Synthesis, crystal structures and magnetic properties of a new radical NIT-1′-MeBzIm and the corresponding complexes of Ni(II), Co(II) and Zn(II) containing NIT-1′-MeBzIm

Abstract: A new chelating radical ligand NIT-1′-MeBzIm (1) (NIT-1′-MeBzIm=2-{2′-[(l’-methyl)benzimidazolyl]}-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) and three corresponding complexes [M(NIT-1′-MeBzIm)2(NO3)(CH3OH)]·(NO3)(CH3OH) (M=Ni (2), Co (3)), [Zn(NIT-1′-MeBzIm)2(CH3OH)2]·(ClO4)2(H2O)2(CH3OH) (4) have been prepared and structurally characterized by X-ray diffraction method and variable-temperature magnetic susceptibility measurements. In the crystal structures, radical 1, complexes 3 and 4 crystallize isomorphously in monoclinic, with the space groups are P2(1)/n, P2(1)/c, and P2(1), respectively. Complex 2 crystallizes in orthorhombic space group Pna2(1). The metal ions of the three complexes embed in distorted octahedron geometry centers and coordinated by two NIT-1′-MeBzIm radicals from the equatorial positions to form trans configuration, the axial positions are occupied by one methanol molecule and one nitrate anion for 2 and 3, but by two methanol molecules for 4. Magnetic measurement demonstrates that the intramolecular exchange couplings in 2 and 3 are antiferromagnetic with J =−41.25 and −38.1cm−1, where the spin Hamiltonian is defined as Ĥ =−2J(Ŝ rad1 Ŝ M + Ŝ M Ŝ rad2) based on the molecular structure of radical-metal-radical, while that in 4 is weak ferromagnetic with J =1.65cm−1 where the spin Hamiltonian is defined as Ĥ =−2JŜ 1 Ŝ 2 within the complexes. Intermolecular exchange couplings in 1 is also weak ferromagnetic with J =1.32cm−1 where the spin Hamiltonian is defined as Ĥ =−2JŜ 1 Ŝ 2 between radical and radical. Compounds 2–4 exhibit intermolecular antiferromagnetic interaction with the zJ′=−0.52cm−1, θ =−0.75K and zJ′=−0.49cm−1 for compounds 2, 3 and 4, respectively, which should ascribe to the weak interactions. The crystal structures for 1–4 have intermolecular hydrogen bonding interactions (and π–π piling interactions for 1 and 3) which form the single crystals into 1-D, 2-D, 3-D structures and seems to play an important role in molecular packing and in magnetic coupling. [Copyright &y& Elsevier]