Lanthanide ions, complexing

The detection of aromatic carboxylates via the formation of ternary complexes using lanthanide ion complexes of functionalised diaza-crown ethers 30 and 31 has been demonstrated [134]. Like the previous examples, these complexes contained vacant coordination sites but the use of carboxylic acid arms resulted in overall cationic 2+ or 1+ complexes. Furthermore, the formation of luminescent ternary complexes was possible with both Tb(III) and Eu(III). A number of antennae were tested including picolinate, phthalate benzoate and dibenzoylmethide. The formations of these ternary complexes were studied by both luminescence and mass spectroscopy. In the case of Eu-30 and Tb-30, the 1 1 ternary complexes were identified. When the Tb(III) and Eu(III) complexes of 30 were titrated with picolinic acid, luminescent enhancements of 250- and 170-fold, respectively, were recorded. The higher values obtained for Tb(III) was explained because there was a better match between the triplet energy of the antenna and a charge transfer deactivation pathway compared to the Eu(III) complex. 

The kinetics of the hydrolysis of di(2,4-dinitrophenyl) phosphate (DDNPP) were studied in basic solutions buffered with Bis-Tris propane (BTP) in the presence of La3+, Sm3+, Tb3+, and Er3+. Two equivalents of the 2,4-dinitrophenolate ion were liberated for each equivalent of DDNPP and the reaction showed first-order kinetics. Potentiometric titrations showed the formation of dinuclear complexes such as [Ln2(BTP)2(OH) ](6 " i, with values of n varying as a function of pH for all studied metals. Hence the catalytic effect depends on the formation of dinuclear lanthanide ion complexes with several hydroxo ligands.97... 

The problematic of metal and lanthanide ion complexation by macrocyclic ligands.309... 

The other important classes of molecules/ions containing more than one unpaired electron are transition-metal and lanthanide ion-complexes. In general (although not always) these do not exhibit the reactions of Scheme 1.1 and hence are not usually classed as radicals. Often they are very stable, examples being high-spin Mn(II) and Ni(II) the major reaction linking them with radicals is that of electron transfer. (Transition-metal complexes can have up to 5(d) unpaired... 

Table 4.1 lists log[/3i] values for La + and Lu +as well as Sc + and Y +with a number of common ligands, whilst Table 4.2 gives the log[jSi] values for all the lanthanide ions complexing with EDTA", DTPA, and fluoride. 

Wolbers, M.RO., van Veggel, F.C.J.M., SnelUnk-Ruel, B.H.M., et al. (1998) Photophysical studies of m-terphenyl-sensitized visible and near-infrared emission from organic 1 1 lanthanide ion complexes in methanol solutions. Journal of the Chemical Society, Perkin Transactions, 2, 2141. 

Lanthanide ions exhibit long-lived, strong luminescence in the visible region. Their f f absorption bands are, however, very weak and FRET to lanthanide ions is thus inefficient. Efficient FRET and even two-photon absorption118 can be achieved by complexation with appropriate chromophores as an antenna. Lanthanide ion complexes (Figure 2.21) are used... 

Figure 10.19 Polylysine dendritic ligand for lanthanide ion complexation.

Biologically Relevant Structural Coordination Chemistry of Simple Lanthanide Ion Complexes... 

The electronic structure of lanthanide ion complexes is governed by two important factors First, due to the large value of Z, the spin... 

Further applications inlude in vivo targeting and localisation of tumours using appropriate lanthanide-ion complexes (Hider and Hall 1991, Lauffer 1987). 

While the coordination chemistry of lanthanide ions in water is extensive, it is of course not limited to this solvent. In the 1970s, considerable interest developed in the synthesis of lanthanide ion complexes soluble in apolar solvents for their use as lanthanide shift reagents in NMR spectroscopy. Typically, such complexes were neutral and based on chelating 1,3-diketonate ligands, one of their attractive features being that not only did they cause normally overlapping resonances to be spread out and resolved but that they could readily be prepared from optically active ligands and thus used to... 

Because of ligand-field factors, certain transition metal ions, notably Cr + and Co +, almost exclusively exhibit a coordination number of six in their complexes. The kinetically inert nature of Cr and Co complexes, dramatically different from that of the extremely labile lanthanide solvento ions, facilitates the isolation of isomeric species and was crucial in enabling Alfred Werner to formulate the fundamental tenets of coordination chemistry. For simple lanthanide ion complexes, their lability and the lack of a marked sensitivity of their visually observed colors to the nature of the coordination sphere renders Wernerian procedures inapplicable, such that the establishment of high and variable coordination numbers as a characteristic of lanthanide ions has depended largely on modem spectroscopic and crystallographic measurements. 

Some polyhedra are relatively common for lanthanide ion complexes, and they will be discussed here in more detail. They are the square antiprism, the tticapped trigonal prism and the monocapped square antiprism, shown below in Fig. 1.8. The metal ion is situated in the centre of the polyhedron and the ligands, as point charges, are located at the vertices. The proper axis of highest symmetry is chosen to coincide with the z-axis, as mentioned before. 

The most commonly utilised way to measure the unknown emission efficiency of a lanthanide ion complex x is by comparison to a standard ST of known emission efficiency. 

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