| Abstract
| - A new chelating radical ligand 4ImNNH (2-(4-imidazolyl)-4,4,5,5-tetramethylimidazolin-1-oxyl 3-oxide) was prepared,and complexation with divalent transition metal salts gave complexes, [M(4ImNNH)2X2], which showed intermolecularferromagnetic interaction in high probability (7 out of 10 paramagnetic compounds investigated here). The nitratecomplexes (X = NO3; M = Mn (1), Co (2), Ni (3), Cu (4)) crystallize isomorphously in monoclinic space groupP21/a. The equatorial positions are occupied with two 4ImNNH chelates and the nitrate oxygen atoms are locatedat the axial positions. Magnetic measurements revealed that the intramolecular exchange couplings in 1, 2, and 4were antiferromagnetic, while that in 3 was ferromagnetic with 2J/kB = +85 K, where the spin Hamiltonian isdefined as H = −2J(S1·S2 + S2·S3) based on the molecular structures determined as the linear radical−metal−radical triads. The intramolecular ferromagnetic interaction in 3 is interpreted in terms of orthogonality between theradical π* and metal dσ orbitals. Compounds 1−3 exhibited intermolecular ferromagnetic interaction ascribable toa two-dimensional hydrogen bond network parallel to the crystallographic ab plane. Complex 3 became anantiferromagnet below 3.4 K and exhibited a metamagnetic transition on applying a magnetic field of 5.5 kOe at1.8 K. The complexes prepared from metal halides, [M(4ImNNH)2X2] (X = Cl, Br; M = Mn, Co, Ni, Cu), showedintramolecular antiferromagnetic interactions, which are successfully analyzed based on the radical−metal−radicalsystem. The crystal structures determined here on 1−4, [Mn(4ImNNH)2Cl2], and [Cu(4ImNNH)2Br2] always haveintermolecular hydrogen bonds of H(imidazole)···X(axial ligand)−M, where X = NO3, Cl, Br. This interaction seemsto play an important role in molecular packing and presumably also in magnetic coupling.
- Complexation of a new radical chelating ligand, 4ImNNH, with MX2 gave [M(4ImNNH)2X2] (M = Mn, Co, Ni, Cu; X = NO3, Cl, Br), which showed intermolecular ferromagnetic interaction in high probability (7 out of 10 paramagnetic compounds prepared here). Intra- and intermolecular ferromagnetic interactions were observed for [Ni(4ImNNH)2(NO3)2], which underwent an antiferromagnetic phase transition at 3.4 K. Hydrogen bonding seems to play an important role in molecular packing and presumably also in magnetic coupling.
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