Chiral and achiral helical coordination polymers of zinc and cadmium from achiral 2,6-bis(imidazol-1-yl)pyridine: Solvent effect and spontaneous resolution

Abstract

Four 2D helical coordination polymers (CPs) (1–4) were synthesized using achiral 2,6-bis (imidazol-1-yl)pyridine (pyim2) ligand with metal nitrates (metal = zinc and cadmium), which showed that variation in the solvent condition leads to difference in geometry around the central metal ion and results in chiral/achiral behaviour of these CPs. By using (pyim2), [trans-Zn(pyim2)2(NO3)2]n (1) was obtained by unary solvent (MeOH), while [trans- Cd(pyim2)2(NO3)2] n (2) was formed under binary solvent mixtures (DMF/MeOH). On the other hand, in ternary solvent mixture (DMF/MeOH/H2O) it resulted into an achiral {[trans-Zn(pyim2)2(H2O)2] ·(NO3)2}n (3) and homochiral {[cis-Cd(pyim2)2(H2O)2] ·(NO3)2}n (4) coordination polymer, respectively. The homochiral behaviour of the coordination polymer (4) was further studied by solid state CD spectra and also its optical behaviour was analyzed by polarimetry.