Achiral and Chiral Coordination Polymers Containing Helical Chains: The Chirality Transfer Between Helical Chains

Abstract

Four achiral two-dimensional (2D) coordination polymers of [M(HIDC)(H2O)(prz)0.5]n (M = Fe, 1; Mn, 2; Cd, 3) and [Co(HIDC)(H2O)(pyz)0.5]n (4), one chiral 2D coordination polymer of [Mn(HIDC)(H2O)]n (5), and one 2D coordination polymer of [Fe(HIDC)(H2O)]n (6) (H3IDC = imidazole-4,5-dicarboxylic acid, prz = piperazine, pyz = pyrazine) were hydrothermally synthesized and characterized by single-crystal X-ray diffraction. In 1–3, the HIDC2− anions alternately bridge the M(II) cations to form a one-dimensional (1D) infinite helical chain of [M(HIDC)]∞ along the 21 axis. The chirality of the original formed helical chain is transferred oppositely to neighboring helical chains through the parallel coordination interactions of prz molecules between two adjacent chains, resulting in an achiral 2D sheet of [M(HIDC)(H2O)(prz)0.5]n, in which the helical chains are packed in an alternating left- and right-handed chirality. A similar achiral 2D coordination polymer of 4 was obtained when pyz was used as a linker. Compound 5 crystallizes in a chiral space group P21. In 5, the HIDC2− anions also alternately bridge the Mn(II) to form a 1D right-handed helical chain of [MnHIDC]∞ along the 21 axis, and the right-handed chirality of [MnHIDC]∞ is transferred to neighboring helical chains through the zigzag interchain coordination interactions, leading to the formation of a homochiral 2D sheet, in which all the helical chains are packed in right-handed chirality. In addition, the bulk crystallization of 5 is enantiomeric excess rather than racemic, as evidenced by the results of solid-state vibrational circular dichroism (VCD) and CD spectroscopy. In the 2D structure of 6, the HIDC2− anions alternately bridge the Fe(II) to form a 1D zigzag chain of [FeHIDC]∞ instead of a 1D helical chain, in which all the HIDC2− anions locate on the same side within the chain. Compound 3 displays strong blue fluorescent emission at room temperature. Magnetic susceptibility measurements of 2 and 5 exhibit antiferromagnetic interactions between the nearest Mn(II) within the sheet, with J = −0.48 cm−1, g = 2.10 for 2, and J = −0.51 cm−1, g = 2.03 for 5.