A possible solution: Flexible porous materials Materials that switch from closed to open Rigid Porous Materials Switching Porous Materials Working capacity always <uptake for rigid materials But only one flexible material has potential capacity better than CNG But most flexible materials are irreversible 1

Isotherm types of flexible porous materials Yet to be classified by IUPAC Rigid MOMs Gradual (Open to more open) Sudden (Open to more open) 2nd cycle Type F-V 1st cycle Gradual (Close to open) Sudden (Close to open) Shape Memory See Q. Y. Yang, et al., Angew. Chem. Int. Ed. 2018, 57, 5684. 2

Potential applications Literature Survey of flexible porous materials only ca. 130 examples Total Structural changes Typical examples Potential applications Type F-I 71 Open to more open (gradual) MIL-53 Cu(aip)(H2O) Separation Type F-II 15 (Sudden) Cu(bpy)2(OTf)2 (ELM-12) Type F-III 16 Closed to open Zn(ndc)(o-phen) Zn2(bdc)2(bpy) Type F-IV 29 ELM-11 Co(bdp) X-dia-1-Ni Storage Type F-V 2 Open to more open (1st) No phase change (2nd) Cu2(bdc)2(bpy) X-pcu-3-Zn-3i Memory effect 3

Type F-IV isotherm exhibited for methane Only 2 materials meet high uptake criteria for ANG Co(bdp) X-dia-1-Ni X-dia-1-Ni-a1 X-dia-1-Ni-c1 P-DSC J. R. Long, et al., Nature, 2015, 527, 357; Q. Y. Yang, et al., Angew. Chem. Int. Ed. 2018, 57, 5684. 4

sql-1-Co-NCS Type F-IV isotherms also exhibited by layered materials The layered packing of the (A) closed (guest-free) and (B) CO2- loaded phases of sql-1-Co-NCS. Recyclability test at 273 K. (A) N2 (77 K) and CO2 (195 K) sorption isotherms for sql-1-Co-NCS. (B) High-pressure CO2 sorption isotherms for sql-1-Co-NCS collected at 253, 265, 273, 283 and 298 K. S.Q. Wang, et al., Chem. Commun., 2018, 54, 7042--7045 5

Sorption 501: finding the right material First we need the right haystack, then the right material 6

So many haystacks 7 Hybrid Ultramicroporous Materials Porous Molecular Crystals Metal Organic Cages Zeolites Covalent Organic Frameworks Porous Molecular Glasses Polymer Networks Porous Organic Cages Metal Organic Frameworks Hydrogen-Bonded Organic Frameworks (HOFs) Periodic Mesoporous Organosilica (PMO) Porous Organic Polymers (POPs) Nanoparticles (e.g. FeO) Porous Ceramics 7

The Solution? Taxonomy The “chemistree” of sorbents 8

Take home messages Keep it simple – pure crystalline materials from readily available, safe molecular building blocks = platforms Pore size should match target: <0.4 nm for CO2; >1.5 nm for crystalline sponges Pore chemistry should match target: inorganic anions for CO2, CO, Xe, NOx, SOx (HUMs); hydrocarbons for NG (MOMs); supramolecular synthons (cocrystals) Modeling, database mining and in situ SCXRD afford critical insight There is more to life than carboxylic acids and carboxylate anions Small structure/chemistry changes can have a big effect New highs for Qst towards CO2, Xe, C2H2 and CH4 Selectivity benchmarks: CO2/N2, C2H2/C2H4, CO2/C2H2, CO2/CO, Xe/Kr Better solubility, stability and bioavailabilty of drug substances without new chemistry These improvements are more than incremental 9

Think Supramolecularly 10