Two homochiral crystals of anion-directed Cu(I) and Zn(II) helical coordination polymers

Abstract

Two chiral coordination polymers [CuI(TMBP)(CH3CN)2·ClO4]n (1) and [ZnII(TMBP)(SCN)2]n (2) have been synthesized with 3,3’,5,5’-tetramethyl-4,4’-bipyrazole (TMBP) as ligand. Their structures were determined by single-crystal X-ray diffraction (SCXRD) analysis and further characterized by power X-ray diffraction (PXRD) analysis, FT-IR spectroscopy, and thermogravimetric (TG) analysis. 1 is constructed by left-handed double-stranded helices with the same chirality, while 2 possesses right-handed single-helical chains. The existence of ClO4− in 1 might be the main reason for forming double-stranded helices, while it leads to single-helical chains under induction of SCN−, exhibiting a anion-directed synthesis process. The selected two single crystals are both homochiral according to the Flack parameters (≈0) from crystal refinement. The bulk sample of 1 exhibits a negative solid-state Cotton effect, while that of 2 shows a positive one. In addition, the crystal sample of 1 exhibits strong ligand-based and metal to ligand charge transition (MLCT) emission in solid-state luminescence with comparison to weakly luminous 2 at room temperature.