Chelate tetradentate tripodal ligands

Exciting metal complexes can also be obtained with chelating tri- and tetradentate ligands. Iron(III) and chromium(III) complexes of the tripodal tricarbene ligand 25 in the form [M(25)2 ]+ have been described (Fig. 11) [112, 113]. 

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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