 

The reaction of anhydrous MnCl2 with Ar Li in THF was performed by following the same routine used for the preparation of the chromium chlorides. However, instead of the simple chloride-bridged species Ar Mn(p,-Cl) 2 , colorless crystals of the LiCl inclusion complex (Ar MnCl)2Li2Cl2(THF)3 (13) [31] were isolated. 

The inertness of the dinuclear complexes is greatest in slightly acidic solutions, which therefore have been employed for the reprecipitation reactions. Apparently the chromium systems are much more labile toward bridge breaking than are the cobalt systems. In aqueous solution the meso-[(en)2Cr(OH)2Ci(en)2] cation (I) enters into a rapidly established (t 1 min. at room temperature) equilibrium with the mono-ju-hydroxo complex [(OHXen)2Cr(OH)Cr(en)2-(HaO)] (n) The equilibrium constant K = [II]/[I] is 0.83 in 1 Af NaC104 at 0°. The salts (dithionate, bromide, chloride, and perchlorate) of the di-p-hydroxo cation are less soluble than the respective salts of the mono-/i-hydroxo cation. It is therefore possible to precipitate the pure salts of the di-/i-hydroxo cation from the equilibrium mixture following the procedure given above. 

Synthesis of amine-chromium(III) complexes often involves controlled solid-phase heating, with ammonium halide catalysts employed to break up the crystal lattice. Recently the effect of ammonium chloride on the deamination of [Cr(en)3]X3 has been investigated. When X = Cl", cw-[Cr(en)2X2]X is known to form, and when X = NCS" the trans product is produced.However, in the presence of a large amount of NH4NCS some cw-dithiocyanato complex is also formed. Bridged complexes are believed to be involved [e.g., Cr3(en)7Cl9]. 

Catalysis.—An investigation of the catalysis of aquation of cis- and /ra/ij-[Cr(OH2)4Q2] by Hg + has been followed by an investigation of catalysis of these reactions by species HgX+, where X = Cl, Br, I, or CN rate laws and activation parameters are reported for these four catalysts. Whereas there is evidence for a doubly bridged intermediate in the Hg +-catalysed aquation of c/j-[Cr(OH2)4Cl2l+, there is no evidence for such an intermediate in the HgQ+-catalysed aquation of this complex. This difference in behaviour reflects the much lower stability of HgCla" units than of HgCla- The relative effectiveness of metal ions M"+, for example Ag+, Hg +, or Tl +, in promoting aquation of chromium(in)-chloride complexes can be correlated with the hardness or softness of these catalysts. ... 

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