Anion-Driven Conformational Polymorphism in Homochiral Helical Coordination Polymers YuanGuozan ZhuChengfeng LiuYan XuanWeimin CuiYong 2009 Three homochiral 3D frameworks are assembled based on periodically ordered arrays of helices built from axial chiral 3,3′-bipyridine-5,5′,6,6′-tetramethyl-2,2′-dimethoxy-1,1′-biphenyl ligands and linearly coordinated Ag(I) ions. The aggregation behavior of silver salts and the ditopic ligand in solutions was investigated by a variety of techniques, including <sup>1</sup>H NMR, UV−vis, CD, GPC and MALDI-TOF. The cationic polymer skeleton exhibits an unprecedented conformational polymorphism in the solid-state, folding into two-, three- and four-fold helices with NO<sub>3</sub><sup>−</sup>, PF<sub>6</sub><sup>−</sup> and ClO<sub>4</sub><sup>−</sup> as the counteranion, respectively. The two-fold helices cross-link <i>via</i> argentophilic Ag−Ag interactions to form sextuple helices, which lead to a three-dimensional (3D) chiral framework. The three-fold or four-fold helices, on the other hand, self-associates in pairs to form three-dimensional tubular architectures. This anion-dependent self-assembly behavior can be rationalized by considering the sizes, geometries and binding abilities of the counteranions and subsequent chain conformation to minimize steric repulsions and maximize secondary interactions.