Mixed metal Co^II _{1- x}Zn^II _x-organic frameworks based on chains with mixed carboxylate and azide bridges: Magnetic coupling and slow relaxation

A series of isomorphous three-dimensional metal-organic frameworks [Co^II _1-xZn^II _x(L)(N₃)]·H₂O (x = 0.26, 0.56 and 0.85) based on bimetallic Co^II _1-xZn^II _x (x = 0.26, 0.56 and 0.85) chains with random metal sites have been synthesized and magnetically characterized. The Co^II _1-xZn^II _x series, which intrinsically feature random anisotropic/diamagnetic sites, shows complex magnetic interactions. By gradually introducing the diamagnetic Zn^II ions into the pure anisotropic Co^II single-chain magnets system, the ferromagnetic interactions between Co^II ions are gradually diluted. Moreover, the slow magnetic relaxation behaviour of the mixed metal Co^II _1-xZn^II _x systems also changes. In this bimetallic series Co^II _1-xZn^II _x, the Co-rich materials exhibit slow relaxation processes that may arise from SCM mechanism, while the Zn^II-rich materials show significantly low slow magnetic relaxation. A general trend is that the activation energy and the blocking temperature decrease with the increase in diamagnetic Zn^II content, emphasizing the importance of anisotropy for slow relaxation of magnetization.