Lanthanide complexes Schiff-base ligands

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. 

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]. 

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]. 

NOs , Cr and DOS (dodecylsulfate). In Figure 2.53, the structure of the LH ligand N-octadecyl-4-tetradecyloxysalicylaldimine is shown. In the complex, three monodentate Schiff base ligands bind in a zwitterionic form to the lanthanide ion. The coordination sphere of the lanthanide ion is completed by coordination to the counter anions. All the complexes [LmILHIsXs] form a smectic A phase. The lowest transition temperatures are observed for the dodecylsulfate complexes.Although the studies of the magnetic anisotropy have been largely been focused on Schiff base complexes, a few data for /3-enaminoketone complexes are available. 

Mono- and bimetallic lanthanide complexes of the tren-based macrobicyclic Schiff base ligand have been synthesized and... 

TABLE 4 Thermal Behavior of the Lanthanide Complexes Schiff s Base Ligands L4H with Nitrate Counter Ions > of the One-Ring... 

Polynuclear Lanthanide Complexes with Conjugated Schiff-Base Ligands 282... 

Polynuclear Lanthanide Complexes and Lanthanide Coordination Polymers with Flexible Schiff-Base Ligands 286... 

The synthesis, structures, and luminescence properties of polynuclear lanthanide complexes and lanthanide coordination polymers, which are formed from multidentate oxygen and nitrogen-containing Schiff-base ligands, are described in this chapter. 

POLYNUCLEAR LANTHANIDE COMPLEXES WITH CONJUGATED SCHIFF-BASE LIGANDS... 

Recently, the use of pthalocyanines and porphyrins by Ishikawa and coworkers enabled tiie synthesis of several so-called double-decker or triple-decker lanthanide complexes, described as stacked Ji-conjugate molecules. The photophysical properties of lantiianide ious depeud markedly on their coordination environments. Since a multidecker framework can effectively keep solvent molecules away from Ln centers, it is assumed that enhanced luminescent properties can be achieved witii these types of architectures. We discovered that the use of two conjugated Schiff-base ligands H2Lh can stabihze novel multidecker framewoiks (Scheme 1). 

Multidecker lanthanide complexes (1-5) have been synthesized from the reactions of lanthanide salts with conjugated Schiff-base ligands H2L . An interesting emerging feature exhibited by these complexes is the self-assembly of stacked multidecker stmctures in which Ln ions are sandwiched between alternating layers of the Schiff-base ligands. 

Two kinds of salen-type Schiff-base ligands, conjugated and flexible, have been used in the synthesis of polynuclear lanthanide complexes and lanthanide coordination polymers Lanthanides Coordination Chemistry, Rare Earth Metal Cluster Complexes. The stoichiometry and structures of these complexes are dependent on the Schiff-base... 

In these lanthanide complexes, the multidentate Schiff-base ligands can stabilize Ln centers and act as antenna sensors for lanthanide luminescence. With the Ln + centers protected by the Schiff-base hgands from solvent and water molecules, those lanthanide complexes with multidecker and cage-like structures show improved luminescence properties. 

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... 

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