Coordination spheres of Cd

A special situation is met in systems containing Cd or Hg combined with cyano-complexes of other elements. In these cases, the coordination sphere of Cd or Hg is fully or partly made up of the N-ends of cyano-groups C-bonded to another metal. 

Hydroxo complexes of Cd are rare. In one example, two /i-OH groups link two Cd centers to a distorted square Cd2(OH)2 (rav(Cd—O) 222.5 pm) otherwise two tetradentate N,S-donor ligands complete the coordination sphere of Cd. Remarkably, in a reaction with C02 the two /i-OH groups are replaced by one /i-carbonato group.260... 

Other chiral hosts with considerably more potential are metal complexes where the ligands in the parent complex are chiral. Solutions of the complex will have a CD spectrum which, depending upon the choice of metal, might lie in the visible range and therefore remote from UV interferences. Diastereomers are formed when the isomers of a racemic or partially racemic mixture displace the chiral ligands in the first coordination sphere of the parent complex according to the equilibrium reaction ... 

Thiocyanate ion is known to react with oxyhemocyanin to remove oxygen from the coordination sphere of the copper ions (76, 77). We observed that an addition of NCS" to the purple hemocyanin produces a little more reddish and transparent solution, whose absorption spectrum apparently differs from that of the purple hemocyanin, as shown in Figure 5. A drastic decrease of the absorption band at around 340 nm in Figure 5 indicates that the coordinated oxygen ligand is removed with the addition of NCS". The variation in CD spectrum accompanied by the addition of NCS" is so remarkable that the CD band centering at 430-490 nm of the purple hemocyanin almost disappears, as seen in Figure 6. 

Ligand-substitution reactions in aqueous solutions rarely proceed directly. Instead, the leaving ligand is first replaced by H2O, which is present in aqueous solution at a concentration of 55 M, the entering ligand then substitutes the metal-bound H2O (M-OH2) inthe so-called anationreaction. Therefore, the rate constant of forward reactions, which could be considered as the reactivity of aquo-metal species, will parallel the order of water substitution in the inner coordination sphere of the corresponding metal ions Cs > Ba > Hg2+ > K+ > Cr2+ Cu + > Na+ > Sr + Li+ > Ca + > Cd + > Mn2+ Zn + > Fe + > Co + > Mg + > nP+ > Pd + > Pt + > cases, the interactions between... 

The combination of potentiometric equilibrium measurements and NMR, EPR, CD, EXAFS and MSssbauer structural studies of metal complexes of small models of the moie of glycoproteins vdiich connects the protein and carbohydrate parts of the macromolecule peimitted determination of the composition and structure of the coordination sphere of the metal in equilibrium species in solution. 

To model the moiety of glycoproteins which coimects the protein and carbohydrate parts of the molecule, amino acid - carbohydrate adducts (e.g. V-D-gluconylamino acids, thiazolidine-4-carboxylic acid derivatives of carbohydrates, " D-fructose amino acid derivates, etc.) have been synthetized. The protonation and metal ion (Cu2+, Ni2+, Co ", Zn2+ and Et2Sn2+) coordination equilibria of these model compounds have been studied by means of potentiometric equilibrium measurements. CD, EPR, NMR, EXAFS and MSssbauer investigations (the latter in frozen solutions) have been used to determine the structure and symmetry of the coordination sphere of the complexes. >6... 

Toxic Properties. The toxic properties of metal ions such as Pb +, Hg +, Cd +, etc. are the result of the incorporation of some biological structure into the coordination sphere of the metal ion. The direct consequence of this is to alter the biological properties of these newly coordinated species, often by deactivation of any normal enzymatic activity. This can be clearly seen in the anemia characteristic of lead intoxication. Thus Pb2+ reacts with and reduces the activity of three of the enzymes involved in the synthesis of heme and reduces the ability of the stem cells in the bone marrow to form normal red blood cells (29). 

M = Mn, Cu, Zn, Cd ) synthesized were studied by W NMR spectroscopy and it was indicated that the solid-state polyoxoanion structures of the diamagnetic Zn and Cd derivativesare preserved in solution. The charges on metal cations of the coordination sphere of polyoxometalates (POM) of V, Mo and W were calculated using the EHMO method, and obtained values were compared with the Mo and NMR chemical shifts of the corresponding nuclei as mentioned above. ... 

The Pd-Cd-bonded complex [CdPd(CH3COO).j-CH3COOH]2] (123) was obtained from the reaction between palladium acetate and cadmium acetate in glacial acetic acid [89], The crystal structure shows that the coordination sphere of cadmium adopts a trigonal-prismatic geometry. Ozerov et al. prepared the Pd-Zn-bonded complex 124 through different reaction pathways (Scheme 12.37) [90]. Complex 124 represents the first Pd-Zn-bonded compound with Pd-Zn distances of2.3793(10) and 2.3723(10) A. 

That A log cu/ATP/Bistris is with -1.65 log units rather low, is no surprise because of the Jahn-Teller distorted coordination sphere of Cu " [128]. The value of A log cd/ATP/Bistris = -1.33 impUes again that the Cd(ATP) 70H interactions are not very prrMiounced as already indicated by the Cd(ATP)(Tris) data. 

The stability constants of the two examples for binary M(Bicinate) and ternary M(ATP)(Bicinate) complexes (no value for Cd " is known) provide an order and speak for themselves. These values are so large (Table 13) that Bicine, if used as buffer in the presence of metal ions, will certainly complex a very significant amount of metal ions present. It is further clear that the hydroxyl groups of Bicinate participate at least to some extent in metal ion binding. To put the observed negative values for A log m/atp/l overall into perspective, it may be helpful to recall that the expected statistical value for a regular octahedral coordination sphere of (e.g., Co " ) and the coordination of two different but simple and symmetrical tridentate ligands amounts already to A log A 3.3/s,at/oh = -103 [213]. 

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