Fluctuation-Driven Switching of Magnetic Exchange and Charge Transport in Ni(dmit)2 Salts with [24]crown-8-Based Supramolecular Cations

Countercation dynamics play a crucial yet largely unexplored role in governing the electronic properties of molecular conductors. Herein, we demonstrate that the fluctuations of flexible supramolecular cations in [Ni(dmit)2]-based molecular conductors (dmit2− = 2-thioxo-1,3-dithiol-4,5-dithiolate) can directly modulate their correlated electronic states. Two salts with nearly spherical supramolecular cations featuring Na+ and Cs+ ions encapsulated by unsubstituted [24]crown-8, Na([24]crown-8)[Ni(dmit)2]3 and Cs2([24]crown-8)2[Ni(dmit)2]7, are synthesized and systematically compared. Detailed crystallographic, magnetic, and transport studies reveal a striking contrast between the two systems. In Na([24]crown-8)[Ni(dmit)2]3, the structural distortion of the Na+-encapsulating [24]crown-8 enables thermally activated large-amplitude out-of-plane fluctuations, thus selectively enhancing the vibrational motion of terminal S atoms in [Ni(dmit)2] layers and leading to the temperature-dependent modulation of transfer integrals, anomalous magnetic behavior requiring a temperature-dependent exchange interaction, and one-dimensional variable-range hopping transport. In contrast, Cs2([24]crown-8)2[Ni(dmit)2]7 features a planar-confined Cs+-based supramolecular cation and suppressed fluctuation transfer to anion layers, thus exhibiting conventional Heisenberg-chain magnetism and Arrhenius-type semiconducting behavior. These results establish supramolecular-cation dynamics as a powerful design parameter for controlling electronic correlation and transport in molecular conductors.