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.