Crystal Structures and Magnetic Properties of Complexes of M^IICl₂ (M = Cu, Ni, and Co) Coordinated with 4-(<i>N</i>-<i>tert</i>-butyloxyamino)-2-(methoxymethylenyl)pyridine: 2D Magnetic Anisotropy of the Aminoxyl-Co^II Complex in the Crystalline State

Three metal complexes, [MIICl2(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 (Cradical··· Cβ = 3.17 and 3.23 Å) 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 (Cradical···Cα = 3.46 and 3.52 Å for 2 and 3, respectively) to form the 2-D structures. The temperature dependence of the χmolT 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 χmolT vs T plot for 1, we estimated the intra- and intermolecular (intrachain) exchange coupling constants to be J1/kB = 60.2 and J2/kB = −7.02 K, respectively. On the other hand, complexes 2 and 3 showed steep increases of the χmolT value below ca. 3 K, indicating that the long-range magnetic ordering is operating. The 1/χmol vs T plot for 2 was analyzed by a Curie−Weiss model to give θ = 6.25 K and C = 2.02 cm3 K mol-1 with gNi = 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 Tc = 2.14 K and exhibited a glasslike magnetic behavior below Tc.