Cobalt complexes thiocyanates

According to X-ray data, 2,5-diamino-l,3,4-triazole retains its diamino form in the heterovalent cobalt complex 375 (91IC4858) and in the polymeric complex with manganese thiocyanate (93ICA53). 

One-phase titration methods have also been developed. These methods are not truly one-phase titrations but the term is used to indicate the absence of a second organic phase. One of these methods, applied to the analysis of sodium and triethanolamine lauryl sulfates and lauryl ether sulfates, use a quaternary amine as a titrant and cobalt(II) thiocyanate as indicator. Centrimide was found to avoid the use of chloroform which was not possible with other titrants examined, such as domiphen bromide and oxyphenonium bromide. The pink color of the indicator changes to violet as an excess of titrant forms a complex with the indicator [238]. 

Hassan et al [65] used a method for the determination of primaquine and other antimalarials, through ternary complex formation. The analytical aspects of the reaction between the widely used antimalarial drugs with cobalt and thiocyanate to form ternary complexes are described. Alternatively, determination of the cobalt content of the nitrobenzene extract using atomic absorption spectroscopy provided an indirect method for the determination of the drugs. Both methods are applied to the analysis of pharmaceutical preparation and the results obtained agreed well with those obtained with official methods. 

Dr. Pearson presented data on the optical density observed when the nitrato-cobaltic complex reacts with thiocyanate ion, and there is nothing to object to in these results. But I think one might be concerned about the theoretical curve calculated using the competition ratio in a table wrhich Haim and Taube presented in the journal. 

The amount of ammonia volatilized was determined from the amount of standard sulfuric acid consumed in the traps. Ethylenediamine was determined by the salicylaldehyde method (14). The sample for cobalt(II) determination was made slightly acidic with hydrochloric acid immediately upon removal of the sample from the reaction flask, in order to prevent further oxidation of the cobalt (18). The carbon was removed by filtration, and the cobalt (II) concentration was determined spectrophotometrically as the cobalt-ammonium thiocyanate complex, (NH4)2Co(NCS)4 (28). 

Electronic effects become apparent in the M—NCS/M—SCN linkage switches observed in a series of Pd11 (iso)thiocyanate complexes. Ligands positioned trans to the pseudohalide and that are suited to accept electron density from the metal into empty orbitals (backbonding) stabilize the Pd—NCS linkage isomer. However, this rationale is contradicted by the trend in Co—(NCS) bonding in a series of cobalt complexes (see ref. 204b for a review). 

Bautista and Hard (B8) made a comparative study of the extractability of. several of the first-transition metals from thiocyanate solutions using methyl isobutyl ketone as the organic solvent. The transition metals readily extracted were scandium (III), iron (III), and cobalt (II) while chromium (II) and manganese (II) were not. The principal extractable species were found to be the neutral scandium and iron trithiocyanate complexes, while the extractable cobalt complex was the negatively charged tetrathiocyanate radial Co(SCN)4 . The distribution ratio for scandium, iron, and cobalt decreased with increase in metal ion concentrar tion but increased with increasing ionic strength of the solutions. 

The cobalt(ll) thiocyanate complex can be extracted with oxygen-containing solvents, such as a mixture of diethyl ether with isoamyl alcohol (1+1), MIBK, or acetylacetone [23,24], The molar absorptivity, e, of the complex in the ether-isoamyl aleohol mixture is about 30% smaller than in the aqueous acetone media. 

The anionic cobalt(II) thiocyanate complex reacts with many organic bases to form ion-associates which can be extracted into CHCI3, or other non-polar solvents. Organic reagents used for this purpose include DAM [25], TOA [26], triphenylsulphonium ion [27], or 2,4-dichlorobenzyltriphenylphosphonium ion [28],... 

Amodiaquine reacts with cobalt and thiocyanate to yield stable ternary complexes. These complexes are readily extractable in nitrobenzene to give a greenish-blue color with maximum absorption at 625 nm that can be used for quantitative determination. The mean recoveries for authentic samples of amodiaquine hydrochloride are 100.81 1.77% (p = 0.05). Alternatively, determination of the cobalt content of nitrobenzene extract by atomic absorption spectroscopy provides an indirect method for the determination of the drug with a mean recovery of 99.99 2.16%. Both the methods have been successfully applied to the assay of the drug in pharmaceutical preparations (30). 

As with most complexation and drug solubility situations, pH b a critical variable. Cocaine base b not soluble in water, and if the drug b in thb form rather than a soluble salt, no reaction occurs. Acid b needed to ensure that the cocaine b in the water-soluble ionic form to allow for the formation of a complex. The color b the result of an ion-pair compound formed from the cationic cocaine and the anionic cobalt complex. As with all amine bases, such as ammonia, the base becomes protonated in acidic solution. The pKg of the base determines the ratio of the protonated, ionized form to the neutral form. It is possible to add too much HQ, because cobalt forms a water-soluble pink complex with chloride [CoCy . The pH can also influence the type of complex and ion pair formed. Under acidic conditions, the ion pair favored b [Co(cocaine)2l(SCN)2 (which b pinkbh and soluble in water), while in the neutral-to-basic ranges, the ion pair b assigned the structure [cocaine-H ]2 [Co(SCN)4] (which b a blue solid and soluble in chloroform). The important points of the cobalt thiocyanate reaction with cocaine are summarized in Figures 7.24r-7.26. 

Mercury(n) is also an effective catalyst for pseudohalide leaving groups, for example thiocyanate. In this connection, recently determined equilibrium data for complex formation between cobalt(ra)-thiocyanate complexes and mercury(n) are of relevance. ... 

The thiocyanate ion SCN forms an intensely red-coloured complex (most simply represented as [Fe(SCN)(H20)5] ) which is a test for iron(III). However, unlike cobalt(III), iron(lll) does not form stable hexammines in aqueous solution, although salts containing the ion [FefNHj) ] can be obtained by dissolving anhydrous iron(III) salts in liquid ammonia. 

Arsonium salts have found considerable use in analytical chemistry. One such use involves the extraction of a metal complex in aqueous solution with tetraphenyiarsonium chloride in an organic solvent. Titanium(IV) thiocyanate [35787-79-2] (157) and copper(II) thiocyanate [15192-76-4] (158) in hydrochloric acid solution have been extracted using tetraphenyiarsonium chloride in chloroform solution in this manner, and the Ti(IV) and Cu(II) thiocyanates deterrnined spectrophotometricaHy. Cobalt, palladium, tungsten, niobium, and molybdenum have been deterrnined in a similar manner. In addition to their use for the deterrnination of metals, anions such as perchlorate and perrhenate have been deterrnined as arsonium salts. Tetraphenyiarsonium permanganate is the only known insoluble salt of this anion. 

For colorimetric or gravimetric determination l-nitroso-2-naphthol can be used. For chromatographic ion exchange (qv), cobalt is isolated as the nitroso-(R)-salt complex. The cyanate complex is used for photometric determination and the thiocyanate for colorimetry. A rapid chemical analysis of... 

Thiocyanate ions form stable complex salts, e. g. intense red with iron(lll) and pale blue with cobalt(ll) cations. 

A warmed alcoholic solution of cobalt(Il) nitrate and 2-formylpyridine S-methyldithiocarbazate, 6, yielded diamagnetic [Co(6-H)2]N03 [126]. However, cobalt(II) chloride, bromide and thiocyanate yielded complexes with cobalt(III) cations and cobalt(II) anions, [Co(9-H)2]2 [C0A4]. 

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