Nitroxide Radicals as Templating Agents in the Synthesis of Magnets Based on Three-Dimensional Oxalato-Bridged Heterodimetallic Networks

Abstract

Stable free radicals can be trapped inside a three‐dimensional (3D) inorganic network. The formation of a new type of mixed‐metal oxalate [MnII(H2O)CrIII(ox)3]− is induced by the presence of a cationic nitronyl nitroxide radical (rad+). The figure shows a stylized view of the 3D network ○ = Mn, • = Cr). This hybrid organic–inorganic compound behaves as an antiferromagnet at 6 K.

Multifunctionality in hybrid magnetic materials based on bimetallic oxalate complexes

“…In this context, two types of templating spin carriers have been used: decamethylferricinium cations and nitronyl nitroxide (NN) cationic free radicals. [54][55][56][57] The main difference between these two families of hybrid organic/inorganic magnets is that, while the spin density of the decamethylferricinium cations is buried between the cyclopentadiene units, NN radicals offer their spin density to the environment interacting with the extended inorganic counterpart. Consequently, in the first family of compounds the two magnetic sub-lattices are completely independent and the paramagnetic cations behave as excellent local probes of the internal field created by the metallic layers.…”

[Cr(dpa)(ox)2]–: a new bis-oxalato building block for the design of heteropolymetallic systems. Crystal structures and magnetic properties of PPh4[Cr(dpa)(ox)2], AsPh4[Cr(dpa)(ox)2], Hdpa[Cr(dpa)(ox)2]·4H2O, Rad[Cr(dpa)(ox)2]·H2O and Sr[Cr(dpa)(ox)2]2·8H2O (dpa = 2,2′-dipyridylamine)

“…The bond distances and angles found for the radical cation agree with previous Ðndings for N-alkylpyridinium nitronyl nitroxide radicals. 23,45,46 The pyridyl ring is planar and it makes a dihedral angle of 8.96¡ with the mean plane of the O( 11)ÈN( 11)ÈC( 21)ÈN( 12)ÈO(12) p system containing the unpaired electron. This is a rather small value compared with those generally reported in substituted nitronyl nitroxides.…”

Layered ferromagnets hosting tetraalkylammonium-substituted nitronyl nitroxide free radicals

“…Any attempt to crystallize the materials led to novel oxalato-bridged networks of lower symmetry. 6,7 To solve this problem, we have developed the synthesis of tetraalkylammonium NN free radicals. Tetraalkylammonium cations can have a C 3 local symmetry similar to that of the hexagonal layers and combine with them to form crystalline phases.…”