High capacity hydrogen adsorption in Cu(II) tetracarboxylate framework materials: the role of pore size, ligand functionalization, and exposed metal sites

X Lin, I Telepeni, A J Blake, A Dailly, C M Brown, J M Simmons, M Zoppi, G S Walker, K M Thomas, Timothy J Mays, P Hubberstey, N R Champness, M Schroder

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Abstract

A series of isostructural metal−organic framework polymers of composition [Cu2(L)(H2O)2] (L= tetracarboxylate ligands), denoted NOTT-nnn, has been synthesized and characterized. Single crystal X-ray structures confirm the complexes to contain binuclear Cu(II) paddlewheel nodes each bridged by four carboxylate centers to give a NbO-type network of 64·82 topology. These complexes are activated by solvent exchange with acetone coupled to heating cycles under vacuum to afford the desolvated porous materials NOTT-100 to NOTT-109. These incorporate a vacant coordination site at each Cu(II) center and have large pore volumes that contribute to the observed high H2 adsorption. Indeed, NOTT-103 at 77 K and 60 bar shows a very high total H2 adsorption of 77.8 mg g−1 equivalent to 7.78 wt% [wt% = (weight of adsorbed H2)/(weight of host material)] or 7.22 wt% [wt% = 100(weight of adsorbed H2)/(weight of host material + weight of adsorbed H2)]. Neutron powder diffraction studies on NOTT-101 reveal three adsorption sites for this material: at the exposed Cu(II) coordination site, at the pocket formed by three {Cu2} paddle wheels, and at the cusp of three phenyl rings. Systematic virial analysis of the H2 isotherms suggests that the H2 binding energies at these sites are very similar and the differences are smaller than 1.0 kJ mol−1, although the adsorption enthalpies for H2 at the exposed Cu(II) site are significantly affected by pore metrics. Introducing methyl groups or using kinked ligands to create smaller pores can enhance the isosteric heat of adsorption and improve H2 adsorption. However, although increasing the overlap of potential energy fields of pore walls increases the heat of H2 adsorption at low pressure, it may be detrimental to the overall adsorption capacity by reducing the pore volume.
LanguageEnglish
Pages2159-2171
Number of pages13
JournalJournal of the American Chemical Society
Volume131
Issue number6
Early online date21 Jan 2009
DOIs
StatusPublished - 18 Feb 2009

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Adsorption
Pore size
Hydrogen
Metals
Ligands
Weights and Measures
Hot Temperature
Neutron Diffraction
Powder Diffraction
Neutron powder diffraction
Organic polymers
Vacuum
Acetone
Potential energy
Binding energy
Heating
Isotherms
Porous materials
Enthalpy
Wheels

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High capacity hydrogen adsorption in Cu(II) tetracarboxylate framework materials: the role of pore size, ligand functionalization, and exposed metal sites. / Lin, X; Telepeni, I; Blake, A J; Dailly, A; Brown, C M; Simmons, J M; Zoppi, M; Walker, G S; Thomas, K M; Mays, Timothy J; Hubberstey, P; Champness, N R; Schroder, M.

In: Journal of the American Chemical Society, Vol. 131, No. 6, 18.02.2009, p. 2159-2171.

Research output: Contribution to journalArticle

Lin, X, Telepeni, I, Blake, AJ, Dailly, A, Brown, CM, Simmons, JM, Zoppi, M, Walker, GS, Thomas, KM, Mays, TJ, Hubberstey, P, Champness, NR & Schroder, M 2009, 'High capacity hydrogen adsorption in Cu(II) tetracarboxylate framework materials: the role of pore size, ligand functionalization, and exposed metal sites', Journal of the American Chemical Society, vol. 131, no. 6, pp. 2159-2171. https://doi.org/10.1021/ja806624j
Lin, X ; Telepeni, I ; Blake, A J ; Dailly, A ; Brown, C M ; Simmons, J M ; Zoppi, M ; Walker, G S ; Thomas, K M ; Mays, Timothy J ; Hubberstey, P ; Champness, N R ; Schroder, M. / High capacity hydrogen adsorption in Cu(II) tetracarboxylate framework materials: the role of pore size, ligand functionalization, and exposed metal sites. In: Journal of the American Chemical Society. 2009 ; Vol. 131, No. 6. pp. 2159-2171.
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abstract = "A series of isostructural metal−organic framework polymers of composition [Cu2(L)(H2O)2] (L= tetracarboxylate ligands), denoted NOTT-nnn, has been synthesized and characterized. Single crystal X-ray structures confirm the complexes to contain binuclear Cu(II) paddlewheel nodes each bridged by four carboxylate centers to give a NbO-type network of 64·82 topology. These complexes are activated by solvent exchange with acetone coupled to heating cycles under vacuum to afford the desolvated porous materials NOTT-100 to NOTT-109. These incorporate a vacant coordination site at each Cu(II) center and have large pore volumes that contribute to the observed high H2 adsorption. Indeed, NOTT-103 at 77 K and 60 bar shows a very high total H2 adsorption of 77.8 mg g−1 equivalent to 7.78 wt{\%} [wt{\%} = (weight of adsorbed H2)/(weight of host material)] or 7.22 wt{\%} [wt{\%} = 100(weight of adsorbed H2)/(weight of host material + weight of adsorbed H2)]. Neutron powder diffraction studies on NOTT-101 reveal three adsorption sites for this material: at the exposed Cu(II) coordination site, at the pocket formed by three {Cu2} paddle wheels, and at the cusp of three phenyl rings. Systematic virial analysis of the H2 isotherms suggests that the H2 binding energies at these sites are very similar and the differences are smaller than 1.0 kJ mol−1, although the adsorption enthalpies for H2 at the exposed Cu(II) site are significantly affected by pore metrics. Introducing methyl groups or using kinked ligands to create smaller pores can enhance the isosteric heat of adsorption and improve H2 adsorption. However, although increasing the overlap of potential energy fields of pore walls increases the heat of H2 adsorption at low pressure, it may be detrimental to the overall adsorption capacity by reducing the pore volume.",
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T1 - High capacity hydrogen adsorption in Cu(II) tetracarboxylate framework materials: the role of pore size, ligand functionalization, and exposed metal sites

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AU - Telepeni, I

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AU - Dailly, A

AU - Brown, C M

AU - Simmons, J M

AU - Zoppi, M

AU - Walker, G S

AU - Thomas, K M

AU - Mays, Timothy J

AU - Hubberstey, P

AU - Champness, N R

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