Multirotations of (anilinium)([18]crown-6) supramolecular cation structure in magnetic salt of [Ni(dmit)2]-.

A solid-state dynamic supramolecular structure consisting of (anilinium)([18]crown-6) was arranged as the cation in a salt of [Ni(dmit)2]- (dmit = 2-thioxo-1,3-dithiole-4,5-dithiolate). With the ammonium moiety of anilinium located within the cavity of [18]crown-6, a hydrogen-bonded supramolecular structure is formed, with an orthogonal arrangement between the pi plane of anilinium and the mean O6 plane of [18]crown-6. In this supramolecular cation, both anilinium and [18]crown-6 act as dynamic units with different rotational modes in the solid state. The uniform stacks of cations form an antiparallel arrangement, thus producing a layer structure. Sufficient space for the 180 degree flip-flop motion of the phenyl ring and the rotation of [18]crown-6 was observed in the cation layer. Thermally activated 180 degree flip-flop motions, with a frequency of 6 MHz at room temperature and an activation energy of 31 kJ mol(-1), were confirmed by temperature-dependent 2H NMR spectra of ([D5]anilinium)-([18]crown-6)[Ni(dmit)2]. A double-minimum potential for the molecular rotation of anilinium, with a barrier of approximately 40 kJ mol(-1), was indicated by ab initio calculations. The wide-line 1H NMR spectra indicated a thermally activated rotation of [18]crown-6 at temperatures above 250 K. Therefore, multiple molecular motions of the 180 degree flip-flop motion of the phenyl ring and the rotation of [18]crown-6 occur simultaneously in the solid state. The temperature-dependent dielectric constants revealed that the molecular motion of [18]crown-6, other than the flip-flop motion, dominates the dielectric response in the measured temperature and frequency range.