NANOPOROUS MATERIALS

Design and control of gas diffusionprocess in a nanoporous soft crystalCheng Gu1*, Nobuhiko Hosono1†‡, Jia-Jia Zheng1,2, Yohei Sato1, Shinpei Kusaka1§,Shigeyoshi Sakaki2, Susumu Kitagawa1†

Design of the gas-diffusion process in a porous material is challenging because acontracted pore aperture is a prerequisite, whereas the channel traffic of guest moleculesis regulated by the flexible and dynamic motions of nanochannels. Here, we presentthe rational design of a diffusion-regulatory system in a porous coordination polymer(PCP) in which flip-flop molecular motions within the framework structure providekinetic gate functions that enable efficient gas separation and storage. The PCP showssubstantial temperature-responsive adsorption in which the adsorbate molecules aredifferentiated by each gate-admission temperature, facilitating kinetics-based gasseparations of oxygen/argon and ethylene/ethane with high selectivities of ~350and ~75, respectively. Additionally, we demonstrate the long-lasting physicalencapsulation of ethylene at ambient conditions, owing to strongly impeded diffusionin distinctive nanochannels.

Porous materials are ubiquitous; they areused to capture, sieve, and separate liq-uids, solids, and gases in our daily lives.Advancements in the science of porousmaterials have facilitated the production

of a variety of porous adsorbents with controlledpore sizes and surface areas for molecular ad-sorption. Zeolites and microporous carbons aretypical industrial adsorbents that have contrib-uted substantially to conventional gas storageand separation technologies (1, 2), in which rigidand persistent pore structures are prerequisitesfor such functions (Fig. 1A) (3–5). Apart fromthese successes, gas-diffusion processes in suchporous materials remain difficult to rationallydesign and control; not only are narrow, con-tracted pores in these materials essential require-ments for diffusion control, local and/or globalframework flexibility plays an important rolethat regulates guest traffic in channels, as wellas guest recognition for separation (6–9).Some traditional zeolites (such as zeolite 4A

and “trapdoor” chabazite) (7–9) and microporous(metal-) organic materials (10–16) are known toshow distinct temperature-dependent adsorptionbehavior in which the gas-diffusion process isstrongly impeded at low temperatures, result-

ing in a dramatically lower gas uptake than ex-pected on the basis of the actual pore volume,whereas diffusion is facilitated at elevated tem-peratures (7–10). This phenomenon has beenascribed to the “pore-blocking effects” of mobileconstituents (such as guest cations/molecules)(8–10) trapped in cavities and/or the vibrationalmotion of the framework (Fig. 1A) (11–17), inwhich local thermodynamic motions or pertur-bations in the crystalline framework affect theguest-diffusion process. However, neither rational-design nor function-led syntheses that enablesuch diffusion-regulatory pore systems, in whichthe local dynamics of flexible molecular entitiesin the framework are required to be predesignedwith molecular-level precision, have been pro-posed so far.Porous coordination polymers (PCPs) and

metal-organic frameworks (MOFs) are highly des-ignable porous platforms that facilitate suchprecise molecular pore-engineering approaches(6, 18–20). Here, we present a rational PCP de-sign strategy that encodes dynamic flip-flop mo-lecular motions into diffusion-regulatory gatefunctionality. Specifically, the presented PCP fea-tures a robust framework with a caged cavityand thermally adjustable bottleneck gates forregulating gas diffusion (Fig. 1), exhibitingtemperature-regulated sorption behavior inwhich the adsorbate molecules are differentiatedby each gate-admission temperature (Fig. 2). Thisfeature not only enables efficient kinetic gasseparation but also storage through the phys-ical entrapment of gases at room temperatureand ambient pressure.We designed a Cu-based PCP with a butterfly-

type ligand comprising isophthalic acid andphenothiazine-5,5-dioxide (OPTz) moieties(OPTz-ipa) (supplementary materials, figs. S1to S10), with the latter moieties exhibitingeffective local motion with low rotation andflipping energies of only 20 and 8.9 kJ mol–1,

respectively (fig. S11). The as-synthesized PCP—namely, Cu(OPTz) (1) (figs. S12 to S14, table S1,and data file S1)—was evacuated at 393 K toproduce an activated phase (1a) (figs. S15 to S18).The crystal structure of 1a was determined bymeans of Rietveld refinement of synchrotronpowder x-ray diffraction (PXRD) data (fig. S19,table S2, and data file S2). Activation resultedin the structural transformation of 1 into arobust three-dimensional structure (Fig. 1B).The structure of 1a features only one type ofnanocage comprising eight channels as poten-tial diffusion pathways for guest molecules, withfour of these channels oriented toward (111) orð�111Þ planes and the other four aligned parallelto the b axis (Fig. 1C). The former and latterchannel types facilitate intra- and interlayerdiffusion, respectively. Additionally, the inter-layer channels are surrounded by three neighbor-ing OPTz rings of the same layer, whereas inthe intralayer channels, one benzene ring ofthe OPTz moiety and one isophthalic unit pointtoward each other to form a small gate only 3 Åin size. Therefore, the thermal flipping of theOPTz units is expected to gradually enlarge thesize of the cage gate, facilitating the admissionof gas molecules at high temperatures (Fig. 1D)and blocking them at low temperatures. At lowtemperatures [around the boiling point tem-perature (Tbp) of the investigated gases], com-pound 1a adsorbed negligible amounts of avariety of gases (H2, O2, Ar, N2, CO, CH4, C2H4,and C2H6) (fig. S20), but these amounts sub-stantially increased with increasing temper-ature, as indicated by adsorption isobars (Fig. 2and fig. S21) at 1 bar. Taking C2H4 as an ex-ample (fig. S22), the amount adsorbed increasedfrom 9 to 62 mL g–1 as the temperature wasincreased from 180 to 320 K but decreasedto 42 mL g–1 as the temperature was furtherincreased to 370 K. These observations re-veal distinctive adsorption behavior that ispromoted by varying the temperature from180 to 320 K (table S3).Additional analyses (figs. S23 to S26) con-

firmed that the observed adsorption behavior isthe result of kinetic factors, as opposed to otherpossible factors, such as the thermal breathingeffect (21), crystallographic phase transitions (22),and strong gas-framework affinities resultingfrom chemisorption (20). To characterize thediffusion process, we used Crank theory to quan-tify the diffusion rate for every C2H4 adsorptionplot synchronously constructed from the corre-sponding isotherms in the 250 to 370 K range(supplementary materials), which allowed usto produce global P–Ds/R

2–V and T–Ds/R2–V

landscapes, where V (milliliter per gram),P (kilopascal), T (kelvin), and Ds/R

2 (per second)denote uptake volume, pressure, temperature,and diffusion rate, respectively, where R denotesthe radius of a 1a particle. (Fig. 3, A and B). Theabove landscapes reveal that remarkably slowdiffusion at low temperature prevents C2H4

adsorption, whereas the diffusion rate steadilyincreases with increasing temperature and pres-sure, with adsorption amounts consequently also

RESEARCH

Gu et al., Science 363, 387–391 (2019) 25 January 2019 1 of 5

1Institute for Integrated Cell-Material Sciences, Kyoto UniversityInstitute for Advanced Study, Kyoto University, YoshidaUshinomiya-cho, Sakyo-ku, Kyoto 606-8501, Japan. 2FukuiInstitute for Fundamental Chemistry, Kyoto University, TakanoNishihiraki-cho 34-4, Sakyo-ku, Kyoto 606-8103, Japan.*Present address: State Key Laboratory of Luminescent Materialsand Devices, Institute of Polymer Optoelectronic Materials andDevices, South China University of Technology, No. 381 WushanRoad, Tianhe District, Guangzhou 510640, P. R. China.†Corresponding author. Email: nhosono@k.u-tokyo.ac.jp (N.H.);kitagawa@icems.kyoto-u.ac.jp (S.Ki.) ‡Present address:Department of Advanced Materials Science, Graduate School ofFrontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha,Kashiwa, Chiba 277-8561, Japan. §Present address: Department ofMaterials Chemistry, Graduate School of Engineering, NagoyaUniversity, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan.

on March 13, 2020

http://science.sciencem

ag.org/D

ownloaded from

increasing with temperature up to 320 K (Tmax).As a consequence, we observed an uptake peakat 1 bar and 320 K, with Ds/R

2 = 1.89 × 10−4 s–1.The optimal adsorption behavior observed atTmax can be viewed as a consequence of twoconflicting factors: the gas-framework affinityand the diffusion limitation (9). C2H6 exhibiteda much higher Tmax than C2H4 (Fig. 2B) becausethe larger size of the former species impedes itsdiffusion compared with that of the latter, whereasthe corresponding adsorption affinities were ex-pected to be similar. Hence, the obtained resultsindicate that gas diffusion can be regulated bythermally controlling the size of the narrow dif-fusion path of 1a, which consequently promoteseffective gas separation. Additionally, by alteringthe temperature sweep directions in isobar ad-sorption experiments (figs. S27 and S28), wedemonstrated the occurrence of a self-promotedadsorption process, in which preabsorbed gasmolecules facilitate subsequent adsorption. Theassistance of temperature is essential because the

maximum adsorption amount cannot be reachedat low temperature, even over an extremely longexposure time (fig. S29).To uncover the essence of the observed ad-

sorption behavior from a structural perspective,in situ PXRD patterns were collected duringthe adsorption process. Patterns obtained duringthe adsorptions of C2H4 and C2H6 at a constanttemperature of 320 K did not reveal any struc-tural changes (figs. S30 and S31). By contrast,PXRD experiments at variable temperature re-vealed that the peak corresponding to the (111)plane shifted slightly to lower angles [the dif-ference value of (111) peak positions from 180 to370 K (D2q) = 0.065°] with increasing temperatureunder vacuum (fig. S32), which is consistent withthe expansion of the [111] axis. Because the OPTzmoieties were oriented parallel to the (111) plane,this small expansion can be correlated with theextent of thermal flipping, which enlarges thecage gates, accelerating gas diffusion in re-sponse to increasing temperature (fig. S33). By

contrast, CO2 exhibited exceptional behavior,inducing a structural transformation in 1a thatresulted in a substantially different PXRD pat-tern (fig. S34); consequently, the diffusion-regulation mechanism is no longer effective.Monte Carlo simulations revealed the two

most plausible C2H4 adsorption sites (I and II)of 1a, each with an occupancy of eight (Fig. 3Cand fig. S35). Hence, in total 16 C2H4 moleculesare accommodated in one unit cell. For adsorp-tion at both sites, the density functional theory(DFT)–optimized cell parameters did not differmuch from those of pristine 1a (table S4), whichis in good agreement with the experimental ob-servation that C2H4 adsorption induces littlestructural transformation (fig. S30). DFT cal-culations followed by spin component–scaledsecond-order Møller-Plesset (SCS-MP2) correctionshowed that the adsorption of C2H4 at sites Iand II occurred with similar binding energies—namely, –27.8 and –31.4 kJ mol–1, respectively(table S4)—which indicates that C2H4 adsorption

Gu et al., Science 363, 387–391 (2019) 25 January 2019 2 of 5

Fig. 1. Depicting the structure of a diffusion-regulatory PCP. (A) Schematic representationsof diffusion-regulatory pore systems.(B) Crystal structure of 1a viewed along thec axis. The rectangle depicts the unit cell.Carbon, gray; nitrogen, blue; sulfur, yellow;oxygen, red; copper, light blue. Hydrogen atomsare omitted for clarity. (C) Cross-sectionalview of a Connolly surface of the void in 1a, wherea small probe radius of 0.8 Å was used tovisualize that the cage structure is intercon-nected with narrow channels. The void volume is1028 Å3 and corresponds to 24.5% of the unitcell volume, which is calculated with Monte Carlomethod by using He as a probe. The innerand outer surfaces of the cage are drawn in yellowand gray, respectively. The blue and red arrowsindicate each of the cage channels for inter- andintralayer diffusion, respectively. Intralayerdiffusion is regulated by the dynamic aperture.(D) Schematic diagram of the void structure of 1aat low and high temperatures. The voids arecolored yellow and orange for the low- andhigh-temperature states, respectively. The cross-sectional view of the ac plane is depicted,in which only the cages and intralayer diffusionchannels are in view. At low temperature, thecage entrances are smaller than the kineticdiameters of the gases; hence, the cages areisolated, which impedes the adsorption of gasmolecules. With increasing temperature, thecage entrances become larger because ofthe thermal flipping of the OPTz moieties,and the cages open for gas adsorptionat the given temperature. The red arrowsdenote intralayer diffusion pathwaysthat are allowed at high temperature.

RESEARCH | REPORTon M

arch 13, 2020

http://science.sciencemag.org/

Dow

nloaded from

at both sites is energetically favorable. Experi-mental evidence obtained by means of synchro-tron PXRD analysis of 1a sealed in a C2H4-filledcapillary allowed us to successfully determine thelocation of C2H4 at sites I and II throughRietveldrefinement of the data acquired at 180 K (fig.S36, table S2, and data file S3). The actual guestlocation at each site was identical to that calcu-lated (fig. S36), although the site occupancy underthe given conditions was smaller (4.1 C2H4 perunit cell) than the theoretical value in the fullyloaded state, as a result of slow diffusion at lowtemperature. On the basis of the above theoret-

icalmodel, we investigated intracage, intralayer,and interlayer C2H4 diffusion and found that thelatter two diffusion processes occur (Fig. 3D). Theintracage diffusion barrier was calculated to be2 kJ mol–1 (fig. S37), suggesting that diffusionwithin the same cage is not the factor thatlimits gas diffusion and adsorption. The intra-layer diffusion barrier in 1a was quite large at73.4 kJ mol–1; it decreased by 24.1 kJ mol–1 forthe C2H4-saturated phase (fig. S38A). Theseresults support the occurrence of a self-promotedadsorption process, as also revealed by the rel-ative diffusion coefficients calculated for various

temperatures and adsorbed phases (fig. S38B).This is presumably due to weakening of C2H4-framework interactions with increasing amountsof adsorbed C2H4 (table S5) (16). Last, the energybarrier for interlayer diffusion is clearly largerthan that for intralayer diffusion (fig. S39), sug-gesting that the latter processmay dominate theadsorption behavior.The sorption mechanism inspired us to use

1a to separate gas mixtures, such as O2/Ar andC2H4/C2H6. Compound 1a was found to exhibitmolecular-sieving behavior; Tmax was positivelycorrelated mainly to the kinetic diameter of thegas (table S3), irrespective of polarity or elec-tronic properties, allowing gases that are phys-ically alike, such as mixtures of O2/Ar (20) andC2H4/C2H6 (table S6) (20, 23), to be effectivelyseparated by using the predesigned differencesin Tmax. According to the adsorption isobars foreach gas, the maximum uptake ratio of O2/Arwas 6.1 at 180 K (Fig. 2A). The O2/Ar combinationis the most challenging air component mixturefor separation; to the best of our knowledge,few porous materials with high O2/Ar selectiv-ities have been reported to date (24–26). TheO2/Ar uptake ratio can be manipulated by tem-perature; 1a adsorbed O2 in preference to Ar inthe 100 to 240 K range, with reverse selectivityobserved in the 250 to 370 K range. Conversely,C2H4 was adsorbed in preference to C2H6 in the200 to 370 K temperature range, with a maxi-mum C2H4/C2H6 uptake ratio of 6.0 observed at270 K (Fig. 2B).

Gu et al., Science 363, 387–391 (2019) 25 January 2019 3 of 5

Fig. 2. Gas adsorption behavior of 1a between 100 and 370 K. (A) O2 and Ar adsorption isobarsat 1 bar and the O2/Ar uptake ratio. (B) C2H4 and C2H6 adsorption isobars at 1 bar and theC2H4/C2H6 uptake ratio.

Fig. 3. Diffusion rates andpathways. (A) Global-pressure–diffusion-rate–adsorption-amount (P–Ds/R

2–V) landscape.(B) T–Ds/R

2–V landscape, whereT is the global temperature.R denotes the radius of a 1aparticle. (C) Simulated structureof the C2H4-adsorbed phaseof 1a. Intracage (positions 1 to 2),intralayer (positions 3 to 4),and interlayer (positions 4 to 5)diffusion pathways in 1a areconsidered in this work. C2H4

molecules adsorbed at sites Iand II are drawn in gold andgreen, respectively. (D) Inter-layer (blue arrow) and intralayer(red arrow) diffusion and struc-ture of transition states in theactivated phase of 1a.

RESEARCH | REPORTon M

arch 13, 2020

http://science.sciencemag.org/

Dow

nloaded from

The promising features of 1a motivated usto carry out dynamic separation experimentswith a temperature-swing protocol; these wereconducted at 180 K with an O2/Ar mixture(50.0/50.0 v/v, 1 bar in total) (fig. S40). Com-pound 1a selectively adsorbed O2 from theO2/Ar mixture within a short exposure timeof 1 hour, leading to marked O2 enrichment,with a composition as high as 96.0% in theadsorbed phase (Fig. 4A and fig. S41) and aseparation factor of 24.0 (Fig. 4B and fig. S42).The separation factor decreased with prolongedexposure time, indicating that O2 was adsorbedmuch faster than Ar and occupied most of theavailable space, which excluded the latter gas bya molecular sieving mechanism as a consequence,in contrast to the simultaneous competitive ad-sorption of mixed gases observed for traditionalPCPs. 1a facilitated O2 enrichment over a widerange of feed-gas compositions (figs. S43 toS50); for example, even in the case of a 4.9:95.1(v/v) O2/Ar mixture, we observed an O2 fractionin the adsorbed phase of up to 94.9% (Fig. 4A),which corresponds to an outstanding separationfactor of 353.5 (Fig. 4A). By virtue of a high—yetconstant—O2 concentration in the adsorbedphase, the separation factor was only inverselyproportional to the O2 concentration in thefeed gas, which was responsible for the highO2 selectivity of 1a. Regarding C2H4/C2H6 sep-aration, 1a selectively adsorbed C2H4 over awide range of feed-gas compositions (figs. S51to S59) at 270 K. Even in the case of a 4.9:95.1(v/v) C2H4/C2H6 mixture, the C2H4 concentra-tion in the adsorbed phase and the corre-sponding separation factor were remarkable at79.8 and 74.9%, respectively (Fig. 4B). Staticmixed-gas co-adsorption experiments demon-strated more practical aspects of the separationcapability of 1a. A 1:1 (v/v) mixture of C2H4/C2H6 (2 bar in total) underwent selective adsorp-

tion by 1a, in which the selectivity of C2H4 overC2H6 was observed to be in the 2.5 to 4.1 rangeat 298 K (fig. S60).The diffusion regulatory pore system pro-

vides a potential molecular trap for gas-storageapplications, in which impeded gas diffusion attemperatures below Tmax results in a lack ofrelease of the preadsorbed gas molecules, facil-itating long-lasting retention at ambient tem-perature in air. We demonstrated this conceptin temperature-programmed desorption (TPD)experiments, in which 1a was subjected to con-secutive adsorption (393 to 298 K) and de-sorption (25°C) processes at 1 bar under a flowof C2H4 and He, respectively. The fraction ofencapsulatedC2H4was determinedby compellingdesorption from 1a at an elevated temperature(~393 K) (supplementary materials, fig. S61). Theresults revealed that half (49.4%) of the encap-sulated C2H4 was still retained by 1a after 6 hoursat 298 K under continuous exposure to He flow(15 sccm) at 1 bar (Fig. 4C), which is superior tothe capacity of HKUST-1, a conventional PCP,which retains only 4.4% after 1 hour under thesame conditions.We could provide a platform for PCPs that

possesses a mechanism of diffusion control andconfinement of guest molecules, which resultsfrom cooperation of the global dynamics of awhole crystal and local dynamics of organic con-stituents. This rationale can provide a blueprintfor a wide range of gas adsorbents for efficientseparation and storage.

REFERENCES AND NOTES

1. Oak Ridge National Laboratory, Materials for SeparationTechnologies: Energy and Emission Reduction Opportunities(Oak Ridge National Laboratory, 2005).

2. S. M. Auerbach, K. A. Carrado, P. K. Dutta, Handbook of ZeoliteScience and Technology (Marcel Dekker, 2003).

3. D. W. Beck, Zeolite Molecular Sieves (John Wiley & Sons, 1974).4. R. C. Bansal, M. Goyal, Activated Carbon Adsorption

(Taylor & Francis Group CRC Press, 2005).

5. R. Xu, W. Pang, J. Yu, Q. Huo, J. Chen, Chemistry of Zeolitesand Related Porous Materials: Synthesis and Structure(John Wiley and Sons, 2007).

6. S. Horike, S. Shimomura, S. Kitagawa, Nat. Chem. 1, 695–704(2009).

7. D. W. Breck, J. Chem. Educ. 41, 678 (1964).8. J. Shang et al., J. Am. Chem. Soc. 134, 19246–19253 (2012).9. G. K. Li et al., Nat. Commun. 8, 15777 (2017).10. Q. Gao, J. Xu, D. Cao, Z. Chang, X.-H. Bu, Angew. Chem. Int. Ed.

55, 15027–15030 (2016).11. F. Vallejos-Burgos, F.-X. Coudert, K. Kaneko, Nat. Commun. 9,

1812 (2018).12. R. Matsuda et al., Chem. Sci. (Camb.) 1, 315–321 (2010).13. S. Ma, D. Sun, X.-S. Wang, H.-C. Zhou, Angew. Chem. Int. Ed.

46, 2458–2462 (2007).14. J.-P. Zhang, X.-M. Chen, J. Am. Chem. Soc. 130, 6010–6017

(2008).15. D. Zhao, D. Yuan, R. Krishna, J. M. van Baten, H.-C. Zhou,

Chem. Commun. (Camb.) 46, 7352–7354 (2010).16. R. J. Verploegh, S. Nair, D. S. Sholl, J. Am. Chem. Soc. 137,

15760–15771 (2015).17. P. J. Bereciartua et al., Science 358, 1068–1071 (2017).18. A. G. Slater, A. I. Cooper, Science 348, aaa8075 (2015).19. S. Kitagawa, R. Kitaura, S. Noro, Angew. Chem. Int. Ed. 43,

2334–2375 (2004).20. E. D. Bloch et al., Science 335, 1606–1610 (2012).21. S. Henke, A. Schneemann, R. A. Fischer, Adv. Funct. Mater. 23,

5990–5996 (2013).22. F. Salles et al., Angew. Chem. Int. Ed. 47, 8487–8491 (2008).23. Z. R. Herm, E. D. Bloch, J. R. Long, Chem. Mater. 26, 323–338

(2014).24. J. Sebastian, R. V. Jasra, Ind. Eng. Chem. Res. 44, 8014–8024

(2005).25. J. Sebastian, S. A. Peter, R. V. Jasra, Langmuir 21, 11220–11225

(2005).26. R. S. Pillai, J. Sebastian, R. V. Jasra, J. Porous Mater. 18,

113–124 (2011).

ACKNOWLEDGMENTS

We thank M. Gochomori and N. Shimanaka for their experttechnical synthesis support and single-crystal XRD analyses.S. Furukawa and S. Ikemura are acknowledged for their supportsurrounding the synchrotron PXRD experiments. We alsoappreciate valuable discussions with S. Horike and S. S. Nagarker.The synchrotron PXRD experiments were conducted at theBL5S2 line at the Aichi Synchrotron Radiation Center (proposal201701039) and at the BL02B2 line at SPring-8 (proposal2017A1180). Funding: This work was supported by a KAKENHIGrant-in-Aid for Specially Promoted Research (JP25000007) andScientific Research (S) (JP18H05262) from the Japan Society

Gu et al., Science 363, 387–391 (2019) 25 January 2019 4 of 5

Fig. 4. Mixed gas separation and physical storage. (A) McCabe-Thielediagram for O2/Ar separation by 1a at 180 K, with the dashed line representingthe theoretical behavior of a material showing no selectivity. (Inset) Thecorrelation between O2 concentration (x) in the feed gas and the separationfactor (a), with the black curve depicting the theoretical-fitting results byusing the empirical relationship a = –9.292 + 1892.71x–1. (B) McCabe-Thiele

diagram for C2H4/C2H6 separation by 1a at 270 K. (Inset) The correlationbetween the C2H4 concentration in the feed gas and the separation factor.(C) Release-time dependences of C2H4 fractions retained in 1a andHKUST-1 under He flow at 298 K at 1 bar.The data were obtained throughrepetitive TPD experiments (supplementary materials, fig. S61). Broken linesare double-exponential-decay fits that are included as visualization supports.

RESEARCH | REPORTon M

arch 13, 2020

http://science.sciencemag.org/

Dow

nloaded from

for the Promotion of Science (JSPS). N.H. acknowledges JSPS fora KAKENHI Grant-in-Aid for Young Scientists (B) (JP16K17959),Scientific Research (B) (JP18H02072), and the Regional InnovationStrategy Support Program (Next-generation Energy SystemCreation Strategy for Kyoto) from the Ministry of Education,Culture, Sports, Science and Technology (MEXT), Japan. S.Ki.acknowledges the ACCEL program (JPMJAC1302) of JapanScience and Technology Agency (JST) for financial support.Author contributions: C.G. performed experiments associatedwith molecular synthesis, crystal growth, and gas sorptionexperiments. C.G. and S.Ku. carried out gas separation and

coadsorption experiments. N.H. performed TPD experiments. C.G.,N.H., and Y.S. conducted single-crystal and PXRD studies andstructure analyses. J.-J.Z. and S.S. carried out calculation studies.All authors contributed to the writing and editing of themanuscript. N.H. and S.Ki. conceived the project and directed theresearch. Competing interests: None declared. Data andmaterials availability: All data are available in the manuscript orthe supplementary materials. Crystallographic data reported inthis paper are listed in the supplementary materials and depositedin the Cambridge Crystallographic Data Centre (CCDC) underreference numbers CCDC 1879450 to 1879452.

SUPPLEMENTARY MATERIALS

www.sciencemag.org/content/363/6425/387/suppl/DC1Materials and MethodsFigs. S1 to S61Tables S1 to S6References (27–59)

Data Files S1 to S3

14 January 2018; resubmitted 23 October 2018Accepted 28 November 201810.1126/science.aar6833

Gu et al., Science 363, 387–391 (2019) 25 January 2019 5 of 5

RESEARCH | REPORTon M

arch 13, 2020

http://science.sciencemag.org/

Dow

nloaded from

Design and control of gas diffusion process in a nanoporous soft crystalCheng Gu, Nobuhiko Hosono, Jia-Jia Zheng, Yohei Sato, Shinpei Kusaka, Shigeyoshi Sakaki and Susumu Kitagawa

DOI: 10.1126/science.aar6833 (6425), 387-391.363Science 

, this issue p. 387Scienceambient conditions.and enabled the separation of oxygen from argon and of ethylene from ethane as well as long-term gas storage under functional groups underwent flipping motions. The change in gate size could lead to high selectivity for gas absorptionthat contains phenothiazine-5,5-dioxide. The entrances to the porous cages changed size with temperature, when these

designed a copper-based PCP with a ligandet al.their internal pores that can assist in gas separation and storage. Gu Soft materials such as porous coordination polymer (PCP) can exhibit temperature-dependent flexible motions of

Flexibility in gas absorption

ARTICLE TOOLS http://science.sciencemag.org/content/363/6425/387

MATERIALSSUPPLEMENTARY http://science.sciencemag.org/content/suppl/2019/01/23/363.6425.387.DC1

REFERENCES

http://science.sciencemag.org/content/363/6425/387#BIBLThis article cites 51 articles, 4 of which you can access for free

PERMISSIONS http://www.sciencemag.org/help/reprints-and-permissions

Terms of ServiceUse of this article is subject to the

is a registered trademark of AAAS.ScienceScience, 1200 New York Avenue NW, Washington, DC 20005. The title (print ISSN 0036-8075; online ISSN 1095-9203) is published by the American Association for the Advancement ofScience

Science. No claim to original U.S. Government WorksCopyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of

on March 13, 2020

http://science.sciencem

ag.org/D

ownloaded from