Syntheses, structures, and magnetic properties of three two-dimensional cobalt(II) single-ion magnets with a CoIIN4X2 octahedral geometry

Three two-dimensional Co-II complexes, namely, [Co(dps)(2)Cl-2](n) (1), [Co(dps)(2)Br-2](n) (2), and [Co(dps)(2)(H2O)(2) center dot I-2 center dot(H2O)(4)](n) (3) (where dps = 4,4'-dipyridyl sulfide), have been synthesized using a rationally designed synthetic approach and characterized structurally and magnetically. Although they crystallize in different space groups, these compounds all have similar two-dimensional (4,4) layer structures where the Co2+ centers are bridged by the bis.monodentate) ligand dps. In addition, the coordination geometry of the Co2+ centers is of a general CoN4X2 octahedral environment formed by four equatorial N atoms from four dps ligands and two X atoms (X = Cl, Br, and O atoms for 1-3, respectively) in the axial positions. Ab initio calculations revealed that due to the strong spin-orbit coupling, the spin Hamiltonian containing the zero-field splitting parameters D and E cannot be used to describe their magnetic anisotropy. According to the calculation, the g(z) values for the spin-orbit ground doublets of 1-3 are larger than the g(x) and g(y) values, which indicates the easy-axis magnetic anisotropy of these compounds. Due to the existence of the magnetic anisotropy, field-induced single-ion magnet behavior can be observed in all these complexes. This work illustrated that care should be taken to interpret the magnetic data of octahedral Co-II compounds. In addition, extended frameworks with long and flexible organic spacers are good candidates for the construction of SIMs with different axial ligands and different magnetic properties.