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 π-stacking and metal–metal interactions in the crystal of single-helical dinuclear complexes [L2M2] (M = Pd, Ni) having an acyclic bis­(N2O2)-type ligand. The difference in the helical winding angle of the constituents (401.7° for [L2Pd2]; 421.3° for [L2Ni2]) led to variation of the helical pitches of the helical array (72 helix for [L2Pd2]; 62 helix for [L2Ni2]).