An Efficient Strategy for Self-Assembly of DNA-Mimic Homochiral 1D Helical Cu(II) Chain from Achiral Flexible Ligand by Spontaneous Resolution

Four helical copper complexes Cu[N(CN)(2)](2)(Hhmp) (1), {Cu[N(CN)(2)](2)(Hhmp)}(infinity) (2), (L-{Cu-4[N(CN)(2)](2)(hmp)(4)(CH3COO)(2)center dot CH3CN}(infinity) (3a), and D-{Cu-4[N(CN)(2)](2)(hmp)(4)(CH3COO)(2)center dot CH3CN}(infinity) (3b) (Hhmp = 2-(hydroxymethyl)pyridine) have been prepared toward a mimic DNA structure. By changing the solvent and supplementary ligand, the structures can be successfully tuned from quasi-double-helical (complex 1) to racemic 1D single helix (complex 2), then the right (3a)-/left (3b)-handed double helices. The topologies of 3a and 3b may be considered as a mimic of DNA, where the Cu-O bonds between the two strands replace the hydrogen-bonding interactions in DNA. Solid-state circular dichroism spectra confirmed that 3a and 3b are optically active, respectively. Magnetic measurements for 1-3 indicated all complexes to be antiferromagnetic interactions. The best fitting results to the magnetic susceptibilities were J = -0.80 cm(-1), g = 2.11 for I and J(1)= -9.22 cm(-1), J(2)= 3.56 cm(-1), J(3) = -9.49 cm(-1), g = 2.27 for 3.