Mixed metal Co Zn -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 Zn (L)(N)]·HO ( = 0.26, 0.56 and 0.85) based on bimetallic Co Zn ( = 0.26, 0.56 and 0.85) chains with random metal sites have been synthesized and magnetically characterized. The Co Zn series, which intrinsically feature random anisotropic/diamagnetic sites, shows complex magnetic interactions. By gradually introducing the diamagnetic Zn ions into the pure anisotropic Co single-chain magnets system, the ferromagnetic interactions between Co ions are gradually diluted. Moreover, the slow magnetic relaxation behaviour of the mixed metal Co Zn systems also changes. In this bimetallic series Co Zn , the Co-rich materials exhibit slow relaxation processes that may arise from SCM mechanism, while the Zn-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 content, emphasizing the importance of anisotropy for slow relaxation of magnetization.