STABILITY AND LABILITY OF DICOPPER DOUBLE-STRANDED HELICATES IN SOLUTION

Stability constants have been measured for a series of ligands based o n a 2,2'-(pyridine-2,6-diyl)bis[1H-benzimidazole] unit which forms din uclear double-stranded helical complexes with copper(I). Variation of different structural parameters confirms the importance of the coordin ate bond, the stacking interactions, and the weakly bridging pyridine units observed by X-ray crystallography. The stabilities of the comple xes depend strongly on the solvent, and in MeCN, which is a good solve nt for copper(I), the complexes are less stable and assemble in a step wise manner. The interconversion of the enantiomers may be followed by H-1-NMR and takes place on a millisecond time scale around room tempe rature. The trends in lability are similar to those found for the stab ility of the complexes.