Lanthanide complexes nuclearities

Schiff base approaches have beenusedto synthesize mono-, di-, andtri-nuclear lanthanide complexes (73-78). Complexes of the macrobicyclic... 

Nuclear relaxation in paramagnetic lanthanide complexes for extracting R-nucleus distances... 

For any nucleus i of a paramagnetic lanthanide complex in the absence of significant chemical exchange, the experimental longitudinal (l/7 p) and transversal (1 /7 xp) nuclear relaxation rates are given by eqs. (4), (5) in which 7]dia corresponds to the characteristic relaxation times of the same nucleus i in the analogous diamagnetic complex (R = La, Y, Lu) and 7)para are... 

Since the spin delocalisation in lanthanide complexes is small (see sect. 2.1), the unpaired electrons can be considered as spatially confined onto the metal, thus producing an electronic magnetic point dipole which may interact with peripheral nuclear magnetic momenta via dipolar interactions (eq. (23), Bertini and Luchinat (1996)). 

Up to about the 1960 s, elemental analysis coupled with absorption spectra and infrared spectra and X-ray crystallography were the primary methods used in the studies of complexes. Later on with the developments in nuclear magnetic resonance (NMR) spectroscopy, especially multinuclear NMR, this technique has been invariably used in the studies of structural features of lanthanide complexes. To illustrate these points some references to literature are herein pointed out. The studies on the rare earth 1,3-diketonates, where 1,3-diketones are acetyl acetone, benzoyl acetone, dibenzoyl methane and 2-thienoyl tri-fluoroacetone totally relied on elemental analysis, UV-Vis and IR spectra to establish the nature of the complexes [89]. The important role played by X-ray crystallography in the elucidation of the structures of lanthanide complexes has been extensively discussed in Chapter 5 and the use of this technique goes as far back as the 1960 s. Nevertheless it continues to play a major role in the studies of lanthanide complexes. 

In the case of rapid reactions of lanthanide complexes if Tie the electron spin relaxation time is short compared to the rotational reorientation time, rr, the electron—nuclear dipolar interaction will give rise to nuclear relaxation rates given by [27]... 

Desreux, J.F. (1980) Nuclear magnetic resonance spectroscopy of lanthanide complexes with a tetraacetic tetraaza macrocycle. Unusual conformation properties. Inorganic Chemistry, 19 (5), 1319—1324. 

In addition, pyrazoyl-azaxanthone can also be used as a sensitizer of lanthanide complexes. An emissive terbium complex Tb-58 incorporating a pyrazoyl-l-aza-xanthonechromophore (Figure 13.25) exhibits cellular uptake and possesses a much lower sensitivity to excited state quenching. For example, Tb-58 was incubated for varying periods of time (from 1 to 12 h 50 or 100 xM complex) with CHO or NIH/3T3 cells. Examination of the loaded cells by luminescence microscopy revealed complex uptake, and localization within endosomes in the cytoplasm, presumably following receptor mediated endocytosis, but no tendency to nuclear localization [75]. 

Deuterium quadrupole coupling constants can also be obtained from electron nuclear double resonance (ENDOR).19 30 An observation of the hyperfine structure caused by quadrupole coupling in the electron paramagnetic resonance (EPR) spectrum, as for many lanthanide complexes, has not been reported for deuterium. The determination of nuclear quadrupole coupling constants from Mossbauer spectroscopy is not applicable to the deuterium nucleus. 

A large number of dinuclear lanthanide complexes have been reported in the literature. No specific efforts will be made for their general discussion. However, where appropriate, such species are included to provide necessary context for the discussion of the formal assembly of higher-nuclearity clusters from these well-defined, recognizable building blocks. 

Despite all these efforts, the chemistry of molecular lanthanide hydroxides, regardless of the complex nuclearity, has yet to be developed to any significant extent. However, based on the limited number of reports, some general conclusions may already be drawn ... 

Any variation of the slope for linear plots of Y / Sz)j versus 5ip/ Sz)j along a series of lanthanide complexes j implies that the ratio of the geometrical factor Gi/G changes, hence the structure of the complex does too. The systematic application of nuclear relaxation measurements (Eqs. (28) and (29)) for obtaining R Fj-iuclei distances, combined with the detailed analysis of NMR paramagnetic shifts with the help of the two nuclei method (Eq. (37), detection of isostructural series) as well... 

It is well known from spectra in the visible and the ultra-violet that the width of absorption bands indicates the difference in the bonding character of the excited state and the ground state. Thus, the potential surfaces of the excited 4f i states of lanthanide complexes, or of some of excited 3ds states of manganese(II) complexes (75, 102) have the same intemuclear distances as the ground states, whereas in other cases, when the excited states prefer either much shorter or much longer inter-nuclear distances, the absorption bands (and emission bands of luminescence) are broad. 

Jauregui M, Perry WS, Allain C, Vidler LR, Willis MC, Kenwright AM, Stasiuk G, Lowe MP, Faulkner S (2009) Changing the local coordination environment in mono- and bi-nuclear lanthanide complexes through click chemistry. Dalton Trans 6283-6285... 

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