1,10-Phenanthroline complexes, lanthanid

Fig. 2. A plot of the chemical shifts of the proton signals (ppm) for the 1,10-phenanthroline complexes of the lanthanides in D2O. The shifts are below the methyl signals of tert-butyl alcohol...

Figure 4.16 The structures of (a) Nd(15)3(NCS) and (b) [Ho(15)4(H20)(OH)]" + [31, 32], (Reproduced from Polyhedron, 22, S.A. Cotton et al, Synthesis of complexes of 2,2 6, 2"-terpyridine and 1,10-phenanthroline with lanthanide thiocyanates the molecular structures of [Ln(terpy)2(NCS)3] (Ln = Pr, Nd), [Nd(terpy)2(NCS)3]-2EtOH and [Ln(phen)3(NCS)3]-EtOH (Ln = Pr, Nd), 1489, 2003, with permission from Elsevier and redrawn from D.Y. Wei, Y.Q. Zheng and J.L. Lin, Synthesis, crystal structure and magnetic property of [Ho2(phen)4(H20)4(OH)2](phen)2(N03)4, Acta Chimica Sinica, 7, 1248, 2002.)...

The enantiotopic protons of the prochiral methyl groups in the iminium salt 36 exhibited distinct resonances in the presence of Eu(hfc)3 . As already discussed for achiral lanthanide S-drketonates, the system likely forms an ion pair between the organic cation and the species [Ln( S-dik)3X]. The spectrum of racemic 37, which as its bromide salt has been studied as an ionic liquid, exhibits nonequivalence in the presence of Eu(tfc)3 and Eu(hfc)3. No splitting of the resonance occurs in the presence of Eu(fod)3. In addition to the likely ion-pairing interaction of 37 with [Ln(/ -dik)3X] , rather substantial shifts of some of the OCH2 protons implied that the ether oxygen atoms also likely coordinated with the europium ion. A similar ion-paired system explains the enantiomeric discrimination observed in the spectrum of the tris(phenanthroline) complexes of Ru(II) ([Ru(phen)3]Cl2) in the presence of Eu(tfc)3 . 

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),... 

Assays based on luminescent lanthanide ions were developed initially in the 1970s, when instrumentation became available which could distinguish long-lived luminescence from a shortlived background. Leif and co-workers reported the first attempts to use lanthanide complexes (in this case europium complexes with 1,10-phenanthroline and 7-diketonates, i.e., [Eu(phen)(diketo-nate)3]) as tags for antibodies.107 These proved kinetically unstable in the pH regime required... 

A broad range of metal centers have been used for the complexation of functional ligands, including beryllium [37], zinc, transition metals such as iridium [38], and the lanthanide metals introduced by Kido [39], especially europium and terbium. Common ligands are phenanthroline (phen), bathophenanthrolin (bath), 2-phenylpyridine (ppy), acetylacetonate (acac), dibenzoylmethanate (dbm), and 11 thenoyltrifluoroacetonate (TTFA). A frequently used complex is the volatile Eu(TTFA)3(phen), 66 [40]. 

Numerous macrocyclic and macropolycyclic ligands featuring subheterocyclic rings such as pyridine, furan or thiophene have been investigated [2.70] among which one may, for instance, cite the cyclic hexapyridine torands (see 19) [2.39] and the cryptands containing pyridine, 2,2 -bipyridine (bipy), 9,10-phenanthroline (phen) etc. units [2.56,2.57,2.71-2.73]. The [Na+ c tris-bipy] cryptate 20 [2.71] and especially lanthanide complexes of the same class have been extensively studied [2.74, 2.75] (see also Sect. 8.2). 

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... 

By redesigning the above acyclic podand-type ligand 3 into a cyclic cryptate, the issue of stability can be resolved resulting in kinetically stable complexes (Scheme 4) [102]. The Tb(III) and Eu(III) complexes of cryptate 5 show an increase in lanthanide emission lifetimes of 0.72 ms and 0.41 ms, respectively, upon excitation at 310 nm. Similar results are found with the phenanthroline analogue 6 with Eu(III). A large number of modifications of these cryptates have been reported, all showing enhancements in the lanthanide ion emission [103-106]. 

Figure 136 EL spectra of various organic LEDs employing lanthanide complexes as emitters, (a) ITO/TAD (triphenyldiamine derivative)/Eu(TTA)3(phen)(phen l,10-phenanthroline + 4,7-diphenyl-l,10-phenanthroline)/Alq3/MgAg (according to Ref. 425) (b) ITO/Eu (TTA)3 PBD/PBD/LiF/Mg, at the different voltages (after Ref. 539) (c) ITO/TPD/Tb (acac)3/Al, transitions of 4f electrons of the terbium Tb3+ ion are indicated on the sharp peak positions of this spectrum (after Ref. 19).

We have noted that N-bonded thiocyanate complexes dissociate readily in solution. Mixed ligand complexes of lanthanides with thiocyanates and L = ethanol, pyridine, triphenyl phosphorous oxide, phenanthroline, etc. have been synthesized. 

Lanthanide complexes of 1,10-phenanthroline (phen) have been obtained as chlorides, nitrates, sulfates, perchlorates acetates, thiocyanates and selenocyanates from various solvents. 

Both tris and tetrakis phenanthroline perchlorates, Ln(phen)3(C104)3 and Ln(phen)4(C104)3 are known. Coordinated perchlorate of C3V symmetry has been detected. This is true of only lighter lanthanides and only ionic perchlorate being detected in the heavier lanthanide complexes [241], The complexes of the type [239] Ln(phen)3(NCS)3 show no evidence for Ln-NCS bonding while the corresponding Ln(phen)3(NCSe>3 shows the Ln-NCSe bonding with a coordination number of 9. 

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],... 

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