How linker s modification controls swelling properties of. highly flexible iron(iii) dicarboxylates MIL-88

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1 SUPPORTING INFORMATION How linker s modification controls swelling properties of highly flexible iron(iii) dicarboxylates MIL-88 Patricia Horcajada, 1* Fabrice Salles, 2 Stefan Wuttke, 1,3 Thomas Devic, 1 Daniela Heurtaux, 1 Guillaume Maurin, 2 Alexandre Vimont, 3 Marco Daturi, 3 Olivier David, 1 Emmanuel Magnier, 1 Norbert Stock, 4 Yaroslav Filinchuk, 5,6 Dmitry Popov, 7 Christian Riekel, 8 Gérard Férey, 1 Christian Serre 1* 1 Institut Lavoisier, (UMR CNRS 8180), Université de Versailles, 45, Avenue des Etats-Unis, 78035, Versailles Cedex (France). 2 Institut C. Gerhardt Montpellier, UMR CNRS 5253, UM2, ENSCM, Place E. Bataillon, Montpellier cedex 05 (France). 3 Laboratoire Catalyse et Spectrochemie LCS, UMR CNRS 6506, ENSICAEN, 6 Boulevard du Maréchal Juin, Caen Cédex 4, France 4 Institute of Inorganic Chemistry, Christian-Albrechts-Universität, Otto-Hahn-Platz 6/7, Kiel, Germany 5 SNBL at ESRF, rue Jules Horowitz, Grenoble (France). 6 HPCAT, Geophysical Laboratory, Carnegie Institution of Washington, 9700 South Cass Ave., Bldg. 434E, Argonne, IL 60439, USA 7 ESRF, 6 rue Jules Horowitz, B.P.2, Grenoble (France). for correspondence: horcajada@chimie.uvsq.fr; serre@chimie.uvsq.fr S1

2 EXPERIMENTAL SECTION X Ray Powder Diffraction: XRPD patterns have been collected in a Siemens D5000 diffractometer (radiation CuKα λ Cu =1,5406 Å, mode θ-2θ) at room temperature. X ray diffraction powder data for the hydrated and suspended modified MIL-88 solids were collected at the Swiss-Norwegian Beamline BM01A at the ESRF (Grenoble, France), using a MAR345 image plate detector and a sample to detector distance of mm. The data were integrated using the Fit2D program and a calibration measurement of a NIST LaB 6 standard sample. The unit-cells were determined by X ray powder pattern indexing followed by a structureless pattern profile refinement using respectively the DICVOL 1 and FULLPROF 2,3 softwares from the WINPLOTR suite. Specific surface area measurement: Experiments were performed at 77 K on a Micromeretics ASAP- apparatus using nitrogen as the probing gas. The activated modified MIL-88(Fe) samples (50-0 mg) were outgassed at 0-0 C under vacuum for one night prior to measurement. Thermogravimetric Analyses: TGA were performed on a TA-instrument 50 under O 2 atmosphere (0 ml min -1 ), between room temperature and 600 C in an aluminum crucible (heating speed 1-2 C/min) using 5- mg of hydrated products. X Ray Thermodiffractometry: were performed under air in a furnace of a Siemens D5000 diffractometer working at the CoKα radiation in the (θ-θ) mode in the -400 C temperature range with a C step. Single Crystal X Ray Diffraction: Only suitable single crystal of the as-prepared MIL- 88B(4CH 3 ) and MIL-88B(2OH) solids could be obtained, allowing the single crystal data collection at ID13 beamline at ESRF using a microdiffraction setup. The beam from an undulator is monochromated and focused on the sample by a pair of mirrors, which enables us to reach a flux density at the sample of up to 3 photons s 1 µm 2 at about 0.97 Å wavelength. A set of micro-apertures is used for background reduction. In order to reach the necessary rotational accuracy, a microgoniometer combining a low-wobble air-bearing spindle and a piezomicromanipulator carrying a magnetic-base sample support was used. The optical alignment precision was about 1 µm using an integrated optical microscope with a low-vibration sample stage. The crystal was rotated around a direction close to the six-fold axis coinciding with the crystal elongation. The data reduction was performed with the Crysalis software; owing to the small crystal size, no absorption correction was required. The structure was solved and refined by full-matrix least-squares techniques, based on F 2, using the SHELX-TL software package. All non hydrogen atoms were refined anisotropically expect the µ 3 -O atom in MIL-88B(4CH 3 ). In MIL-88B(2OH), the OH groups were found disordered on the phenyl ring. Hydrogen atoms were introduced geometrically and not refined on the OH groups (MIL-88B(2OH)) and CH 3 groups (MIL-88B(4CH 3 )); but no hydrogen atoms were introduced on the µ-oh and µ-oh 2 moieties. Crystallographic data are summarized in Table S1. S2

3 Table S1: crystallographic parameters of MIL-88B(2OH) and MIL-88B(4CH 3 ) Compound MIL-88B(2OH) MIL-88B(4CH 3 ) Empirical formula C 48 H 38 Fe 6 O 44 C 72 H 82 Fe 6 O 32 Formula weight (g.mol -1 ) Temperature (K) 0 0 Wavelength (Å) Crystal system hexagonal hexagonal Space group P6 3 /mmc P6 3 /mmc Unit cell dimension (Å) a = (2) c = (4) a = (2) c = (3) Volume (Å 3 ) 62.8(6) (9) F(000) Crystal size (mm) 0.02x0.01x x0.01x0.01 Theta range for data collection( ) Limiting indices -11 < h < < k < 11 - < l < S3-13 < h < < k < < l < 16 Reflections collected R int Refinement method Full-matrix least square on F 2 Data/restraints/parameters 497/0/51 750/4/49 Goodness-of-fit on F Final R indices [I>2σ(I)] R 1 = ; wr 2 = R 1 = ; wr 2 = R indices (all data) R 1 = ; wr 2 = R 1 = ; wr 2 = Largest diff. peak and hole and e -.Å and 1.5 e -.Å -3 FTIR Spectroscopy: The samples were deposited on a silicon wafer after dilution in ethanol. This was done in order to observe all structure bands clear and sharp in the IR spectrum. The mixture is dried in air and placed in an IR quartz cell equipped with KBr windows. A movable quartz sample holder permits adjustment of the sample in the infrared beam for acquisition of spectra and to displace it into a furnace at the top of the cell for thermal treatments. The cell is connected to a vacuum line for evacuation and calcinations. The compounds are activated in vacuum from RT to 300 C, with a plateau of 30 minutes at each temperature chosen (one spectrum every 50 C). IR spectra were recorded on a Nicolet Magna 550 spectrometer equipped with a liquid nitrogen cooled MCT detector in transmission mode and purged by a dry nitrogen flow. The resolution was 4 cm -1 and 128 scans were co-added for each spectrum, in a transmission range of cm -1. IR spectra of MIL-88B and MIL-88D samples are shown under high vacuum at various temperatures. In black: spectra for which no degradation is detected. In red: spectra for which degradation is detected through the decrease of the intensity and the modification of structure bands (indicated by an asterisk). Computational section: Our computational effort consisted of determining the structures of each modified MIL-88 form existing in the closed (dry state) and the open forms. We consider for the open forms the structures fully open when immerged in solvents. It thus leads us to consider the experimental unit cell parameters collected when using alcohols (ethanol or methanol) or pyridine as solvent to further build the open structures of each modified MIL-88.

4 To perform simulations consistent with experimental data (in which to compensate the cationic framework, counter anions are bonded directly onto the metal centres (X=F, OH)), we saturate only one Fe (over three) with F atoms for the closed structures, while all the Fe centers are saturated with one Fe and two OH groups (coming from the solvent). Keep in mind that the solvent molecules are not simulated in the structures and that the host-guest interactions are not reproduced: only the imposed cell parameters influence the form of the structures. The initial atomic coordinates of the non modified MIL-88 framework for the different forms (A, B, C, D) in both dry state and in the presence of solvent were first taken from the refined structure obtained by X ray diffraction. The starting configurations for each modified MIL-88B and D structures were then built by (i) substituting the phenyl rings by the corresponding terephtalate linkers (ii) imposing the corresponding unit cell parameters obtained from the XRPD refinement on both the dry state and in the presence of ethanol. Further, for each modified MIL-88, several initial models were generated corresponding to different positions of the modified terephtalate linkers over the various phenyl rings available per unit cell. All these models were then energy minimized in the space group P1 by keeping the cell parameters fixed, using the universal force field (UFF) and charges calculated from the Electronegativity Equalization method as implemented in the Materials Studio software. Such strategy based on the same UFF force field has been successfully employed to construct plausible structure of various MILs including the MIL-53(Fe) series and more recently the chromium 2,6-naphtalendicarboxylate MIL-1 system. The Ewald summation was considered for calculating the electrostatic interactions while the short range interactions were evaluated using a cut-off distance of 12 Å. The convergence criteria were set to kcal mol -1 (energy), kcal mol -1 Å -1 (forces), and Å (displacement) respectively. As a preliminary step, we carefully checked that this strategy allowed reproducing accurately the structure of the non modified MIL-88A, B, C, D solids in the dry state. All of the geometry optimizations converged to provide a plausible crystallographic structure for each modified MIL-88 form experimentally detected in the dry state and in the presence of solvent. We further validated all these simulated structures by a good agreement between the corresponding calculated XRPD patterns and those experimentally obtained. SYNTHESIS PROCEDURES MIL-88B(Fe) or Fe 3 O[C 6 H 4 (CO 2 ) 2 ] 3 X nh 2 O (X=F, Cl, OH) Synthesis :270 mg (1 mmol) of FeCl 3.6H 2 O (Alfa Aesar, 98%) and 116 mg (1 mmol) of 1,4- benzenedicarboxylic acid (Aldrich, 98%) were dispersed in 5 ml of dimethylformamide (DMF, Fluka, 98%) with 0,4 ml of NaOH 2M (Alfa Aesar, 98%). The mixture was placed in a Teflon-lined autoclave (23 ml) for 12 hours at 0 C. Then, the orange solid was recovered by filtration and washed with deionised water and acetone. Activation : 0 mg of MIL-88B-as were suspended in 0 ml of deionised water under stirring for 12 hours, recovering the solid by filtration. Thus, the residual solvent into the pores was removed, obtaining the RT form MIL-88B-RT. S4

5 Characterisation d - Scale 5 Figure S1: XRD patterns of as-synthesised (black) and activated RT (red) forms of MIL-88B Lost weight (%) % H2O MIL88B 56.7% BDC Figure S2: TGA of activated MIL-88B Temperature ( C) The MIL-88B shows no accessible porosity for nitrogen at 77 K due to the large contraction of the pores after dehydration (S BET = 8 m 2 /g). Figure S3: IR spectra of MIL-88B evacuated under vacuum at various temperatures. In black: spectra for which no degradation is detected. In red: spectra for which degradation is detected (indicated by an asterisk). S5

6 Table S2 : Elemental analysis of activated MIL-88B MIL-88B % Fe % C Experimental Theoretical Fe 3 O(OH)[C 6 H 3 Cl(CO 2 ) 2 ] 3 6.5H 2 O MIL-88D(Cr) or Cr 3 O[C 12 H 8 (CO 2 ) 2 ] 3 X nh 2 O (X=F, OH) Synthesis: MIL-88D(Cr) was obtained as previously described, 4 starting from a solution with the following composition in molar ratio CrNO 3: 4,4 -biphenyldicarboxylic acid :HF: Pyridine : H 2 O 1 : 1.25 : 1 : 38 :116. The mixture was placed in a Teflon-lined autoclave (23 ml) for 16 hours at 2 C with a heating ramp of 1 hour and a cooling ramp of 1 hour. Then, the green solid was recovered by filtration and washed with deionised water and acetone. Activation: 0 mg of MIL-88D(Cr)as were suspended 3 h in 15 ml of DMF (under stirring at RT) and washed after three times with 30 ml of methanol in order to remove DMF. Then, the solid were recovered by filtration and dried at 0 C. MIL-88B(Cl) (Fe) or Fe 3 O[C 6 H 3 Cl(CO 2 ) 2 ] 3.X nh 2 O (X=F, Cl, OH) Chloroterephtalic acid synthesis: 6 g (0,043 mol) of 2-chloro-p-xylene (Aldrich, > 99%), 16 ml of nitric acid (VWR, 70%) and 60 ml of deionised water were placed in a Teflonlined autoclave (1 ml) at 170 C for 12 h. Then, the brown solid was recovered by filtration and washed with deionised water (yield 75%). NMR 1 H (300 MHz, d6-dmso) : δ (ppm) : 7,86 (d, J = 7,8 Hz), 7,93 (dd, J = 7,8; 1,2 Hz), 7,96 (d, J = 1,2 Hz) Synthesis: 270 mg (1 mmol) of FeCl 3.6H 2 O (Aldrich, 99%) and 0 mg (1 mmol) of 2- chloroterephthalic acid were dispersed in 5 ml of DMF (Fluka, 98%). The mixture was placed in a Teflon-lined autoclave (23 ml) for 3 days at 0 C. Then, the brown solid was recovered by filtration and washed with deionised water and acetone. Activation: 0 mg of MIL-88B(Cl)as were suspended in ml of absolute EtOH under stirring at room temperature for 3 h. This activation was repeated three times and then, dried at 0 C. S6

7 d - Scale Figure S4 : XRD patterns of the as-synthesis (black) and activated RT forms (red) of MIL- 88B(Cl) 1 lost weight (%) % H2O 63.98% Cl BDC Temperature ( C) Figure S5: TGA of activated MIL-88B(Cl) The MIL-88B(Cl) shows almost no accessible porosity for nitrogen at 77 K (S BET = 19 m 2 /g) due to the large contraction of the pores after dehydration S7

8 Figure S6: IR spectra of MIL-88B(Cl) evacuated under vacuum at various temperatures. In black: spectra for which no degradation is detected. In red: spectra for which degradation is detected (indicated by an asterisk). Table S3: Elemental analysis of activated MIL-88B(Cl) MIL-88B(Cl) % Fe % C % Cl Experimental Theoretical Fe 3 OCl[C 6 H 3 Cl(CO 2 ) 2 ] 3 4.1H 2 O MIL-88B(Br) (Fe) or Fe 3 O[C 6 H 3 Br(CO 2 ) 2 ] 3 X nh 2 O (X=F, Cl, OH) Synthesis: 1350 mg (5 mmol) of FeCl 3.6H 2 O (Alfa Aesar, 98%) and 1.25 g (5 mmol) 2- bromoterephthalic acid (Fluka, 95%) were dispersed in 50 ml of DMF (Fluka, 98%).The mixture was placed in a Teflon-lined autoclave (125 ml) at 0 C for 12 h. Then, the solid was recovered by filtration and washed with deionised water. Activation: The obtained solid was suspended in 50 ml of DMF under stirring at room temperature for 2 h and then dried 150 C under vacuum for 15 h. Characterisation d - Scale 5 Figure S7: XRD patterns of the as-synthesis (black) and activated RT forms (red) of MIL- 88B(Br). S8

9 The MIL-88B(Br)shows no accessible porosity for nitrogen at 77 K (S BET < 1 m 2 /g) due to the large contraction of the pores after dehydration 0 4.9% H2O Loss weight % % Br-BDC Temperature ( C) Figure S8: TGA of activated MIL-88B(Br) Figure S9: IR spectra of MIL-88B(Br) evacuated under vacuum at various temperatures. In black: spectra for which no degradation is detected. In red: spectra for which degradation is detected (indicated by an asterisk). Table S4 : Elemental analysis of activated MIL-88B(Br) MIL-88B(Br) % Fe % C % Br % Cl Experimental Theoretical Fe 3 OCl 0.84 (OH) 0.16 [C 6 H 3 Br(CO 2 ) 2 ] 3 3.8H 2 O MIL-88B(NH 2 ) (Fe) or Fe 3 O[C 6 H 3 NH 2 (CO 2 ) 2 ] 3 X nh 2 O (X=F, Cl, OH) Synthesis: 270 mg (1 mmol) of FeCl 3.6H 2 O (Alfa Aesar, 98%) and 180 mg (1 mmol) of 2- aminoterephthalic acid (Fluka, 98%) were dispersed in 5 ml of absolute ethanol. The mixture was placed in a Teflon-lined autoclave (23 ml) for 3 days at 0 C. Then, the brown solid was recovered by centrifugation (000 rpm/15 min) and washed with deionised water and acetone. S9

10 Activation: 0 mg of MIL-88B(NH 2 )as were suspended 1 h in 15 ml of DMF (under stirring at RT) and washed after three times with 30 ml of methanol in order to remove DMF. Then, the solid were recovered by centrifugation (000 rpm/15 min) and dried at 0 C. Characterisation d - Scale Figure S: XRD patterns of as synthesised (black) and activated RT form (red) of MIL- 88B(NH 2 ) % H2O lost weight (%) % NH2 BDC Temperature ( C) Figure S11: TGA of activated MIL-88B(NH 2 ) Figure S12: IR spectra of MIL-88B(NH 2 )evacuated under vacuum at various temperatures. In black: spectra for which no degradation is detected. In red: spectra for which degradation is detected (indicated by an asterisk). The MIL-88B(NH 2 ) shows no accessible porosity for nitrogen at 77 K (S BET =14 m 2 /g) due to the large contraction of the pores after dehydration S

11 Table S5: Elemental analysis of activated MIL-88B(NH 2 ) MIL-88B(NH 2 ) % Fe % C % N %Cl Experimental Theoretical Fe 3 OCl[C 6 H 3 NH 2 (CO 2 ) 2 ] H 2 O MIL-88B(NO 2 ) (Fe) or Fe 3 O[C 6 H 3 NO 2 (CO 2 ) 2 ] 3 X nh 2 O (X=F, Cl, OH) Synthesis: 270 mg (1 mmol) of FeCl 3.6H 2 O (Alfa Aesar, 98%) and 211 mg (1 mmol) of 2- nitroterephthalic acid (Acros, 99%) were dispersed in 5 ml of deionised water. The mixture wass placed in a Teflon-lined autoclave (23 ml) for 12 hours at 0 C. Then, the orange solid was recovered by filtration and washed with deionised water and acetone. Activation: 0 mg of MIL-88B(NO 2 )as were suspended in ml of absolute ethanol in a Teflon-lined (23 ml) at 0 C for 12 hours for removing the free acid from the pores. Then, the solid were recovered by filtration and dried at 0 C. Characterisation d - Scale 9 8 Figure S13: XRD patterns of as-synthesised (green) and activated RT (red) forms of MIL- 88B(NO 2 ) 0 7.3% H2O lost weight (%) % NO2 BDC Temperature ( C) Figure S14: TGA of activated MIL-88B(NO 2 ) S11

12 Figure S15: IR spectra of MIL-88B(NO 2 )evacuated under vacuum at various temperatures. In black: spectra for which no degradation is detected. In red: spectra for which degradation is detected (indicated by an asterisk). The MIL-88B(NO 2 ) shows almost no accessible porosity for nitrogen at 77 K (S BET = 15 m 2 /g) due to the large contraction of the pores after dehydration Table S6: Elemental analysis of activated MIL-88B(NO 2 ) MIL-88B(NO 2 ) % Fe % C % N % Cl Experimental <0.01 Theoretical Fe 3 O(OH)[C 6 H 3 NO 2 (CO 2 ) 2 ] H 2 O MIL-88B(2OH) (Fe) or Fe 3 O[C 6 H 2 (OH) 2 (CO 2 ) 2 ] 3 X nh 2 O (X=F, Cl, OH) Synthesis: 354 mg (1 mmol) of Fe(ClO 4 ) 3.xH 2 O (Aldrich, 99%) and 198 mg (1 mmol) of 2,5- dihydroxoteryphthalic acid (obtained from the hydrolysis of the corresponding diethylester, Aldrich 97%) were dispersed in 5 ml of DMF (Fluka, 98%). The mixture was placed in a Teflon-lined autoclave (23 ml) for 12 hours at 85 C. Then, the deep red solid was recovered by filtration and washed with deionised water and acetone. Activation: 0 mg of MIL-88B(2OH)as were suspended in ml of absolute ethanol for 3 hours for removing the free acid from the pores. Then, the solid were recovered by filtration and dried at 80 C. Characterisation S12

13 MIL88B-2OH (H2O) MIL88B-2OH as d - Scale 8 Figure S16: XRD patterns of MIL-88B(2OH)as synthesised (black) and activated RT forms (red) lost weight (%) % H2O 67.22% 2OH-BDC Temperature ( C) Figure S17: TGA of activated MIL-88B(2OH) Figure S18: IR spectra of MIL-88B(2OH)evacuated under vacuum at various temperatures. In black: spectra for which no degradation is detected. In red: spectra for which degradation is detected (indicated by an asterisk). The MIL-88B(2OH)shows no accessible porosity for nitrogen at 77 K (S BET = 3 m 2 /g) due to the large contraction of the pores after dehydration S13

14 Table S7: Elemental analysis of activated MIL-88B(2OH) MIL-88B(2OH) % Fe % C % Cl Experimental 15,4* 36,5* <0.01 Theoretical *presence of iron oxyde Fe 3 O(OH)[C 6 H 2 (OH) 2 (CO 2 ) 2 ] 3 4.9H 2 O MIL-88B(CH 3 ) (Fe) or Fe 3 O[C 6 H 3 CH 3 (CO 2 ) 2 ] 3 X nh 2 O (X=F, Cl, OH) Synthesis: 354 mg (1 mmol) of Fe(ClO 4 ) 3.xH 2 O (Aldrich, 99%) and 180 mg (1 mmol) of 2- methylterephthalic acid (synthesised as previously reported by Anzalone et al.) 5 were dispersed in 5 ml of methanol (Fluka, 99%). The mixture was placed in a Teflon-lined autoclave (23 ml) for 3 days at 0 C. Then, the brown solid was recovered by filtration and washed with deionised water and acetone. Activation: 0 mg of MIL-88B(CH 3 )as were suspended in 25 ml of absolute EtOH under stirring at room temperature for 12 h. The washing process was repeated 2 times and then, the solid was dried at 0 Cduring one night. Characterisation d - Scale 5 Figure S19: XRD patterns of MIL-88B(CH 3 ) as-synthesised (black) and activated RT form (red) S14

15 Figure S: IR spectra of MIL-88B(CH 3 ) evacuated under vacuum at various temperatures. In black: spectra for which no degradation is detected. In red: spectra for which degradation is detected (indicated by an asterisk) as-synthesized EtOH washed (dry at 150 C) DMF washed (dry at 0 C) Volume (cm 3 /g) ads des Wavenumber (cm -1 ) ,2 0,4 0,6 0,8 1 P/P 0 EtOH washed (dry at 150 C) DMF washed (dry at 0 C) Theta Figure S21: On the top left: IR spectroscopy of the as-synthesised and the activated MIL- 88B(CH 3 ) (washed with DMF, then with EtOH and dried at 150 C), as well as the DMF washed and dried at 0 C MIL-88B(CH 3 ). On the top right: Nitrogen adsorption isotherm of as-synthesised MIL-88B(CH 3 ) (outgassed under vacuum at 0 C) at 77 K (P 0 = 1 atm). On the bottom: XRPD of the activated MIL-88B(CH 3 ) washed with DMF, then with EtOH and dried at 150 C (in blue) and that DMF washed and dried at 0 C (in green). S15

16 Even if different ways seem to be adapted for easily taking off the free acid, this step is quite delicate. When the as-synthesized powder is washed with DMF and outgassed under vacuum at 0 C, the acid is removed but the pores are still partially open because of a part of DMF remaining inside (see IR spectrum; Figure S21). Like this, the specific BET surface stays significant (347 m 2 /g). On the other hand, washing the solid with ethanol followed by outgassing under vacuum at 150 C leads to more contracted empty pores (S BET = 83 m 2 /g) Weightloss(%) % H 15.7% 2 O 59.6% CH 3 -BDC Figure S22: TGA of activated MIL-88B(CH 3 ) Temperature( C) Table S8: Elemental analysis of activated MIL-88B(CH 3 ) MIL-88B(CH 3 ) % Fe % C % H % Cl Experimental Theoretical Fe 3 OCl[(O 2 C) 2 -C 6 H 2 -CH 3 ] 3.37H 2 O MIL-88B(2CH 3 ) (Fe) or Fe 3 O[C 6 H 2 (CH 3 ) 2 (CO 2 ) 2 ] 3 X nh 2 O (X=F, Cl, OH) 2,5-dimethylterephthalic acid was prepared according to the published procedure. 6 Synthesis: 354 mg (1 mmol) of Fe(ClO 4 ) 3.xH 2 O (Aldrich, 99%) and 194 mg (1 mmol) of 2,5- dimethylterephthalic acid (synthesised as previously reported by Anzalone et al.) 5 were dispersed in 5 ml of methanol (Fluka, 99%). The mixture was placed in a Teflon-lined autoclave (23 ml) for 3 days at 0 C. Then, the brown solid was recovered by centrifugation (000 rpm/15 min). Activation: 0 mg of MIL-88B(2CH 3 )as were suspended two times in ml of DMF under stirring at room temperature for 1 h, then recover by centrifugation. The solid was washed 3 times with absolute EtOH at RT and then, the solid was dried at 0 C. S16

17 Characterisation d - Scale 5 Figure S23: XRD patterns of as-synthesised (black) and activated RT forms (red) of MIL- 88B(2CH 3 ) lost weight (%) % H2O 65.8% 2CH3-BDC Temperature ( C) Figure S24: TGA of activated MIL-88B(2CH 3 ) Figure S25: IR spectra of MIL-88B(2CH 3 ) evacuated under vacuum at various temperatures. In black: spectra for which no degradation is detected. In red: spectra for which degradation is detected (indicated by an asterisk). S17

18 The MIL-88B(2CH 3 ) shows a Langmuir and BET surface area of 96 and 64 m 2 /g after outgassing at 250 C under vacuum. 1 0 ads des Volume (cm 3 /g) ,2 0,4 0,6 0,8 1 P/P 0 Figure S26: Nitrogen adsorption isotherm of activated MIL-88B(2CH 3 ) at 77 K (P 0 = 1 atm) Table S9: Elemental analysis of activated MIL-88B(2CH 3 ) MIL-88B(2CH 3 ) % Fe % C % H % Cl Experimental Theoretical Fe 3 OCl[(O 2 C) 2 C 6 H 2 (CH 3 ) 2 ] C H O H 2 O MIL-88B(4CH 3 ) (Fe) or Fe 3 O[C 6 (CH 3 ) 4 (CO 2 ) 2 ] 3 X nh 2 O (X=F, Cl, OH) Synthesis of the 2,3,5,6-tetramethylterephtalic acid: 1,4-dibromo-2,3,5,6-tetramethylbenzene Tetramethylbenzene (.4 g, mmol) was dissolved in 75 ml of chloroform and 0 mg of aluminum was added as small pieces. Then after strict protection of the flask from the daylight, the mixture was cool to 0 C and bromine (15.6 ml, 304 mmol, 2 equiv.) was added dropwise over a two hours period. The stirring was maintained for two hours and ml of water was then added. The volatiles were removed by evaporation under vacuum. The residue was redissolved in ~300 ml of boiling toluene and the solution was filtered while hot and then allowed to cool to room temperature. The compound crystallized as off-white needles, the filtration gave 33.5 g of pure title compound. Cooling the mother liquor to freezer temperature allowed obtaining a second crop of 6 g. Global yield: 89% 1,4-dicyano-2,3,5,6-tetramethylbenzene: Dibromo derivative (30.3 g, 3 mmol) was dissolved in 0 ml of NMP (N-methyl-2-pyrrolidone), the solution was degassed with argon before adding 37,2 g of copper cyanide (415 mmol, 4 equiv.) Caution, the quality of the copper salt is of critical importance! The suspension was then heated to 2 C with an oil bath to determine the reflux of the solvent. After 48h under reflux, the black mixture was allowed to cool to RT and was then poured in a 2 L separatory funnel containing 500 ml of concentrated ammonia and 500g of crushed ice. The dark brown suspension was extracted S18

19 three times with 500 ml portions of diethylether. The collected organic phases were washed with water and brine and the solvent evaporated. The residue was filtrated over silica gel eluting with pure DCM (dichloromethane; R f = 0.5). Evaporation of the solvent gave 17.7 g of a light-brown solid with a yield of 92% Proton NMR (CDCl3, 300MHz, ppm) δ: 2.5 (s, 12H) Carbon NMR (CDCl3, 75MHz, ppm) δ: 138.5, 118.0, 116.9, ,3,5,6-tetramethylbenzene-1,2-dicarboxamide:We employed the procedure described by J. N. Moorthy and N. Singhal. 7 2,3,5,6-tetramethylterephtalic acid: Crude diamide 1 g (5.69 mmol) was suspended in a mixture of ml of sulphuric acid and 5 ml of water and heated to 90 C. Small portions of solid sodium nitrite were added over a period of four hours. After stirring for one more hour, the mixture was poured into ice-cold water and then extracted five times with ethylacetate. The organic phases were dried over magnesium sulphate and filtrated. After evaporation of the solvent the brown residue was redissolved in 2 M sodium hydroxide solution (~ ml) and active charcoal was added (~5 g). The suspension was stirred vigorously for two hours and filtrated; the charcoal was rinsed with water. Aqueous phases were acidified with concentrated hydrochloric acid and the white precipitate was collected by filtration. After five washings with cold water the solid was dried under high vacuum to give 7 mg of pure diacid, 60% yield. Scheme S1: Synthesis of 2,3,5,6-tetramethylterephtalic acid Synthesis: 270 mg (1 mmol) of FeCl 3.6H 2 O (Alfa Aesar, 98%) and 222 mg (1 mmol) of 1,4- tetramethylterephthalic acid (Chem Service, 95%) were dispersed in 5 ml of DMF (Fluka, 98%). The mixture was placed in a Teflon-lined autoclave (23 ml) at 0 C for 16 h. Then, the solid was recovered by filtration and washed with distilled water. Activation: The obtained solid was suspended in ml of distilled water under stirring at room temperature for 12 h. The solid was recovered by filtration. S19

20 Characterisation d - Scale 5 Figure S27: XRD patterns of the as-synthesis (black) and activated RT forms (red) of MIL- 88B(4CH 3 ). 0 lost weight (%) % H2O 52.2% 4CH3 BDC Temperature ( C) Figure S28: TGA of activated MIL-88B(4CH 3 ) Figure S29: IR spectra of MIL-88B(4CH 3 ) evacuated under vacuum at various temperatures. In black: spectra for which no degradation is detected. In red: spectra for which degradation is detected (indicated by an asterisk). S

21 The activated solid (outgassed at 130 C under vacuum for the nitrogen sorption measurement) shows a Langmuir and BET surface area of 17 and 1216 m 2 /g, respectively, since the porosity in the dry form (6-7 Å) is blocked by the steric hindrance of the four methyls, allowing the N 2 access. Volume (cm 3 /g) adsorption desorption 0,0 0,2 0,4 0,6 0,8 1,0 P/P 0 Figure S30: Nitrogen adsorption/desorption isotherms of activated MIL88B(4CH 3 ) at 77 K (P 0 =1atm) outgassed at 130 C under vacuum during a night Table S: Elemental analysis of activated MIL-88B(4CH 3 ) MIL-88B(4CH 3 ) % Fe % C % Cl Experimental <0.01 Theoretical Fe 3 O(OH)[C 6 (CH 3 ) 4 (CO 2 ) 2 ] 3.7.8H 2 O MIL-88B(2CF 3 ) (Fe) or Fe 3 O[C 6 H 2 (CF 3 ) 2 (CO 2 ) 2 ] 3 X nh 2 O (X=F, Cl, OH) Synthesis of 2,5-bis(trifluoromethyl)terephthalic acid: H 2 BDC-(CF 3 ) 2 was synthesised according to the reported procedure 8 19 g (88.7 mmol) of 1,4-bis(trifluoromethyl)benzene, 250 ml of trifluoroacetic acid and 60 ml of 95% sulfuric acid were stirred under reflux for min g (267 mmol) of N-bromosuccinimide were slowly added during 5 h and maintained at 60 C under stirring for 48 h. The 2,5-dibromo-1,4-bis(trifluoromethyl)benzene was precipitated by cooling of this solution in an ice bath, filtering and drying the solid under vacuum (1 mm Hg) for 24 h. The product was purified by sublimation to obtain 91% of a white solid. NMR (CDCl 3 ) 1 H: 8.01 (2H, s); 19 F: (CF 3, s). A solution of 38,4 ml of BuLi at -78 C (2.5 M in hexane, 96 mmol) in 75 ml of THF (75 ml) was added dropwise to a previously formed solution of 16 g (43 mmol) of 2,5-dibromo-1,4- bis(trifluoromethyl)benzene in 0 ml of THF. After 30 min of stirring at -78 C, 0 mg of carbonic ice was introduced in the reaction. After the mixture warmed up to room temperature, the dilithium salt was extracted with a 2 M aqueous solution of sodium hydroxide (3 times 0 ml). This solution was further acidified (2 M HCl) up to ph = 1. The resulting white precipitate was recovered by filtration, dried under vacuum (1 mmhg) for 24 h. Yield = 11 g (84%). NMR (d 6 -acetone) 1 H: 8.31 (2H, s aromatic); 19 F: (CF 3, s). S21

22 Synthesis: 675 mg (2.5 mmol) of FeCl 3.6H 2 O (Alfa Aesar, 98%) and 755 mg (2.5 mmol) 2,5- perfluoroterephthalic acid (synthesised as described above) were dispersed in 25 ml of absolute ethanol (Aldrich, 99%). The mixture was placed in a Teflon-lined autoclave. The synthesis was performed by microwave route with a heating ramp of 30 s at 0 C for 5 min (400 W). Activation: The obtained solid was suspended in 25 ml of acetone under stirring at room temperature for 4 h and then dried at 0 C. Characterisation d - Scale Figure S31: XRD patterns of the as-synthesis (black) and activated RT forms (red) of MIL- 88B(2CF 3 ) % H 2 O Lost weight (%) % BDC-2CF 3 Figure S32: TGA of activated MIL-88B(2CF 3 ) Temperature ( C) S22

23 Figure S34: IR spectra of MIL-88B(2CF 3 ) evacuated under vacuum at various temperatures. In black: spectra for which no degradation is detected. In red: spectra for which degradation is detected (indicated by an asterisk). The MIL-88B(2CF 3 ) shows a Langmuir and BET surface area of 476 and 335 m 2 /g, respectively Volume (cm 3 /g) ads des 0 0,2 0,4 0,6 0,8 1 P/P 0 Figure S33: Nitrogen adsorption isotherm of activated MIL-88B(2CF 3 ) at 77 K (P 0 = 1 atm) (outgassed at 150 C under vacuum during 5 h (note: if the outgassing time increases, the specific surface of this compound decrease) Table S11: Elemental analysis of activated MIL-88B(2CF 3 ) MIL-88B(2CF 3 ) % Fe % C % F % Cl Experimental Theoretical Fe 3 OCl[(O 2 C) 2 -C 6 H 2 -(CF 3 ) 2 ] H 2 O S23

24 MIL-88B(4F) (Fe) or Fe 3 O[C 6 F 4 (CO 2 ) 2 ] 3 X nh 2 O (X=F, Cl, OH) Synthesis: 270 mg (1 mmol) of FeCl 3.6H 2 O (Alfa Aesar, 98%) and 230 mg (1 mmol) of tetrafluoroterephthalic acid (Aldrich, 98%) were dispersed in ml of distilled water. The mixture was placed in a Teflon-lined autoclave (23 ml) at 85 C for 12 h. Then, the solid was recovered by filtration and washed with deionised water. Activation: The obtained solid was suspended in ml of distilled water under stirring at room temperature for 2 h. The procedure was repeated 3 times. The solid was recovered by filtration. Characterisation d - Scale 5 Figure S34: XRD patterns of the as-synthesised (black) and activated RT form (red) of MIL- 88B(4F). 0.4% H2O lost weight (%) % 4F BDC Figure S35: TGA of activated MIL-88B(4F) Temperature ( C) S24

25 Figure S36: IR spectra of MIL-88B(4F) evacuated under vacuum at various temperatures. In black: spectra for which no degradation is detected. In red: spectra for which degradation is detected (indicated by an asterisk). The MIL-88B(4F) activated shows a Langmuir and BET surface area of 50 and 32 m 2 /g. Volume (cm 3 /g) adsorption desorption 5 0 0,0 0,2 0,4 0,6 0,8 1,0 P/P 0 Figure S37: Nitrogen adsorption isotherm of activated MIL-88B(4F) outgassed at 150 C under vacuum at 77 K (P 0 = 1 atm) Table S12: Elemental analysis of activated MIL-88B(4F) MIL-88B(4F) % Fe % C % F % Cl Experimental <0.01 Theoretical Fe 3 O(OH)[C 6 F 4 (CO 2 ) 2 ] 3 3.2H 2 O S25

26 MIL-88D(4CH 3 ) (Fe) or Fe 3 O[C 12 H 4 (CH 3 ) 4 (CO 2 ) 2 ] 3 X nh 2 O (X=F, Cl, OH) Synthesis of 3,3,5,5 -tetramethylbiphenyl-4,4 -dicarboxylic acid: Tetramethylbenzidine (CAUTION! this compound is closely related to carcinogenic benzidine, thus one is to take all required protective measures to avoid any contact).2 g (42.4 mmol) were suspended in 39 ml of concentrated hydrochloric acid (~12 equiv., 12 mol.l -1 ) and the slurry was then cool to 0 C with an ice bath. Diazotation was effected by addition of sodium nitrite (6 g, 2.05 equiv., M = 69) in solution in 50 ml of cold water. After 15 min. of stirring at 0 C, the resulting violet slurry was added slowly to a solution of potassium iodide 70 g (424 mmol, equiv.) in 0 ml of water. The mixture turned to dark brown and foamy. After completion of the addition of the bis diazonium salt, the mixture was further stirred for 2 hours at RT. The black suspension was filtrated to collect a black precipitate, after washing with water, the solid was suspended in dichloromethane and a saturated solution of sodium thiosulfate was added, causing the decoloration of the whole. After 1 hour of stirring the organic phase was decanted and the aqueous phase was extracted with DCM. Drying with sodium sulfate, filtration and evaporation gave the crude iodide as an off-white solid. This last was deposited on top of a short silica column and elution with pure pentane eluted the bis-iodobiphenyl along with mono iodobiphenyl. The mixture of these was directly used in the lithiation procedure (71% of crude iodide). The crude iodide 7.2 g was dissolved in 0 ml of THF, after cooling at -78 C, 35 ml of n- butyllithium 2.5 M in cyclohexane was added (~4.5 equiv.) The cooling bath was removed to allow the solution to warm up to RT. After 2 hours, a white suspension was obtained, this was cool back to -78 C and 12 ml (13.5 g, 8 equiv.) of ethylchloroformate was added in one portion. The solution was then allowed to warm up to RT, after 1 hour a pale yellow limpid solution was obtained. Partition between water and dichloromethane followed by extraction with dichloromethane, gave the crude diester. The pure compound was obtained after chromatography on silica gel, eluting with Et 2 O/Pentane : 1/9 mixture, (R f = 0.3) to give 6.3 g of a white colorless solid (42 % from the starting benzidine). Diester: 1 H NMR (300 MHz, CDCl 3 ): 1.29 (t, J = 7.2 Hz, 6H), 2.29 (s, 3H); 4.31 (q, J = 7.2 Hz, 4H); 7.12 (s, 4H). 13 C NMR (75 MHz, CDCl 3 ): 14.3 (CH 3 ), 19.9 (CH 3 ), 61.0 (CH 2 ), (CH), (Cq), (Cq), (Cq), Cq). The diester was finally saponified with 9.7 g of potassium hydroxide (12 equiv.) in 0 of 95% ethanol, under reflux for 5 days. The solution was then concentrated under vacuum and redissolved in water, the addition at 0 C of concentrated hydrochloric acid until ph 1 gave a white precipitate. The product was filtrated, washed with water and dry by repeated azeotropic distillation with toluene, to give 5.3 g of a white solid, (quantitative, 42 % from the starting benzidine). The diester was already prepared via an oxidative homocoupling catalysed by Pd(II) and Cu(II), the yield (3.57 %) was nevertheless unusable on large scale. 9 S26

27 Diacid: 1 H NMR (300 MHz, DMSO-d 6 ): 2.34 (s, 12H), 7.38 (s, 4H). 13 C NMR (75 MHz, DMSO-d 6 ): 19.4 (CH 3 ), (CH), (Cq), (Cq), (Cq), (Cq). NH 2 I COOEt COOH 1. NaNO 2, HCl 2. KI 1. n-buli, THF 2. ClCOOEt 1. KOH, EtOH 2. HCl NH 2 I COOEt COOH Scheme S2: Synthesis of 3,3,5,5 -tetramethylbiphenyl-4,4 -dicarboxylic acid Following the same procedures detailed above, starting from 12.1 g of 3,3'-dimethylbenzidine (CAUTION! this compound is closely related to carcinogenic benzidine, thus one is to take all required protective measures to avoid any contact), 18.4 g of 3,3 -dimethyl-4,4 - diiodobiphenyle was obtained as the sole product (Yield: 74%). Synthesis: 354 mg (1 mmol) of Fe(ClO 4 ) 3.xH 2 O (Aldrich, 99%) and 298 mg (1 mmol) of tetramethylbiphenyl-4,4 -dicarboxylic acid were dispersed in 5 ml of DMF (Fluka, 98%) with 0,2 ml of NaOH 2M (Alfa Aesar, 98%). The mixture was placed in a Teflon-lined autoclave (23 ml) at 0 C for 12 h. Then, the solid was recovered by filtration and washed with deionised water. Activation: The obtained solid was suspended in methanol, under stirring, at room temperature for 30 minutes. This procedure was repeated three times. The activated compound was recovered by centrifugation and dried at 0 C during one night. Characterisation d - Scale 5 Figure S38: XRD patterns of the as-synthesis (black) and activated RT forms (red) of MIL- 88D(4CH 3 ). The MIL-88D(4CH 3 ) shows a Langmuir and BET surface area of 326 and 8 m 2 /g, respectively, after the out gassing of the activated solid at 0 C under vacuum. S27

28 Volume (cm 3 /g) adsorption desorption 0,0 0,2 0,4 0,6 0,8 1,0 P/P 0 Figure S39: Nitrogen adsorption isotherm of activated MIL-88D(4CH 3 ) at 77 K (P 0 = 1 atm) % H2O lost weight (%) % 4CH3 BiPh Temperature ( C) Figure S40: TGA of activated MIL-88D(4CH 3 ) Figure S41: IR spectra of MIL-88D(4CH 3 ) evacuated under vacuum at various temperatures. In black: spectra for which no degradation is detected. In red: spectra for which degradation is detected (indicated by an asterisk). S28

29 Table S13: Elemental analysis of as-synthesised MIL-88D(4CH 3 ) MIL-88D(4CH 3 ) % Fe % C % N % H % Cl Experimental <0.01 Theoretical Fe 3 O(OH)[C 12 H 4 (CH 3 ) 4 (CO 2 ) 2 ] C 3 H 7 NO MIL-88D(2CH 3 ) (Fe) or Fe 3 O[C 12 H 6 (CH 3 ) 2 (CO 2 ) 2 ] 3.X nh 2 O (X=F, Cl, OH) Synthesis of 3,3 -dimethylbiphenyl-4,4 -dicarboxylic acid: Following the same procedures detailed above, starting from 12.1 g of dimethylbenzidine (CAUTION! this compound is closely related to carcinogenic benzidine, thus one is to take all required protective measures to avoid any contact), 18.4 g of 3,3 dimethyl-4,4 -diiodobiphenyle was obtained as the sole product (Yield: 74%). Diiodide: 1 H NMR(300 MHz, CDCl 3 ): 2.54 (s, 6H), 7. (dd, J = 2.2 and 8.1 Hz, 2H), 7.46 (d, J = 2.2 Hz, 2H), 7.90 (d, J = 8.1 Hz, 2H). 13 C NMR(75 MHz, CDCl 3 ): 28.3 (CH 3 ), 0.3 (Cq), (CH), (CH), (CH), (Cq), (Cq). From this 18.4 g of diiodide, 6.9 g of 3,3 -dimethylbiphenyl-4,4 -dicarboxylic acid was obtained (Yield: 45 % from the starting benzidine). The diester and the diacide showed identical spectroscopic signatures as those reported in the literature. 9 Error! Bookmark not defined. NH 2 I COOEt COOH 1. NaNO 2, HCl 2. KI 1. n-buli, THF 2. ClCOOEt 1. KOH, EtOH 2. HCl NH 2 I COOEt COOH Scheme S3: Synthesis of 3,3,5,5 -dimethylbiphenyl-4,4 -dicarboxylic acid Synthesis : 270 mg (1 mmol) of FeCl 3.6H 2 O (Alfa Aesar, 98%) and 268 mg (1 mmol) dimethylbiphenyl-4,4 -dicarboxylic acid were dispersed in 5 ml of DMF (Fluka, 98%) with 0,25 ml of HF 5M (SDS, 50%). The mixture was placed in a Teflon-lined autoclave (23 ml) at 150 C for 12h. Then, the solid was recovered by filtration and washed with deionised water. Activation: The obtained solid was dried at 150 C under vacuum for 15 h. S29

30 Characterisation MIL88B-4F(H2O) MIL88B-4F as d - Scale 9 8 Figure S42: XRD patterns of the as-synthesis (black) and activated RT (red) forms of MIL- 88D(2CH 3 ). The MIL-88D(2CH 3 ) shows almost no accessible porosity for nitrogen at 77 K (S BET = 29 m 2 /g) due to the large contraction of the pores after dehydration % H2O lost weight (%) % 2CH3 BiPh Temperature ( C) Figure S43: TGA of activated MIL-88D(2CH 3 ) Figure S44: IR spectra of MIL-88D(2CH 3 ) evacuated under vacuum at various temperatures. In black: spectra for which no degradation is detected. In red: spectra for which degradation is detected (indicated by an asterisk). S30

31 Table S14: Elemental analysis of activated MIL-88D(2CH 3 ) MIL-88D(2CH 3 ) % Fe % C % Cl Experimental Theoretical Fe 3 O(OH) 0.71 Cl 0.29 [C 12 H 6 (CH 3 ) 2 (CO 2 ) 2 ] 3 6.2H 2 O MIL-88D(4CH 3 ) (EtOH) MIL-88D(2CH 3 ) (Pyr) MIL-88B(4F) (EtOH) MIL-88B_(2CF 3 ) (MeOH) MIL-88B_(4CH 3 ) (MeOH) MIL-88B(2CH 3 ) (MeOH) MIL-88B(CH 3 ) (EtOH) MIL-88B(2OH) (EtOH) MIL-88B(NO 2 ) (MeOH) MIL-88B(NH 2 ) (EtOH) MIL-88B(Br) (EtOH) MIL-88B(Cl) (EtOH) MIL-88B (MeOH) Figure S45: Synchrotron XRPD of the open form of MIL-88 solids in different solvents. S31

32 Table S15: Cell parameters of the open form of MIL-88 solids in different solvents. Phase Solvent a (Å) c (Å) V (Å 3 ) MIL-88B methanol MIL-88B(Cl) ethanol MIL-88B(Br) ethanol MIL-88B(NH 2 ) ethanol MIL-88B(NO 2 ) methanol MIL-88B(2OH) ethanol MIL-88B(CH 3 ) ethanol MIL-88B(2CH 3 ) methanol MIL-88B(4CH 3 ) methanol MIL-88B_(2CF 3 ) methanol MIL-88B(4F) ethanol MIL-88D(2CH 3 ) pyridine MIL-88D(4CH 3 ) ethanol S32

33 7 7 MIL88B_Br (H2O) MIL88B_Cl (H2O) MIL88B (EtOH) Theta - Scale 2-Theta - Scale 2-Theta - Scale MIL88B_NO2 (H2O) MIL88B_NH2 (H2O) 6 MIL88B_2OH (H2O) 6 2-Theta - Scale 7 2-Theta - Scale 2-Theta - Scale MIL88B_CH3 (H2O) MIL88B_2CH3 (EtOH) MIL88B_4CH3 (EtOH) Theta 7 2-Theta - Scale MIL88B_2CF3 (H2O) Theta - Scale MIL88B_4F (H2O) 21 2-Theta - Scale Theta - Scale MIL88D_Cr 6 MIL88D_2CH3 (EtOH) MIL88D_4CH3 (as, EtOH) 6 2-Theta - Scale 2-Theta - Scale 6 2-Theta - Scale Figure S46: X ray powder thermodiffractometry (λco = Å) under air atmosphere of the water or ethanol form of MIL-88 solids; each red pattern corresponds to a multiple of 0 C. S33

34 MIL88B_Cl MIL88B_2CH3 MIL88B_Br MIL88B_4CH3 MIL88B_NH2 MIL88B_2CF3 MIL88B_NO2 MIL88B_4F MIL88B_2OH MIL88B_2CH3 MIL88B_CH3 MIL88D_4CH Wavelenght (cm -1 ) Wavelenght (cm -1 ) Figure S47. FTIR spectra of RT (red) and as-synthesised (black) MIL-88 modified solids. (Infra-red spectra collected with a Nicolet Nexus spectrometer). S34

35 Figure S48 : Pattern matching of the MIL-88B(4CH 3 ) sample heated (overnight) at 150 C (λ Cu ~ Å). COMPUTATIONAL SECTION The computational effort consisted of determining the structure models of each modified MIL-88 form existing in the closed (dry state) and the open forms. To perform simulations consistent with the collected experimental data (in which to compensate the cationic framework, counter anions are bonded directly onto the metal centres (X=F, OH)), we saturated only one Fe (over three) with F atoms for the closed structures, while all the Fe centers were saturated with one F and two OH groups (coming from the solvent) for the open form. Some additional closed structures (where all the Fe centers are saturated with either F or OH groups) were built to estimate the energetic cost for the structural transition between closed form to open form. The initial atomic coordinates of the non modified MIL-88 framework for the different forms (A, B, C, D) in both dry state and in the presence of solvent were first taken from the refined structure obtained by X ray diffraction. The starting configurations for each modified MIL-88B and D structures were then built by (i) substituting the phenyl rings by the corresponding terephtalate linkers (ii) imposing the corresponding unit cell parameters obtained from the XRPD refinement on both the dry and open states. For this later, we considered the structures fully open when immerged in solvents that led us to consider the experimental unit cell parameters collected when using ethanol, methanol or pyridine as solvent. Further, for each modified MIL-88 structures, several initial models were generated corresponding to different positions of the modified terephtalate linkers over the various phenyl rings available per unit cell. All these models were then energy minimized in the space group P1 by keeping the cell parameters fixed. The optimized structure corresponding to the S35

36 lowest energy for each modified form was selected. The universal force field (UFF) for the Lennard-Jones parameters and the charges calculated from the Electronegativity Equalization method as implemented in the Materials Studio software, were considered to model the interactions between the whole system. Such a strategy based on the same UFF force field has been successfully employed to construct plausible structure of various MILs including the MIL-53(Fe) series and Co(BDP). 11,12 The Ewald summation was considered for calculating the electrostatic interactions while the short range interactions were evaluated using a cut-off distance of 12 Å. The convergence criteria were set to kcal mol -1 (energy), kcal mol -1 Å -1 (forces), and Å (displacement) respectively. As a preliminary step, we carefully checked that this strategy allowed reproducing accurately the structure of the non modified MIL-88A, B, C, D solids in the dry state. All of the geometry optimizations converged to provide a plausible crystallographic structure for each modified MIL-88 form experimentally detected in the dry state and in the presence of solvent. The accessible surface area of the simulated structure models for MIL-88 was estimated using the strategy previously reported by Düren et al. 13 This surface was calculated from the center of a nitrogen probe molecule rolling across the surface. While the diameter of the nitrogen probe molecule was considered to be Å, the diameters of each atom constituting the MIL-88 structures were taken from the UFF forcefield. Using the same parametrization for the framework, the methodology of Gelb and Gubbins 14 was further used to calculate the pore size distributions (PSD) for each modified structure. Table S16. Evaluation of the theoretical accessible surface area for the different models (Drypenta and Dry-hexa for the closed structures and Open-hexa for the open forms). The comparison with experimental data is given in Exp-dry for the closed form. Surface area is expressed in m 2 /g. MIL88B Dry-penta Exp.-dry Dry-hexa Open-hexa 4H 0 < Cl 0 < Br 152 < NH 2 0 < NO < OH 371 < CH CH CH CF 3 470, F 887, MIL-88D 4H CH CH ,03 40 S36

37 References. 1 Boultif, A.; Louer, D. Journal of Applied Crystallography 1991, 24, Rodriguez-Carvajal, J. A program for Rietveld refinement and pattern matching analysis. In Collected Abstracts of Powder Diffraction Meeting, 1990; Roisnel, T.; Rodriguez-Carvajal, J. In Abstracts of the 7th European Powder Diffraction Conference, Barcelona, Spain, 00, Serre C., Mellot-Draznieks C., Surblé S., Audebrand N., Filinchuk Y., Férey G., Science, 07, 315, Anzalone et al. J. Org. Chem., 1985, 50, Ngola S. M., Kearney P. C., Mecozzi S., Russell K., Dougherty D. A., J. Am. Chem. Soc. 1999, 121, Moorthy J. N., Singhal N., J.Org.Chem. 04, 70, Kim, Y.; Swager, T. M., Chem. Commun 05, Akinori S., Z. Naturforsch. 1994, 49, 12, K. Rappé, C.J. Casewit, K.S. Colwell, W.A. Goddard III, W.M. Skiff, J. Am. Chem. Soc. 1992, 114, Devic T., Horcajada P., Serre C., Salles F., Maurin G., Moulin B., Heurtaux D., Clet G., Vimont A., Grenèche J-M., Le Ouay B., Moreau F., Magnier E., Filinchuk Y., Marrot J., Lavalley J-C., Daturi M., Férey G., J. Am. Chem. Soc.,, 132, Salles F., Maurin G., C. Serre, Llewellyn P.L., Knöfel C., Choi H.J., Filinchuk Y., Oliviero L., Vimont A., Long J.R., Férey G., J. Am. Chem. Soc., 132(39), Düren T., Millange F., Férey G., Walton K. S., Snurr R. Q., J. Phys. Chem. C, 07, 111, Gelb L. D., Gubbins K. E. Langmuir, 1999, 15, 305 S37