Chromium thiocyanate

SCN- is the thiocyanate ion). Consider the oxidation number of chromium to be +3 and the coordination number to be 6 in both compounds. Estimate... 

The salt, prepared in carbon tetrachloride solution, exploded feebly several times as the reaction proceeded. Oxidation of thiocyanate by chromium(VI) is postulated. 

Nitric acid, fuming phite, thiocyanates Organic matter, nonmetals, most metals, ammonia, chlorosulfonic acid, chromium trioxide, cyanides, dichromates, hydrazines, hydrides, HCN, HI, hydrogen sulfide, sulfur dioxide, sulfur halides, sulfuric acid, flammable liquids... 

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. 

Trithiocyanato-triammino-chromium, [Cr(NH3)3(SCN)3], is formed by heating thioeyanato-pentammino-chromie thiocyanate, [Cr(NH3)5SCN](SCN)2, at 130° to 140° C. till the odour of ammonia disappears. The residue is rubbed with water, any unchanged pent-ammino-salt dissolves, and treatment is continued until the filtrate is only very feebly coloured trithiocyanato-triammino-chromium is thereby left as a light red powder. It is almost insoluble in cold water, sparingly soluble in hot water, and soluble in pyridine.3... 

Nondestructive reactions of trisacetylacetonates of chromium(lll), cobalt(lll), and rhodium(lll) are reviewed. Halogenation, nitration, thiocyanation, acylation, formylation, chloromethylation, and aminomethylation take place at the central carbon of the chelate rings. Trisubstituted chelates were obtained in all cases except acylation and formylation. Unsymmetrically and partially substituted chelates have been prepared. Substitutions on partially resolved acetylacetonates yielded optically active products. NMR spectra of unsymmetrically substituted, diamagnetic chelates were interpreted as evidence for aromatic ring currents. Several groups were displaced from the chelate rings under electrophilic conditions. The synthesis of the chromium(lll) chelate of mal-onaldehyde is outlined. 

The vast majority of known chromium(III) complexes with the ambidentate chalcogenocyan-ate ligands NCO-, NCS-, NCTe- are those containing JV-bonded thiocyanate. 

The products of reduction of Fe(NCS)2+ by Cr2+ in aqueous solution containing thiocyanate ions (equation 36), include the isomers of [Cr(NCS)(SCN)(H20)4]+, which contains both bland S-bonded thiocyanate ligands.641 These isomers undergo spontaneous decomposition by parallel aquation (loss of the S-thiocyanato ligand) and isomerization (Cr—SCN— Cr—NCS) reactions. Details of the solution visible spectra of these isomers as well as those of similar chromium(III) complexes for comparison are listed in Table 68. From the compiled data it is apparent that the S-bonded thiocyanate ligand lies very close to Br- in the spectrochemical series while the N-bonded form lies between Nj and NO. 

The addition of en or 1,3-diaminopropane to a mixture of chromium(III) acetate hexahy-drate and diacetyl under reflux, followed by addition of NaC104, has given the complexes [Cr(diacen)(H20)2]C104 and [Cr(diacpn)(H20)2]C104, which contain the tetradentate Schiff bases (234).1119 The thiocyanates [CrL(H20)(NCS)](NCS)2 were also isolated. From their IR spectra, and because the coordinated Schiff base would not react with another molecule of diacetyl to form a macrocycle, they have been assigned cis configurations. 

Twenty grams of chromium nitrate 9-hydrate, or 0.05 moles of the hydrated sulfate or chloride, are fused with 30g of potassium thiocyanate as in (I), and the melt allowed to cool in a desiccator and then triturated with 25ml portions of ethyl acetate until no more material dissolves. The violet liquid is filtered a small green residue remains behind together with the potassium nitrate, sulfate, or chloride. The ethyl acetate extract is evaporated to dryness on the steam bath and the violet residue is further dried in vacuo. The anhydrous salt is violet. 

This analogue is easily prepared by evaporating the equivalent quantities of chromium chloride 6-hydrate and ammonium thiocyanate in aqueous solution to dryness on the steam bath and extracting the residue with absolute alcohol. Evaporation of the alcoholic extract yields the red salt. 

Ten grams of dl tris(ethylenediamine)chromium (III) thiocyanate monohydrate are heated at 130-135°C in an open Petri dish as for the cts-dichloro chloride (No. 124). The heating may be performed in a sand bath or thermostat oven. When the material lias lost at least 16% of its original weight (theory = 18.4%) the decomposition is complete for practical purposes. The crude material is quickly recrystallised from water at 50-60°C, filtered, then dried in air,... 

PROBLEM 20.4 What is the formula of the chromium(III) complex that contains two ammonia and four thiocyanate (SCN-) ligands ... 

Reducing substances, hexavalent chromium and colored matter, interfere with the test. Reducing substances that may reduce Fe3+ to Fe2+ and thus prevent the formation of thiocyanate complex, may be destroyed by adding a few drops of H202. Add FeS04 to convert CC+ to Cr3+ at a pH below 2. Cr3+ and Fe3+ so formed are precipitated out when the pH is raised to 9 with NaOH. 

Bis(2,4-pentanedionato)oxovana-dium(IV), 5 113-115 Bis(8-quinolinolato)dioxouranium-(VI), and its addition compound with 8-quinolinol, 4 101 Jrans-Bis (thiocyanato)bis (ethylene-diamine)chromium(III) thiocyanate, 2 200, 202 Bis(triphenylgermyl)oxide, 5 78 Bis[tris(2,4-pen tanediono)titanium-(IV) jhexachlorotitanate(I V), 2 119... 

Tris (ethylenediamine) chromium-(III) iodide, 1-hydrate, 2 199 Tris (ethylenediamine) chromium-(III) sulfate, 2 198 Tris (ethylenediamine) chromium-(III) thiocyanate, 1-hydrate, 2 199... 

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