Modulating crystal structures and magnetic properties of 1-alkyl-4-aminopyridinium bis(maleonitrodithiolato)nickel- ate ionic mesogens by alkyl chain of cations

Eight metal–dithiolene compounds, [Cn-Apy][Ni(mnt)2] (Cn-Apy+ = 1-alkyl-4-aminopyridinium with n = 2–5 and 7–10; mnt2− = maleonitriledithiolate), were synthesized and characterized, amongst which the crystal structures were determined for six compounds (n = 3, 5, 7–10). The anions and cations form alternatively layered arrangement. The anion layer is built from the irregular stacks, the neighboring stacks are aligned along the long molecular axis direction of anions, and the alignment pattern is related to hydrocarbon chain length in 1-alkyl-4-aminopyridinium. Seven compounds exhibit the thermotropic liquid crystalline behaviors with the smetic A phase fingerprints. The mesophase observed in a propyl chain compound is uncommon compared with the suggested rule that a dodecyl hydrocarbon chain is necessary at least in the pyridinium-based ionic liquid crystals. The [Cn-Apy][Ni(mnt)2] compounds showed distinct magnetic behaviors. This is due to the magnetic couplings between anions being achievable through pathways of weakly intermolecular interactions.