- Photoresponsive Crown Ethers. 12. Photocontrol of Metal Ion Complexation with Thiacrown Ethers
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Thiacrown ethers with a photofunctional azolinkage were synthesized to control their binding ability by an on-off light switch: They are the N2S4 crowns capped with 2,2'-azopyridine (1) or azobenzene (2).The cis-trans isomerism occurred reversibly by photoirradiation.The binding ability; evaluated by solvent extraction, showed that (i) the order of the affinity for Hg2+ is N,N'-dibenzoylated N2S4 crown (4) ca. photoirradiated 1>trans-1>photoirradiated 2>trans-2, (ii) neither trans-2 nor 4 shows significant affinity toward heavy metal ions such as Cu2+, Co2+, Ni2+, and Pb2+, (iii) trans-1 has a slight affinity (Expercent 5.9percent) for Cu2+, whereas photoisomerized 1 shows the remarkably enhanced affinity (Expercent 93.9percent) with Cu2+, and (iv) such light-induced improvement is not seen for 2.The relatively poor binding ability of 2 and 4 is rationalized in terms of the unfavorable inside-out conformation of the N2S4 crown ring.The remarkable affinity change in cis-1 is probably due to the cooperative contribution of the thiacrown and the azopyridine cap constructing a new ligand site. 1 was used as a carrier for Cu2+ transport through a liquid membrane.It was found that the rate is efficiently accelerated by UV-light irradiation.
- Shinkai, Seiji,Honda, Yoshihiro,Ueda, Kaori,Manabe, Osamu
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- Stability Constants of Silver(I) Complexes with Diaza-18-Crown Ethers in Polar Solvents
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The stability constants of Ag+ complexes with macrocyclic diaza-crown ethers of constant ring size, but with different donor atom distributions in the ligand bridges, are strongly dependent upon solvent.The effect of solvent, however, is essentially independent of the ligand involved, and this extends even to bicyclic cryptand ligands.Thus, the stability constants of any one ligand are linearly related to those of the other ligands across a wide range of polar solvents.A more detailed analysis of the results in terms of the free energies of solvation and transfer of the species involved in the complexation reaction shows that, although the dominant influence is normally the solvation of Ag+, specific solvation of either the complexed cation or the free ligand can influence complex stabilities in some cases.Effects due to the former, although relatively weak, are evident in complexes of monocyclic diaza-ligands in strongly coordinating solvents, such as dimethylformamide and dimethyl sulfoxide, and the latter is quite marked in solvents possessing acidic hydrogen atoms, such as water, methanol, and nitromethane. - Keywords: Complex Compounds / Crown Ethers / Solutions / Thermodynamics
- Burchard, T.,Cox, B. G.,Firman, P.,Schneider, H.
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p. 1526 - 1533
(2007/10/02)
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- Complexes of macrocyclic compounds
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Novel macrocyclic (monocyclic and bicyclic) compounds having nitrogen bridgehead atoms and having in the hydrocarbon bridging chains at least two additional hetero atoms selected from the group consisting of sulfur, oxygen, and nitrogen, when admixed with a compatible cation-donor compound form stable cation-containing macrocyclic complexes which, in turn, can be conveniently dissociated by addition of acid or a quaternizing agent. The novel macrocyclics are valuable for use in the same way and for the same purposes as chelating agents.
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- Monocyclic macrocyclic compounds and complexes thereof
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Novel monocyclic macrocyclic compounds having nitrogen bridgehead atoms and having in the hydrocarbon bridging chains at least two additional hetero atoms selected from the group consisting of sulfur, oxygen, and nitrogen, when admixed with a compatible cation-donor compound form stable cation-containing macrocyclic complexes which, in turn, can be conveniently dissociated by addition of acid or a quaternizing agent. The novel macrocyclics are valuable for use in the same way and for the same purposes as chelating agents.
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