Systems Based on Directly-linked, Oligo-pyridines

2 Systems Based on Directly-linked, Oligo-pyridines 

In an extensive series of studies, Constable et investigated the complexation 

As an aside, it is noted that the latter may not be a hard and fast rule, at least when other ligand types are present. Sauvage, Balzani et alP used NMR data as well as absorption and fluorescence results to demonstrate the protonation-driven formation of a double-helical structure involving two ligand strands derived from a pair of 2-/ -anisyl-l,10-phenanthroline units linked in their 9-positions by a 1,3-phenylene spacer. In this case, the first protonation step does not simply represent mono-protonation of one of the phenanthroline units but rather appears to involve a co-operative interaction with a pair phenanthroline units (on different strands). 

Other species. In a study by the Che group, it proved possible to prepare a composite complex that spans both categories. Thus, oxidation (either chemical or electrochemical) of the double-helical [Ru2L2(H20)2] (L = quinquepyridine) cation in aqueous solution results in a product containing both a photoactive ruthenium centre and a high-valent Ru=0 centre in the one complex. 

In an early study by Lehn et al., it was also demonstrated that quaterpyridine (36) forms a monomeric copper(I) species (that is not helical), whereas with cop-per(II) a dimeric species is obtained these complexes may be interconverted elec-trochemically. The above monomeric copper(I) complex was shown by X-ray diffraction to have a tetragonal pyramidal structure [four basal nitrogens and an axial oxygen (water)] in the solid state. This ligand also yields a dinuclear complex with ruthenium(II) of type [Ru2L2] .  

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