Heptadentate cyclen

It is only recently that S. Faulkner took advantage of the kinetic inertness of Lnm cy-clen macrocyclic complexes for producing the neutral pure heterotrimetallic compound [Yb(116b)] (fig. 96) in which convergent directional intramolecular Tbm - Ybm processes are responsible for the sensitization of the NIR Yb(2F5/2) emission (Faulkner and Pope, 2003). The complex is stable in water and according to the lifetime measured (1.83 and 4.22 ps in H2O and D2O, respectively), the hydration number of Yb111 is close to zero ([Pg.370]

Dickins et al. (1998) reported that Eu + and Tb complexes with heptadentate cyclen 28 sensed bicarbonate anion in neutral aqueous solution. Among F , Cl , Br , 1 , NOJ,... 

Fig. 15. Rare earth complexes with octadentate cyclen 27 and heptadentate cyclen 28. Redrawn, with permission,...

Fig. 16. Crystal structures of highly coordinated ternary complexes between rare earth complexes of heptadentate cyclen 28 and amino acid anions. Redrawn, with permission, after Dickins et al. (2004).

As described above for complex 28, rare earth complexes with derivatized cyclen ligands are amenable to binding by hydrogen carbonate and other bidentate anions. When the Gd + complex with chiral heptadentate cyclen 86 (scheme 17) was used as an MRI probe (Dickins et al., 1998), the two bound water molecules were replaced by bidentate hydrogen catbonate anion (HCO ) at higher pH. Thus, this Gd + complex has water proton relaxivity which is responsive to the pH of the system (Aime et al., 1999a). 

Gunnlaugsson, T., Harte, A.J., Leonard, J.R, and Nieuwenhuyzen, M. (2002) Delayed lanthanide luminescence sensing of aromatic carboxylates using heptadentate triamide Tb(III) cyclen complexes the recognition of salicylic acid in water. Chemical Communications, 2134-2135. 

We present the preparation of a new heptadentate ligand containing pendant amide groups in addition to a pendant 4-nitrobenzyl. The selective monoalkylation of cyclen is accomplished by a method similar to that published previously. ... 

Gunnlaugsson et al. isolated the luminescent diaqua Eu " and Tb " complexes with cyclens 55 [135]. The X-ray analysis revealed that cyclen 55b worked as a heptadentate ligand. These non-chromophoric complexes were photophysically silent upon excitation at 300 nm, but their Tb " complexes displayed characteristic emissions via highly coordinated complex-ation with chromophoric salicylate anion. The excited coordinated sah-cylate anion sensitized the lanthanide center, and luminescence enhancement factors of ca. 680 and 220 were observed with the two Tb " complexes. Since acetylsalicylate anion gave no sensitization, both complexes worked as effective chemosensors for salicylate anion under physiological conditions. 

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