Podands complexation properties

Complexation and Applications.— The chemistry and complexation properties of multidentate non-cyclic neutral ligands ( podands ), for example (95), have been... 

In this review, we discuss the properties and applications of the complexes between rare earth ions and the following ligand classes coron ds (especially crown ethers and cyclic polyamines), cryptands, and podands. The properties of some complexes with proteins are also presented, in order to illustrate the use of lanthanide ions as spectroscopic probes, but not those pertaining to porphyrin chemistry (with one exception). The papers referred to in this chapter have been found by means of a computer search of Chemical Abstracts up to the end of March 1986. 

Jones, P. L. Amoroso, A. J. Jeffery, J. C. McCleverty, J. A. Psillakis, E. Rees, L. H. Ward, M. D. Lanthanide complexes of the hexadentate N-donor podand tris [3-(2-pyri-dyl)pyrazolyl] hydro ) rate solid-state and solution properties. Inorg. Chem. 1997, 36(1), 10-18. 

Reeves, Z. R. Mann, K. L. V. Jeffery, J. C. McCleverty, J. A. Ward, M. D. Barigelletti, F. Armaroli, N. Lanthanide complexes of a new sterically hindered potentially hexadentate podand ligand based on a tris(pyrazolyl)borate core crystal structures, solution structures and luminescence properties. J. Chem. Soc., Dalton Trans. 1999, 349-355. 

Many polypodands having terminal donor groups are also available, e.g. (39)-(41).33 These also exhibit cation complexation and phase transfer properties. KMn04 and aqueous alkali metal picrates are much more readily taken into organic phases in the presence of these podands than with dibenzo-18-crown-6.239 The KSCN complex of (39) exhibits a novel coordination geometry as all 10 donor atoms participate in coordination of the metal cation, and in order to do this the three arms wrap around the cation in a propeller-like fashion.240... 

Armaroli, N. Balzani, V. Barigelletti, R Ward, M. D. McCleverty, J. A. Luminescence properties of Eu, Tb + and Gd " " complexes of the hexadentate N-podand tris-[3-(2-pyridyl)pyrazol-lyl]hydroborate. Chem. Phys. Lett. 1997, 276,... 

Because the podands were developed from the crown compounds and are seen as their open-chain analogues, properties similar to the crown compounds are to be expected for the podands. This is most evidently shown by the ability to form complexes.in case of the podands, they are called "podates or sometimes poda-plexes. ° This behavior of the podands to act as open-chained multidonor ligands was assessed with a variety of metallic and organic cations.However, due to the acyclic structure of the podands. as contrasted with the macrocyclic crown compounds, there are also differences in the behaviors of the two eompound types, including pros and cons. 

New approaches for development of specific carriers for use in liquid membrane are described (i) computer-aided design of cation-specific carriers and (ii) functionalization of rare earth complexes as anion carriers. A new series of Li(I) and Ag(I) ion-specific carriers are successfully designed using MM2, MNDO and density functional calculations. Computer chemistry provides a rational basis for design and characterization of cation-specific carriers of armed crown ether-and podand-types. Lipophilic lanthanide tris(p-diketonates) are shown to be a new class of membrane carriers. They form 1 1 complexes with anionic guests and mediate transport of amino acid derivatives. Since these complexes exhibit different anion transport properties from those of crown ethers, further applications of rare earth complexes offer promising possibilities in the development of specific anion carriers for liquid membrane systems. 

A systematic study of the luminescent properties of freshly prepared methanolic solutions of Eu(II) complexes with various crown ethers, cryptands, and podands has been undertaken by Adachi et al. (1980,1983, 1985a,b). The stoichiometry of the complexes formed in solution is determined by Job s plots in which the emission intensity is plotted versus the L M molar ratio. Such plots have to be interpreted with care in the case where different complexes form which have similar emission spectra but different quantum yields. Some of these stoichiometries have been confirmed by NMR measurements. The luminescence quantum yields (table 26) are markedly enhanced by complex formation, especially with... 

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