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 approximately 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 pi-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 pi-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 approximately = 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.