Inter-layer magnetic tuning by gas adsorption in π-stacked pillared-layer framework magnets

Magnetism of layered magnets depends on the inter-layer through-space magnetic interactions (JNNNI). Using guest sorption to address inter-layer pores in bulk-layered magnets is an efficient approach to magnetism control because the guest-delicate inter-layer distance (ltrans) is a variable parameter for modulating JNNNI. Herein, we demonstrated magnetic changes induced by the adsorption of CO2, N2, and O2 gases in various isostructural layered magnets with a π-stacked pillared-layer framework, , (M = Co, 1, Fe, 2, Cr, 3; Cp* = η5-C5Me5; 2,3,5,6-F4PhCO2− = 2,3,5,6-tetrafluorobenzoate; TCNQ = 7,7,8,8-tetracyano-p-quinodimethane). Each compound had almost identical adsorption capability for the three types of gases; only CO2 adsorption was found to have a gated profile. A breathing-like structural modulation involving the extension of ltrans occurred after the insertion of gases into the isolated pores between the [Ru2]2–TCNQ ferrimagnetic layers, which is more significant for CO2 than for O2 and N2, due to the CO2-gated transition. While adsorbent 1 with M = Co (S = 0) was an antiferromagnet with TN = 75 K, 1⊃CO2 was a ferrimagnet with TC = 76 K, whereas 1⊃N2 and 1⊃O2 were antiferromagnets with TN = 68 K. The guest-insertion effect was similarly confirmed in 2 and 3, and was characteristically dependent on the type of sandwiched spin in as M = Fe (S = 1/2) and Cr (S = 3/2), respectively. This study reveals that common gases such as CO2, O2, and N2 can serve as crucial triggers for the change in magnetism as a function of variable parameter ltrans.


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n Contents for SI

Fig. S6
Reversibility of alternation on magnetic properties upon gas adsorption for 1·· S15

General procedures and materials
All solvents were dried using common drying agents and distilled under nitrogen before use. All syntheses were performed in an inert atmosphere using standard Schlenk-line techniques in a commercial glove box under a nitrogen atmosphere. All chemicals were of reagent grade and were purchased from commercial sources. [MCp * 2] (M = Co, Fe, and Cr) and TCNQ were purchased from Sigma-Aldrich Co., LLC. Starting material [Ru2(2,3,5,6-F4PhCO2)4(THF)2] was prepared according to a previously reported method. 1 The synthesis of [MCp * 2][{Ru2 II,II (2,3,5,6-F4PhCO2)4}2(TCNQ)] (M = Co, Fe, and Cr) has been previously described. 2

Physical measurement
PXRD patterns were collected in the laboratory using a Rigaku Ultima IV diffractometer with Cu Ka radiation (l = 1.5418 Å). The ground samples were sealed in a soda-lime glass capillary with an inner diameter of 0.5 mm, and the PXRD patterns were obtained with 0.02° steps. Magnetic susceptibility measurements were conducted using a SQUID magnetometer (Quantum Design MPMS-XL) within 1.8-300 K and −7-7 T. The diamagnetic contribution was removed from the experimental data using Pascal constants. 3

Crystallography based on Rietveld refinement of PXRD data
A ground sample of 1 was sealed in a silica glass capillary with an inner diameter of 0.4 mm. The PXRD data for the structural analyses of 1ÉCO2, 1ÉO2, and 1ÉN2 were collected using a synchrotron X-ray beam and a diffractometer with a multimodular system constructed using six MYTHEN detectors on the BL02B2 beamline at the Super Photon ring (SPring-8). 4 The measurement temperature was controlled by flowing low-temperature nitrogen gas. The gas-handling system consisting of valves and pressure gauges for gas dosing and removing was connected to the goniometer head using a stainless steel line to obtain in situ PXRD patterns. Cell parameters were determined using the DIFFRACplus TOPAS ® v4.2 software. Crystal structure of 2 obtained by single crystal Xray diffraction analysis was used to construct the initial structural model. 1 Next, structural refinement using the Rietveld method with the RIETAN-FP program was applied. 5 The peak shape was modeled using the split-Pearson VII function. Soft constraints on the bond angles and bond distances were adapted throughout the refinement. After the framework structure was refined, gas molecules were located using the FOX software 6 with a parallel tempering algorithm while the position of the framework was fixed. Subsequently, the entire structure was refined. In the initial refinement stage, hydrogen atoms were removed from the structural model. After all parameters were refined, hydrogen atoms were attached to the calculated positions, followed by refinement of all parameters. The fractional coordinates of hydrogen atoms were not initially refined. After refinement, the fractional coordinates of the hydrogen atoms were again calculated and modified. This process was repeated until the fractional coordinates of hydrogen atoms became self-consistent. The crystallographic data and Rietveld refinement results are summarized in Table S2. The CIF data for 1ÉCO2, 1ÉO2, and 1ÉN2 were deposited at the Cambridge Crystallographic Data Centre (CCDC) in Supplementary Publication No. CCDC-2219754, -2219755, and -2219756 for 1ÉCO2, 1ÉO2, and 1ÉN2, respectively. Copies of data can be obtained free of charge from the CCDC via https://www.ccdc.cam.ac.uk/structures/. The solvent-accessible volume was estimated using the PRATON software. 7 Structural diagrams were prepared using the VESTA software. 8 The Connolly surface was depicted with a probe radius of 1.4 Å using the Discovery Studio Visualizer software. 9

Gas adsorption measurements
Adsorption isotherm measurements for N2 (at 120 K), O2 (at 90 and 120 K), and CO2 (at 195 K) were performed using an automatic volumetric adsorption apparatus (BELSORP MAX, Microtrac BEL) connected to a cryostat system (ULVAC-Cryo). A known weight (∼30 mg) of the dried sample was placed into the sample cell. Next, before measurements, the cell was evacuated using the degassing function of the analyzer for 12 h at 353 K. The change in pressure was monitored, and the amount of adsorbed gas was determined by the decrease in pressure at the equilibrium state. When the reading of the pressure gauge for 500 seconds was within 0.3%, the system was judged to have reached adsorption equilibrium.

In situ infrared spectroscopy
In situ infrared spectroscopy was conducted through CaF2 windows on a cryostat system (RC102, CRYO Industries) connected to a gas-handling and pressure monitoring system (BELSORP MAX, Microtrac BEL) with a transmission configuration using a JASCO FT-IR 4200 spectrometer. The neat samples were sandwiched between two CaF2 plates.

In situ magnetic measurements under gases
The polycrystalline samples were placed in gelatin capsules. A piece of cotton was placed above the sample to prevent sample movement during gas adsorption. The capsule was then held at the center of the plastic straw. The straw was attached to the edge of a homemade sample rod made of a stainless steel tube and a brass male thread with fluorocarbon tape. 10 The sample was isolated from the surrounding atmosphere by overlaying a closed-ended brass tube, which could be attached to the thread on the open end of the sample rod using screws. An airtight seal between the thread and the brass tube was achieved using a silicon sealant (CAF ® 4, Bluestar Silicones). The stainless steel tube was connected to a gas-handling system with a turbomolecular pump and manometer (BELSORP MAX, Microtrac BEL). Subtracting the background signal from the brass tube was unnecessary.

In situ PXRD at laboratory
The ground sample was sealed in a soda-lime glass capillary with an inner diameter of 0.5 mm. The PXRD pattern was obtained with 0.02° steps using a Rigaku Ultima IV diffractometer with Cu Kα radiation (λ = 1.5418 Å). To obtain the PXRD patterns under gas-adsorbed conditions, the glass capillary was connected to stainless steel lines that possessed valves to dose and remove gas, which were connected to a gas-handling system (BELSORP MAX, MicrotracBEL). The temperature was controlled using a stream of N2 gas. A Le Bail profile fitting algorithm, which affords refined cell parameters, was applied using the RIETAN-FP program. 5

Table S1
Gas pressure dependence of lattice constants of 1 determined by PXRD measurements and Le Bail whole patter decomposition or Rietveld method.     (7) 108.151 (10) 100.708 (9) 2206.9(4) 9.567 5.284 a Inter-layer vertical distance ( Figure S7) where y and f(x) represent the observed intensity and the calculated intensity at a diffraction angle of 2q, respectively. c Ref. 2.

Table S4
Gas pressure dependence of lattice constants of 3 determined by PXRD measurements and Le Bail whole patter decomposition.

Crystal structure under gases of 2 and 3 in SI
In situ PXRD was conducted to gain insights into the crystal structures under gas adsorption conditions.
The PXRD patterns of 2 and 3 collected under vacuum and at 100 kPa of CO2 at 195 K, and under vacuum and at 100 kPa of O2 and N2 at 120 K are shown in Fig. S8 and S9, respectively. The results of the Le Bail analysis of the PXRD patterns under gas adsorption are shown in Fig. S10 and S11, and the lattice constants of 2Égas and 3Égas obtained by Le Bail analysis are summarized in Tables S3 and S4, respectively. Similar to that of 1, the inter-layer distance (ltrans) changed significantly before The IR spectra of 2 and 3 were recorded at 100 kPa of CO2, O2, and N2. The position of peak corresponding to the CN stretching mode in 2/3ÉCO2, 2/3ÉO2, and 2/3ÉN2 remained unchanged in relation to that in 2/3 (Fig. S12), indicating no change in the electronic state before and after gas adsorption for any of the gases.