Creation of a Field‐Induced Co(II) Single‐Ion Magnet by Doping into a Zn(II) Diamagnetic Metal–Organic Framework

Abstract The combination of single‐ion magnets (SIMs) and metal–organic frameworks (MOFs) is expected to produce new quantum materials. The principal issue to be solved in this regard is the development of new strategies for the synthesis of SIM‐MOFs. This work demonstrates a new simple strategy for the synthesis of SIM‐MOFs where a diamagnetic MOF is used as the framework into which the SIM sites are doped. 1, 0.5, and 0.2 mol% of the Co(II) ions are doped into the Zn(II) sites of [CH₆N₃][Zn^II(HCOO)₃]. The doped Co(II) sites in the MOFs perform as SIM with a positive D term of zero‐field splitting. The longest magnetic relaxation time is 150 ms (0.2 mol% Co) at 1.8 K under a static field of 0.1 T. Temperature dependency of the relaxation time suggests suppressing magnetic relaxation by reduction of spin–spin interaction upon doping in the rigid framework. Thus, this work represents a proof of concept for the creation of a single‐ion doped magnet in the MOF. This simple synthetic strategy will be widely applied for the creation of quantum magnetic materials.