Thiourea chromium complexes

A combination of IPC and inductively coupled plasma (ICP) MS was extensively explored for the speciation of phosphorus, arsenic, selenium, cadmium, mercury, and chromium compounds [108-118] because it provides specific and sensitive element detection. Selenium IPC speciation was joined to atomic fluorescent spectrometry via an interface in which all selenium species were reduced by thiourea before conventional hydride generation [119], Coupling IPC separation of monomethyl and mercuric Hg in biotic samples by formation of their thiourea complexes with cold vapor generation and atomic fluorescence detection was successfully validated [120]. The coupling of IPC with atomic absorption spectrometry was also used for online speciation of Cr(III) and Cr(VI) [121] and arsenic compounds employing hydride generation [122]. 

IPC separation of monomethyl and mercuric Hg in biotic samples by formation of their thiourea complexes, coupled to cold vapor generation and atomic fluorescence detection, was successfully validated [18]. The coupling of IPC with atomic absorption spectrometry was also used for online speciation of arsenic compounds employing hydride generation [17]. In the analytical speciation of chromium using in... 

NjPtSioHg, Platinate(II), bis(pentasuIfido)-, bis(tetrapropylammonium), 21 13 NzPtSijHg, Platinate(IV), tris(penta-sulfido)-, diammonium, 21 12, 13 N2SCH4, Urea, thio-chromium(O) complexes, 23 2 N2SC2, Sulfur dicyanide, 24 125 N2SC4H6, 2H-Imidazole-2-thione, 1,3-di-hydro-1-methyl-cobalt complexes, 23 171 N2SCSH12, Thiourea, N,N,N methyl-... 

Although the pathway involving Cr is a minor one, radicals were detected. The principal pathways allow a two-electron transfer to two moles of reductant with incipient disulphide formation in the transition state. The role of the hydrogen ions may be to doubly protonate the chromate complex and allow easier access to coordination of the second thiourea. Labile Cr formed in the rate-determining step reacts with excess thiourea to form a mixture of hexa-aquochromium(m) and a chromium(m)-thiourea complex. 

Non-ionic thiourea derivatives have been used as ligands for metal complexes [63,64] as well as anionic thioureas and, in both cases, coordination in metal clusters has also been described [65,66]. Examples of mononuclear complexes of simple alkyl- or aryl-substituted thiourea monoanions, containing N,S-chelating ligands (Scheme 11), have been reported for rhodium(III) [67,68], iridium and many other transition metals, such as chromium(III), technetium(III), rhenium(V), aluminium, ruthenium, osmium, platinum [69] and palladium [70]. Many complexes with N,S-chelating monothioureas were prepared with two triphenylphosphines as substituents. 

Chromium(III) is a commonly-used crosslinker for preparing profile control gels with polymers having carboxylate and amide functionalities (la,b). Cr(III) is applied in many forms. For example, it can be used in the form of simple chromic salts of chloride and sulfate, or as complexed Cr(III) used in leather tanning (2), or as in situ generated Cr(III) from the redox reaction of dichromate and bisulfite or thiourea. The gelation rate and gel quality depend on which form of Cr(III) is used. 

Complexes of thiourea (tu) with chromium(III) have not been studied in detail and the lack of structural investigations in particular has led to uncertainties regarding the ligand donor sites and geometrical configurations of some of the reported species. 

Protein-Based Adhesives. Protein-based adhesives are normally used as structural adhesives they are all polyamino acids that are derived from blood, fish skin, casein [9000-71-9], soybeans, or animal hides, bones, and connective tissue (collagen). Setting or cross-linking methods typically used are insolubilization by means of hydrated lime and denaturation. Denaturation methods require energy7 which can come from heat, pressure, or radiation, as well as chemical denaturants such as carbon disulfide [75-15-0] or thiourea [62-56-6]. Complexing salts such as those based upon cobalt, copper, or chromium have also been used. Formaldehyde and formaldehyde donors such as hexametliylenetetraamine can be used to form cross-links. Removal of water from a protein will also often denature the material. 

Figure 5. Crystal packing of the 1,3-CHDMn(CO)3--(thiourea)3 complex illustrating the polar alignment. The qrstal structure is isomorphous with the chromium complex shown in Figures 2 and 3.

A series of chromium(II) nitrosyl complexes, [Cr(NO)(S2CNR2)2L] (L = H2O, thiourea), have been prepared, the thiourea resulting from dithiocar-bamate degradation (756). They are characterized by ESR spectroscopy, which suggests that the thiourea hes trans to the nitrosyl. 

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