Polymetallic lanthanide complexes

Cross J-P, Lauz M, Badger PD et al (2004) Polymetallic lanthanide complexes with PAMAM-naphthalimide dendritic ligands luminescent lanthanide complexes formed in solution. J Am Chem Soc 126 16278-16279... 

Axial symmetry according to Bleaney s approach is maintained in polymetallic lanthanide complexes when the metals lie on the molecular threefold or fourfold axes. For n magnetically non-coupled lanthanide ions packed along the symmetry axis, contact and pseudo-contact contributions can be considered as additive and the original model-free equation (eq. (47)) is transformed into eq. (61) in which the sum runs over the n paramagnetic centres, each being located at the origin of its own reference frame associated with a specific set of axial coordinates O 1 and r" (the z axis corresponds to the molecular symmetry axis, fig. 54),... 

The derivation of a general crystal-field independent method for polymetallic lanthanide complexes related to eq. (51) is precluded by the consideration of variable numbers of different crystal-field parameters (maximum n) depending on the exact symmetry of the axial complex (see sect. 4.1.1, Rigault et al. (2000a)). 

Fig. 3 Simplified scheme showing sensitized emission in polymetallic lanthanide complexes...

In a polynuclear or polymetallic lanthanide complex, additional processes become feasible. Figure 3 is a simplified scheme that shows the energy transfer pathways available in a bimetallic lanthanide complex singlet-mediated energy transfer and competitive non-radiative quenching pathways are not shown in the scheme to facilitate interpretation. Not only can both lanthanide ions be sensitized by the excited states of the chromophore, but energy transfer between lanthanide ions is also possible where appropriate spectral overlap exists between the two lanthanide ions. 

Placidi MP, Villaraza AJL, Natrajan LS, Sykes D, Kenwright AM, Faulkner S (2009) Synthesis and spectroscopic properties of azo-dye derivatives of polymetallic lanthanide complexes using diazotization to link metal complexes together. J Am Chem Soc 131 9916-9917... 

Scheme 13.32 Structures of ligands and schematic depiction of the subunit structures in bimetallic or polymetallic lanthanide complexes.

This review focuses on the use and limitations of the model-free methods in axial paramagnetic supramolecular mono- and polymetallic lanthanide-containing complexes. A comprehensive survey of the systems with three- and fourfold symmetry for which these techniques have been applied is proposed together with a detailed discussion of the limitations of Bleaney s approach for the modeling of paramagnetic anisotropies and the detection of structural changes along the lanthanide series. 

Lanthanide chemistry with Schiff bases is quite extensive and numerous acyclic, cyclic, monometallic and polymetallic (4f-4f, 4f-5f, 4f-nd) complexes have been synthesized and studied, in particular with compartmental ligands, owing to the ability of the latter to bind two or more metal ions in close proximity. Asymmetrization of these ligands also provides important diversification of the coordinating sites (Vigato and Tamburini, 2004). On the other... 

Figure 4.19 The structures of four complexes [Sml(p.-I)(17)3]2, Sm(17)8l3, [(17)4Sm]( x-OH) 3(p.3-OH)2 l4, and [(17)5Sm(p.-OH)]2l4 [34], (Reproduced with permission from WJ. Evans, GW. Rabe and J.W. Ziller, Utility of N-methylimidazole in isolating crystalline lanthanide iodide and hydroxide complexes crystallographic characterization of octasolvated [Sm(N-MeIm)8]I3 and polymetallic [Sml( x-I)(N-Melm)3]2, [(N-MeIm)5Sm( X-OH)]2l4, and [(N-MeIm)4Sm(tJi-OH)]3(tJi3-OH)2 l4, Inorganic Chemistry, 33, 3072, 1994. 1994 American Chemical Society.)...

Wang, R., Liu, H., Carducci, M.D., Jin, T, Zheng, C., and Zheng, Z. (2001) Lanthanide coord with a-amino acids under near physiological pH conditions polymetallic complexes containing the cubane-like [Ln (P3-0H)6] cluster core. Inorganic Chemistry, 40, 2743-2750. 

For the better part of two decades, the chemistry of self-assembled systems containing lanthanides has been dominated by hehcate systems [20, 21]. Simple tridentate ligands such as 2,6-dipicolinate, terpyridyl and 6-(diaminocarbonyl)-picolinic acid form stable and luminescent triple helicate complexes in water [21-24]. Polymetallic chelates can be assembled by using related ligand structures that can bridge between two metal centres. 

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