Conformational Effect of 2,6-Bis(imidazol-1-yl)pyridine on the Self-Assembly of 1D Coordination Chains:Spontaneous Resolution,Supramolecular Isomerism,and Structural Transformation

摘要

The achiral 2,6-bis(imidazol-1-yl)pyridine (L) was used as the ditopic organic tecton for the formation of coordination polymers with Zn(ll) ions.Hydrothermal reaction between L and ZnX2 (X = Br,Cl) afforded spontaneous resolved double helical motifs in ZnLCI2 centre dot 0.5H2O (1) and ZnLBr2 centre dot 0.25H2O (2).In the homochiral crystals of 1a and 2a,the helices are of M-helicity,whereas,in 1b and 2b,they are of P-helicity.In contrast,solvothermal reaction between L and ZnCI2 in dried DMF afforded achiral ZnLCI2 (3a),which exhibits a zigzag polymeric motif.An achiral polymorph 3b which contains 2_1 helical chains was obtained in wet DMF.The formation of different 1D motifs was related to the conformations of L.All these compounds were characterized by infrared spectroscopy,elemental analyses,and single-crystal X-ray diffraction.As revealed by thermal gravimetric analysis and powder X-ray diffraction study,the homochiral motif in 1 was stable even upon removal of guest water molecules.Contrastingly,structural transformation from 3a or 3b to 1 is possible upon hydration.