The fixation of linear versus loop-type peptidic structures by metal coordination:: the coordination chemistry of Val-Val- and Val-Val-Val-bridged dicatechol ligands

The Val-Val-bridged dicatechol ligand L-1-H-4 forms triplybridged dinuclear complexes with titanium(IV) ions, while the more flexible Val-Val-Val derivative L-2-H-4 leads to mixtures of complexes containing species with a cyclic arrangement of the ligand; with [cis-MoO2](2+) on the other hand, a well-defined macrocycle [(L-2)MoO2](2-) is formed which possesses a loop-type structure in the peptidic part of the ligand.