Design of Crystalline Spaces for Molecular Rotations in Crystals

4-Methylanilinium
derivatives were used to introduce spaces for
molecular rotation in crystals. The [Ni­(dmit)2]− (dmit2– = 2-thioxo-1,3-dithiole-4,5-dithiolate)
salts with supramolecular cations of dibenzo[18]­crown-6 (DB[18]­crown-6)
and 4-methylanilinium derivatives, (4-methylanilinium+)­(DB­[18]­crown-6)­[Ni­(dmit)2]− (1), (2-fluoro-4-methylanilinium+)­(DB­[18]­crown-6)­[Ni­(dmit)2]− (2), and (3-fluoro-4-methylanilinium+)­(DB­[18]­crown-6)­[Ni­(dmit)2]− (3) were synthesized. The
potential energy curves for the molecular rotations of the cations
in the crystals had double minimum shapes with maxima of 100, 210,
and 230 kJ mol–1 for crystals 1, 2, and 3, respectively. Introduction of a methyl
substituent at the p-position was effective in reducing
the potential energy maxima. For crystals 2 and 3, large dielectric responses originating from the flip-flop
motions of the cationic molecules were observed upon applying an AC
voltage. The temperature-dependent magnetic susceptibilities of complexes 1, 2, and 3 followed the Curie–Weiss
law, showing weak antiferromagnetic interactions.