Segmental ligands

Other ligands of the type whose complexation has been examined in detail include a range of 2,6-bis(5, 6-dialkyl-1,2,4-triazin-3-yl)pyridines, 2,6-bis(benzimidazol-2 -yl)pyridine (bzimpy) and A,A,A, A -tetraethylpyridine-2,6-dicarboxamide. In some cases, segmental ligands have been employed to obtain complexes with stranded helical structures. 

Figure 6.26 Double-helical structures of the complexes 52 and 53 of type [MjL2f [M = Fe(II), Ni(II)] where L is the segmented ligand 51 ...

The development of new segmented ligands with non-identical binding sites, such as 57-59, has led to the formation of a number of both mononuclear and dinuclear, helicates that include mixed-metal species. For example, interaction of 58... 

Two related circular structures have been described recently by Lehn [68] and McCleverty and Ward [69]. The segmental ligand 36 reacts with copper(I) to form a circular dodecanuclear species [Cu]2(36)4] shown in Figure 18 [68]. The metal... 

FIGURE 12 Stereochemical match between (A) bis-tridentate (redrawn after Piguet et al., 1992a) and (B) bis-bidentate segmental ligands with trivalent lanthanides to give triple-stranded, respectively, quadruple-stranded helicates (reproduced by permission from Dong et al., 2007, American Chemical Society). 

Claude Piguet and Jean-Claude G. Btinzli Segmental ligand... 

Designing segmental ligands Principles and synthetic routes... 

FIGURE 41 Synthesis of 3,3, 4,4 -tetrasubstituted diphenylmethane spacers and its incorporation into homotopic C2-symmetrical bis-tridentate segmental ligands (S = spacer). 

Since the bidentate binding units in the segmental ligands are connected by saturated methylene units, which are poor electronic relays, we can expect that the photophysical properties of the helicates can be easily deduced from fhose found in fhe mononuclear friple-helical precursors. 

FIGURE no Segmental ligands for nd-4f triple-stranded heterometallic helicates. 

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