Supporting Information

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1 Supporting Information Cation-Dependent Intrinsic Electrical Conductivity in Isostructural Tetrathiafulvalene-Based Microporous Metal-Organic Frameworks Sarah S. Park, Eric R. Hontz, Lei Sun, Christopher H. Hendon, Aron Walsh, Troy Van Voorhis, and Mircea Dincă * Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA Department of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, United Kingdom mdinca@mit.edu S1

2 Table of Contents Page Materials... S3 Synthesis of Mn2(TTFTB)... S3 Synthesis of Co2(TTFTB)... S3 Synthesis of Cd2(TTFTB)... S3 X-ray diffraction studies... S4 Gas sorption measurements... S4 Single crystal conductivity measurements... S4 Other physical measurements... S4 Computational Details... S5 Figure S1. Calculated band structure of Cd2(TTFTB)... S6 Figure S2. PXRD patterns for Mn2TTFTB, Co2(TTFTB), Zn2(TTFTB) and Cd2(TTFTB)... S7 Figure S3. Thermogravimetric analysis plots for Mn2(TTFTB), Co2(TTFTB) and Cd2(TTFTB)... S8 Figure S4. Isotherms for the adsorption of N2 in desolvated Mn2(TTFTB), Co2(TTFTB) and Cd2(TTFTB) at 77 K... S9 Figure S5. Conductivity values of various batches of Mn2(TTFTB) and Co2(TTFTB) measured by gold-wire method and carbon-paste-probe method... S10 Figure S6. Thermal ellipsoid plot of Mn2(TTFTB)... S11 Table S1. X-ray experimental details for Mn2(TTFTB)... S12 Figure S7. Thermal ellipsoid plot of Co2(TTFTB)... S13 Table S2. X-ray experimental details for Co2(TTFTB)... S14 Figure S8. Thermal ellipsoid plot of Cd2(TTFTB)... S15 Table S3. X-ray experimental details for Cd2(TTFTB)... S16 Table S4. Selected bond distances for Mn2(TTFTB), Co2(TTFTB), Zn2(TTFTB) and Cd2(TTFTB)... S17 Figure S9. Optical images of Zn2(TTFTB) single crystal conductivity measurements... S18 Figure S10. EPR spectra of Zn2(TTFTB) and Cd2(TTFTB)... S19 References... S20 S2

3 Materials. Co(NO3)2 6H2O (ACS grade, %, Alfa Aesar), Mn(NO3)2 xh2o (99.98%, Alfa Aesar), Cd(NO3)2 4H2O (Fisher Chemical), ethanol (ACS grade, J. T. Baker), N,Ndimethylformamide (DMF, 99.9%, Omnisolv), gold wire (0.025 mm, Alfa Aesar) and carbon paste (Electron Microscopy Sciences, graphite conductive adhesive 112) were obtained from commercial sources and used as received. Tetrathiafulvalene tetrabenzoic acid (H4TTFTB) and Zn2TTFTB were prepared according to literature procedures. 1 Mn 2 (C 34 H 16 O 8 S 4 )(H 2 O) 2 (DMF) 0.7 (H 2 O) 1.75 (Mn 2 (TTFTB)). Mn(NO3)2 xh2o (67 mg, 0.27 mmol) was dissolved in 1:1 water/ethanol (8 ml). H4TTFTB (50. mg, mmol) was dissolved in 3:1 DMF/ethanol (8 ml). The manganese nitrate solution was slowly added to the H4TTFTB solution in a 20 ml scintillation vial. The reaction mixture was heated at 75 C for 72 hours, affording dark red single crystals (56 mg, 84%). The crystals were collected by filtration and washed with DMF (20 ml) and ethanol (20 ml). Elemental analysis calcd. for C36.1H28.4Mn2N0.7O12.45S4: C, 47.68; H, 3.15; N, Found: C, 47.55; H, 2.87; N, The crystals were evacuated at 200 C for 12 hours at 4 mtorr. Elemental analysis calcd. for C34H16Mn2O8S4: C, 51.65; H, Found: C, 51.36; H, Co 2 (C 34 H 16 O 8 S 4 )(H 2 O) 2 (DMF) 1.75 (H 2 O) 2 (Co 2 (TTFTB)).Co(NO3)2 6H2O (77 mg, 0.27 mmol) was dissolved in 1:1 water/ethanol (8 ml). H4TTFTB (50. mg, mmol) was dissolved in 3:1 DMF/ethanol (8 ml). The cobalt nitrate solution was slowly added to the H4TTFTB solution in a 20 ml scintillation vial. The reaction mixture was heated at 75 C for 72 hours, affording dark red single crystals (55 mg, 75%). The crystals were collected by filtration and washed with DMF (20 ml) and ethanol (20 ml). Elemental analysis calcd. for C39.25H36.25Co2N1.75O13.75S4: C, 47.21; H, 3.66; N, Found: C, 47.16; H, 3.60; N, The crystals were evacuated at 200 C for 12 hours at 4 mtorr. Elemental analysis calcd. for C34H16Co2O8S4: C, 51.14; H, Found: C, 50.89; H, 1.94; N, <0.02. Cd 2 (C 34 H 16 O 8 S 4 )(μ 2 -OH 2 )(H 2 O) (DMF) 1.5 (H 2 O) 2 (Cd 2 (TTFTB)). Cd(NO3)2 4H2O (172 mg, mmol) was dissolved in 1:1 water/ethanol (12 ml). H4TTFTB (103 mg, mmol) was dissolved in 3:1 DMF/ethanol (8.4 ml). The cadmium nitrate solution was slowly added to the H4TTFTB solution in a 20 ml scintillation vial. The reaction mixture was heated at 75 C for 72 hours, affording dark red needle single crystals (122 mg, 73%). The crystals were collected by filtration and washed with DMF (30 ml) and ethanol (30 ml). Elemental analysis calcd. for C38.5H34.5Cd2N1.5O13.5S4: C, 42.53; H, 3.20; N, Found: C, 42.25; H, 3.49; N, The crystals were evacuated at 220 C for 24 hours at 4 mtorr. Elemental analysis calcd. for C34H19Cd2O9.5S4: C, 43.79; H, Found: C, 43.36; H, X-ray diffraction studies. Low-temperature data were collected on a Siemens three-circle diffractometer coupled to a Bruker-APEX CCD detector with graphite-monochromated Mo Kα S3

4 radiation (λ = Å), performing φ- and ω-scans. The structure was solved by direct methods SHELXS and refined against F 2 on all data by full-matrix least squares with SHELXL All non-hydrogen atoms were refined anisotropically. All hydrogen atoms were included in the model at geometrically calculated positions and refined using a riding model, except for the hydrogen atoms on the O(10) atom in Cd2(TTFTB) (Figure S8). The Cd-O-Cd bond angle, (211), is consistent with known (μ2-oh2)cd2 structures in the CCDC database, confirming that the bridging ligand is water. The proximity of a disordered ethanol solvent molecule inhibited refinement of the hydrogens using a riding model. Details of the data quality and a summary of the residual values of the refinements for Mn2(TTFTB), Co2(TTFTB), and Cd2(TTFTB) are included in Table S1, Table S2 and Table S3, respectively. Gas sorption measurements. A Micromeritics ASAP 2020 Surface Area and Porosity Analyzer was used to measure the nitrogen adsorption isotherm. An oven-dried sample tube equipped with a TranSeal (Micromeritics) was evacuated and tared. The sample was transferred to the sample tube, which was then capped by a TranSeal. The sample was heated to appropriate temperatures as determined by thermogravimetric analysis under a vacuum of 4 mtorr, until the outgas rate was less than 2 mtorr/minute. The evacuated sample tube was weighed again and the sample mass was determined by subtracting the mass of the previously tared tube. The N2 isotherm was measured using a liquid nitrogen bath (77 K). Ultra high purity grade (99.999% purity) N2 and He, oil-free valves and gas regulators were used for all the free space correction and measurement. Single crystal conductivity measurements. A probe station (Janis Cryogenics, ST-500) and a soucemeter (Keithley Instruments model 2450) were used to measure conductivity. Direct current conductivity measurements were performed for hundred-micrometer-sized, needleshaped single crystals using the two-point probe technique. Two gold wires were attached onto both ends of c axis of the crystal with carbon paste for Mn2(TTFTB), Co2(TTFTB), and Cd2(TTFTB), whose crystals are typically longer than 1 mm ( gold-wire method ). In the case of Zn2(TTFTB), crystals are commonly shorter than 300 μm, so contacts were made by attaching the tungsten needle probes of the probe station directly onto the crystal using carbon paste ( carbon-paste-probe method ). This method resulted in comparable conductivity values for Mn2(TTFTB) and Co2(TTFTB) as compared to results obtained with the gold wire method (Figure S5). All of the current-voltage (I-V) measurements were performed in ambient conditions by sweeping the voltage from 1 V to 1 V. Electrical measurements were performed on 24 different crystals of Mn2(TTFTB), 22 different crystals of Co2(TTFTB), 20 different crystals of Zn2(TTFTB), and 22 different crystals of Cd2(TTFTB); the different crystals for each material were selected from 4 or 5 different synthetic batches to confirm reproducibility. Other physical measurements. Thermogravimetric analysis (TGA) was performed on a TA S4

5 Instruments Q500 Thermogravimetric Analyzer at a heating rate of 1.0 C/min under a nitrogen gas flow of 90 ml/min on a platinum pan. Powder X-ray diffraction (PXRD) patterns were recorded on Bruker D8 Discover diffractometer using Nickel-filtered Cu-Kα radiation (λ = Å) with accelerating voltage and current of 40 kv and 40 ma, respectively. Samples for PXRD were prepared by placing a thin layer of the appropriate material on a zero-background silicon crystal plate. Computational Details. All electronic and structural calculations were performed within the Kohn Sham density functional theory (DFT) framework. Born von Karman boundary conditions were employed to represent a framework infinitely repeating in each direction, with no surface termination. The Vienna ab initio simulation package (VASP), a plane-wave basis set code (with PAW scalar-relativistic pseudopotentials), was employed for crystal and electronic structure optimization. A 5 x 5 x 5 k-mesh was used to sample the Brillouin zone for each of the materials. A 500 ev plane-wave cutoff was found to be suitable for convergence of electronic wave functions to give total energies within 0.01 ev/atom. Starting with the experimentally determined unit cells lattice parameters and atomic positions were relaxed with the semi-local Perdew Burke Ernzerhof exchange correlation functional revised for solids (PBEsol). The key electronic properties, including electron density, electrostatic potential, and band gap, were computed using a hybrid exchange correlation functional (HSE06) with 25% of the shortrange semi-local exchange replaced by the exact nonlocal Hartree Fock exchange. In contrast to molecular quantum-chemical calculations, within periodic boundary conditions, the electronic eigenvalues resulting from the solution of the Kohn Sham equations are given with respect to an internal reference (for VASP it is the average electrostatic potential of the repeating cell). The consequence is that absolute values of band energies cannot be compared between two or more frameworks: there is no common vacuum level. It should be noted that for solids, unlike finite systems, the highest occupied Kohn Sham eigenvalue and the electron removal energy (N N 1 system) are equivalent in the dilute limit. For the reference electrostatic potential we use a spherical average of the Hartree potential in a sphere of r = 2 Å with an origin at the center of the pore. The analysis code for this calculation, which can also calculate planar and macroscopic averages of electrostatic potentials and charge densities, is freely available. The electrostatic potential was sampled on a grid of mesh density >14 points/å. S5

6 0-1 Absolute Energy (ev) L E g =1.75 ev S O C Cd T A Figure S1. Calculated band structure and projected density of states (PDOS) of Cd 2 (TTFTB). The work function,, and absolute energy scale are aligned relative to vacuum The coordinates of the reciprocal space points are Γ = (0, 0, 0) and A = (0, 0, 1/2). S6

7 Cd 2 TTFTB Zn 2 TTFTB Co 2 TTFTB Mn 2 TTFTB Simulated θ (deg) Figure S2. PXRD patterns of Mn2(TTFTB), Co2(TTFTB), Zn2(TTFTB) and Cd2(TTFTB) compared to that simulated for Zn2(TTFTB). S7

8 Weight (%) Temperature ( o C) Figure S3. Thermogravimetric analysis plots for Mn2(TTFTB) (red), Co2(TTFTB) (blue) and Cd2(TTFTB) (green). S8

9 200 Quantity Adsorbed (cm 3 /g) Relative Pressure (P/P 0 ) Figure S4. N2 isotherms at 77K for Mn2(TTFTB) (red), Co2(TTFTB) (blue) and Cd2(TTFTB) (green). S9

10 Gold-wire method Carbon-paste-probe method Mn 2 TTFTB batch 1 Mn 2 TTFTB batch 2 Co 2 TTFTB batch 1 Co 2 TTFTB batch Conductivity (S/cm) Figure S5. Conductivity values of various batches of Mn2(TTFTB) and Co2(TTFTB) measured by both the gold-wire method and the carbon-paste-probe method. S10

11 Figure S6. Thermal ellipsoid plot of Mn2(TTFTB) drawn at the 50% probability level. H-atoms and DMF solvent molecules are omitted for clarity. S11

12 Table S1. X-ray experimental details for Mn2(TTFTB) Identification code Mn2TTFTB Empirical formula Formula weight Temperature K Wavelength Å Crystal system Hexagonal Space group P 65 Unit cell dimensions a = (7) Å C40.94 H37.30 Mn2 N1.76 O12.59 S4 b = (7) Å c = (8) Å α = 90 º β = 90 º γ = 120 º Volume (4) Å 3 Z 6 Density (calculated) mg/m 3 Absorption coefficient mm -1 F(000) 3060 Crystal size 0.2 x 0.05 x 0.03 mm 3 θ range for data collection to Index ranges -27<=h<=27, -22<=k<=24, -29<=l<=29 Reflections collected 9445 Independent reflections [Rint = ] Completeness to theta = % Absorption correction None Max. and min. transmission and Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters / 5 / 589 Goodness-of-fit a on F R1 b wr2 c a GOF = (Σ w(f o 2 F c 2 ) 2 /(n p)) 1/2 where n is the number of data and p is the number of parameters refined. b R 1 = Σ F o F c / Σ F o. c wr 2 = (Σ(w(F o 2 F c 2 ) 2 )/ Σ (w(f o 2 ) 2 )) 1/2. S12

13 Figure S7. Thermal ellipsoid plot of Co2(TTFTB) drawn at the 50% probability level. H-atoms and solvent molecules (DMF and ethanol) are omitted for clarity. S13

14 Table S2. X-ray experimental details for Co2(TTFTB) Identification code Co2TTFTB Empirical formula Formula weight Temperature K Wavelength Å Crystal system Hexagonal Space group P 61 Unit cell dimensions a = (7) Å C41.52 H38.08 Co2 N1.64 O12.35 S4 b = (7) Å c = (15) Å α = 90 º β = 90 º γ = 120 º Volume (7) Å 3 Z 6 Density (calculated) mg/m 3 Absorption coefficient mm -1 F(000) 3093 Crystal size 0.4 x 0.15 x 0.1 mm 3 θ range for data collection to Index ranges -24<=h<=24, -24<=k<=24, -26<=l<=26 Reflections collected Independent reflections 9985 [Rint = ] Completeness to theta = % Absorption correction Semi-empirical from equivalents Max. and min. transmission and Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 9985 / 133 / 578 Goodness-of-fit a on F R1 b wr2 c a GOF = (Σ w(f o 2 F c 2 ) 2 /(n p)) 1/2 where n is the number of data and p is the number of parameters refined. b R 1 = Σ F o F c / Σ F o. c wr 2 = (Σ(w(F o 2 F c 2 ) 2 )/ Σ (w(f o 2 ) 2 )) 1/2. S14

15 Figure S8. Thermal ellipsoid plot of Cd2(TTFTB) drawn at the 50% probability level. H-atoms and solvent molecules (DMF and ethanol) are omitted for clarity. S15

16 Table S3. X-ray experimental details for Cd2(TTFTB) Identification code Cd2TTFTB Empirical formula Formula weight Temperature K Wavelength Å Crystal system Hexagonal Space group P 65 Unit cell dimensions a = (3) Å C42 H37 Cd2 N2 O13 S4 b = (3) Å c = (3) Å α = 90 º β = 90 º γ = 120 º Volume 6906(2) Å 3 Z 6 Density (calculated) mg/m 3 Absorption coefficient mm -1 F(000) 3402 Crystal size 0.05 x x mm 3 θ range for data collection to Index ranges -25<=h<=19, -25<=k<=27, -28<=l<=28 Reflections collected Independent reflections [Rint = ] Completeness to theta = % Absorption correction Semi-empirical from equivalents Max. and min. transmission and Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters / 13 / 589 Goodness-of-fit a on F R1 b wr2 c a GOF = (Σ w(f o 2 F c 2 ) 2 /(n p)) 1/2 where n is the number of data and p is the number of parameters refined. b R 1 = Σ F o F c / Σ F o. c wr 2 = (Σ(w(F o 2 F c 2 ) 2 )/ Σ (w(f o 2 ) 2 )) 1/2. S16

17 Table S4. Selected bond distances for Mn2(TTFTB), Co2(TTFTB), Zn2(TTFTB) 1 and Cd2(TTFTB) Mn 2 (TTFTB) Co 2 (TTFTB) Zn 2 (TTFTB) Cd 2 (TTFTB) C1 C (3) 1.336(9) 1.326(5) 1.317(7) S1 C (2) 1.753(7) 1.757(4) 1.751(5) S2 C (2) 1.762(7) 1.753(4) 1.755(5) S3 C (2) 1.754(8) 1.762(3) 1.760(5) S4 C (2) 1.756(7) 1.757(3) 1.753(5) S17

18 a) b) 100 µm 100 µm Figure S9. Optical images of the Zn2(TTFTB) crystal. Contacts made with carbon paste (a) on both ends of c axis and (b) in a direction perpendicular to the c axis. S18

19 Zn 2 TTFTB Cd 2 TTFTB Field (G) Figure S10. EPR spectra of Zn2(TTFTB) and Cd2(TTFTB). S19

20 References [S1] Narayan, T. C.; Miyakai, T.; Seki, S.; Dincă, M. J. Am. Chem. Soc. 2012, 134, [S2] Sheldrick, G. M. Acta Cryst. Sect. A 1990, 46, 467. S20