Two cobalt(II) and nickel(II) sulfonate complexes constructed by mixed bipyridyl-organodisulfonate strategy: syntheses, crystal structures, and magnetic properties

We reported the syntheses, structures, and magnetic properties of two new nickel(II) and cobalt(II) sulfonate complexes, {M(dmbpy)(H2O)3]2(nds)]}·[nds]·2H2O (M = Co2+ (1), Ni2+ (2), dmbpy = 4,4′-dimethyl-2,2′-bipyridyl, H2nds = 1,5-Naphthalenedisulfonic acid). Both complexes were prepared by using a bipyridyl-organodisulfonate strategy via microwave-assisted solvothermal synthesis method. Single-crystal X-ray diffraction studies reveal a binuclear molecule of the complexes, in which two metal centers are bridged by sulfonic acid ligand nds2− with a counter nds2− anions in the lattice. The Co2+ and Ni2+ centers in the binuclear molecules are located in similar distorted octahedral coordination environments with small distortions. Magnetic measurements reveal that the cobalt sulfonate possesses easy-plane magnetic anisotropy with the zero-field splitting parameter D = 77.3 cm−1. Inversely, the nickel sulfonate exhibits easy-axis magnetic anisotropy (D = -11.2 cm−1). AC magnetic susceptibility indicates field-induced slow magnetic relaxation behavior was evidenced in the cobalt sulfonate while no such behavior for the nickel sulfonate. These results suggest complex 1 is a single-ion magnet (SIM) sulfonate while a magnetic sulfonate of complex 2. This work not only provides two magnetic sulfonate complexes but also a potential bipyridyl-organodisulfonate strategy for synthesizing new sulfonate complexes with interesting SIM properties.