Temperature-induced solid-to-solid transformation in helical homochiral coordination polymers.

The reactions of (R)- and (S)-4-(1-carboxyethoxy)benzoic acid (HCBA) with 1,3-bis(2-methyl-1H-imidazol-1-yl)benzene (1,3-BMIB) ligands afforded a pair of homochiral coordination polymers (CPs), namely, poly[[[μ-1,3-bis(2-methyl-1H-imidazol-1-yl)benzene][μ-(S)-4-(1-carboxylatoethoxy)benzoato]zinc(II)] monohydrate], {[Zn(CHO)(CHN)]·HO} or {[Zn{(S)-CBA}(1,3-BMIB)]·HO} (1-L), and poly[[[μ-1,3-bis(2-methyl-1H-imidazol-1-yl)benzene][μ-(R)-4-(1-carboxylatoethoxy)benzoato]zinc(II)] monohydrate] (1-D). Three kinds of helical chains exist in compounds 1-D and 1-L, which are constructed from Zn atoms, 1,3-BMIB ligands and/or CBA ligands. When the as-synthesized crystals of 1-L and 1-D were further heated in the mother liquor or air, poly[[μ-1,3-bis(2-methyl-1H-imidazol-1-yl)benzene][μ-(S)-4-(1-carboxylatoethoxy)benzoato]zinc(II)], [Zn(CHO)(CHN)] or [Zn{(S)-CBA}(1,3-BMIB)] (2-L), and poly[[μ-1,3-bis(2-methyl-1H-imidazol-1-yl)benzene][μ-(R)-4-(1-carboxylatoethoxy)benzoato]zinc(II)] (2-D) were obtained, respectively. The single-crystal structure analysis revealed that 2-L and 2-D only contained one type of helical chain formed by Zn atoms and 1,3-BMIB and CBA ligands, which indicated that the helical chains were reconstructed though solid-to-solid transformation. This result not only means the realization of helical transformation, but also gives a feasible strategy to build homochiral CPs.