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Supramolecular Cation Assemblies of Hydrogen-Bonded (NH4+/NH2NH3+)(Crown Ether) in [Ni(dmit)2]-Based Molecular Conductors and Magnets
journal contribution
posted on 2002-06-29, 00:00 authored by Tomoyuki Akutagawa, Tatsuo Hasegawa, Takayoshi Nakamura, Tamotsu InabeHydrogen-bonded supramolecular cation assemblies of (NH4+/NH2−NH3+)(crown ether), where
the crown ether is [12]crown-4, [15]crown-5, or [18]crown-6, were incorporated into electrically conducting
[Ni(dmit)2] salts (dmit2- = 2-thioxo-1,3-dithiole-4,5-dithiolate). (NH4+)([12]crown-4)[Ni(dmit)2]3(CH3CN)2 had
a pyramidal shape, while ionic channels were observed in (NH4+)0.88([15]crown-5)[Ni(dmit)2]2 and (NH4+)0.70([18]crown-6)[Ni(dmit)2]2. Both (NH4+)0.88([15]crown-5) and (NH4+)0.70([18]crown-6) contained regularly spaced
[Ni(dmit)2] stacks formed by N−H···O hydrogen bonding between the oxygen atoms in crown ethers and
the NH4+ ion. NH4+ occurred nonstoichiometrically; there were vacant ionic sites in the ionic channels. The
ionic radius of NH4+ is larger than the cavity radius of [15]crown-5 and [18]crown-6. Therefore, NH4+ ions
could not pass through the cavity and were distributed randomly in the ionic channels. The static disorder
caused the conduction electrons to be randomly localized to the [Ni(dmit)2] stacks. Hydrazinium (NH2−NH3+) formed the supramolecular cations in (NH2−NH3+)([12]crown-4)2[Ni(dmit)2]4 and (NH2−NH3+)2([15]crown-5)3[Ni(dmit)2]6, possessing a sandwich and club-sandwich structure, respectively. To the best of our
knowledge, these represent the first hydrazinium−crown ether assemblies to be identified in the solid. In
the supramolecular cations, hydrogen bonding was detected between the ammonium or the amino protons
of NH2−NH3+ and the oxygen atoms of crown ethers. The sandwich-type cations coexisted with the [Ni(dmit)2] dimer stacks. Although the assemblies were typically semiconducting, ferromagnetic interaction
(Weiss temperature = +1 K) was detected in the case of (NH2−NH3+)2([15]crown-5)3[Ni(dmit)2]6. The (NH2−NH3+)0.8([18]crown-6)[Ni(dmit)2]2 and (NH4+)0.76([18]crown-6)[Ni(dmit)2]2 crystals were isomorphous. The large
and flexible [18]crown-6 allowed for maintaining the same ionic channel structure through replacement of
the NH4+ cation by NH2−NH3+.
