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An Ideal One-Dimensional Antiferromagnetic Spin System Observed in Hydrogen-Bonded Naphth[2,3-d]imidazol-2-yl Nitronyl Nitroxide Crystal: The Role of the Hydrogen Bond
journal contribution
posted on 2004-05-20, 00:00 authored by Hideaki Nagashima, Hidenari Inoue, Naoki YoshiokaA novel stable organic radical, 2-(naphth[2,3-d]imidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl-3-oxide (4), has been designed, synthesized, and structurally characterized to examine the effects of
ring extension on 2-(benzimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl-3-oxide (2).
4 forms four-centered intramolecular and intermolecular hydrogen bonds, and the hydrogen bonds are repeated
along the c-axis to form a one-dimensional chain structure. This hydrogen-bonding motif contrasts that of 2,
which forms three-centered intramolecular and intermolecular hydrogen bonds. The magnetic susceptibility
measurement of 4 reveals that an antiferromagnetic interaction is dominant between spins, and the magnetic
behavior is reproduced by the Bonner-Fisher model with J = −14 cm-1. Because each hydrogen-bonded
chain is well isolated, a magnetic interaction pathway was thought to exist along the chain direction. Two
interaction pathways have been assumed: (i) through-space interaction between the O atoms of the nitroxide
and (ii) through the NH···ON intermolecular hydrogen bond. We have concluded that pathway (i) is
predominant, by considering the identical magnetic data between the NH nondeuterated and deuterated samples.
The hydrogen bond mainly has a role in crystal scaffolding.