Magnetic Anisotropy in a Verdazyl-Based Complex with Cobalt(II)

A verdazyl-based complex with Co2+ ion, (p-Py-V-p-Br)2[Co(hfac)2], was successfully synthesized. The molecular arrangement indicates that spins on the radical and Co form a one-dimensional (1D) spin chain, where the intermolecular interaction between the radicals and the intramolecular interaction between the radical and Co exhibit threefold periodicity. The strong antiferromagnetic interaction between radical spins forms a nonmagnetic singlet dimer, yielding paramagnetic behavior associated with the residual spins on the Co2+ ion in the low-temperature region. We evaluated the anisotropic g values by analyzing the electron spin resonance powder patterns. Furthermore, we considered the spin- orbit coupling and distorted crystal fields of the Co2+ ion and explained the triaxial anisotropic behavior. We also evaluated the anisotropy of the expected effective exchange interaction between the fictitious spins on the Co2+ ions, indicating the existence of an Ising-like exchange interaction. These results demonstrate that the strong spin-orbit coupling of the Co2+ ion in the present verdazyl-based compound yields an effective spin-1/2 with anisotropic g values and Ising-like exchange interactions.