2,2’-Bipyridyl complexes, lanthanide

Complexes of calixarenes with bipyridyl chromophores can be stabilized by the addition of anionic side arms, such as iminodiacetate units (85). Whilst the lanthanide complexes of ligands [L51]4- and [L52]4- are not soluble in water, their photophysical properties in... 

Recently, two cryptands and their lanthanide complexes have been synthesized which include either a bipyridyl (L56) or pyridyl (L57) chromophore (89). These have proved effective at populating the lanthanide excited states. Aqueous luminescence lifetimes of up to... 

These ligands are now well represented in complexes with the lanthanides, but were not investigated until 1962, when a study in aqueous solution using a Job s plot method, e.g. at 451 nm for Ho ", showed that a complex Ho(phen)2" was formed. Pr, Nd and Er tripositive ions were also studied, but no solid products were characterized. Indeed, stability constants in water are possibly too low for a solid complex to be isolated. A little later, there were several reports of the isolation of bipyridyl and 1,10-phenanthroline complexes from ethanolic solution. It is perhaps of interest that at this time, the lanthanides were believed not to form stable amine complexes and the role of higher coordination numbers in lanthanide complexes was not fully appreciated. Complexes isolated included the stoichiometries M(N03)s(bipy)2, where M = M(NCS)3(bipy)3, where M = La, Ce, Dy M(MeC02)3(bipy),... 

Cryptands have been somewhat deceptive for both coordination chemistry (Sastri et al., 2003) and photophysical properties of the resulting lanthanide complexes despite some commercial uses (Mathis, 1998), in particular of Lehn s Eu cryptate with cryptand 23a (fig. 28). The latter has been tested for the sensitization of the NIR luminescence of Nd and Yb. Characteristic emission from these two ions is seen upon excitation of the bipyridyl chro-mophores at 355 nm. Emission from Yb is reported to be much more intense than the one from Nd and the authors propose that the excitation mechanism depicted in fig. 9 is operative in this case since no transient absorption corresponding to the formation of the triplet state could be detected (Faulkner et al., 2001). Analysis of lifetime measurements in both water (r( F5/2) = 0.52 ps) and deuterated water (5.21 ps) gives a hydration number q = 1.5. Since fitting the luminescence decays to a double exponential function did not improve noticeably the resulting fit, the authors concluded that the non-integer value does not reflect an equilibrium between two different hydration states but, rather, that the distance of close approach of two water molecules is longer note that comparable experiments on Eu and Tb ... 

Mn(II) > Mg(II).270 It should be underlined that titanium and zirconium alkoxides are efficient catalysts for both stages of reaction. Lanthanide compounds such as 2,2/-bipyridyl, acetylacetonate, and o-formyl phenolate complexes of Eu(III), La(III), Sm(III), Er(III), and Tb(III) appear to be even more efficient than titanium alkoxides, Ca or Mn acetates, Sb203, and their mixtures.273 Moreover, PET produced with lanthanides has been reported to exhibit better thermal and hydrolytic stability as compared to PET synthesized with the conventional Ca acetate -Sb203 catalytic system.273... 

Metal complexes like lanthanide chelates (mainly europium or terbium), ruthenium phenanthrolines or bipyridyls, and platinum porphyrins can be used as fluorescent labels for biomolecules. Their long decay times are perfectly suited for a detection by time-resolved imaging, and the labeled target molecules can be used for the determination of intracellular recognition processes or for the screening of DNA and protein arrays. Ratiometric lifetime-based imaging methods in combination with sophisticated data acquisition and evaluation tools can substantially contribute to the development... 

Terpyridyl is a terdentate ligand and behaves like bipyridyl, and o-phenanthroline. The three terpyridyl ligands coordinate to the lanthanide when the anion is perchlorate. The emission spectrum of the Eu(III) complex points to D3 symmetry which has been confirmed by the determination of the structure [242],... 

Ni, J., Zhang, L.-Y, and Chen, Z.-N. (2009) Syntheses, characterization and sensitized lanthanide luminescence of heteronuclear Pt—Ln (Ln = Eu, Nd, Yb) complexes with 2,20-bipyridyl ethynyl ligands. Journal of Organometallic Chemistry, 694, 339. 

Bipyridyl complexes with lanthanide bromides do not seem to have received attention, but the first lanthanide iodide complexes were reported in 1999. In a comparative study with UI3, complexation of bipy with (Ln = Ce, Nd) was investigated. UI3 and Cels both form 1 1 and 1 2 complexes in solution, with a 1 3 complex at high bipy concentrations, whereas Ndls only forms a 1 2 complex. The structure of [Cel3(bipy)2(py)].5py.bipy was reported it has eight-coordinate Ce, with Ce—(bipy) = 2.67(3) A, Ce—I = (average 3.23(3) A) and Ce—N 2.678(9) A. Reaction of [Ndl3(py)4] and bipy in attempts to make the Nd analogue resulted in dimeric [(bipy)3Nd(/i-OH)2Nd(bipy)3]l4 3Py, presumably due to inadvertent hydrolysis. ... 

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