Supporting Information for: A Ferric Semiquinoid Single-Chain Magnet via Thermally-Switchable Metal- Ligand Electron Transfer Jordan A. DeGayner, Kunyu Wang, and T. David Harris* Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston IL 60208-3113 Email: dharris@northwestern.edu J. Am. Chem. Soc. Table of Contents Experimental Section Table S1: Crystallographic data for 1 at 250 and 100 K Figure S1: Structure of 1 at 250 and 100 K Figure S2: Packing diagram of 1 at 250 and 100 K Figure S3: Mössbauer spectrum of 1 at 80 K Figure S4: Raman spectrum of 1 at ambient temperature Figure S5: Derivative of χ MT with respect to T vs T Figure S6: High-temperature dc magnetic susceptibility upon heating and cooling Figure S7: Variable-field magnetization data for 1 Figure S8: Variable-field magnetization data for 1 Figure S9: Variable-field magnetization data for 1 Figure S10: Variable-frequency ac magnetic susceptibility data for 1 Figure S11: Variable-temperature ac magnetic susceptibility data for 1 collected at 1 Hz Figure S12: Variable-temperature dc magnetic susceptibility for 1 Figure S13: Magnetic phase diagram for 1 Figure S14: Variable-frequency ac magnetic susceptibility data for 1 under an applied dc field Figure S15: Arrhenius plot of relaxation times for 1 under an applied dc field Figure S16: Ambient-temperature I-V curve for 1 References S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 S13 S14 S15 S16 S17 S18 S19 S20 S1
Experimental Section General Considerations. The manipulations described below were performed under a dinitrogen atmosphere in an MBraun LABstar glovebox, operated under a humid atmosphere. Dimethylformamide (DMF) and dichloromethane (DCM) were dried using a commercial solvent purification system from Pure Process Technology. All reagents were purchased from commercial vendors and used without further purification. (NMe4)2[LFeCl2] (1). To a DMF solution (6 ml) of FeCl3 6H2O (21.6 mg, 0.080 mmol) was added NMe4Cl (87.2 mg, 0.80 mmol) solid and 230 μl H2O. A solution of chloranilic acid (33.4 mg, 0.16 mmol) in 2mL DMF was then added to give a dark purple suspension. The mixture was heated at 130 for two days to give shiny, brown plates suitable for X-ray analysis in addition to a brown flocculent powder and colorless flakes. After cooling, the mother liquor was decanted and the resulting solid washed with DMF (5 5 ml) to remove the brown powder followed by DCM (4 3 ml) to remove the colorless flakes. The remaining solid was filtered to yield 1 (16.1 mg, 41.7%). FT-IR (ATR, cm 1 ): 3050 (s), 1650 (w) 1495 (xs), 1400 (m), 990 (s), 800 (s), 600 (s), 560 (s). Anal. Calcd. for C14H24FeN2O4Cl4: C, 34.9; H, 5.02; N, 5.81%. Found: C, 34.7; H, 5.00; N, 5.80%. X-ray Structure Determination. A single crystal of 1 suitable for X-ray analysis were coated with deoxygenated Paratone-N oil and mounted on a MicroMounts TM rod. The crystallographic data were collected at 250 K and then cooled to 100 K on a Bruker APEX II diffractometer equipped with a Mo Kα sealed tube microsource with a graphite monochromator. Raw data were integrated and corrected for Lorentz and polarization effects using Bruker APEX2 v. 2009.1, 1 and absorption corrections were applied using SADABS. 2 The space group assignment was determined by examination of systematic absences, E-statistics, and successive refinement of the structure. The structure was solved and refined with SHELXL 3 operated with the OLEX2 interface. 4 Hydrogen atoms for the tetramethylammonium atoms were placed at calculated positions using suitable riding models and refined using isotropic displacement parameters derived from their parent atoms. Thermal parameters were refined anisotropically for all non-hydrogen atoms. Crystallographic data and the details of data collection are listed in Table S1. Magnetic Measurements. Magnetic measurements of 1 were performed on polycrystalline samples restrained in an eicosane matrix and flame-sealed in a quartz tube under vacuum. All data were collected using a Quantum Design MPMS- XL SQUID magnetometer from 1.8 to 300 K at applied dc fields ranging from 5 to +7 T. Ac magnetic susceptibility data were collected under an ac field of 4 Oe, oscillating at frequencies in the range 1-1488 Hz. Dc susceptibility data were corrected for diamagnetic contributions from the sample holder and for the core diamagnetism of each sample (estimated using Pascal s constants 5 ). The coherence of the collected data was confirmed across different measurements. Raman Measurements. Crystals of 1 were deposited onto a silver stage and sealed in a Linkam THMS350V microscope stage. Raman spectra were collected using a Horiba LabRam HR Evolution confocal microscope. Individual crystals were excited with a 532 nm continuous-wave diode laser equipped with a long working distance 50 microscope objective (NA = 0.50; Nikon) and 600 grooves/mm grating at 18.5 μw power at ambient temperature and 220 K and 1.6 μw power at 210 and 200 K power. Spectra were collected for 12 minutes at each temperature. Electrical Conductivity Measurements. Two-point dc conductivity data were collected in a dinitrogen-filled glovebox at ambient temperature using a home-built press and a CHI 760c, as previously described. 6 The powder was pressed between two steel rods of 3 mm diameter inside of a glass capillary. The thickness of the pressed pellets typically ranged from 0.1 to 0.5 mm. Other Physical Measurements. Elemental analyses of 1 was performed on an Elementar Vario EL Cube elemental analyzer instrument. Infrared spectra were recorded on a Bruker Alpha FTIR spectrometer equipped with an attenuated total reflectance accessory. Zero-field iron-57 Mössbauer spectra for 1 were obtained at 80, 200, 210, and 220 K with a constant acceleration spectrometer and a cobalt-57 rhodium source. Prior to the measurements, the spectrometer was calibrated at 295 K with -iron foil. Samples were prepared in a dinitrogen-filled glovebox, covered with deoxygenated Paratone-N oil, and frozen in liquid nitrogen prior to handling in air. The sample of 1 contained approximately 10 mg/cm 2 of iron. The spectra were analyzed using the WMOSS Mössbauer Spectral Analysis Software (www.wmoss.org). S2
Table 1. Crystallographic data for 1 at 250 and 100 K 250 K 100 K empirical formula C 14H 24FeCl 4N 2O 4 C 14H 24FeCl 4N 2O 4 formula weight, g/mol 482.0 482.0 crystal system monoclinic monoclinic space group C2/c C2/c wavelength, Å 0.71073 0.71073 temp, K 250 100 a, Å 16.183(3) 16.100(1) b, Å 9.494(2) 9.3394(8) c, Å 13.961(2) 13.817(1) α, deg 90 90 β, deg 104.87(1) 104.971(5) γ, deg 90 90 V, Å 3 2073.1(6) 2007.0(3) d calc, g/cm 3 1.544 1.595 R 1 (I > 2σ(I)) a 0.0727 0.0653 wr 2 (all) b 0.2055 0.1915 GoF 1.032 1.071 a R1 = F0 FC /Σ F0. b wr2 = [ w(f0 2 FC 2 ) 2 / w(f0 2 ) 2 ] 1/2 S3
Figure S1 Crystal structures of 1 at 250 (upper) and 100 K (lower). Hydrogen atoms have been omitted for clarity. Orange, green, red, and gray spheres represent Fe, Cl, O, and C, respectively. S4
Figure S2 Packing diagram of 1 at 250 (left) and 100 K (right) as viewed along the c-axis with selected distances indicated (Å). Cations have been omitted for clarity. Orange, green, red, and gray spheres represent Fe, Cl, O, and C, respectively. S5
2 % Figure S3 Mӧssbauer spectrum for a crystalline sample of 1 collected at 80 K. The solid line is a fit to the data with = 0.596(2) mm/s and EQ = 1.094(3) mm/s. S6
Figure S4 Solid-state Raman spectrum for 1 collected at ambient temperature following excitation at 532 nm. S7
Figure S5 Derivative of MT with respect to T vs T data collected for 1 under an applied field of 1000 Oe. S8
Figure S6 Plot of MT vs T for 1 upon heating (red) and cooling (blue) under an applied field of 5000 Oe. S9
Figure S7 Variable-field magnetization data for 1 collected at 1.8 K. S10
Figure S8 Variable-field magnetization data for 1 collected at 1.8 K. S11
Figure S9 Variable-field, variable-temperature magnetization data for 1. Inset: plot of dm/dh vs H. S12
Figure S10 Variable-frequency ac susceptibility data for 1 collected under zero applied dc field. Solid lines are guides to the eye. S13
Figure S11 Variable-temperature ac magnetic susceptibility collected at 1 Hz and plotted as ln( MʹT) vs 1/T. Red line indicates a fit to the linear region to give = 22 cm 1. S14
Figure S12 Plot of M vs T for 1 under an applied magnetic field of 100 Oe (red) and 200 Oe (green). S15
Paramagnet Antiferromagnet Figure S13 Magnetic phase diagram for 1 constructed from M v H data (cyan), dc susceptibility data (purple), and ac susceptibility data (orange). S16
Figure S14 Variable-frequency ac susceptibility data for 1 collected under an applied dc field of 400 Oe. Solid lines are guides to the eye. S17
Figure S15 Arrhenius plot of relaxation times for 1 collected under an applied field of 400 Oe. The solid line is a linear regression fit to the data to give = 54(1) cm 1 and 0 = 2.2(5) 10 11 s. S18
Figure S16 I-V curve collected at ambient temperature for a pressed pellet of 1. S19
References 1 APEX2, v. 2009; Bruker Analytical X-Ray Systems, Inc: Madison, WI, 2009. 2 Sheldrick, G. M. SADABS, version 2.03, Bruker Analytical X-Ray Systems, Madison, WI, 2000. 3 Sheldrick, G. M., SHELXTL, Version 6.12; Bruker Analytical X-Ray Systems, Inc.: Madison, WI, 2000. 4 Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A.; Puschmann, H. J. Appl. Crystallogr. 2009, 42, 339. 5 Bain, G. A.; Berry, J. F. J. Chem. Educ. 2008, 85, 532. 6 Wudl, F.; Bryce, M. R. J. Chem. Educ. 1990, 67, 717. S20