Supramolecular cations of the m-fluoroanilinium(dibenzo[18]crown-6) in ferromagnetic salt

Abstract

A supramolecular cation of (m-FAni⁺)(DB[18]crown-6), where m-FAni⁺ and DB[18]crown-6 denote m-fluoroanilinium⁺ and dibenzo[18]crown-6, respectively, which is the polar unit rotating in the ferroelectric crystal of (m-FAni⁺)(DB[18]crown-6)[Ni(dmit)₂]⁻, was introduced into a ferromagnetic [MnCr(oxalate)₃]⁻ salt as the counter cation. The crystal structure of (m-FAni⁺)(DB[18]crown-6)[MnCr(oxalate)₃]⁻(CH₃OH)(CH₃CN) (1) is constructed from alternating layers of a two-dimensional honeycomb layer of [MnCr(oxalate)₃]⁻ and (m-FAni⁺)(DB[18]crown-6) supramolecular cations. The anionic layer is composed of Mn^II and Cr^III ions with S = 5/2 and S = 3/2 spins, respectively, bridged by the oxalate anions, which show ferromagnetic ordering at 5.5 K. The supramolecular structure is formed through the formation of hydrogen bonds between the ammonium hydrogen atoms of the m-FAni⁺ cations and the oxygen atoms of the DB[18]crown-6 cavity. No orientational disorder of the fluorine atoms was observed in our X-ray structural analysis, suggesting that a two-fold flip-flop motion of the m-FAni⁺ cations does not occur in the salt. The rotational freedom of the m-FAni⁺ cations in the salt is restricted by the steric hindrance from neighbouring DB[18]crown-6 molecules. A design strategy for the rotation in a salt is discussed, based on the volume that the supramolecular cations occupy in the unit cell.