Complexes with metal cations

The cyclopentadienide ion, C H , is a common organic anion that forms very stable complexes with metal cations. The anion is derived by removing a proton from cyclopentadiene, QH, with strong base. The molecule has a five-memhered ring of carbon atoms, with four carbon atoms attached to only one proton and one carbon atom bonded to two. Draw the Lewis... 

The complexation of protonated amines, RNHJ, by crown ethers differs in many aspects from the complexation of metal cations. Whereas complexes with metal cations derive their binding energy mainly from electrostatic forces, complexes with ammonium ions are likely also to be stabilized by hydrogen... 

Several other explanations have been put advanced to explain retention hysteresis, including (1) surface precipitation of metallic cations whose hydroxides, phosphates, or carbonates are sparingly soluble (2) chemical reactions with solid surfaces, including organic surfaces, which form complexes with metallic cations and (3) incorporation into the subsurface organic matter through chemical reactions and biochemical transformation. For the case described by Fig. 5.9 or explanations (1) and (2), the contaminant release always exhibits a hysteresis... 

Because of the diversity of polyhedral geometries found in porphyrin complexes with metal cations, additional ligands exhibit many different coordination modes. In Fe11, Co11, Mn11, Zn11, etc. complexes with one extra ligand, MP-L, the metal ion is pushed out of the N4 plane, and the MN4 coordination unit can be described as a pyramid with the M metal atom in the apical position. 

Guanidine, H2N(G=NH)NH2, is the amidine of carbamic acid, H2N(CO)OH. Guanidine forms three types of complexes with metals cationic (in which the guanidinium cation is formed by taking up a proton), adducts with neutral molecules or coordination products with ionic salts, and substitution products. A brief account of each type is presented below. 

The scope of the tether-directed remote functionalization has been expanded from Cgo to the higher fullerene C70, and the described reactions are completely regioselective, featuring, in the case of C70, the kinetically disfavored addition pattern. The crown ether is a real template, since it can be readily removed by transesterification, giving a much-improved access to certain bis-adducts that are not accessible by the direct route. Cation-binding studies by CV reveal that cyclophane-type crown ethers derived from C60 and C70 form stable complexes with metal cations, and a perturbation of the fullerene reduction potentials occurs because the cation is tightly held close to the fullerene surface. This conclusion is of great importance for future developments of fullerene-based electrochemical ion sensors. 

Very recently Geus and co-workers [44, 45] have applied another method based on chemical complexes. This is the complex cyanide method to prepare both monocomponent (Fe or Co) and multicomponent Fischer-Tropsch catalysts. A large range of insoluble complex cyanides are known in which many metals can be combined, e.g. iron(n) hexacyanide and iron(m) hexacyanide can be combined with iron ions, but also with nickel, cobalt, copper, and zinc ions. Soluble complex ions of molybdenum(iv) which can produce insoluble complexes with metal cations are also known. Deposition precipitation (Section A.2.2.1.5) can be performed by injection of a solution of a soluble cyanide complex of one of the desired metals into a suspension of a suitable support in a solution of a simple salt of the other desired metal. By adjusting the cation composition of the simple salt solution, with a same cyanide, it is possible to adjust the composition of the precursor from a monometallic oxide (the case when the metallic cation is identical to that contained in the complex) to oxides containing one or several foreign elements. 

A similar reaction with bis(dimediylamino) chloroiminium chloride was performed at temperatures below -20 °C and led to the fonnation of the bis(dimethylamino) carbene with a conversion of about 60%. For the first time, the bis(dimethylamino) carbene was formed without complexation with metal cations, which usually occurs in the deprotonation method. The C chemical shift of the carbene carbon atom was significantly shifted toward low field compared to the complexed version. To our surprise, the carbene was not found to dimerize at higher temperatures, but instead a complex mixture was obtained with no traces of dimer being detectable. This raises the question whether the cations are necessary for the dimerization process, as already discussed in literature [7]. 

Acetyiene and its derivatives also turned out to be suitable probe-molecules for basic centers in zeolites. Figure 2 depicts IR spectra of acetylene adsorbed on the NaX, Cs/NaX, and Na/Y zeolites. The most intense bands at 3300-2900 cm belong to the stretching vibrations of the C-H bond. Obviously, in the case of alkaline forms of zeolites, two types of complexes with acetylenes may be formed (1) 7t-complexes with metal cations (complex 3) and (2) o-complexes with basic oxygen atoms of the framework (complex4) ... 

These contain chromophore moieties, as in (163), that give rise to color changes on complexation with metal cations. 

The hardness of water can be measured by titrating a sample of water with the ligand ethylenediamine tetraacetic acid (EDTA) and the indicator eriochrome black T. This ligand forms a coordination complex with metal cations (M) in a one-to-one stochiometry in the following association reaction ... 

Helical structures in nature also are formed through complexation with metal cations Some microbes, including Escherichia coli, produce enterobactin a siderophor, which complexes Fe(III) with a very high complex constant of 10 . ... 

Crown ethers and cryptands, complexes with metal cations 79AG613,... 

The method makes use of excellent chelating properties of disodium ethylene diamine tetraacetate (versenate) which forms soluble complexes with metal cations. 

Heavy metal uptake is primarily based on the ability of microbial surfaces to complex with metal cations. The negatively charged sugar units of polysaccharide chains, extending from the microbial cell wall, may complex with metal cations. 

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