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

Abstract

A 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.

Electron Donor−Bridge−Acceptor Molecules with Bridging Nitronyl Nitroxide Radicals: Influence of a Third Spin on Charge- and Spin-Transfer Dynamics

“…Nitronyl nitroxide (NN • ) is a stable, easily functionalized radical that has been studied extensively in the organic magnetic materials field. [43][44][45][46][47][48][49] The spin density distribution of NN • is localized largely on its two N-O groups and not on the molecule to which NN • is appended, 50 so that attachment of NN • to B within D-B-A does not result in significant spin delocalization onto B itself. Modulating the degree of spin delocalization from the appended radical onto B is potentially an important means to control the electron-transfer dynamics through B, and the work presented here is the first step toward this goal.…”

New Set of Multicomponent Crystals as Efficient Heterogeneous Catalysts for the Synthesis of Cyclic Carbonates

“…On the other hand, complex 1b shows antiferromagnetic interaction between two isolated Mn­(II) centers through the same H-bonding. Though vast number of examples is dominating in the literature with magnetic interaction through superexchange pathway in the presence of bridging ligands between paramagnetic centers, but magnetic coupling only by the operation of H-bonding is very rare. − …”

Synthesis and Magnetic Properties of Stable Radical Derivatives Carrying a Phenylacetylene Unit

“…The study of stable organic radicals has attracted a great deal of attention because of their wide applicability for spin probes, molecule-based magnets, and molecular conductors [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ]. To assess the magnetic properties of organic radical solids, it is important to investigate the correlation between molecular arrangement and magnetic properties based on crystal engineering strategies [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 ]. For the purpose of inducing the formation of magnetic molecular self-assemblies, van der Waals interactions [ 9 , 10 , 12 , 13 , 14 , 18 ], hydrogen bonds [ 16 , 17 , 19 , 20 , 21 , 22 , 23 , 25 , 26 ], and aromatic stackings [ 11 , 15 , 24 , 27 ] have been introduced to various stable radical derivatives such as phenoxyl, nitroxyl, etc.…”