Self-Assembly of an Infinite Copper(II) Chiral Metallohelicate

The self-assembly between a chiral polydentate N8O4 ligand, containing a bis-imidazole unit substituted by 4 L-valine groups, and copper(II) ions leads to an optically pure, infinite M-helical chain. The X-ray diffraction studies revealed that the compound crystallizes in the hexagonal chiral space group P6122 with a single [HValbiim]5- unit coordinating three different copper(II) centers. Cul is in a distorted square-pyramidal environment, Cu2 is involved as well in a five-coordinated CuN2O3 chromophore but with a coordination geometry intermediate between a square pyramid and a trigonal bipyramid, and the third copper(II) ion, namely, Cu3, is in a slightly distorted square planar environment defined by three nitrogen atoms and one oxygen atom from two [Hvalbiim]5- ligands. The resulting double bridge (namely, Cu2-042 and Cu2-042) gives rise to the formation of a hexanuclear entity. The found antiferromagnetic behavior, successfully modeled by an isosceles triangle, is consistent with the strong coupling of Cul and Cu2 through a hydroxido group and the coupling of Cu3 with each one of Cul and Cu2 through one of the imidazolato groups from the Biim2- moiety of the ligand.