Tris-2,2 -bipyridine ligands

Fig. 4. A virtual dynamic combinatorial library of oligomeric circular helicates generated from a tritopic tris(2,2 -bipyridine) ligand and metal ions of octahedral coordination. AH constituents of the dynamic library are potentially accessible at any time by reversible interconversion.

Similarly, when a mixture of the two tris-bipyridine ligands 129 and 148 is allowed to react simultaneously with copper(l) and nickel(il) ions, only the double helicate 132 and the triple helicate 149 are formed (Figure 49). Thus, parallel operation of two programmed molecular systems leads to the clean self-assembly of two well-defined helical complexes from a mixture of their four components in a process involving the assembly of altogether 11 particles of four different types into two supramolecular species. 

Cover Illustration Creativity in art and science. The creative power in chemistry is expressed by the design of molecular species, which self-assemble into organized supramolecular assemblies. The cover illustration shows a synthetic double helix, the double stranded helicate containing a tris bipyridine ligand, held together by Cu(l) ions (see Section 9.3.1). The creative power in art is expressed by the sculpture, la Main de Dieu, by Auguste Rodin. Photograph by Bruno Jarret AD AGP, Paris 1955. 

In a similar vein, self-assembly of the dimethyl derivative of the corresponding tris(bipyridine) ligand in the presence of bipyrimidine and copper(I) spontaneously generates the new ladder structure 49. A similar tetranuclear structure derived from the corresponding bis(bipyridine) ligand has also been reported. 

Encapsulation of a Ru atom into a caged [109, 110] or hemicaged [299] tris-bipyridine ligand extends the MLCT excited state lifetime and improves photostability relative to [Ru(bpy)3] ", while retaining the fast (diffusion controlled) bimolecular excited state electron transfer reactivity. In contrast, the [Ru(bpy)3] + in the core of a dendrimer [248] has about the same inherent lifetime as the free complex but the rate of electron transfer quenching rapidly decreases with increasing the number and size of dendrimer branches. 

Terbium clathrochelate showed green emission of very high intensity. The emission spectrum contains the D4 —> Fj transition bands of the encapsulated terbium ion. The same but less intense emission spectrum was observed at higher temperatures. The luminescence quantum yield is close to 1 at 4.4 K and is approximately 0.05 at room temperature [390]. The decrease in intensity of the terbium(III) ion luminescence starts at 100 K (higher than that of free macrobicyclic tris-bipyridine ligand and lower than that of the corresponding europium(III) compound, Fig. 69). It may be... 

Figure 1 Mismatching ligand and metal preferences, combining a semi-flexible tris(bipyridine) ligand with a...

Figure 25 The flexibility of an ether-linked tris-bipyridine ligand leads to formation of an [Fc4L4]...

Zagres, W., Hall, J., and Lehn, J.-M. (1991) Helicity induction in helicate selforganisation from chiral tris(bipyridine) ligand strands, Helv. Chim. Acta, 1843-1852. 

Very efficient reduction of NAD(P) with formate catalyzed by cationic rhodium complexes. /. Chem. Soc. Chem. Commun., 1150-1151 (d) Franke, M. and Steckhan, E. (1988) Tris(2,2 -bipyridyl-5-sulfonic add) rhodium(III), an improved redox catalyst for the light-induced and the electrochemically initiated enzymatic reduction of carbonyl compounds. Angeiv. Chem., Int. Ed., 27, 265-267 (e) Grammenudi, S., Franke, M., Vogde, F., and Steckhan, E. (1987) The rhodium complex of a tris(bipyridine) ligand - its electrochemical behavior and frmction as mediator for the regeneration of NADH from NAD. /. Ind. Phenom. Macrocycl. Chem., 5,695-707 (f) Hollmaim, F., Kleeb, A., Otto, K., and Schmid, A. (2005)... 

A good example is the excited state of the tris(bipyridine)ruthenium(2+) ion, Ru(bpy)5+. This species results from the transfer of an electron from the metal to a ligand. In the language of localized valences, it is a ruthenium(3+) ion, coordinated to two bipyridines and to one bipyridyl radical anion in other words, [Ru3+(bpy)2(bpy )]2+. This excited state is a powerful electron donor and acceptor.17 The following equations show an example of each quenching mode ... 

Bkouche-Waksman, I. Guilhem, J. Pascard, C. Alpha, B. Deschenaux, R. Lehn, J.-M. 110. Crystal structures of the lanthanum(III), europium(III), and terbium(III) cryptates of tris(bipyridine) macrobicyclic ligands. Helv. Chim. Acta 1991, 74,1163-1170. 

The lowest energy MLCT transition of Ru polypyridyl complexes of the type tris-[Ru(4,4/-dicarboxy-2,2/-bipyridine)3] (1), can be lowered so that it absorbs more in the red region of the visible spectrum by replacing one 4,4/-dicarboxy-2,2/-bipyridine (dcbpy) with two thiocyanate donor ligands [Ru(dcbpy)2(NCS)2] (2). In complex 2, the two 4,4/-dicarboxylic acid 2,2 -bipyridine ligands pull while the two thiocyanate donor ligands push electrons. The oxidation potential of the complex 2 is 0.85 V vs. SCE, which is cathodically shifted significantly (0.65 V vs. SCE) compared to the homoleptic type of complex 1, which shows Ru(III/II) couple at 1.5 V vs. SCE. Thus, the... 

Supramolecular Ru and/or Os complexes of tris(bipyridine) bridging ligands. Syntheses, absorption spectra, luminescence properties, electrochemical behavior, intercomponent energy, and electron transfer. [P. Belser, A. von Zelewsky, M. Frank, C. Seel, F. Vogtle, L. De Cola, F. Barigelletti, V. Balzani, J. Am. Chem. Soc. 1993, 225(10), 4076-4086] [ 23]. 

One such example involves a ruthenium tris(bipyridine) complex, illustrated in Fig. 4.24, in which the metal can accept energy from photons and transfer it to the bipyridine ligands. The process of metal to ligand charge transfer is a well known phenomenon in coordination chemistry and the experimental conditions needed to form the complexes are fairly well understood. Added complexity is encountered when the bipyridine units have been modified as in the work of Hammarstrom [47],... 

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