Ligands tren

The tetradentate ligand tren usually forms 1 1 six-coordinate complexes with two additional ligands in cis positions750 as in the complex [Ni(NCS)2(tren)],724 as well as dinuclear complexes of general formula [NiX(tren)]2(BPh4)2 where two X groups are bridging the Ni(tren)2+ moieties.725"728 A common feature of both NJ and NCO- complexes is the marked asymmetry... 

The unsymmetrical linear tetramines [3,3,2-tet (54) and 2,2,3-tet (53)]32,741 have not been widely investigated, presumably because of synthetic difficulties, and the chemistry of the branched chain ligands, tren (57), trtn (58) and trbn (59), has been reviewed by Zipp et al.142... 

Scheme 8. Synthesis of the trimeric ligand TREN(DOTA)3 nonaacid...

Figure 11.41 A prototype pH triggered molecular muscle based on coiling of ligand 11.68 by Pb2+. The binding of Pb2+ is switched on or off according to the protonation state of the competitor ligand tren (reproduced by permission of The Royal Society of Chemistry).

The quadridentate Tripodal Ligand, tren (191), is often found as an impurity in conunercial samples of trien (178) and this has sometimes led to isomeric misinterpretation. Techniques for the separation of these isomers are available when mixtures are suspected. The coordination chemistry of tren and its longer arm analogs has been reviewed. ... 

Figure 5. The tetra-dentate ligand tren coordinates metal ions according to a trigonal-bipyramidal geometry. The fifth coordination site is available for a solvent molecule or for a coordinating anion.

Figure 5.11 A prototype pH-triggered molecular muscle based on coiling of the ligand 5.20 by Pb ". The binding of Pb " is switched on and off according to the protonation state of the competitor ligand tren. A.-M. Stadler, N. Kyritsakas and J.-M. Lehn, Reversible folding/unfoldingof linear molecular strands into helical channel-like complexes upon proton-modulated binding and release of metal ions, Chem. Commun, 2004, 2024-2025. Reproduced by permission of The Royal Society of Chemistry.

When three bipyridine ligands are capped (twice) by a triamine the cage ligand that results can complex three metal atoms simultaneously (in this example the caps are, essentially, the ligand tren, tris(2-aminoethyl)amine)... 

The cadmium(ll) chelate of the tripodal tetradentate ligand tren also yielded the mixed-ligand complex cation of the salt [Cd(tren)(xan)]C104 H20 [29], where the metal ion is only five-coordinated and the anionic xan ligand forms the Cd-N7 bond (2.224 A) reinforced by the intramolecular interligand H-bond (tren)N-H" 06 (2.889 A, 117.6°). In the compotmd traui-[Cd(theo)2(H20)4]-2DMF [30], each theophilinate(l-) anion binds the cadmium(ll) center by the Cd-N7 bond (2.300 A) in cooperation with an intramolecular H-bond (aqua)0-H - 06 (2.689 A, 158.5°). 

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