Solution structures, chromium complexes

A. Levina and P. A. Lay, Solution structures of chromium(V) complexes with glutathione and model thiols, Inorg. Chem., 43 (2004) 324-335. 

Acid dyes include metal-complexed azo structures, where the metals used are cobalt, chromium, and iron.10 Examples are 1 1 and 2 3 chromium complexes and 1 2 cobalt complexes, where the numbers employed represent the ratio of metal atoms to dye molecules. Metal-complexed dyes can be formed inside textile fibers by treating suitably dyed fibers with a solution containing metal ions.11 In this case, the metal-free forms of these azo dyes are known as mordant dyes and contain mainly ortho, ortho -bis-hydroxy or ortho-carboxy, ortho -hydroxy groups (e.g., C.I. Mordant Black 11, Mordant Yellow 8, and Mordant Orange 6). When the metal complexes are formed prior to the dye application process, the resultant dyes are known as... 

Arene tricarbonyl chromium complexes are yellow to red, often crystaUine compounds. They are stable to air in the sohd state and can be stored for long periods provided that they are kept out of light. In solution, they are weakly to moderately air-sensitive. They are best purified by crystalhzation but other methods like sublimation, flash chromatography, and HPLC are generally applicable. This as well as the following sections focus on synthetic procedures. For a description of bonding- and structural characteristics, the reader is referred to the speciahst literature [1]. 

The structure of blue crystals of sodium bis(L-cysteinate)chromium(III) dihydrate, 1, which formed from a neutral aqueous solution of chromium(III) nitrate and L-cysteine, was found to be a slightly distorted octahedron with the Cr bound to two carboxylate oxygens and two amino nitrogens (mutually cis) and to two sulfur atoms (trans). This complex was found to be subject to acid hydrolysis which caused rapid cleavage of the chromium-sulfur bond and resulted in formation of the red-violet complex, Cr(H20)2(L-cysteinate-0,N)2,... 

The crystal structure of L-histidinato-D-pencillaminatochromium(III) monohydrate has been determined The complex was synthesized from chromium(III) chloride, l-histidine and D-penicillamine in aqueous solution. The chromium(III) was coordinated to the N, S, and O of penicillamine and the N, O and imidazole (N) of histidine in an approximately octahedral geometry. Thus, both cysteine and penicillamine form complexes with Cr(III) which contain Cr-S bonds. 

The X-ray crystal structures of the cycloheptatrienc complexes [M(q6-C7Hg)(CO)3] (M = Cr, W) have been determined and their solution structure investigated. The chromium cycloheptatrienc complexes [Cr(n C7H8)(CO)3] was rcported to react with a variety of alkenes to give photoinduced [6jt + 2n] reactions. 

Hexa-aquo complexes of trivalcnt elements are stable in an acidic medium at room temperature. Hydroxylation of these complexes by water may, however, take place by heat treatment (see Section 1.4). Heating of an acid solution of Al(III) ions to about 80-100 °C cau.ses the formation of boehmite 7-AIOOH [67,68]. In similar conditions, Fe(IIl) forms hematite. Thermolysis of acid solutions of chromium causes the formation of oxyhydroxidcs of poorly defined structure, as well as... 

The coupling of Naphtol AS or its phenyl-substituted derivatives with diazonium salts from variously substituted anilines in aqueous alkaline solution (section 4-11) gave incomplete reactions and impure products in some instances, probably because these coupling components have inadequate solubility in aqueous media. Pure dyes in ca. 90% yields were obtained by reaction in dimethylformamide in the presence of sodium acetate. Metallisation of these o,o -dihydroxyazo ligands with sodium chromium salicylate or a cobalt(II) salt gave metal-complex dyes in 80-100% yields [22]. Specific structural isomers of these complexes were identified by i.r., n.m.r., Raman and UV/visible spectroscopy [23]. 

This is an alternative method of introducing copper into an o-hydroxyazo dye structure. The azo compound is treated with a copper(II) salt and an oxidant in an aqueous medium at 40-70 °C and pH 4.5-7.0. Sodium peroxide, sodium perborate, hydrogen peroxide or other salts of peroxy acids may be used as oxidants, the function of which is to introduce a second hydroxy group in the o -position [25]. This process is reminiscent of earlier work on Cl Acid Red 14 (5.51 X = H), an o-hydroxyazo dye that will not react with a chromium (III) salt to form a 1 1 complex but will do so by oxidation with an acidified dichromate solution. This oxidation product was later found to be identical with that obtained by conventional reaction of Cl Mordant Black 3 (5.51 X = OH) with a chromium(III) salt [7]. 

Let us start with the Ni(II) complexes of the already mentioned scorpiand diammac (6,13-diammino-6,13-dimethyl-1,4,8,11-tetraazacy-clotetradecane) in its two cis and trans conformations. In contrast to the previously mentioned chromium-, iron-, and cobalt-diammac complexes, in which the geometry of [M(fra s-diammac)]" + was substantially octahedral and that of the [M(cw-diammac)]" + was substantially trigonal prismatic, in the case of both [Nif/raws-diammac)]2+ and [Ni(m-diammac)]2 + the structural differences are attenuated and both can be viewed as more or less distorted octahedral geometries, with two sets of averaged Ni-N bond lengths of 2.07 A and 2.13 A, respectively.161 162 This is reflected by the fact that both the two complexes exhibit in aqueous solution a chemically reversible Ni(II)/Ni(III) oxidation ([Nif/raws-diammac)]2 + E° = + 0.67 V vs. SHE [Ni(m-diammac)]2 + ... 

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