The design of inexpensive and less toxic porous coordination polymers (PCPs) that show selective adsorption or high adsorption capacity is a critical issue in research on applicable porous materials. Although use of Group II magnesium(II) and calcium(II) ions as building blocks could provide cheaper materials and lead to enhanced biocompatibility, examples of magnesium(II) and calcium(II) PCPs are extremely limited compared with commonly used transition metal ones, because neutral bridging ligands have not been available for magnesium(II) and calcium(II) ions. Here we report a rationally designed neutral and charge-polarized bridging ligand as a new partner for magnesium(II) and calcium(II) ions. The three-dimensional magnesium(II) and calcium(II) PCPs synthesized using such a neutral ligand are stable and show selective adsorption and separation of carbon dioxide over methane at ambient temperature. This synthetic approach allows the structural diversification of Group II magnesium(II) and calcium(II) PCPs.

Artificial molecular rotators were designed in an attempt to achieve unidirectional molecular rotation. Supramolecular assemblies of cations and crown ethers in the solid state were shown to form rotator structures, diverse in their rotational symmetry and frequency. The counter cation of [Ni(dmit)₂]⁻ anion, bearing one S = 1/2 spin, was used to couple molecular rotation to magnetic properties. Random rotation of [18]crown-6 molecules was first observed in the Cs⁺ ₂([18]crown-6)₃ supramolecule, where the rotational freedom of [18]crown-6 rotators was evidently coupled to the magnetic properties of [Ni(dmit)₂]⁻π-dimer. In other cases, dual rotary motions of anilinium([18]crown-6) and rotator–stator assemblies of (adamantylammonium)(dibenzo[18]crown-6) were investigated as a means to control rotational symmetries and frequencies in the solid state. The supramolecular approach for construction of molecular rotator–stator assemblies in the solid state is a convenient approach to the design of molecular rotary functionality in [Ni(dmit)₂]⁻ salts.