Cyanide complexes chromium

Entries where the oxidation state of a metal has been specified occur after all the entries for the unspecified oxidation state, and the same or similar entries may occur under both types of heading. Thus cyanide appears under Chromium complexes, Chromium(O) complexes, Chromium(I) complexes, etc. More specific entries, such as Chromium, hexacyano-, may also occur. Similar ligands may also occur in different entries. Thus a carboxylic acid-metal complex may occur under Carboxylic acid complexes, under entries for specific carboxylic acids, and under the specific metal. Coordination complexes may also be listed in the Cumulative Formula Index. 

Chromium, (ri6-benzene)tricarbonyl-stereochemistry nomenclature, 1,131 Chromium complexes, 3,699-948 acetylacetone complex formation, 2,386 exchange reactions, 2,380 amidines, 2,276 bridging ligands, 2,198 chelating ligands, 2,203 anionic oxo halides, 3,944 applications, 6,1014 azo dyes, 6,41 biological effects, 3,947 carbamic acid, 2,450 paddlewheel structure, 2, 451 carboxylic acids, 2,438 trinuclear, 2, 441 carcinogenicity, 3, 947 corroles, 2, 874 crystal structures, 3, 702 cyanides, 3, 703 1,4-diaza-1,3-butadiene, 2,209 1,3-diketones... 

After these subcategorization bases were evaluated, raw waste characterization was selected as the basis for subcategorization. The raw waste characterization is divided into two components, inorganic and organic wastes. These components are further subdivided into the specific types of wastes that occur within the components. Inorganics include common metals, precious metals, complexed metals, hexavalent chromium, and cyanide. Organics include oils and solvents. 

There is a difference between the thermodynamic terms stable and unstable and the kinetic terms labile and inert. Furthermore, the differences between the terms stable and unstable, and labile and inert are relative. Thus, Ni(CN)4 and Cr(CN)6 are both thermodynamically stable in aqueous solution, yet kinetically the rate of exchange of radiocarbon-labeled cyanide is quite different. The half-life for exchange is about 30 sec for the nickel complex and 1 month for the chromium complex. Taube has suggested that those complexes that react completely within about 60 sec at 25°C be considered labile, while those that take a longer time be called inert. This rule of thumb is often given in texts, but is not in general use in the literature. Actual rates and conditions are superior tools for the evaluation of the kinetic and thermodynamic stability of complexes. 

The extensive organometallic chemistry of chromium, i.e. the hexacarbonyl and its derivatives, organochromium compounds without carbonyl ligands, cyanide and isocyanide complexes, alkene, allyl, diene, cyclopentadiene and arene derivatives, and complexes of a-donor carbon ligands, has been recorded in Chapters 26.1 and 26.2 of Volume 3 of Comprehensive Organometallic Chemistry .1 In the present section, chromium complexes... 

Rollier, M. A. and E. Arreghini Structure of Copper Salts of Some Complex Cyanides I. Structure of Copper Salts of the Hexacyanides of Cobalt and Chromium. Gazz. chim. Ital. 69, 499 (1939). 

As with the analogous chromium complexes (420), anions (R ) such as hydride, cyanide, alkoxide, etc., add to cyclohexa- or cyclohepta-dienyliron complexes to form the sub.stituted species of structure (107) (299). Reduction of the cycloheptadienyliron cation with zinc dust... 

The chromous salts, derived from the oxide CrO, arc analogous to the salts of divalent vanadium, manganese, and iron. This is seen in the isomorphism of the sulphates of the type R" SOj-THgO. The stability of such salts increases in the order of the atomic number of the metal. The chief basic oxide of chromium is the sesquioxidc CraO, which is closely allied to ferric oxide, and, like the latter, resembles aluminium oxide. The hydroxide, Cr(OH)3, with bases yields chromites analogous to, but less stable than, the aluminates. Chromic sulphate enters into the formation of alums. The chromic salts are very stable, but in the trivaJent condition the metal shows a marked tendency to form complex ions, both anions and cations thus it resembles iron in producing complex cyanides, whilst it also yields compounds similar to the cobaltamines. 

The entire electroplating process generates complex wastewater streams. For the purpose of treatment these can be considered to occur in four segments — acid, alkali, chromium and cyanide streams [29]. The acid and alkali wastes are combined and the pH adjusted. The chromium is reduced from Cr to Cr " with sulphur dioxide at pH 2-3. The cyanides are destroyed with chlorine or hypochlorite. Destruction of cyanides is essential for effective precipitation of the heavy metals, as they form strong complexes with the metals and thereby increase... 

The peach-colored band containing this species can be eluted from the cation-exchange column with 0.10 M sodium perchlorate solution at pH 2.5. (Analysis of such solutions gave chromium to cyanide ratios of 1 to 2.00 within experimental error.) The visible and ultraviolet absorption spectrum of the dicyanp complex is shown in Fig. 4 and is independent of pH in the region from 2.0 to 4.0. The position of the maxima (in mfi) and corresponding... 

This complex was found to constitute 20 % of the hydrolysis mixture and can be eluted from the column with 0.6 M sodium perchlorate solution adjusted to pH 2.0. A chromium to cyanide ratio of 1 1.00 was determined by analysis for this pink, permanganate-colored species. The visible and ultraviolet spectrum of cyanopentaaquochromium(III) ion is independent of pH in the regions from 2 to 3.5 and is included in Fig. 4. The positions of the maxima (in mp) and corresponding molar absorbancy indices (in / mole cm ) in 0.6M sodium perchlorate are 525 (26.0), and 393 (20.5). The strong absorption band in the ultraviolet shows a point of inflection a = 268 I mole" cm" ) at 235 mp. The positions of the absorption maxima are identical to those reported by Espenson. Dilute solutions (pH 2) of the monocyano complex can be stored at 0° for several days without serious decomposition. 

In the plating industry, rinse waters contain many of the following contaminants, usually in intolerable amounts hexavalent chromium sodium cyanide complex cyanides of the heavy metals, such as cadmium, copper, zinc, and sometimes silver and gold soluble nickel salts strong mineral acids and strong alkalis. Of these, the most toxic are the hexavalent chromium and cyanide ions. 

Precipitation is often applied to the removal of most metals from wastewater including zinc, cadmium, chromium, copper, fluoride, lead, manganese, and mercury. Also, certain anionic species can be removed by precipitation, such as phosphate, sulfate, and fluoride. Note that in some cases, organic compounds may form organometallic complexes with metals, which could inhibit precipitation. Cyanide and other ions in the wastewater may also complex with metals, making treatment by precipitation less efficient. A cutaway view of a rapid sand filter that is most often used in a municipal treatment plant is illustrated in Figure 4. The design features of this filter have been relied upon for more than 60 years in municipal applications. 

This is by far the most stable and best-known oxidation state for chromium and is characterized by thousands of compounds, most of them prepared from aqueous solutions. By contrast, unless stabilized by M-M bonding, molybdenum(III) compounds are sparse and hardly any are known for tungsten(III). Thus Mo, but not W, has an aquo ion [Mo(H20)g] +, which gives rise to complexes [MoXg] " (X = F, Cl, Br, NCS). Direct action of acetylacetone on the hexachloromolybdate(III) ion produces the sublimable (Mo(acac)3] which, however, unlike its chromium analogue, is oxidized by air to Mo products. A black cyanide,... 

The reaction is a sensitive one, but is subject to a number of interferences. The solution must be free from large amounts of lead, thallium (I), copper, tin, arsenic, antimony, gold, silver, platinum, and palladium, and from elements in sufficient quantity to colour the solution, e.g. nickel. Metals giving insoluble iodides must be absent, or present in amounts not yielding a precipitate. Substances which liberate iodine from potassium iodide interfere, for example iron(III) the latter should be reduced with sulphurous acid and the excess of gas boiled off, or by a 30 per cent solution of hypophosphorous acid. Chloride ion reduces the intensity of the bismuth colour. Separation of bismuth from copper can be effected by extraction of the bismuth as dithizonate by treatment in ammoniacal potassium cyanide solution with a 0.1 per cent solution of dithizone in chloroform if lead is present, shaking of the chloroform solution of lead and bismuth dithizonates with a buffer solution of pH 3.4 results in the lead alone passing into the aqueous phase. The bismuth complex is soluble in a pentan-l-ol-ethyl acetate mixture, and this fact can be utilised for the determination in the presence of coloured ions, such as nickel, cobalt, chromium, and uranium. 

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