Mechanical Gas Capture and Release in a Network Solid via Multiple Single Crystalline Transformations

Transcription

1 Supporting Information for: Mechanical Gas Capture and Release in a Network Solid via Multiple Single Crystalline Transformations Brett D. Chandler, Gary D. Enright, Konstantin A. Udachin, John A. Ripmeester, Shane Pawsey, David T. Cramb* and George K. H. Shimizu* Department of Chemistry, University of Calgary Calgary, Alberta, T2N 1N4, Canada AUTHOR ADDRESS dcramb@ucalgary.ca and gshimizu@ucalgary.ca 1

2 Synthesis and Crystal Growth Synthesis of L: Sodium benzene-1,3-disulfonate (20.0 g, mmol) was added to 20% oleum (50.0 ml ) and HgSO 4 (800 mg, 2.68 mmol, 4 wt%). The reaction mixture was heated at 290 o C for a period of 24 hours and then cooled to room temperature. The dark brown mixture was poured into water (600 ml ) and quenched with 30% NaOH (aq) until the solution was at a ph of >10 then diluted to 1200 ml. This solution was filtered using a 5 μm sintered glass frit to remove the precipitated mercury hydroxide leaving a clear yellow solution. Next, a solution containing tetrabutylammonium(tba) hydrogen sulfate (38.9 g, mmol) dissolved in water (20 ml ) was mixed together with the reactant mixture and stirred for 10 minutes. TBA(L) was extracted from the basic aqueous mixture using dichloromethane extractions (six x 125 ml). The yellow solution was passed through a carbon plug in a sintered frit, resulting in a clear transparent solution. The solvent was removed under reduced pressure to give quantitatively pure tristetrabutylammonium benzene-1,3,5-trisulfonate, TBA 3 (L), (24.05 g, 32% yield). Found C, 61.89; H 10.92; N, Calc for (TBA) 3 L, C, 62.20; H 10.73; N, H NMR (300 MHz D 2 O) (t, 36H, J = Hz), (m, 24H, J = ), (m, 24H, J = ), (t, 24H, J = ), (s, 3H). 13 C NMR (300 MHz DMSO) (C-SO 3 ), (C-H), ( -CH 2 ), ( -CH 2 ), ( -CH 2 ), (CH 3 ). 2

3 Crystal Growth of: Ba 3 (H 2 O) 3 (L2) 2 (H 2 O) 8 (1), Ba 3 (H 2 O) 6 (L2) 2 (H 2 O) 2 (2a) 250 mg of TBA 3 (L) (0.239 mmol) was dissolved in 2 ml of water in a 10 ml vial mg of BaCl 2 2H 2 O (0.359 mmol) was dissolved in 2 ml of water in a second 10 ml vial. The two solutions were mixed and were heated on a heating mantle for 10 minutes. Single crystals were grown by vapour diffusion using 1 ml of the heated solution in 2 ml vials which were then placed into clean 10 ml vials containing methanol as the diffusing solvent and capped. Between four and five days, large ( 0.5 mm x 0.68 mm x 0.5 mm) transparent crystalline blocks had grown of Ba 3 (H 2 O) 6 (L) 2 (H 2 O) n (1), and were of sufficient quality for X-ray analysis. In most cases, the crystals had to be cut in order to analyze by single X-ray crystallography due to the large size. Alteration of the diffusion solvent from methanol to acetone generated a second polymorph with nearly identical numbers of water molecules per unit cell. Crystals of the acetone diffusion, (2a), grew over a period of ten to fifteen days, and while much smaller than the methanol polymorph, were of sufficient size and quality for X-ray analysis. 3

4 General X-ray Crystallography Table 1: Crystallographic data for (1), (2a), (3) and (4) Compound (1) (2a) (3) (4) Formula Sum Formula Weight Ba 3 L 2 (H 2 O) 11.8 Ba 3 L 2 (H 2 O) 8 Ba 3 L 2 (H 2 O) 2 Ba 3 L H 2 O (wt %) Crystal System Space Group Orthorhombic Monoclinic Orthorhombic Trigonal Pccn P2 1 /c Pbcn P3 1 c a (Å) (19) (5) 9.461(2) (14) b (Å) (8) (5) (4) (14) c (Å) (16) (5) (4) (3) (deg) , (deg) (5) 90 90, (deg) V, (Å 3 ) (6) (19) (10) (4) Z F D calc (g cm - 3 )

5 μ (mm -1 ) (Å) goof a R b R w b a R F o Fc F o when I > 2 (I). b R w w F 2 2 o c w F F 2 o 2 2 for all reflections Detailed Structure Descriptions for 1-4 Structure of 1: The initial structure solution of compound 1 gave poor R 1 values (> 8% - 9%) indicating the modeled electron density was only satisfactory in describing the structure despite the collection of good quality high angle data ( > 30 o ). It quickly becomes apparent from the initial structure solution that compound 1 is a heavily hydrated three-dimensional structure containing two-dimensional channels approximately 9.7 x 9.5 Å in size. Therefore, when the crystals are removed from the supernatant, it is likely that the crystals begin desolvating resulting in the flexing of the structure. Flash freezing the crystals as they are removed from the aqueous methanol mixture solves this problem. Flash frozen crystals of compound 1 crystallize in an orthorhombic crystal system (Pccn) giving an excellent structure model with good statistics (Table S1). The asymmetric unit of 1 (Figure S1) is composed of a single ligand, L, two unique barium metal centers, Ba1, Ba2, and approximately 15 disordered water molecules with only the most stable metal-coordinated molecules; stability based on well behaved displacement parameters. In the extended structure two sulfonates, S1, and S2, are coordinated to three barium atoms, one Ba2 and two Ba1 centers, each in a μ 3 3 5

6 binding mode. The third sulfonate group, S3, is coordinated to two Ba1 barium atoms in a μ 2 2 binding mode with one oxygen remaining uncoordinated. In the extended structure, each ligand of L is paired up with a second unit to form dimers that sit in a staggered conformation; rows of dimers form one-dimensional columns along the a-axis (Figure S2). Subsequent crosslinking of these columns with Barium, Ba1, results in the formation of two-dimensional sheets (Figure 1). Since two of the oxygen atoms of S3 are bound to Ba1 atoms, S3 serves as an exclusive sheet assembling functionality while the oxygen atoms, O1, O2, of S1 and O4, O6, of S2 also contribute to the two-dimensional sheet formation. This is significant since out of nine possible sulfonate oxygen atoms that can bind with Barium, six of the nine are responsible for the formation of the two-dimensional sheets; each Ba1 center is an eight coordinate square antiprism with water occupying two of the eight positions. Figure S1: Asymmetric unit of 1 in Pccn with ellipsoids at 60%. Disordered channel water molecules have been removed from the structure. 6

7 Figure S2: Crosslinking of Ba1 sheets into the third-dimension via the four coordinate Ba2 metal centers for compound 1. All water molecules have been removed for clarity. Structure of 2a: Diffusion of acetone into the aqueous mixtures of Ba 2+ and L yields single crystals of 2a. Compound 2a is a three-dimensional framework, ~12% hydrated, and more densely packed than 1. The asymmetric unit contains three unique barium atoms, Ba1 Ba3, and two full crystallographically distinct ligands (Figure S3). 7

8 Figure S3: Asymmetric unit of 2a in P2 1 /c with ellipsoids at 60%. All water molecules have been removed to provide clarity. In 2a, pairs of ligands sit in a staggered conformation, as in 1, but are not perfectly offset with respect to each other removing much of the symmetry observed in 1. Whereas the dimer is the basic structural motif in compound 1, tetramers are the basic motif that repeat throughout 2 and sit at a 45 o off axis angle in the ac-plane (Figure 1c,d). Figure S4: Extended structure for 2a. Blue and red color designations are used to visually distinguish tetramers in three-dimensional space a) Benzene core of tetramers viewing 8

9 down the c-axis in the ab-plane. b) Barium crosslinking of selected tetramers along the c- axis. c) Formation of two-dimensional sheets via barium crosslinking along b-axis. The tetramer units crosslink with three barium centers, Ba1, Ba2, Ba3, along the c-axis to form one-dimensional pillars. Figure S4a presents a visual representation of the tetramers in the extended structure. Red and blue rows of tetramers (i.e. from left to right) run along the a-axis, while the alternating colors correspond to the tetramer pillars along the c-axis (Figure S4b). The two-dimensional sheets are formed by the crosslinking of tetrameric sulfonate pillars with three barium atoms, Ba1, Ba2, Ba3, along the b-axis resulting in a pseudo-hexagonal sheet (Figure S4c). The two-dimensional tetrameric sheets traverse the ab-plane and are approximately 11.51(3) Å across. The sheets are assembled into the third dimension along the a-axis via the coordination of three sulfonate groups, S3, S5, S6, on three different ligands to Ba2 (Figure S5). Figure S5: Illustration of one-dimensional channels in compound 2a with transitions from ball and stick, space filling L tetramer pillars, to full space filling model. Viewed along the c-axis in the ab-plane. Water molecules have been removed for clarity. 9

10 The enhanced crosslinking of the bridging atoms results in the loss of a onedimensional channel and subsequent contraction of the remaining channel compared to 1 giving a final pore dimension of ~ 5.6 x 5.1 Å. The bridging Ba2 atoms and sheet assembling Ba1 atoms each ligate five water molecules that are directed into the channel itself, while the other sheet assembling Ba3 atoms coordinate four well resolved water molecules also directed into the channels. Structure of 3: Compound 3, obtained by direct dehydration of 1, is 3.34 % water by weight and crystallizes in an orthorhombic crystal system. The space group is Pbcn and the asymmetric unit shown in Figure S6. The asymmetric unit contains one full ligand, two unique barium atoms, and a single coordinated water molecule per formula unit. Each of the two barium atoms is mildly disordered with a Ba1:Ba2 occupancy ratio of 95:5, and a Ba3:Ba4 occupancy ratio of 76:24. Figure S6: Asymmetric unit of 3 in Pbcn with ellipsoids at 60%. 10

11 Compound 3 lays on the line between compounds 2 and 4 (Figure 1e,f). Compared to 2a, the aryl groups are not as efficiently stacked as the pores, at this stage of dehydration, are beginning to reopen. The tetramer aromatic motif is no longer observed. The mutual orientation of L molecules also approaches a more ideal value, only being tilted by 2.57 o relative to a perfectly staggered conformation. In compound 3, each sulfonate functionality remains coordinated to three barium centers. The coordination mode for S1 remains the same between the two structures with only minor displacement and closer contacts to the S1 atom (< Å). While S2 keeps the same coordination mode in both compounds, the sulfonate undergoes an ~ 41 o rotation and coordinates to different atoms again with a small decrease in the barium sulfonate distances ( < Å). Finally, S3 forms a motif with two metals bridged in a bidentate fashion and the third remaining singly coordinated. As was evidenced by the other two sulfonate groups, only small decreases are observed for the barium to sulfonate distances ( < Å). Structure of 4: Compound (4) crystallizes in the high symmetry trigonal P3 1 c space group (Figure S7). The asymmetric unit contains only two unique carbon atoms per ligand, C1, C2 and C3, C4, along with one sulfonate group per ligand, S1, S2, and three unique barium atoms BA1, BA2, and BA3. The first ligand, C1, C2, which is composed of three sulfonates, S1, due to the symmetry of the system, has three barium atoms bound to each sulfonate in a similar motif as seen for compound (1). The second ligand, C3, C4, only 11

12 has two barium atoms bound to each sulfonate in the common and basic μ 2 binding mode. This binding mode is somewhat unexpected due to the fact it is a decrease in three barium-oxygen coordinate bonds resulting in a six coordinate barium metal as compared to the nine coordinate barium cations observed in compound (3). The final structure of (4) adopts a trigonal symmetry with pillars of ligands traversing the c-axis. The trigonal symmetry arises due to the repeating arrangement pattern of barium atoms in a hexagon, followed by three barium atoms in a triangle motif in the unit cell giving the system an overall trigonal symmetry. (Figure 1g,h) Figure S7: Asymmetric unit of (4) in P3 1 c. with ellipsoids at 50%. Non-labelled atoms correspond to symmetry equivalents and are shown for clarity Instead of the symmetrical overlapping of ligands in a staggered conformation, each ligand in the unit cell is rotated by ~9 o in the ab-plane. Each gap between pairs of ligands is separated by either a trigonal or hexagonal arrangement of barium atoms resulting in ligand separations of 4.19(1) Å and 4.05(1) Å respectively for (4). This is in stark contrast to the 4.04(1) Å and 3.70(1) Å distances observed for (3) or the uniform distance of 3.66(1) Å for pairs of ligands in the original compound (1). 12

13 Additional Characterization TGA When crystals of compound (1) are heated at a rate of 10 o C min -1 in air, they undergo a steady loss of water up to 150 o C at which point a significant increase is observed concurrent with an endothermic spike in the DSC (103.8 J g -1 ) and resulting in a total water loss of 9.74 %. This value is lower than the crystallographically predicted water content of (1) due to the rapid desolvation that occurs during equilibration of the mass balance in the instrument. After the initial water loss, the sample reaches a plateau and remains stable for over 400 o C until it rapidly undergoes decomposition at 578 o C. Figure S8: TGA/DSC analysis of compound (1) in air. Carrying out the DSC/TGA in a different atmosphere results in notable changes in the temperature of decomposition (Figure S9). Under N2, the decomposition temperature is 574 C and, under Ar, it is 567 C. These values are reproducible. 13

14 Figure S9: TGA/DSC analysis of compound (1) under dinitrogen Sorption The specific reversibility of compound (4) tested via water sorption studies performed at room temperature (298 K) are presented in Figure S10. Figure S10: Water sorption study performed for compound (4). 14

15 At a partial pressure of 1.0, the water vapour condenses. Below this pressure (4) exhibits a steady state increase in the concentration of the water with a marked hysteresis. The increase in the water concentration indicates that the sample undergoes a structural change from the closed pore structure of (4) to a more open structure. In addition, the hysteresis indicates that the final compound is in fact different than the original due to the two-fold increase in water content at any given partial pressure. Experiments performed using the TGA independently verify that crystalline samples of (4) reversibly sorb up to 80% of the water determined crystallographically from compound (1). Determination of the specific pore characteristics and surface area of (4) using CO 2 revealed minimal sorption (Fig. S11). The Dubinin Radushkevich plot is linear over the adsorption range and gives a surface area of 35.3 m 2 g -1. This low value is evidence of a dense phase that undergoes surface adsorption and desorption only at low pressures. Figure S11: CO 2 sorption isotherm of compound (4) at K 15

16 Figure S12. Calculated spot overlays for 1 and 4, shown with the measured initial (top) and final (bottom) X-ray diffraction patterns for the heating of a single crystal of 1. 16

17 Figure S13. PXRD patterns showing the dehydration of a bulk sample after standing for a) 5 minutes, b) 15 minutes, c) 60 minutes, and d) after heating to 200 C for 4 hours. Simulated PXRD patterns for 1, 2a, 3, and 4 are provided in Figure S15. 17

18 Figure S14. PXRD patterns showing the rehydration of a bulk sample of 4. a) Sample immediately after heating to 200 C, b) after standing in air for 5 minutes, c) after addition of a drop of 25% water in methanol, and d) after addition of 5 drops of 25% water in methanol. Simulated PXRD patterns for 1, 2a, 3, and 4 are provided in Figure S15. 18

19 Figure S15. PXRD patterns for 1, 2a, 3, and 4 simulated from single crystal data. 19

20 Figure S16. Expanded comparison of PXRD patterns of a) 4 simulated from single crystal data, and b) 4 as prepared by heating 1 to 200 C for 4 hours. Caption for Video: 300 mg of single crystalline samples of 1 were taken, ground into a powder using a mortar and pestle and dried at 350 o C for two hours under an atmosphere of N 2. The mass loss was monitored via gravimetric analysis and once a stable plateau had been reached they were cooled to room temperature under an atmosphere of N 2. The powder was then placed into a pellet press ( ~2000 psi) and compressed into 7 mm pellets. The video was obtained by suspending the pellets in dry acetone; a solvent that compounds 1-4 have shown no solubility in via NMR. Next, a single drop of 18 M water from a Pasteur pipette was added to the acetone solution. The water begins to both open pores and dissolve the network, subsequently releasing the trapped gas. 20

21 129 Xe NMR spectroscopy Xenon Polarizer. HP 129 Xe gas was produced under continuous flow (CF) conditions using an optical pumping setup similar to that previously reported. i,ii The polarizer was located within the fringe field of the spectrometer s superconducting magnet and a 30 W CW diode laser from OptoPower, operating at a wavelength of 785 nm, was used as the source of optical excitation. The gas mixture of xenon, helium, and nitrogen with volume composition of 1%-96%-3% respectively, and flow rates of scc/min (gas flow normalized to standard conditions) was delivered through 1.5 mm ID plastic tubing from the polarizer directly to the sample contained in a modified Morris Instruments NMR probe equipped with a 5 mm coil. 129 Xe NMR. The CF HP 129 Xe NMR experiments were performed on a Bruker AMX-300 spectrometer operating at MHz (magnetic field of 7.04 T). For all single pulse experiments 1024 scans were acquired with a pulse recycle time of 1 s. Variable temperature experiments were performed over the range of K at 15 degree intervals regulated by a Bruker BVT3000 temperature controller unit. The chemical shifts of 129 Xe were referenced to xenon gas extrapolated to zero pressure. Before experiments were repeated the next day the sample was left in the probe under a room temperature flow of argon gas. A week later the sample was probed again at which point it was heated in a 120 C oven for six hours before NMR experiments were performed. Void space modeling The program Atoms was used to model the pore space in the Ba sulfonate compound. The surface of the cage shown in Fig. 5 is that enclosing the possible centre point locations of the sphere with a radius of 1.2 A. Van der Waals radii of R C =1.70Å, R O =1.52 Å, R S =1.80 Å, R H =1.20 Å, were used for the host atoms on the the surfaces of the cages. i Moudrakovski, I. L.; Lang, S.; Ratcliffe, C. I.; Simard, B.; Santyr, G.; Ripmeester, J. A. J. Magn. Res. 2000, 144, 372. ii Driehuys, B.; Cates, G. D.; Miron, E.; Sauer, K.; Walter, D. K.; Happer, W. Appl. Phys. Lett. 1996, 69,