The helical structure enhances the stability of a chiral one-dimensional dysprosium phosphonate in solvent

Abstract

Artificial micro/nanowires derived from coordination polymers (CPs) are highly attractive due to their unique physicochemical properties; however, their stability in solution has remained a significant challenge. Herein we propose an innovative strategy, i.e., enhancing their stability in solvents by forming CP superhelix structures. The study focuses on the chiral lanthanide phosphonate compounds, specifically R- and S-Dy(pempH)3·H2O with one-dimensional (1D) chain structures, which can exist in both crystalline (R-, S-1c) and helical forms (R-, S-1h). We initially assessed the stability of R-1c crystals immersed in various solvents. At ambient conditions, R-1c crystals proved stable in water but swelled to varying extents when exposed to alkyl alcohol (MeOH, EtOH, n-PrOH, n-BuOH), and quickly exfoliated in halomethane (CH2Cl2, CHCl3, CH2Br2, CHBr3) to form gels. All-atom molecular dynamics simulations indicated that solvent-chain interactions, solvent-solvent interactions, and the size of solvent molecules collectively influence the swelling or striping rate of R-1c crystals. Interestingly, chiral aerogels obtained by supercritical carbon dioxide treatment of the R-1c gels formed in CHCl3 (12.0 mmol/L) exhibited enantioselective adsorption properties toward chiral molecules of R- and S-2-butanol. Moreover, after a 2 min dispersion in a dilute CHCl3 solution of R-1c (0.12 mmol/L), ultralong nanowires of R-1nw were produced, which fragmented into nanoparticles within 10 min of dispersion. In contrast, the R-1h superhelix remained stable within 10 min in the same dilute CHCl3 solution. These findings suggest that the formation of helical structures enhances interchain interactions, significantly improving the stability of 1D CP micro/nanowires in solvents. This research may provide valuable insights for developing functional CP micro/nanowires for practical applications.