[18]Crown-6 rotator in spin-ladder compound of m-aminoanilinium([18]crown-6)[Ni(dmit)2]−

Abstract

Supramolecular cations of HOPD⁺([18]crown-6) and HMPD⁺([18]crown-6) were introduced into [Ni(dmit)₂]⁻ salts (HOPD⁺: o-aminoanilinium, HMPD⁺: m-aminoanilinium, and dmit²⁻: 2-thioxo-1,3-dithiole-4,5-dithiolate). Alternate layers of cations and anions were observed in the two new salts of (HOPD⁺)([18]crown-6)[Ni(dmit)₂]⁻ (1) and (HMPD⁺)([18]crown-6)[Ni(dmit)₂]⁻ (2). From X-ray crystal structural analyses, solid state ¹H nuclear magnetic resonance (NMR) spectra, and dielectric constants, the thermal rotations of [18]crown-6 in both of the (HOPD⁺)([18]crown-6) and (HMPD⁺)([18]crown-6) supramolecules occurred at temperatures above ∼200 K based on the orientational disorder in the crystal structures. The two-fold flip-flop motions of HOPD⁺ and HMPD⁺ cations in salts 1 and 2 were suppressed, due to the relatively large potential energy barriers. The [Ni(dmit)₂]⁻ anion formed π-dimer arrangements in both salts, with a layer structure by lateral sulfur–sulfur interatomic contacts. Although the simple dimer model reproduced the magnetic properties of salt 1, the ladder arrangement of the π-dimer in salt 2 yielded the magnetic behavior of a spin-ladder with a spin-gap of 92.5 K. The temperature dependent magnetic susceptibility of salt 2 was well reproduced by the magnetic anisotropy of J₁/J₂≈ 8 between the ladder-leg (J₁: intra-dimer interaction) and ladder-rung (J₂: inter-dimer interaction). The [18]crown-6 supramolecular rotator of (HMPD⁺)([18]crown-6) was coexistent with the spin-ladder chain of [Ni(dmit)₂]⁻ anions in salt 2.