Schiff-bases lanthanide complexes

Schiff base macrocyclic complexes of lanthanides have been prepared by a metal-template condensation of a diamine and 2,6-diacetyl or 2,6-diformyl derivative of pyridine or p-cresol [74]. The yield of these complexes depends on the radius of the metal ion and the donor ability of the counterion [75]. The acetate anion gave high yields while chloride and perchlorate anions gave poor yields [76]. In general the template synthesis... 

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

Mono- and bimetallic lanthanide complexes of the tren-based macrobicyclic Schiff base ligand [L58]3- have been synthesized and structurally characterized (Fig. 15), and their photophysical properties studied (90,91). The bimetallic cryptates only form with the lanthanides from gadolinium to lutetium due to the lanthanide contraction. The triplet energy of the ligand (ca. 16,500 cm-1) is too low to populate the terbium excited state. The aqueous lifetime of the emission from the europium complex is less than 0.5 ms, due in part to the coordination of a solvent molecule in solution. A recent development is the study of d-f heterobimetallic complexes of this ligand (92) the Zn-Ln complexes show improved photophysical properties over the homobinuclear and mononuclear complexes, although only data in acetonitrile have been reported to date. 

Lanthanide-labeled oligonucleotide probes are now available commercially (161). Oligonucleotides are synthesized containing free amino groups, which are then labeled with a lanthanide chelate via a Schiff base conjugation [similar to the reaction shown in Fig. 19 but with a monoaldehyde functional group (linker) of a lanthanide complex in place of glutaraldehyde]. b. 

Casellato, U. Tamburini, S. Tomasin, P. Vigato, P. A. Botta, M. Lanthanide(III) complexes with a podand Schiff base containing an N403 coordination site. Inorg. Chim. Acta 1996, 247,143-145. 

Howell, R. C. Spence, . V. N. Kahwa, I. A. White, A. J. P. Williams, D. J. The preparation and crystal and molecular structures of new luminescent Schiff-base complexes featuring coupled lanthanide(III) cations. J. Chem. Soc., Dalton Trans. 1996, 961-968. 

Aspinall, H. C. Black, J. Dodd, I. Harding, M. M. Winkley, S. J. A lanthanide-templated Schiff-base condensation reaction to give a trinuclear macrocyclic complex. J. Chem. Soc., Dalton Trans. 1993, 709—714. 

There has been recent interest in lanthanide complexes of ligands of the type (21). These are in some sense nitrogen analogues of the crown ethers. As Schiff bases, their lanthanide complexes may be synthesized by a template condensation, for example from 2,6-diacetylpyridine, 1,2-diaminoethane and lanthanum nitrate. These components react in alcohols to give [La(N03)3L], where the aza-crown L = (21 R = Me). This compound has a structure (Figure 6), quite analogous to that of [La(N03)3(18-crown-6)], in which La—N... 

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... 

Complexation of macrocyclic ligands to lanthanide cations has been studied extensively [207,208], One main reason for the current interest in those macro-cyclic complexes are their intrinsic paramagnetic and luminescent properties. There is also the steadily increasing number of tailor-made macrocyclic ligands [209], This section will focus on complexes which contain macrocycles as discrete counterions and in particular on the coordination chemistry of phthalocyanine (Pc) and porphyrin (Por) ligands. Schiff base ligands which display another source of amine functionalities are usually not deprotonated under the prevailing reaction conditions [210]. 

The importance of the chelate effect combined with the construction of multidentate ligands is well known in lanthanide chemistry. This is expressed in the rich coordination chemistry of / -diketonates [88] or complexes with Schiff bases [89] and macrocyclic polyethers [90] where lanthanide cations achieve steric saturation by high coordination numbers. Entrapment of the cation in a macrocyclic cavity results in greater complex stability. However, simply functionalized ligands such as ethanolamines can also supply a suitable ligand sphere [91-93],... 

Figure 28 shows another two examples of trivalent Schiff base ligands. The macrocyclic ligand was generated in a template condensation of 2,6-diacetyl-pyridine with l,3-diamino-2-hydroxypropane in the presence of lanthanide salts [187]. The La(N03)3 H20-reaction yielded a trinuclear complex of composition [La3U/ 3-0HX0H)(N03)4]-7H20 [188]. 

Lanthanide complexes with diketones and Schiff bases.266... 

Lanthanides form complexes with Schiff bases or imines quite readily. The important ligands are obtained by the condensation of an amine with salicylaldehyde derivative or a /6-diketone. Schiff base complexes have been prepared by the reaction of ligand with a lanthanide 2-propanolate. The solvent medium is benzene and the liberated propanol during the complexation reaction is removed by distillation as alcohol-benzene azeotrope [57,58]. 

Since Schiff bases are relatively acidic, the complexes can be prepared with a hydrated lanthanide salt in pure ethanol. A mild base such as sodium acetate or triethylamine can be added slowly to achieve deprotonation [59]. 

Schiff base complexes of lanthanides derived from -diketones and imines can be prepared [60] in acetone-water medium by dropwise addition of ammonia to adjust the pH to 5-6. In the absence of addition of ammonia simple adducts between lanthanide salt and imine are formed [61]. 

The complexation with Schiff bases is ambiguous. Lanthanides form complexes with f-butylsalicylidenimine (Sal) of the formula La(Sal)2-3H20 with the loss of phenolic proton and the ligand in the anionic form is bonded to the lanthanide [251]. In contrast, complexes of the type [Y(SalH)3Cl2]Cl containing neutral ligand have been reported based on elemental analysis and conductivity data [255]. 

Cryptate complexes with macrobicychc hgands containing three bipy units, in which the Ln + ion is contained within a hgand cavity, have been synthesized. Such hgands will complex Ln + ions, such as Eu + and Sm +, under conditions where Ln + ions are not. An application has been using lanthanide cryptates of the early lanthanides (La, Ce, Eu) as catalysts in the hydrolysis of phosphate monoesters, diesters, and triesters. Schiff base complexes can be synthesized by the reaction of a lanthanide salt with a diamine and a suitable carbonyl derivative such as 2,6-diacetylpyridine. 

Both GC and LC behavior of metal complexes of various ligand types including salicy-laldimines and Schiff bases and fluorinated /3-diketones was reported. Metal ions included the lanthanides, transition metals, Pt, Pd and Zn. Dissociation and thermal instabilities were found to be the main limitations in the chromatography of such derivatives. The data indicate that pre-column derivatization and GC is unlikely to provide a viable method for the ultratrace determination of metal ions except in rare circumstances. On the other hand, LC of complexed metal ions was found as a valuable technique that combines the advantages of versatility, specificity and sensitivity with the capacity for simultaneous determination and speciation. Diastereoisomers of oxovanadium(IV) complexes of tetradentate Schiff bases could be resolved by both GC and LC . ... 

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