Double-Stranded Binuclear Helicates and Helicity Modulation

All of the reported self-assembled complexes of <i>cis</i>-Pd₂L′₂L₂ formulation, where L′ stands for a chelating bidentate ligand and L for a nonchelating bidentate ligand, are “non-helical”. We disclose here the debut of the long awaited “helicate” type architecture of the <i>cis-</i>Pd₂L′₂L₂ formulation. In the present work, the term L′ stands for tetramethylethylenediamine (<i>tmeda</i>) and L stands for a (1<i>H</i>-imidazolyl)­methyl-appended bidentate nonchelating ligand having a rigid spacer. The torsion angle between the two coordination PdN₄ planes of a given “helicate” is considered here as its magnitude of helicity. Length of spacer unit (i.e., 1,4-benzene, 4,4′-biphenyl and 4,4′-<i>p</i>-terphenyl) crafted in the backbone of L is found to impart such conformation to the bound ligand moieties that the magnitude of helicity is modulated