Cadmium complexes metals

A second synthesis of cobyric acid (14) involves photochemical ring closure of an A—D secocorrinoid. Thus, the Diels-Alder reaction between butadiene and /n j -3-methyl-4-oxopentenoic acid was used as starting point for all four ring A—D synthons (15—18). These were combined in the order B + C — BC + D — BCD + A — ABCD. The resultant cadmium complex (19) was photocyclized in buffered acetic acid to give the metal-free corrinoid (20). A number of steps were involved in converting this material to cobyric acid (14). 

Several solvents, such as cupriethylenediamine (cuen) hydroxide [111274-71 -6] depend on the formation of metal—ion complexes with ceUulose. Although not as widespread in use as the viscose process, cuen and its relatives with different metals and ammonium hydroxide find substantial industrial use (87). The cadmium complex Cadoxen is the solvent of choice in laboratory work (91). 

Bayer and Schretzmann 25) came to the conclusion that reversible oxygenation is a characteristic property of group VIII metals. However, work has shown that the cadmium complex CdEt2 can take up dioxygen reversibly in the ratio 1 2 (Cd O2). But it was found that the oxygenated complex (II(P) or 11(G) orientation) can undergo spontaneous catalytic oxidation to form bis(ethylperoxy) cadmium ... 

According to R. Brdicka and K. Vesely the carbonyl form of formaldehyde is reduced and the limiting kinetic current is given by the rate of the chemical volume reaction of dehydration. An analogous situation occurs for the equilibria among complexes, metal ions and complexing agents if the rates of complex formation and decomposition are insufficient to preserve the equilibrium. A simple example is the deposition of cadmium at a mercury electrode from its complex with nitrilotriacetic COO"... 

Stolzberg [143] has reviewed the potential inaccuracies of anodic stripping voltammetry and differential pulse polarography in determining trace metal speciation, and thereby bio-availability and transport properties of trace metals in natural waters. In particular it is stressed that nonuniform distribution of metal-ligand species within the polarographic cell represents another limitation inherent in electrochemical measurement of speciation. Examples relate to the differential pulse polarographic behaviour of cadmium complexes of NTA and EDTA in seawater. 

One unexpected square planar complex [Cd(OAr)2(thf)2] (Fig. 12.4) has recently been reported.13 It is the first example in this geomelry for d10 Cd2. Inasmuch as a closely related complex of the smaller zinc ion, [Zn(OAr )2(thf)2], has distorted tetrahedral geometry,14 simple steric factors cannot account for the pseudo-C2/i symmetry of the cadmium complex, though to be sure, the steric relaxation of the target metal atom and the perpendicular planes of the thf and phenoxide rings are nicely accommodated by it. Furthermore, octahedral geometry would rot be unusual in ad10... 

A considerable number of NQR studies have been made on zinc and cadmium complexes, for example, the 35C1, 81Br and 127I NQR spectra of a number of CdX2-polyether complexes have been reported and indicate that the compounds are dimeric in solution, with symmetrical halogen bridges between the metal atoms.69 A number of amino acids and peptide complexes of cadmium(II) have been investigated by 14N NQR spectroscopy.70... 

Schiff bases, especially multidentate ones, are powerful ligands for metal ions and zinc and cadmium complexes are well represented in this area. The findings of structural studies are interesting in that the ligand can control the stereochemistry of the complex and provide us with numerous examples of unusual geometry about the central metal ion, thus serving to illustrate the coordination flexibility of these ions. 

The involvement of zinc in nicotinamide-based hydride-transfer reactions has led to numerous studies of Group IIB complexes of pyridine carboxylic acid derivatives. Cadmium complexes of 2-pyridinecarboxylic acid, 5 3-pyridinecarboxylic add497 and 3-pyridinecarboxamide498 have been reported. The crystal structure of [Cd(HC02)2L2(H20)2] (L = 3-pyridinecarboxamide) has also been described the metal is in an octahedral environment in which the amide acts as a monodentate N donor.498... 

Cadmium complexes of macrocyclic ligands have not been as widely studied as the corresponding zinc complexes, but the fact that cadmium macrocycles undergo easy metal exchange should make them attractive subjects for future study. The crystal structure of [Cd(TPP)(dioxane)j and its 113CdNMR characteristics have been reported.1144 The formation... 

Because of the ease with which dimercaptopropanol can be broken down in the body there is a danger that chelation, followed by breakdown, will simply result in the translocation of the metal ions to other tissues such as brain or liver. High doses of dimercaptopropanol can adversely affect a number of essential metal-activated enzymes, such as catalase, carbonic anhydrase and peroxidase, and also produce dangerous systemic effects. Dimercaptopropanol cannot be used to remove cadmium because its cadmium complex is toxic to kidney tissue54). 

Despite the fact that the compounds of the type 802 are formally tridentate ligands, a substitution of the proton of the NH group to the metal does not take place even under electrosynthesis conditions. This was confirmed by H NMR data of zinc and cadmium complexes and x-ray diffraction data of 803 (M = Zn, R = 2,4-dimethyl) [593],... 

Two crystalline modifications of mercury(n) NN-diethyldithiocarbamate have been reported.208 The a-form consists of dimeric Hg2(S2CNEt2)4 units, in which the metal atom is five-co-ordinate, in a manner similar to analogous zinc and cadmium complexes. The P-form is composed of essentially monomeric Hg(S2CNEt2)2 units, with the two ligand molecules co-ordinated in a plane through the S atoms (Hg—S = 2.40 A). 

N3CI plane (207). The other halids and the cadmium complexes are isomor-phous with the appropriate forms, and undoubtedly possess related five-coordinate structures. A number of studies of the vibrational spectra of the [M(terpy)X2] species have been described, all of which support the formulation as isomorphous five-coordinate complexes (124, 171, 225, 371). The copper(II) complexes [Cu(terpy)Cl2] are isostructural, and a number of studies of the paramagnetic species doped into a host matrix of [Zn(terpy)Cl2] have been reported (23, 213). The zinc complex [Zn(terpy)Cl2] exhibits absorption maxima at 22,650 and 18,000 cm (23, 348). The mercury(II) halide adducts are not so well characterized, but may be prepared by the direct reaction or HgX2 with terpy (171) or by trans-metallation of [Ph2Sn(terpy)Cl2] with HgCl2 (471). They are thought to possess similar, five-coordinate structures. The structures of the 1 1 adducts of the nitrates M(N03)2 terpy are not known with any certainty (171,328). A Cd NMR study of Cd(N03)2 terpy has been reported (430). 

---