Exploring VOCs Adsorption in a New Series of Hg(II) Bispidine-Based Coordination Polymers

Bispidine-based coordination polymers (CPs) were obtained by reacting ligand 1 and HgCl2 under various conditions. Slow crystallization experiments resulted in single crystals of two CP polymorphs, 1-HgCl2SC−I and 1-HgCl2SC−II, both with linear zig-zag chain structures, and of a chloroform solvate CP, 1-HgCl2-TCMSC, featuring a helical topology. When possible, these structures were analyzed using single-crystal X-ray diffraction (SC-XRD), Hirshfeld surface analysis, and Powder X-ray diffraction (P-XRD). Among the two polymorphs, 1-HgCl2SC−I, which is less densely packed, demonstrated the capacity to adsorb dichloromethane through a single crystal-to-single crystal (SC-to-SC) process while maintaining its original 3D structure. The same experiment conducted on the corresponding microcrystalline phase confirmed this result, but, at the same time, evidenced the inability of the CP to retain the solvent over time. This feature revealed a potentially different adsorption behavior for less densely packed zig-zag 1D CPs, usually considered not adsorbent altogether and unnoticed in previous investigations. However, 1-HgCl2SC−II confirms the inability of the zig-zag structure to adsorb, thus highlighting its structural robustness, probably strengthened by stable C–Haliph⋯π interactions, which are missing in 1-HgCl2SC−I. This allows us to speculate that the differing adsorption tendencies may be closely linked to small variations in the overall packing.