Cobalt ions, cryptands

The anion-binding carcerand 11 was described by the Amouri group [31]. This complex contains a tetrafluoroborate anion coordinated to two cobalt(II) ions. Each cobalt ion adopts a square-pyramidal geometry. Four benzimidazole arms of the bridging ligands fill the equatorial positions, and solvent molecules (acetonitrile) coordinate to the outside axial positions. Inside the complex the included tetrafluoroborate anions interacts with the cobalt ions whose inside axial positions are otherwise coordinatively unsaturated. No exchange of the anion was observed even at 60 °C. A detailed study of the anion-binding properties in the crystal state of similar metalla-macrotricyclic cryptands has been performed by Adarsh et al. [32],... 

Mannich-type condensation of 4,4, 4"-ethylidyne-tris(3-azabutane-l-amine) complex 220 with excess of paraformaldehyde, phosphine, and triethylamine gave cryptand 221 with an encapsulated cobalt ion (Scheme 12.78). The phosphine was partly oxidized in the course of reaction and structure of corresponding oxide 222 was established by X-ray analysis [208]. 

There are now several structural studies on cobalt(II) crown ether and cryptand complexes (Table 78), which show the coordination mode to be markedly sensitive to the macrocycle cavity diameter. Both 12-crown-4 and 15-crown-5 (cavity diameters 120-150 pm and 170-220 pm respectively) can include ions to form structures in which every ether oxygen atom is bound to the metal. In contrast Co—O (ether) bonding is destabilized in the larger 18-crown-6 and dicyclohexyl-18-crown 6 polyethers. In the blue complexes obtained from the reaction of these compounds with C0CI2 the role of the cyclic polyether is to solvate discrete [Co(H20)6] cations and [CoC ] " anions and there are no direct Co—O (ether) bonds.A similar effect is seen in the Co" complex of a 27-membered-ring macrocycle where the pentacoordinate structure (267) features only one long Co—O (ether) bond. " ... 

The mechanism of 1 1 complex formation between palladium(II) and catechol and 4-methylcatechol has been studied in acidic media, and the rate of 1 1 (and 1 2) complex formation between silver(II) and several diols is an order of magnitude higher in basic solution than in acidic. The kinetics of formation and dissociation of the complex between cop-per(II) and cryptand (2,2,1) in aqueous DMSO have been measured and the dissociation rate constant, in particular, found to be strongly dependent upon water concentration. The kinetics of the formation of the zinc(II) and mercury(II) complexes of 2-methyl-2-(2-pyridyl)thiazolidine have been measured, as they have for the metal exchange reaction between Cu " and the nitrilotriacetate complexes of cobalt(II) and lead(II). Two pathways are observed for ligand transfer between Ni(II), Cu(II), Zn(II), Cd(II), Pb(II) and Hg(II) and their dithiocarbamate complexes in DMSO the first involves dissociation of the ligand from the complex followed by substitution at the metal ion, while the second involves direct electrophilic attack by the metal ion on the dithiocarbamate complex. As expected, the relative importance of the pathways depends on the stability of the complex and the lability and electrophilic character of the metal ion. 

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