Coordination lanthanide ions

As hard metal centers, lanthanide(III) ions have a general preference for hard donor atoms (33,34). Much of their early coordination chemistry involved anionic oxygen donors and it is well established that carboxylates and (3-diketonates are very good at coordinating lanthanide ions. 

The trihalides MBr3 and MI3 are known for all the lanthanide elements. The early lanthanide tribromide (La to Pr) adopt the LaCh structure, while the later tribromides (from Nd to Lu) and the early triiodides (from La to Nd) form a layer structure with eight-coordinate lanthanide ions. 

Compounds of the type Ln[Al(OC3H7)4]3 have been reported [205]. The compounds are monomeric in benzene and a structure consists of a six-coordinate lanthanide ion in which one half of the isopropoxide ions form bridges of the type Ln-O-Al. 

Another concern is that, for a 9-coordinate lanthanide ion in aqueous solution bound to a single tridentate DPA ligand, the six coordinated water molecules will strongly quench the luminescence (92). To eliminate the potential for solvent quenching and improve the sensitivity of the assay, we explored the use of a hexadentate ancillary ligand to encapsulate the Tb ion and exclude solvent from the coordination sphere without impeding dipicolinate chelation. 

The compositions of new phosphates with langbeinite structure type with 9-coordinated lanthanide ions have been proposed in [103, 104], The phosphates with composition Ai 5Lno,5[Fe2(P04)3] with A = K, Rb, Cs were s mthesized, and characterized by X-ray diffraction. The predicted cubic modification, space group P2i3 has been confirmed. This prediction seems to be promising for the actinide phosphate as well. 

Figure 10 Illustration of the sensitization of a coordinated lanthanide ion by absorption of a directly coordinated chromophore (a) or by absorption of a distant coordinated chromophore (b)...

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