Seven-coordinate lanthanide complexes

Seven-Coordinated Lanthanide Complexes with -Diketones... 

Seven-coordinate lanthanide complexes with p-diketones are lacking, such an example is [Yb(TFPP)(L ) (H2O)] (see Figiue 10) where H2TFPP = 5,10,15,20-tetia(4-fluorophenyl)porphyrin. Water that binds to ytterbium(ni) ion quenches the NIR emission of Yb +, resulting a shorter lifetime of 2.4ps. 

Figure 9.23 A seven coordinate lanthanide complex that responds to change in phi through aggregation when in the deprotonated state, triggering an increase in the luminescence signal...

This is the first example of electrochemical tuning of lanthanide luminescence and opens up new opportunities for signal manipulation and responsive imaging [60]. The seven-coordinate lanthanide complex with an appended carboxylate-containing arm (Fig. 9.23) has been used as pH responsive probe through change in the molecular structure in solution. An increase in pH deprotonates the carboxylic moiety that in turn binds to the unsaturated lanthanide. This affords dimeric entities in solution where the displacement of solvent molecules triggers an increase in emission intensity proportional to pH [65]. 

Polypyrazolylborates. This area of chemistry has developed considerably. [LnTp3] have nine-coordinate stmctnres for early lanthanides (e g. Pr, Nd), bnt eight-coordinate for the later metals (e g. Yb). Seven-coordinate bis complexes [Ln(Tp)2Cl] are formed nsing totally moisture-lfee conditions, bnt these readily add a Lewis base, for example, water forming [Ln(Tp)2Cl(H20)]. A very wide range of componnds, many of Sm, En, and Yb, in both the -1-2 and -T3 states, has been synthesized with Tp , this time with a maximum of two Tp bound. In triflate complexes... 

Pope, S.J.A., Burton-Pye, B.P., Berridge, R., et al. (2006) Self-assembly of luminescent ternary complexes between seven-coordinate lanthanide(lll) complexes and chromophore bearing carboxylates and phosphonates. Dalton Transactions, 2907. 

The very useful lanthanide shift reagents, which facilitate analysis of molecular stereochemistry because of their line-broadening characteristics in NMR spectra, were studied when bound as a chelate complex to thietanes. X-Ray analysis of the adduct 3,3-dimethylthietane 1-oxide with tris(dipivalo-methanato)europium(III) [Eu(dpm)3] revealed the structure of a seven-coordinate complex (271). ... 

The present volume is a non-thematic issue and includes seven contributions. The first chapter byAndreja Bakac presents a detailed account of the activation of dioxygen by transition metal complexes and the important role of atom transfer and free radical chemistry in aqueous solution. The second contribution comes from Jose Olabe, an expert in the field of pentacyanoferrate complexes, in which he describes the redox reactivity of coordinated ligands in such complexes. The third chapter deals with the activation of carbon dioxide and carbonato complexes as models for carbonic anhydrase, and comes from Anadi Dash and collaborators. This is followed by a contribution from Sasha Ryabov on the transition metal chemistry of glucose oxidase, horseradish peroxidase and related enzymes. In chapter five Alexandra Masarwa and Dan Meyerstein present a detailed report on the properties of transition metal complexes containing metal-carbon bonds in aqueous solution. Ivana Ivanovic and Katarina Andjelkovic describe the importance of hepta-coordination in complexes of 3d transition metals in the subsequent contribution. The final chapter by Sally Brooker and co-workers is devoted to the application of lanthanide complexes as luminescent biolabels, an exciting new area of development. 

A review of expanded porphyrin hgands can be fonnd. The texaphyrins (8) can be considered as 22-tt-electron benzaimnlene systems with an IS-tt-electron delocahzation path, based on crystal stmctnre data as well as NMR. The cadminm complex of the macrocycle is fonnd to be planar with pentadentate coordination of the macrocycle to cadminm, which becomes seven-coordinate as a resnlt of axial coordination to two pyridine molecnles. The cavity is nearly circular with a center-to-nitrogen distance of 2.39 A. Because of the larger size of this macrocycle, metal ion coordination is generally seen with the larger transition metals and lanthanides. 

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