Terbium structure

Fig. 6.8. Structures of some common fluorophores. DPH = diphenylhexatriene NBD = nitrobenzoxadiazole Tb-DTPA-csl24 = terbium diethylenetriaminepentacetate-carbostyril 124, DAPI = 4, 6-diamidino-2-phenylindole Nile red = 9-(diethylamino)-5H-benzo-[a]phenoxazin-5-one.

Figure 2.1 Structure of (a) terbium phthalocyaninato derivative, (b) [Ln(W5018)2]9 ion, (c) [Ln(P2-SiW11039)2]13 ion and (d) Preyssler anion [l nP5W30O110]12-.

The lanthanide trichlorides have three different crystal structures. The trichlorides of the lighter lanthanides (La—Gd) have the UCI3 type (P63/OT) structure, while the trichlorides of the lanthanides heavier than terbium have the YCI3 type (C2/ot) structure 67, 174, 175). Terbium trichloride and a second form of DyCls have a third structure (PuBr3 type, Cmcni) 176). 

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. 

Bkouche-Waksman, I. Guilhem, J. Pascard, C. Alpha, B. Deschenaux, R. Lehn, J.-M. 110. Crystal structures of the lanthanum(III), europium(III), and terbium(III) cryptates of tris(bipyridine) macrobicyclic ligands. Helv. Chim. Acta 1991, 74,1163-1170. 

Since the backup ions other than aluminum are of a size similar to the terbium ion, it is reasonable to assume that the structure of the glass matrix over the whole series is the same. Therefore, the concentration dependence of the lifetime is unequivocally due to terbium ions being packed closer and closer together. Pearson and Peterson postulate that, as the ions are situated closer and closer together, the quenching mechanism of Dexter and Schulman (45) becomes operative. That is, the excitation jumps from ion to ion by a resonance process until it reaches a sink. 

Figure 16-4 The dinuclear iron center or ferroxidase center of human ferritin based on the structure of a terbium(III) derivative.73 Courtesy of Pauline Harrison.

Tb-Cu-Sb. A ternary compound of terbium with copper and antimony of the 3 3 4 stoichiometric ratio was identified and studied by means of X-ray analysis by Skolozdra et al. (1993). Tb3Cu3Sb4 was found to have the Y3Au3Sb4 type structure with a lattice parameter of a = 0.9522 (X-ray powder diffraction). For experimental details, see the Y-Cu-Sb system. 

In 1923 CeC>2 was found to have the fluorite structure (Goldschmidt and Thomas-sen, 1923), and in 1926 PrC>2 was found to have the same structure (Goldschmidt, 1926). In 1950 the intermediate compositions in the PrO system were reported to have the fluorite structure of variable lattice parameters (the superstructure reflections were not observed). In 1951 TbC>2 was also shown to have the fluorite structure (Gruen et al., 1951). By this time the basic fluorite structure had been established for all the known higher oxides of cerium, praseodymium and terbium. 

Another example of a different type of correlation of structural to photophysical properties is shown in a study of a unique terbium compound [63]. This compound will be briefly discussed and is depicted in Figure 7.9 with its nonlinear emission properties with excitation at 800 nm. The photophysical properties are atypical and rather extraordinary due to the unusual molecular structure of the co-crystallization compound (4) of the organic chromophore and the terbium salt This compound shows both multiphoton absorption induced green f-f emission from the terbium ion as well as second-harmonic generation. However, unlike previously... 

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