SELF-ASSEMBLY OF DINUCLEAR HELICAL AND NONHELICAL COMPLEXES WITH COPPER(I)

The ligand 1,3-bis(1-methylbenzimidazol-2-yl)benzene (mbzimbe, L3) reacts with copper(I) to give [Cu2(L3)2](ClO4)2. The crystal structure of this compound (Cu2C44H36N8Cl2O8, a = 13.661 (1) angstrom, b = 19.829 (3) angstrom, c = 15.413 (2) angstrom, orthorhombic, Pbca, Z = 4) shows a dinuclear centrosymmetrical nonhelical structure in which each copper is linearly coordinated by a benzimidazole group of each ligand. The complex displays a weak intramolecular stacking interaction between the benzene groups. This complex can be considered as a stereoconformer of the double-helical complex [Cu2(L1)2](ClO4)2 (L1; 2,6-bis(1-methylbenzimidazol-2-yl)pyridine). Conductivity measurements and UV-visible spectra show that the dimeric structures are maintained in solution in polar aprotic solvents. H-1 NMR measurements show that [Cu2(L1)2]2+ retains its helical structure in solution. Comparison of helical and nonhelical structures with those formed by Cu(I) with related ligands allows discussion of the factors favoring the formation of self-assembled dinuclear complexes.