Inorganic Chemistry, Vol.44, No.17, 6004-6011, 2005
Crystal structures and magnetic properties of complexes of (MCl2)-Cl-II (M = Cu, Ni, and Co) coordinated with 4-(N-tert-butyloxyamino)-2-(methoxymethylenyl)pyridine: 2D magnetic anisotropy of the aminoxyl-Co-II complex in the crystalline state
Three metal complexes, [(MCl2)-Cl-II(4NOPy-OMe)(2)] (M = Cu (1), Ni (2), and Co (3)), were prepared by mixing the corresponding metal chloride and 4-(N-tert-butyloxyamino)-2-(methoxymethylenyl)pyridine, 4NOPy-OMe, in 1:2 ratio. Complex 1 has two structures (complexes A and B) with similar coordination geometries, compressed octahedrons. In the crystal structure, complexes A and B locate alternately in short distances (C-radical(...) C-beta = 3.17 and 3.23 angstrom) to form a 1-D chain structure. Complexes 2 and 3 are isomorphous and have a slightly distorted octahedral structure. In the crystal structure, both complexes have intermolecular short contacts ((CradicalCalpha)-C-... = 3.46 and 3.52 A for 2 and 3, respectively) to form the 2-D structures. The temperature dependence of the chi(mol)T values for the three complexes indicated that the magnetic interactions between the radicals and the metal ions within the complexes were ferromagnetic. By fitting a modified Fisher 1-D model to the data of the chi(mol)T vs T plot for 1, we estimated the intra- and intermolecular (intrachain) exchange coupling constants to be J(1)/k(B) = 60.2 and J(2)/k(B) = -7.02 K, respectively. On the other hand, complexes 2 and 3 showed steep increases of the chi(mol)T value below ca. 3 K, indicating that the long-range magnetic ordering is operating. The 1/chi(mol) vs T plot for 2 was analyzed by a Curie-Weiss model to give theta = 6.25 K and C = 2.02 cm(3) K mol(-1) with g(Ni) = 2.25. Complex 3 was investigated in more detail using an orientated sample. Magnetic behavior strongly depends on the direction of the applied field, in which the c* axis perpendicular to the ab plane is an easy axis for magnetization. Direct current (dc) and alternating current (ac) magnetic susceptibility measurements revealed that complex 3 had a magnetic phase transition of T-c = 2.14 K and exhibited a glasslike magnetic behavior below T-c.