Thiocyanates metal complexes

I , oxidation with I2, oxidation with lOT j oxidation of thiocyanate-metal complexes, bromination and reduction with I , Sn2 substitution and oxidation with Br2, and complexation of cations with ethylenediaminetet-raacetic acid (EDTA) in the presence of Pb(I03)2. 

The amplification of SCN can be used as a basis for the amplification of metals by oxidation of thiocyanate metal complexes and several examples of this have been published, such as the ampHfication of Pb after formation of Pb(SCN)3[N(C4H9)4], in which lPb=114I, or after forming Pb3[Cr(SCN)6]2, in which lPb= 1521, and the amplification of bismuth via formation of Bi[Cr(SCN)6] or Bi(SCN)6[N(C4H9)4]3, in which cases an amplification factor of 228 is obtained. 

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. 

In some cases, the metal complex contains both piperidine and thiocyanate as ligands, as illustrated by the following equation ... 

The efficiency of the extraction depends on the coordinating ability of the solvent, and on the acidity of the aqueous solution which determines the concentration of the metal complex. Coordinating ability follows the sequence ketones > esters > alcohols > ethers. Many metals can be extracted as fluoride, chloride, bromide, iodide or thiocyanate complexes. Table 4.5 shows how the extraction of some metals as their chloro complexes into diethyl ether varies with acid concentration. By controlling... 

Boucabeille C, Bories A, Ollivier P, et al. 1994b. Microbial degradation of metal complexed cyanides and thiocyanate from mining wastewaters. Environ Poll 84(l) 59-67. 

At the Homestake Mine in Lead, South Dakota, 48 RBCs were installed to treat 5.5 million gallons of discharge water per day. The system degraded thiocyanate, free cyanide, and metal-complexed cyanides, and also removed ammonia, which is a by-product of cyanide degradation. Over time, as the system became more efficient, the cost to treat cyanide dropped from 11.79 to 3.10/kg (D15372K, p. 6). 

The effect of halide, cyanate, cyanide, and thiocyanate ions on the partitioning of Hg in [BMIM][PF6]/aqueous systems (Figure 3.3-2) has been studied [8]. The results indicate that the metal ion transfer to the IL phase depends on the relative hydrophobicity of the metal complex. Hg-I complexes have the highest formation constants, decreasing to those of Hg-F [42]. Results from pseudohalides, however, suggest a more complex partitioning mechanism, since Hg-CN complexes have even higher formation constants [42], but display the lowest distribution ratios. 

While the liquid-liquid extraction of inorganic elements as coordination complexes with thiocyanate ions can be traced back to Skey (1867), the extraction from hydrochloric acid into ether of iron(III) (J. W. Rothe, 1892) or gallium (E. H. Swift, 1924) depends on the formation of solvated acido complexes derived from HMC14 extractions of metal complexes from nitric, thio-cyanic, hydrofluoric, hydrochloric and hydrobromic acids were studied exhaustively by Bock and his collaborators (1942—1956).6... 

Acoustic emission diazine metal complexes, 80 Acrylonitrile metal complexes, 263 Actinide complexes cupferron, 510 dimethyl sulfoxide IR spectra, 490 phosphines SHAB theory, 1040 phthalocyanines, 864 thiocyanates, 236 Actins, 973 Acylates H3-ligands... 

Many agents that reduce blood pressure in man have metal-complexing ability, including sodium azide, sodium thiocyanate, dimercaptopropanol, hydralazine and, possibly, sodium nitroprusside. 

Seven-coordinate three-dimensional metal complexes are considered to be quite unstable and kinetically labile species, and their solution chemistry is largely undefined. Over the last few years it was shown that these species exhibit extremely interesting chemical properties and catalytic activity. They can catalyze disproportionation of deleterious superoxide radicals, even faster than natural enzymes, and therefore this became a challenging research area. Recently, Rudi van Eldik reported a detailed rapid-scan stopped-flow kinetic study of the substitution behavior of the seven-coordinate [Fe(dapsox)(L)2]C104 complex with thiocyanate as a function of the thiocyanate concentration, temperature, and pressure in protic and aprotic organic solvents. 

Ultrasonic nebulizers have also been employed in continuous flow systems as interfaces between sample preparation steps in the analytical process and detection by virtue of their suitability for operating in a continuous mode. Thus, preconcentration devices have commonly been coupled to atomic spectrometers in order to increase the sensitivity of some analytical methods. An enhancement factor of 100 (10 due to USNn and 10 due to preconcentration) was obtained in the determination of platinum in water using a column packed with polyurethane foam loaded with thiocyanate to form a platinum-thiocyanate complex [51]. An enhancement factor of 216 (12 with USNn and 18 with preconcentration) was obtained in the determination of low cadmium concentrations in wine by sorption of metallic complexes with pyridylazo reagents on the inner walls of a PTFE knotted reactor [52]. One special example is the sequential determination of As(lll) and As(V) in water by coupling a preconcentration system to an ICP-AES instrument equipped with a USN. For this purpose, two columns packed with two different resins selective for each arsenic species were connected via a 16-port valve in order to concentrate them for their subsequent sequential elution to the spectrometer [53]. 

A number of mixed metal complexes containing bridging thiocyanate groups have been described in the previous section. In general, the sulfur atom coordinates to the class b or softer metal and the nitrogen end of the bridge bonds to the class a or harder metal. 

The advantage of this explanation of thiocyanate coordination is that it does allow a description that fits both classes a and b metal complexes, although there are some examples that do not fit. It is not clear Avhy in Rh(PPhg)2L(CNS) the N isomer should be obtained for L = pip, and the S isomer for L = MeCN (35). Manganese(I) has to be treated as a class a acid, the same approach as is used for it to fit with... 

---