Terbium halides

An interesting method for obtaining a pure sample of terbium is to place one of the terbium halides (fluorine or chlorine) in a crucible and heat it in a helium atmosphere. The two elements will separate as a result of different densities. When the sample cools, the terbium can be separated from the halide. 

Parker, D., Senanayake, P. K., Williams, J. A. G., Luminescent sensors for pH, p0(2), halide and hydroxide ions using phenanthridine as a photosensitiser in macrocyclic europium and terbium complexes. J. Chem. Soc., Perkin Trans. 21998, 2129-2139. 

The luminescence of terbium (42) and europium macrocyclic complexes have been studied and found to depend upon pH. The phenanthridine sidechain acts as a photosensitizer and (42) exhibits luminescence quenched by molecular oxygen corresponding Eu compounds exhibit halide-quenched emisssion. ... 

In contrast, the anhydrous trichlorides, tribromides and triiodides and the reduced halides are extremely air sensitive materials and are rapidly hydrated or hydrolyzed in air. The triiodides are especially moisture sensitive and deliquesce. Unlike the trifluorides, the other trihalides are very soluble in water at 25°C. Solubilities of the trichlorides vary from 3.89 moles/ for lanthanum, to a minimum of 3.57 moles/ at terbium and back up to 4.10moles/ at lutetium with pH values of the saturated solutions in the range 1.0-2.0 (Spedding et al., 1974a). At high temperatures, the trichlorides, tribromides and triiodides also... 

Halide addition caused little change to the metal-based emission. For example addition of 30 mM NaCl to the terbium complex 7b caused only a 14% reduction in the intensity of the Tb emission at 545 nm with the monocationic complex 5b, an even smaller reduction was observed. 

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