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Browsing by Author "Duyker, SG"

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Adsorption of CO2 and CD4 in UiO-66: a combination of neutron diffraction and modelling
(Australian Institute of Physics, 2015-02-06) Chevreau, H; Laing, W; Kearley, GJ; Duyker, SG; D’Alessandro, DM; Peterson, VK
Over the last twenty years, tremendous progress has been achieved in the field of Metal Organic Frameworks. Among these materials, the zirconium terephthalate UiO-66(Zr) [1] has attracted a growing attention because of its interesting thermal, chemical and water stability and has shown to be a promising material for the separation of CO2/CH4 gas mixtures. In order to get a better understanding of its sorption behavior towards CO2 and CH4, a Neutron Powder Diffraction (NPD) investigation of UiO-66 loaded with sequential doses of CO2 and CD4 has been carried out on the High Resolution Powder Diffractometer instrument “Echidna” at the OPAL reactor (ANSTO, Sydney). In total, three adsorption sites for CO2 and three adsorption sites for CD4 within the UiO- 66(Zr) have been located by neutron powder-diffraction then characterised by a combination of first-principles Density Functional Theory (DFT) calculations and Quantum Atoms In Molecules (QTAIM) theory. An example of the first CO2 adsorption site is given in figure 1.
Anisotropic thermal and guest-induced responses of an ultramicroporous framework with rigid linkers
(John Wiley & Sons, Inc, 2018-02-16) Auckett, JE; Duyker, SG; Izgorodina, EI; Hawes, CS; Turner, DR; Batten, SR; Peterson, VK
The interdependent effects of temperature and guest uptake on the structure of the ultramicroporous metal–organic framework [Cu3(cdm)4] (cdm=C(CN)2(CONH2)−) were explored in detail by using in situ neutron scattering and density functional theory calculations. The tetragonal lattice displays an anisotropic thermal response related to a hinged “lattice-fence” mechanism, unusual for this topology, which is facilitated by pivoting of the rigid cdm anion about the Cu nodes. Calculated pore-size metrics clearly illustrate the potential for temperature-mediated adsorption in ultramicroporous frameworks due to thermal fluctuations of the pore diameter near the value of the target guest kinetic diameter, though in [Cu3(cdm)4] this is counteracted by a competing contraction of the pore with increasing temperature as a result of the anisotropic lattice response. © 2018 Wiley-VCH Verlag GmbH & Co.
Atomic-scale explorations of stimulus-responsive framework properties in an ultramicroporous gas sorbent
(Society of Crystallographers in Australia and New Zealand, 2017-12-03) Auckett, JE; Duyker, SG; Izgorodina, EI; Hawes, CS; Turner, DR; Batten, SS; Peterson, VK
Functional microporous materials capable of efficiently separating and/or storing gases at noncryogenic temperatures are sought for a wide variety of important industrial applications, including pre- and post-combustion carbon capture, hydrogen fuel storage, and the purification of component gases from air. Understanding the atomic-scale interactions between the host material and guest species under variable operating conditions is essential for obtaining information about adsorption and separation mechanisms, which can in turn be used to design better sorbents targeted at specific applications. The ultramicroporous metal-organic framework [Cu3(cdm)4] (cdm = C(CN)2CONH2 -) was recently reported to exhibit moderately selective adsorption of CO2 over CH4, along with excellent exclusion of elemental gases such as H2 and N2 [1]. Although the very small pore diameter (3–4 Å) results in unpromisingly slow diffusion dynamics, its close similarity to the kinetic diameters of many small gas molecules [2] also raises the prospect of altering the gas sorption and selectivity characteristics of the material via minor structural modifications, such as might be introduced by changing the temperature and/or guest concentration during sorbent operation under industrially relevant conditions. Using a combination of in situ neutron scattering experiments and density functional theory-based calculations, we examine in detail the interplay between lattice shape, pore size, temperature, and CO2 concentration in [Cu3(cdm)4]. The rare and interesting fundamental property of areal negative thermal expansion (NTE) in [Cu3(cdm)4] is attributed to a new variation of a well-known NTE mechanism, and is triggered by dynamic motions of the rigid cdm ligand within the constraints of the complicated framework topology. Although the thermal response of the pore diameter is surprisingly insignificant due to competition between multiple effects, the potential for similar materials to exhibit temperature induced changes in adsorption properties is clearly demonstrated. This study illustrates the breadth and depth of information that can be obtained by combining the power of experimental and theoretical characterisation in an approach that is generally applicable to crystalline sorbent systems.
Atomic-scale understanding of CO2 adsorption processes in metal-organic framework (MOF) materials using neutron scattering and ab-initio calculations
(Australian Institute of Physics, 2016-02-04) Auckett, JE; Peterson, VK; Duyker, SG
The dependence of the industrialised world on fossil-fuel energy generation technologies and consequent increase in atmospheric CO2 concentrations has been blamed for emerging adverse climate effects, including an increase in global mean temperatures. Until renewable, carbon-free energy sources can be efficiently harnessed to meet the world’s energy needs, interim measures are sought to suppress the atmospheric release of CO2 from traditional coal and natural gas combustion processes. Microporous materials such as zeolites and metal-organic frameworks (MOFs) are therefore being investigated for the separation and capture of CO2 at various stages of the combustion cycle. MOFs represent one of the most promising classes of materials for this application, offering unrivalled tunability of structural and chemical characteristics via the substitution of metals and choice and functionalisation of ligands. In order for a MOF to be rationally tuned for improved performance, the nature of the interactions between the host framework and guest molecules must be well-understood at the atomic level. Our research targets this detailed understanding of MOFs using neutron scattering and computational methods. We are currently investigating several MOFs which display unexpected sorption properties such as “reverse sieving” – that is, selectively absorbing larger gas molecules while rejecting smaller ones – and unusual lattice expansion effects. Using in situ diffraction to locate the preferred binding sites of guest molecules in the framework, inelastic neutron scattering to probe system dynamics, and density functional theory-based molecular dynamics simulations to validate and interpret our experimental results, we are able to gain detailed information about the mechanisms of gas uptake and diffusion in these exciting new MOF materials.
Concentration-dependent binding of CO2 and CD4 in UiO-66 (Zr)
(American Chemical Society, 2015-04-02) Chevreau, H; Liang, WB; Kearley, GJ; Duyker, SG; D'Alessandro, DM; Peterson, VK
Porous metal–organic frameworks (MOFs) have emerged as promising materials for the capture of carbon dioxide (CO2) and its separation from methane (CH4) during the industrially important “sweetening” of sour natural-gas. The excellent thermal and chemical stability of the highly porous UiO-66(Zr) material, combined with good selectivity for CO2 over CH4, makes this material a prime candidate for such applications. Using a combination of neutron powder-diffraction and density-functional theory, we examine the details of the binding of CO2 and CH4 in UiO-66(Zr) over the industrially relevant 3.6–9.0 mmol/g concentration range, corresponding to the material that is half to fully saturated with CO2. This work builds on the previously reported preferred site for CO2 and CH4 in UiO-66(Zr), establishing further sites and determining the strength and nature of the guest–host interaction at these. We find the UiO-66(Zr)···CO2 interactions are significantly affected by the concentration of CO2 as the binding of CO2 is enhanced by interguest interactions. © 2015 American Chemical Society
Continuous negative-to-positive tuning of thermal expansion achieved by controlled gas sorption in porous coordination frameworks
(Springer Nature, 2018-11-19) Auckett, JE; Barkhordarian, AA; Ogilvie, SH; Duyker, SG; Chevreau, H; Peterson, VK; Kepert, CJ
Control of the thermomechanical properties of functional materials is of great fundamental and technological significance, with the achievement of zero or negative thermal expansion behavior being a key goal for various applications. A dynamic, reversible mode of control is demonstrated for the first time in two Prussian blue derivative frameworks whose coefficients of thermal expansion are tuned continuously from negative to positive values by varying the concentration of adsorbed CO2. A simple empirical model that captures site-specific guest contributions to the framework expansion is derived, and displays excellent agreement with the observed lattice behaviour. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License.
Coordination frameworks: host-guest chemistry and structural dynamics
(Australian Institute of Nuclear Science and Engineering (AINSE), 2012-11-07) Ogilvie, SH; Duyker, SG; Peterson, VK; Kepert, CJ
Coordination frameworks employ metal ions possessing well defined coordination geometries and an extensive range of molecular bridging ligands with a vast array of functional groups to produce microporous materials with a range of interesting and useful properties. My PhD research is focused towards characterising the structural behaviour of three of these properties in metal-cyanide and metal-imidazolate materials: 1) gas adsorption; 2) metal insertion and; 3) anomalous thermal expansion. Neutron diffraction and scattering are central to all three areas and provide essential information that cannot be readily obtained from other techniques. This is largely due to their sensitivity to light atoms, important for determining the location of light atoms (e.g. CO2 and Li+ ions); their highly penetrating nature, allowing the use of highly specialised sample environments; and their inelastic scattering to provide information on host-guest binding energetics. Gas Adsorption: The primary goal is to elucidate the packing and ordering behaviours of carbon dioxide. These frameworks contain a variety of functional groups which have a known affinity for interaction with CO2, making them suitable for the selective separation of gas mixtures commonly found as flue gas streams of combustion power sources. Metal insertion: The goal is to develop structural understandings of the redox-insertion of lithium and sodium into metal-cyanide phases for the development of new battery electrode materials. Recent work from our group has shown very high reversible loadings of Li into these materials, with in-situ NPD at OPAL used to determine the structures during insertion. Anomalous thermal expansion: Our group has previously investigated the anomalous thermal expansion behaviour in a range of coordination frameworks. Using both NPD and INS, the goal of this project is to develop an even greater understanding of guest influence on these temperature dependent structural behaviours.
Experimental and theoretical approaches to understanding selective gas adsorption in metal-organic frameworks
(Australian Institute of Nuclear Science and Engineering, 2016-11-29) Auckett, JE; Duyker, SG; Peterson, VK
Porous solids such as metal-organic frameworks (MOFs) are considered promising candidates for many industrial gas-separation applications, especially due to their structural and chemical versatility with respect to traditional solid sorbents such as zeolites [1]. Rational tuning of such materials for improved performance requires that the interactions between the host framework and guest molecules be well-understood at the atomic level. Our research targets this detailed understanding of framework-guest systems using in situ and operando neutron scattering experiments, in which structure and dynamics are probed as a function of guest loading and temperature, along with comprehensive atomistic density functional theory-based (DFT) calculations from which various physical and dynamical properties can be extracted. We are currently investigating several MOFs which display interesting sorption behaviours, such as shape-dependent binding, “reverse sieving” (i.e. selectively absorbing larger gas molecules while rejecting smaller ones) [2], and guest-responsive negative thermal expansion (NTE). This talk describes the suite of conventional and unconventional tools we have used to explore the structural and dynamic properties of these frameworks, yielding highly detailed information about their behaviour. Many of these methods can also be applied to a wide variety of systems involving host guest interactions.
Host–guest adsorption behavior of deuterated methane and molecular oxygen in a porous rare-earth metal–organic framework
(Cambridge Core, 2014-11-17) Ogilvie, SH; Duyker, SG; Southon, PD; Peterson, VK; Kepert, CJ
The yttrium-based metal–organic framework, Y(btc) (btc = 1,3,5-benzenetricarboxylate), shows moderate uptake of methane (0.623 mmol g−1) and molecular oxygen (0.183 mmol g−1) at 1 bar and 308 K. Neutron powder-diffraction data for the guest-free, CD4-, and O2-loaded framework reveal multiple adsorption sites for each gas. Both molecular guests exhibit interactions with the host framework characterised by distances between the framework and guest atoms that range from 2.83 to 4.81 Å, with these distances identifying interaction most commonly between the guest molecule and the carboxylate functional groups of the benzenetricarboxylate bridging ligand of the host. © 2014, International Centre for Diffraction Data.
Hydration as a trigger for new properties in inorganic materials
(Australian Institute of Nuclear Science and Engineering, 2016-11-29) Duyker, SG; Peterson, VK; Kearley, GJ; Studer, AJ; Kepert, CJ; Hill, JA; Howard, CJ; Goodwin, AL
The humble water molecule binds to metal ions strongly enough that it can have a significant distortive influence on the coordination geometry, yet weakly enough that it can be readily removed, thus providing scope for reversible chemical switching between structural forms. When this principle is applied in 3D coordination frameworks, the unique topological constraints of the framework can lead to new behaviours. Examples from our work will be presented, including anomalous mechanical properties enabled by unsaturated coordination spheres,[1] and new kinds of symmetry breaking transformations triggered by (de)hydration[2] (see figure).
Identification of bridged CO2 binding in a Prussian blue analogue using neutron powder diffraction
(Royal Society of Chemistry, 2013-01-01) Ogilvie, SH; Duyker, SG; Southon, PD; Peterson, VK; Kepert, CJ
Neutron powder diffraction measurements were carried out on the evacuated and CO2-loaded Prussian blue analogue, Fe3[Co(CN)6]2, identifying two distinct CO2 adsorption sites: site A, in which CO2 uniquely bridges between two bare-metal sites, and site B, in which it interacts in a face capping motif. The saturation of site A at low loadings of CO2 demonstrates the favourable nature of the interaction of CO2 with bare-metal sites within the material. © 2013, Royal Society of Chemistry.
Insights into selective gas sorbent functionality gained by using time-resolved neutron diffraction
(John Wiley & Sons, Inc, 2018-05-05) Auckett, JE; Duyker, SG; Turner, DR; Batten, SR; Peterson, VK
An understanding of the atomic-scale interactions between gas sorbent materials and their molecular guests is essential for the identification of the origins of desirable function and the rational optimization of performance. However, characterizations performed on equilibrated sorbent–guest systems may not accurately represent their behavior under dynamic operating conditions. The emergence of fast (minute-scale) neutron powder diffraction coupled with direct, real-time quantification of gas uptake opens up new possibilities for obtaining knowledge about concentration-dependent effects of guest loading upon function-critical features of sorbent materials, including atomic structure, diffusion pathways, and thermal expansion of the sorbent framework. This article presents a detailed investigation of the ultramicroporous metal–organic framework [Cu3(cdm)4] as a case study to demonstrate the variety of insights into sorbent performance that can be obtained from real-time characterizations using neutron diffraction. © 2018 Wiley-VCH Verlag GmbH & Co
Lowering the energetic landscape for negative thermal expansion in 3D-linker metal–organic frameworks
(ACS Publications, 2023-11-30) Chen, C; Maynard-Casley, HE; Duyker, SG; Barbarao, R; Kepert, CJ; Evans, JD; Macreadie, LK
Tuning the coefficient of thermal expansion (CTE) of functional materials is paramount for their practical implementation. The multicomponent nature of metal–organic frameworks (MOFs) offers an opportunity to finely adjust negative thermal expansion (NTE) properties by varying the metal ions and linkers used. We describe a new strategy to adjust the NTE by using organic linkers that include additional rotational degrees of freedom. Specifically, we employ cubane-1,4-dicarboxylate and bicyclo[1.1.1]pentane-1,3-dicarboxylate to form the MOFs CUB-5 and 3DL-MOF-1, respectively, where each linker has low torsional energy barriers. The core of these nonconjugated linkers is decoupled from the carboxylate functionalities, which frees the relative movement of these components. This results in enhanced NTE compared to the analogous, conjugated system; VT-PXRD results were used to calculate the CTE for 3DL-MOF-1 (αL = −13.9(2) × 10–6 K–1), and CUB-5 (αL = −14.7(3) × 10–6 K–1), which is greater than the NTE of MOF-5 (αL = −13.1(1) × 10–6 K–1). These results identify a new route to enhanced NTE behaviors in IRMOF materials influenced by low energy molecular torsion of the linker. © American Chemical Society
Mechanism and kinetics of carbon dioxide adsorption in metal organic frameworks
(Australian Institute of Nuclear Science and Engineering (AINSE), 2012-11-07) Das, A; Duyker, SG; Peterson, VK; D'Alessandro, DM
Metal-organic frameworks (MOFs) are a class of porous material possessing high crystallinity, which may be specifically targeted to carbon dioxide (CO2) capture and separation in order to meet global targets associated with the reduction of CO2 emissions from industrial sources. The selectivity of MOFs for CO2 uptake over other gases (e.g. N2) may be improved through the introduction of functional groups known to interact with carbon dioxide, e.g. amines, which react with CO2 in an acid- base mechanism. The specific mechanisms and kinetics of CO2 adsorption in such materials are not widely understood, but may be elucidated using neutron diffraction techniques. We have previously employed neutron diffraction in preliminary experiments to investigate the in situ concentration-dependent behaviour of CO2 adsorption in [Ni2(dobdc)] (dobdc = 2,5-dioxido-1,4-benzenedicarboxylate) and our recently published piperazine-functionalised framework [Ni2(dobdc)(pip)0.5]. We are further expanding our repertoire of materials and types of functional groups investigated using this method; in particular, we are investigating the interaction of CO2 molecules with pendant functional groups such as sulfones, primary amines and secondary amines. The nature of these interactions may be explored using X-ray diffraction, gas sorption, gravimetric analysis using mixed gas streams and infrared spectroscopy; however, neutron diffraction presents a powerful and unique in situ technique to probe the temperature- and concentration-dependent behaviour of CO2 binding to identify intermediate binding species, fully explore the binding mode of CO2 and investigate structural effects in the adsorbate material. Mixed gas (CO2/N2) experiments will be used to explore the specificity of the host-guest behaviour in these functionalised frameworks. Based upon this data, it will be possible explore specific chemical factors contributing to selective CO2 capture, and in doing so contribute to the design of new materials or improve upon existing ones for CO2 uptake.
Metal organic frameworks for CO2 capture
(Australian Institute of Nuclear Science and Engineering (AINSE), 2013-12-03) Chevreau, H; Duyker, SG; Peterson, VK
Since 1970, the global emission of carbon dioxide (CO2) has increased by approximately 80%, largely due to our use of fossil fuels for energy generation leading to drastic environmental change. The 'Science and Industry Endowment Fund' (SIEF)-Energy Waste Research Project aims to solve this issue, namely the development of new materials and processes for the capture and utilization of CO2. One of the most promising classes of materials of the recent years are the Metal Organic Frameworks (MOFs), also named Porous Coordination Polymers (PCPs), which are built up from inorganic moieties and organic molecules to give rise to a 3D porous network. They have attracted attention owing to their properties such as gas storage, separation, energy storage, catalysis and biomedicine. Our work has thus been focused on the understanding of the CO2 uptake within these materials by using Neutron Powder Diffraction (NPD) combined with first principle Density Functional Theory (DFT) calculations. Our recent study have been carried out on the famous Zr (IV)-based UiO-66 2.
Negative thermal expansion in LnCo(CN)6 (Ln=La, Pr, Sm, Ho, Lu, Y): mechanisms and compositional trends
(John Wiley and Sons, 2013-04-09) Duyker, SG; Peterson, VK; Kearley, GJ; Ramirez-Cuesta, AJ; Kepert, CJ
Negative thermal expansion (NTE) is a comparatively rare phenomenon that is found in a growing number of materials.1 The discovery of new NTE materials and the elucidation of mechanisms underpinning their behavior is important both in extending the field and enabling tailored thermal expansion properties. NTE has been found throughout a broad family of cyanide coordination frameworks,2 arising from thermal population of low-energy transverse vibrations of the cyanide bridges, which reduce the average metal–metal distances, and thus the lattice parameters, with increasing temperature. More complex mechanisms have been established in metal–organic framework materials, in which both local and long-range modes contribute to NTE.3 The low-energy dynamics of metal-based materials are often modeled in terms of rigid unit modes (RUMs), wherein the metal-centered polyhedra are treated as rigid, with only the linkage being flexible. © 2013, Wiley-Vch Verlag GmbH & Co.
Neutron diffraction and in situ gas-loading investigations of functional MOFs for energy-relevant gas separations
(Australian Institute of Nuclear Science and Engineering (AINSE), 2012-11-08) Duyker, SG; Peterson, VK; Ogilvie, SH; Turner, DR; Hill, MR; D'Alessandro, DM; Kepert, CJ
Intense research is currently directed towards realising metal-organic frameworks (MOFs) for industrially-applied gas separation and storage due to their unique structural properties, including: robustness; thermal and chemical stability; unprecedented internal surface area; and high void volume. A particular focus of current research is the development of MOFs for the separation of CO, from the other components of flue gas in fossil-fuelled power plants. The use of NPD to study gas adsorption in framework materials is a relatively new but growing field. Structural measurements, which show the arrangement of both the host and guest, allow derivation of the nature of the host-guest interaction, and the host's response to the guest. The capability to perform these measurements, with accurate gas dosing and temperature control, has recently been realised at ANSTO's Bragg Institute. Using these techniques, we have investigated the adsorption mechanisms of a number of gases in selected new and established MOFs that display impressive selectivity for specific gases. The location and orientation of industrially-relevant gases including D2, 02, CO2, and CD4, within their crystal structures provide insights into the modes of binding, which will help to tune the materials' performance and benefit the design and development process for the next generation of materials.
Square grid metal–chloranilate networks as robust host systems for guest sorption
(John Wiley & Sons, Inc, 2019-02-02) Kingsbury, CJ; Abrahams, BF; Auckett, JE; Chevreau, H; Dharma, AD; Duyker, SG; He, QL; Hua, C; Hudson, TA; Murray, KS; Phonsri, W; Peterson, VK; Robson, R; White, KF
Reaction of the chloranilate dianion with Y(NO3)3 in the presence of Et4N+ in the appropriate proportions results in the formation of (Et4N)[Y(can)2], which consists of anionic square-grid coordination polymer sheets with interleaved layers of counter-cations. These counter-cations, which serve as squat pillars between [Y(can)2] sheets, lead to alignment of the square grid sheets and the subsequent generation of square channels running perpendicular to the sheets. The crystals are found to be porous and retain crystallinity following cycles of adsorption and desorption. This compound exhibits a high affinity for volatile guest molecules, which could be identified within the framework by crystallographic methods. In situ neutron powder diffraction indicates a size-shape complementarity leading to a strong interaction between host and guest for CO2 and CH4. Single-crystal X-ray diffraction experiments indicate significant interactions between the host framework and discrete I2 or Br2 molecules. A series of isostructural compounds (cat)[MIII(X-an)2] with M=Sc, Gd, Tb, Dy, Ho, Er, Yb, Lu, Bi or In, cat=Et4N, Me4N and X-an=chloranilate, bromanilate or cyanochloranilate bridging ligands have been generated. The magnetic properties of representative examples (Et4N)[Gd(can)2] and (Et4N)[Dy(can)2] are reported with normal DC susceptibility but unusual AC susceptibility data noted for (Et4N)[Gd(can)2]. © 2019 Wiley-VCH Verlag GmbH & Co
Topotactic structural conversion and hydration-dependent thermal expansion in robust LnMIII(CN)6·nH2O and flexible ALnFeII(CN)6·nH2O frameworks (A = Li, Na, K; Ln = La–Lu, Y; M = Co, Fe; 0 ≤ n ≤ 5)
(Royal Society of Chemistry, 2014-06-04) Duyker, SG; Halder, GJ; Southon, PD; Price, DJ; Edwards, AJ; Peterson, VK; Kepert, CJ
The structures of the AxLnM(CN)6·nH2O (A = Li, Na, K; Ln = La–Lu, Y; M = Co, Fe; x = 0, 1; 0 ≤ n ≤ 5) cyanide frameworks, their thermal expansion behaviour, and their transformations upon dehydration are explored using X-ray and neutron single crystal diffraction and X-ray powder diffraction. Modification from positive to negative thermal expansion in the LnCo(CN)6·nH2O phases is achieved by removal of the guest water molecules. Most notable is the unprecedented flexibility demonstrated by the “coiling” of KLnFe(CN)6·nH2O frameworks upon their dehydration, wherein the lanthanoid coordination geometry reversibly converts from a 9-coordinate tri-capped trigonal prism to a 6-coordinate octahedron via a single-crystal-to-single-crystal process, accompanied by a large (14–16%) decrease in unit cell volume. © 2014, The Royal Society of Chemistry.
Ultramicroporous MOF with high concentration of vacant Cu 11 sites
(American Chemical Society, 2015-07) McCormick, LJ; Duyker, SG; Thornton, AW; Hawes, CS; Hill, MR; Peterson, VK; Batten, SR; Turner, DR
An ultramicroporous metal–organic framework (MOF) is reported that contains 0.35 nm nanotube-like channels with an unprecedented concentration of vacant CuII coordination sites. The nonintersecting, narrow channels in [Cu3(cdm)4] (cdm = C(CN)2(CONH2)−) align in two perpendicular directions, structurally resembling copper-doped carbon nanotubes with CuII embedded in the walls of the channels. The combination of ultramicroporosity with the exposed CuII coordination sites gives size-based selectivity of CO2 over CH4, based on pore-size distribution and modeling. Neutron powder diffraction and molecular dynamics simulations show the close packing of single rows of guests within the tubular nanostructure and interaction of CO2 with the exposed metal sites. © 2014, American Chemical Society.

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