Hierarchical Helix of Helix in the Crystal: Formation of Variable-Pitch Helical π-Stacked Array of Single-Helical Dinuclear Metal Complexes

Unique helix of helix structures were formed via intermolecular pi-stacking and metal-metal interactions in the crystal of single-helical dinuclear complexes [(LM2)-M-2] (M = Pd, Ni) having an acyclic bis(N2O2)-type ligand. The difference in the helical winding angle of the constituents (401.7 degrees for [(LPd2)-Pd-2]; 421.3 degrees for [(LNi2)-Ni-2]) led to variation of the helical pitches of the helical array (7(2) helix for [(LPd2)-Pd-2]; 6(2) helix for [(LNi2)-Ni-2]).