Dynamics of Ligand and Guest in 1D Hg(II)-Bispidine Coordination Polymers With Different Topologies Investigated by Solid-State NMR

1D coordination polymers (CPs) made of parallel, weakly interacting chains have been recently proposed for the selective adsorption of volatile organic compounds (VOCs), one of the main sources of air and water pollution. Since the efficiency of adsorption for VOC removal strongly depends on the specific and stable interactions between the volatile species and the CP framework, the characterization at the atomic level of host-guest interactions and guest dynamics is of particular interest. Here, low- and high-resolution solid-state NMR experiments were applied to acquire information on ligand and guest dynamics for two 1D CPs (1-ClBz and 2-ClBz), both containing a bispidine organic ligand, Hg(II) as a metal center, and chlorobenzene trapped within the framework, but featuring different topologies. By combining analyses of on-resonance ¹H free induction decays (FIDs), ¹H and ¹³C longitudinal relaxation times, and ²H quadrupole echo spectra, it was found that chlorobenzene undergoes fast dynamics, mainly isotropic, in 1-ClBz, while it shows slower anisotropic motions in 2-ClBz, indicating stronger interactions between framework and adsorbate in the latter associated with the lower available free volume. Ligands are quite rigid for both CPs in the investigated frequency scale, apart from methyl groups, which undergo fast motions about their ternary symmetry axes.