Complexes triple helical

Spontaneous self assembly of a dinuclear triple helical complex is observed with linked bis-[4,5]-pineno-2,2 -bipyridines. Studies by electrospray mass spectrometry, CD and NMR determined that the major species in solution was a complex of Zn L = 2 3 stoichiometry with a triple helical structure and an enantiomerically pure homochiral configuration at the metal centers. The preference for the formation of one of the possible stereoisomers over the other is of interest.265 Another binuclear triple helical complex is formed from zinc addition to bis[5-(l-methyl-2-(6-methyl-2 -pyridyl)benzimidazolyl)]methane. Spectrophotometric titrations with a zinc solution... 

Piguet, C. Biinzli, J.-C. G. Bernardinelli, G. Hopfgartner, G. Williams, A. F. Self-assembly and photophysical properties of lanthanide dinuclear triple-helical complexes. J. Am. Chem. Soc. 1993,115, 8197-8206. 

Triple Helicates. The steric information contained in the oligo-bipy strands based on bipy units connected in the 6,6 positions is designed to yield double helices on complexation of metal ions undergoing tetrahedral coordination. Steric effects due to the 6,6 -disubstitution hinder the binding of metal ions of octahedral coordination geometry, which would be expected to lead to triple helical complexes. 

Once again, it is possible to extend these ideas to the formation of complexes containing progressively more metal centres. As an example, consider the ligand 7.57. This contains a total of three didentate 2,2 -bipyridine-like domains. Upon reaction with nickel(n) salts, a trinuclear triple-helical complex, [Ni3(7.57)3]6+ 7.58, is formed, in which each of the six-co-ordinate nickel(n) centres is co-ordinated to a didentate metal-binding domain from each of three ligand threads. 

Figure 10.18 Self-assembly of the europium triple helicate complex of ligand 10.9 (= L) (Copyright Wiley-VCH Verlag GmbH Co. KGaA. Reproduced by permission).

Other examples of self-assembled, NIR-emitting triple helical complexes are described in secbon 3.3.4. 

Figure 9 Stereoview of the triple-helical complex [602(20)3]. permission of the Royal Society of Chemistry...

Figure 6 A triple helical complex in which three his-bidentate ligands link two chiral octahedral centres.

The catecholato ligands investigated by Raymond [45] show rather different behaviour. The triple helical complex [Ga2(20)3] undergoes racemization on the NMR timescale as studied by the coalescence of signals due to diastereotopic groups on the terminal amide ligands. The analogous mononuclear complex had been... 

The use of semirigid tridentate binding units restricts the structural issues to [] (L ) ] whereby n = 1-3 characterizes the number of strands wrapped about the central metal. The target Cs-symmetrical triple-helical complex [f (L )3] can be further produced as the major species thanks to a strict control of the conditional information expressed in the stoichiometric ratio f L = l 3 (i.e., entropic selection). 

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