Solvent induced conformational transformation of helical chains in new copper(II) coordination polymers

Two isomeric copper-containing coordination polymers, which are constructed from chiral ligand thiazolidine 2,4-dicarboxylic acid (H2L), have been synthesized with the same formula of [CuL(DMF)]n (1 and 1′). Complex 1 was prepared through the reaction of H2L and Cu(ClO4)2·6H2O in the mixture of N,N-dimethylformamide (DMF) and methanol (V/V = 1:1). With the same reactants 1′ was obtained only using DMF as solvent. Single-crystal X-ray diffraction analysis exhibited that 1 is left-handed helical chain and crystallizes in chiral space group P212121, while 1′ is right-handed helix with chiral and polar space group P21. In addition, both coordination polymers show obvious chiral and non-linear optical (NLO) properties, which were characterized by circular dichroism (CD) and second harmonic generation (SHG) measurements.