Alex Greenaway

Exceptional Thermal Stability in a Supramolecular Organic Framework: Porosity and Gas Storage

Reaction of β-amino-β-(pyrid-4-yl)acrylonitrile with the aromatic dicarboxaldehydes 9,10-bis(4-formylphenyl)anthracene and terephthalaldehyde affords the dihydropyridyl products 9,10-bis(4-((3,5-dicyano-2,6-dipyridyl)dihydropyridyl)phenyl)anthracene (L(1)) and 1,4-bis(4-(3,5-dicyano-2,6-dipyridyl)dihydropyridyl)benzene (L(2)), respectively. In the solid state [L(1)]·2.5DMF·3MeOH (SOF-1) crystallizes in the monoclinic space group P2(1)/c and forms a 3D stable supramolecular organic framework via strong N-H···N(py) hydrogen bonds and π-π interactions. The material incorporates pyridyl-decorated channels and shows permanent porosity in the solid state. The pore volumes of the desolvated framework SOF-1a calculated from the N(2) isotherm at 125 K and the CO(2) isotherm at 195 K are 0.227 and 0.244 cm(3) g(-1), respectively. The N(2) absorption capacity of SOF-1a at 77 K is very low, with an uptake of 0.63 mmol g(-1) at 1 bar, although saturation N(2) adsorption at 125 K is 6.55 mmol g(-1) (or 143 cm(3) g(-1)). At ambient temperature, SOF-1a shows significant CO(2) adsorption with approximately 3 mol of CO(2) absorbed per mole of host at 16 bar and 298 K, corresponding to 69 cm(3) g(-1) at STP. SOF-1a also adsorbs significant amounts of C(2)H(2), with an uptake of 124 cm(3) (STP) g(-1) (5.52 mmol g(-1)) at 1 bar at 195 K. Methane uptake at 195 K and 1 bar is 69 cm(3) (STP) g(-1). Overall, gas adsorption measurements on desolvated framework SOF-1a reveal not only high capacity uptakes for C(2)H(2) and CO(2), compared to other crystalline molecular organic solids, but also an adsorption selectivity in the order C(2)H(2) > CO(2) > CH(4) > N(2). Overall, C(2)H(2)(270 K)/CH(4)(273 K) selectivity is 33.7 based on Henrys Law constant, while the C(2)H(2)(270 K)/CO(2)(273 K) ratio of uptake at 1 bar is 2.05. The less bulky analogue L(2) crystallizes in the triclinic space group P1 as two different solvates [L(2)]·2DMF·5C(6)H(6) (S2A) and [L(2)]·2DMF·4MeOH (S2B) as pale yellow tablets and blocks, respectively. Each L(2) molecule in S2A participates in two N-H···O hydrogen bonds between dihydropyridyl rings and solvent DMF molecules. Packing of these layers generates 1D nanochannels along the crystallographic a and b axes which host DMF and benzene molecules. In S2B, each L(2) ligand participates in hydrogen bonding via an N-H···O interaction between the N-H of the dihydropyridyl ring and the O of a MeOH and also via an N···H-O interaction between the N center of a pyridine ring and the H-O of a second MeOH molecule. The presence of the L(2)-HOMe hydrogen bonds prevents ligand-ligand hydrogen bonding. As a result, S2B crystallizes as one-dimensional chains rather than as an extended 3D network. Thermal removal of solvents from S2A results in conversion to denser phase S2C which shows no effective permanent porosity.

A zeolite family with expanding structural complexity and embedded isoreticular structures

The prediction and synthesis of new crystal structures enable the targeted preparation of materials with desired properties. Among porous solids, this has been achieved for metal–organic frameworks, but not for the more widely applicable zeolites, where new materials are usually discovered using exploratory synthesis. Although millions of hypothetical zeolite structures have been proposed, not enough is known about their synthesis mechanism to allow any given structure to be prepared. Here we present an approach that combines structure solution with structure prediction, and inspires the targeted synthesis of new super-complex zeolites. We used electron diffraction to identify a family of related structures and to discover the structural ‘coding’ within them. This allowed us to determine the complex, and previously unknown, structure of zeolite ZSM-25 (ref. 8), which has the largest unit-cell volume of all known zeolites (91,554 cubic ångströms) and demonstrates selective CO2 adsorption. By extending our method, we were able to predict other members of a family of increasingly complex, but structurally related, zeolites and to synthesize two more-complex zeolites in the family, PST-20 and PST-25, with much larger cell volumes (166,988 and 275,178 cubic ångströms, respectively) and similar selective adsorption properties. Members of this family have the same symmetry, but an expanding unit cell, and are related by hitherto unrecognized structural principles; we call these family members embedded isoreticular zeolite structures.

Stabilization of Scandium Terephthalate MOFs against Reversible Amorphization and Structural Phase Transition by Guest Uptake at Extreme Pressure

Previous high-pressure experiments have shown that pressure-transmitting fluids composed of small molecules can be forced inside the pores of metal organic framework materials, where they can cause phase transitions and amorphization and can even induce porosity in conventionally nonporous materials. Here we report a combined high-pressure diffraction and computational study of the structural response to methanol uptake at high pressure on a scandium terephthalate MOF (Sc2BDC3, BDC = 1,4-benzenedicarboxylate) and its nitro-functionalized derivative (Sc2(NO2-BDC)3) and compare it to direct compression behavior in a nonpenetrative hydrostatic fluid, Fluorinert-77. In Fluorinert-77, Sc2BDC3 displays amorphization above 0.1 GPa, reversible upon pressure release, whereas Sc2(NO2-BDC)3 undergoes a phase transition (C2/c to Fdd2) to a denser but topologically identical polymorph. In the presence of methanol, the reversible amorphization of Sc2BDC3 and the displacive phase transition of the nitro-form are completely inhibited (at least up to 3 GPa). Upon uptake of methanol on Sc2BDC3, the methanol molecules are found by diffraction to occupy two sites, with preferential relative filling of one site compared to the other: grand canonical Monte Carlo simulations support these experimental observations, and molecular dynamics simulations reveal the likely orientations of the methanol molecules, which are controlled at least in part by H-bonding interactions between guests. As well as revealing the atomistic origin of the stabilization of these MOFs against nonpenetrative hydrostatic fluids at high pressure, this study demonstrates a novel high-pressure approach to study adsorption within a porous framework as a function of increasing guest content, and so to determine the most energetically favorable adsorption sites.

In situ synchrotron IR microspectroscopy of CO2 adsorption on single crystals of the functionalized MOF Sc2(BDC-NH2)3.

Synchrotron radiation (SR) IR microspectroscopy has enabled determination of the thermodynamics, kinetics, and molecular orientation of CO2 adsorbed in single microcrystals of a functionalized metal–organic framework (MOF) under conditions relevant to carbon capture from flue gases. Single crystals of the small-pore MOF, Sc2(BDC-NH2)3, (BDC-NH2=2-amino-1,4-benzenedicarboxylate), with well-defined crystal form have been investigated during CO2 uptake at partial pressures of 0.025-0.2 bar at 298–373 K. The enthalpy and diffusivity of adsorption determined from individual single crystals are consistent with values obtained from measurements on bulk samples. The brilliant SR IR source permits rapid collection of polarized spectra. Strong variations in absorbance of the symmetric stretch of the NH2 groups of the MOF and the asymmetric stretch of the adsorbed CO2 at different orientations of the crystals relative to the polarized IR light show that CO2 molecules align along channels in the MOF.

Structural changes of synthetic paulingite (Na,H-ECR-18) upon dehydration and CO2 adsorption

Abstract The structure of dehydrated calcined ECR-18, synthetic paulingite, topology type PAU, unit cell composition Na132H28Si512Al160O1344, has been determined by Rietveld refinement against synchrotron X-ray powder diffraction data. Upon dehydration the symmetry of Na,H-ECR-18 changes from Im3¯m

A combined high-pressure diffraction and computational study on scandium MOFs

Im\bar 3m

The Potential Applications of Nanoporous Materials for the Adsorption, Separation, and Catalytic Conversion of Carbon Dioxide

to I4¯3m,

High-nuclearity metal-organic nanospheres: a Cd66 ball.

I\bar 43m,

Adsorption Materials and Processes for Carbon Capture from Gas-Fired Power Plants- AmpGas

with a corresponding decrease of cubic unit cell a parameter from 34.89412(1) Å to 33.3488(3) Å. This occurs as the framework distorts to afford closer coordination of Na+ cations by framework O atoms in 8-ring window sites of the seven cage types present. Na+ cations in 8R sites block the access of N2 molecules to the internal pore space at 77 K but CO2 adsorption at 308 K is observed, and is postulated to occur via a ‘trapdoor’ mechanism. In situ PXRD during CO2 adsorption at pressures up to 10 bar show reversible broadening of diffraction peaks that is attributed to local crystallographic strain.

Synthesis and Formation Mechanism of Textured MOF-5

Previous high-pressure experiments have shown that pressure-transmitting fluids composed of small molecules can be forced inside the pores of metal organic framework materials, where they can cause phase transitions and amorphization and can even induce porosity in conventionally non-porous materials.1 Here we present a combined high-pressure diffraction and computational study of the structural response to methanol uptake at high pressure on a scandium terephthalate MOF (Sc2BDC3, BDC=1,4benzenedicarboxylate)2 and its nitro-functionalized derivative (Sc2(NO2-BDC)3)3 and compare it to direct compression behaviour in a non-penetrative hydrostatic fluid, Fluorinert-77. In Fluorinert-77, Sc2BDC3 displays amorphization above 0.1 GPa, reversible upon pressure release, whereas Sc2(NO2-BDC)3 undergoes a phase transition (C2/c to Fdd2) to a denser but topologically-identical polymorph. In the presence of methanol, the reversible amorphization of Sc2BDC3 and the displacive phase transition of the nitroform are completely inhibited (at least up to 3 GPa). Upon uptake of methanol on Sc2BDC3, the methanol molecules are found by diffraction to occupy two sites, with preferential relative filling of one site compared to the other: grand canonical Monte Carlo simulations support these experimental observations and molecular dynamics simulations reveal the likely orientations of the methanol molecules, which are controlled at least in part by H-bonding interactions between guests. As well as revealing the atomistic origin of the stabilization of these MOFs against non-penetrative hydrostatic fluids at high pressure this study demonstrates a novel high pressure approach to study adsorption within a porous framework as a function of increasing guest content, and so to determine the most energetically favourable adsorption sites.