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- x Zn II x (L)(N 3 )]·H 2 O ( x = 0.26, 0.56 and 0.85) based on bimetallic Co II 1- x Zn 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- x Zn 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- x Zn II x systems also changes. In this bimetallic series Co II 1- x Zn 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.