Lanthanide complexes nitrogen donors

Nitrogen donors usually form weak complexes with the lanthanides in aqueous solution. Sinha and Green 26) have measured the NMR spectra of complexes formed between 1,10-phenanthrohne and Ce(III), Pr(III), Nd(HI) and Eu(IH) in D2O. As the spectra were measured at room temperature, only time-average signals for the phenanthrohne protons were obtained. However, a plot of the shift of the protons as a function of the mole ratios of the hgand and metal ion (Fig. 2)... 

The impetus for the development of synthesis and characterization of complexes of lanthanides with organic nitrogen donor ligands is due to the search for more efficient luminescent rare earth compounds. One of the difficulties is the risk of precipitating lanthanide hydroxides in the process of synthesis of lanthanide complexes with organic amines. In the early stages, lanthanide complexes of heterocyclic bases of low basicities were prepared in aqueous alcoholic media [224], In the synthesis section it was appropriately pointed out the need for the anhydrous conditions and involved procedures for the preparation of lanthanide complexes of ligands of non-ionizable nature. Some representative complexes of both aliphatic and aromatic amines are listed in Table 4.19. 

Lanthanide complexes with nitrogen donor ligands.659... 

Figure 4.43 The structure of [La(24)(N03)3] [70]. (Reproduced from J.D.J Backers-Dirks et aL, Preparation and properties of complexes of lanthanides with a hexadentate nitrogen-donor macrocycle X-ray crystal structure of the complex [La(N03)31], Journal of the Chemical Society, Chemical Communications, 11 A, 1979, by permission of The Royal Society of Chemistry.)...

In addition to this wide range of uses for yttrium, new applications of yttrium complexes are under continual development. Examples include hydrate with halide and other simple ligands, with oxygen donor ligands with lanthanides, or mixed (e.g., metal diyttrium-barium and yttrium-copper), with nitrogen donor ligands, with... 

Z10 Electronic Spectra of Lanthanide Complexes 39.Z11 Lanthanides in the Dipositive Oxidation State 39.Z11.1 Hydrated species 39. Z 11.2 Other solvated species 39. Z 11.3 Complexes with nitrogen donors... 

Mainly as a result of the inaccessibility of the f-electrons, directed bonding typically observed in the transition elements is not seen in the lanthanides. In many respects, the lanthanides behave more like the alkaline earth elements than like the transition elements. The lanthanides behave as hard-acid cations in solution, preferring interaction with hard-base donors like oxygen and fluoride to that with sulfur or heavy halide donors. Significant lanthanide interaction with nitrogen donors is observed only when steric factors force the interaction (as in aminopolycarboxylic acid complexes). 

The size of the metal ion has an evident control on the synthesis of the monometallic macrocyclic complexes. For example, all lanthanide(III) ions promote the formation of the six-nitrogen-donor macrocycles with an 18-atom cavity and flexible aliphatic diimine side-chains, even though the yields become progressively lower as the metal atom size decreases. However, when the six-nitrogen, 18-atom macrocycles contain rigid o-phenylene side chains, the smaller lanthanides actually fail to promote... 

Both the synthetic trends and the reactivity of the metal macrocycle complexes considered in this review find some rationalization in the strudural data obtained from X-ray analysis. In the series of complexes containing the six-nitrogen, 18-atom macrocycles with aliphatic side-chains, the macrocydic moiety can flex to a different extent in each metal complex, thus allowing the most favorable metal-donor distance to be achieved for all donor atoms. These favorable metal-donor distances, together with appropriate geometries of the donor atoms and low steric strain, must account for the unique inertness displayed by these metal-macrocycle entities under conditions (dilute aqueous solution, presence of acids, bases and competing ligands) that would cause most other lanthanide complexes to decompose instantly. 

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