Two Interpenetrated Cobalt(II) Metal–Organic Frameworks with Guest-Dependent Structures and Field-Induced Single-Ion Magnet Behaviors

Abstract

Two cobalt­(II) metal–organic frameworks with 2-fold vertically interpenetrated (4,4) grids, namely, [Co­(bpg)2(SCN)2]·3MeOH (1) and [Co­(bpg)2(SCN)2]·2DMF (2) (bpg = meso-α,β-bi­(4-pyridyl) glycol), were prepared under different conditions. The two complexes crystallize in different space groups (orthorhombic Pccn for 1, and tetragonal P̅421 c for 2) with different guest molecules. Although their structures are very similar, different guest molecules subtly change the coordination environments of the CoII centers, the intergrid supramolecular interactions (hydrogen bond), and the dihedral angles of those two sets of interpenetrated grids. Magnetically, these modifications of the structures lead to the changes on their magnetism, especially the dynamic magnetic properties at low temperatures. Both compounds exhibit slow magnetic relaxation under an external field. For 1, we could not observe the peak maxima of the ac susceptibilities in our magnetometer at the lowest temperature and highest frequency because the relaxation time is never slow enough. In contrast for compound 2, the estimated energy barrier is significantly higher than that of 1, leading to much slower magnetic relaxation. The difference of magnetic properties between 1 and 2 illustrates the role of the metal–organic frameworks on the development of the tunable single-ion magnets and the prominent guest effect in the MOF based SIMs.

Slow Magnetic Relaxation in a One-Dimensional Coordination Polymer Constructed from Hepta-Coordinate Cobalt(II) Nodes

“…It was found that the matrix element of the transition moment between the ground state KDs is somewhat larger (1.5 µ B ) than the required value (0.1 µ B ) for efficient relaxation. This demonstrates the significant effect of QTM on the slow relaxation process, even under the most optimal DC field, and it is very common for Co II -based SMMs, as reported earlier [46,47,56,57]. Although we have limitation in our instrument (frequency range 0-800 Hz) but the extrapolation of the frequency dependence plots up to 10,000 Hz using the Debye model shows clear peak maxima in both χM' and χM″ (Figure 4).…”

Slow Magnetic Relaxation Triggered by a Structural Phase Transition in Long-Chain-Alkylated Cobalt(II) Single-Ion Magnets

“…This suggests that a relaxation process other than the Orbach process may play a role below 3.9 K or that there is more than one thermally activated relaxation process occurring in this system. Although there are several reports about similar six-coordinated Co­(II) SIMs showing similar relaxation times, ,− it seems that the relaxation time obtained is obviously too large for an Orbach process in comparison with those found for other Co­(II) SIMs. In fact, the barrier height assuming a purely thermal relaxation pathway (2| D |) is 95.0 cm –1 , which is considerably higher than the fitted barrier height, indicating that the thermal Orbach mechanism is not the main contributor to the temperature dependence.…”

Highly Efficient I2 Sorption, CO2 Capture, and Catalytic Conversion by Introducing Nitrogen Donor Sites in a Microporous Co(II)-Based Metal–Organic Framework

“…Nowadays, porous metal–organic frameworks (MOFs) have been extensively considered for their charming topologies and properties. , MOFs often show exceptional applications in various fields, such as gas separation, , catalysis, , sorption, , sensing, , magnetism, and so on. Because MOFs have the advantages of large surface areas, − adjustable porosity diameters, , and decorative surfaces, , there is prospect that diverse analytes including explosives, drugs, dyes pollutants, − and nuclear wastes − can be effectively captured by MOFs.…”