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Chemistry, an Asian journal

Conformational polymorph of o-aminoanilinium(dibenzo[18]crown-6) supramolecules in [Ni(dmit)2]- salts.


PMID 20029890

Abstract

The supramolecular (HOPD(+))(DB[18]crown-6) cation, in which HOPD(+) and DB[18]crown-6 are o-aminoanilinium and dibenzo[18]crown-6, respectively, was introduced into [Ni(dmit)(2)](-) salts (dmit(2-) = 2-thioxo-1,3-dithiole-4,5-dithiolate). Conformational polymorphs were observed as tetragonal (HOPD(+))(DB[18]crown-6)[Ni(dmit)(2)](-) (1) and monoclinic (HOPD(+))(DB[18]crown-6)[Ni(dmit)(2)](-) (2). The ammonium group of HOPD(+) in salts 1 and 2 formed the N-H(+)O hydrogen bonds at the bottom and upper positions of V-shaped DB[18]crown-6, respectively, thereby producing a different supramolecular conformation. The [Ni(dmit)(2)](-) anion arrangements in salts 1 and 2 were 4(1)-helical pi stacking and a two-dimensional layer, respectively, depending on the conformation of the supramolecular cations. The magnetic behavior of salts 1 and 2 obeyed the Curie-Weiss law at room temperature with S = 1/2 spin on the [Ni(dmit)(2)](-) anion. However, the g value and line width in the electron resonance spectra of salt 1 showed a magnetic anomaly at 28 K, which was owing to antiferromagnetic ordering in the 4(1)-helical [Ni(dmit)(2)](-) pi stack. Large temperature- and frequency-dependent dielectric responses were observed for salt 2 at temperatures above 200 K, whereas no particular dielectric responses were observed in salt 1. The molecular motion of HOPD(+) within the cationic layer of salt 2 contributed to the dielectric response, and this was supported by ab initio calculations showing the potential-energy curve for pendulum motion and by the large thermal parameters in the X-ray crystal structure analysis. The fixed (HOPD(+))(DB[18]crown-6) arrangement in the crystal of salt 1 was consistent with the small dielectric response. The steric hindrance of the o-amino group of HOPD(+) in the supramolecular cation structure yielded the conformational polymorph with different dielectric and magnetic properties.

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