Creation of Co(II) single-ion magnets by doping into Zn(II) diamagnetic metal-organic frameworks

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 mol%, 0.5 mol%, and 0.2 mol% of the Co(II) ions are doped into the Zn(II) sites of [CH6N3][ZnII(HCOO)3]. The doped Co(II) sites in the MOFs perform as SIM with a positive D term of zero-field splitting. Temperature dependency of the relaxation time suggests suppressing spin- lattice relaxation by the rigid framework. Thus, this work represents a proof of concept for the creation of single-ion doped magnets in MOFs. This simple synthetic strategy will be widely applied for the creation of quantum magnetic materials.

Tuning the spin qubit property of diamagnetic Zn(II) metal– organic frameworks via Cu(II) doping

“…Previously, a doped MOF, i.e., [CH 6 N 3 ][Co II x Zn II 1−x (HCOO) 3 ] ([CH 6 N 3 ] + = guanidium; x = 0.01, 0.005, 0.002), was reported to exhibit single-ion magnetism with a positive D term of zero-field-splitting in a S = 3/2 system. 36 Since this guanidium-type MOF is more simple than that containing [CH 3 (NH 2 ) 2 ] + because it lacks a phase transition derived from cations, 37 it seems a suitable candidate to investigate the slow magnetic relaxation and spin coherence phenomena. Herein, the systematic doping of Cu(II) into diamagnetic [CH 6 N 3 ][Zn II (HCOO) 3 ] (Zn-MOF, Figure 2a) is reported, and the concentration dependency of magnetic dynamism and spin qubit properties in the S = 1/2 system is discussed.…”

“…This spin-doping method, which involves the self-assembly of Cu(II) and Zn(II) solvated ions and organic components, offers a general route for the synthesis of doped MOFs and provides a new platform for the application of MOFs as quantum materials having fine-tuning ability.MethodsMaterials. Zn II (NO 3 ) 2 •6H 2 O, Cu II (NO 3 ) 2 •3H 2 O, formic acid (HCOOH), methanol (MeOH), and N,N-dimethylformamide (DMF) were purchased from Fujifilm Wako Pure Chemical Corp. Guanidinium carbonate ([CH 6 N 3 ] 2 CO 3 ) was purchased from Sigma-Aldrich.Synthesis of [CH 6 N 3 ][Zn II (HCOO) 3 ] (Zn-MOF).The synthetic protocol was same as previously as follows 36. Formic acid (811 L, 21.5 mmol) was added into a suspension of [CH 6 N 3 ]CO 3 (1.55 g, 8.60 mmol) in MeOH (20 mL), afforded a colorless solution.…”