Gas Adsorption in R2-MOF-5 Difunctionalized with Alkyl Groups

Article abstract of DOI:10.1002/ejic.202100466

Zinc terephthalate metal?organic framework (MOF) MOF-5 and some of its dialkylated derivatives (R₂-MOF-5; R=Me, Et, Pr, Bu) were obtained from a solvothermal synthesis using 2,5-dialkyl-1,4-benzenedicarboxylic acids with zinc nitrite. The effect of the solvent on the solvothermal synthesis of R₂-MOF-5 was investigated. For R=H and Me, interpenetrating or non-interpenetrating MOFs obtained depending on the choice of reaction solvent, while for R=Et, Pr, and Bu, no such solvent effect was observed, and only jungle-gym-type MOFs were generated. All compounds were fully characterized using powder X-ray diffraction analysis (PXRD), Fourier-transform infrared (FT-IR) spectroscopy, and thermogravimetric analysis (TGA). After activation, all these compounds exhibit significant porosity, as confirmed by N₂-, H₂-, and CO₂-sorption experiments. The N₂-adsorption capacity of these compounds depends on the size of the attached alkyl groups, while the H₂-uptake values tend to increase for the alkyl-functionalized MOFs relative to the unfunctionalized parent MOFs and exhibit a maximum value for Pr₂-MOF-5.

Full text of DOI:10.1002/ejic.202100466

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Gas Adsorption in R2-MOF-5 Difunctionalized with Alkyl
Groups
Koh Sugamata,*[a] Sho Kobayashi,[a] Teruyuki Iihama,[a] and Mao Minoura*[a]
Zinc terephthalate metalÀ organic framework (MOF) MOF-5 and
some of its dialkylated derivatives (R2-MOF-5; R=Me, Et, Pr, Bu)
were obtained from a solvothermal synthesis using 2,5-dialkyl-
1,4-benzenedicarboxylic acids with zinc nitrite. The effect of the
solvent on the solvothermal synthesis of R2-MOF-5 was
investigated. For R=H and Me, interpenetrating or non-inter-
penetrating MOFs obtained depending on the choice of
reaction solvent, while for R=Et, Pr, and Bu, no such solvent
effect was observed, and only jungle-gym-type MOFs were
generated. All compounds were fully characterized using
powder X-ray diffraction analysis (PXRD), Fourier-transform
infrared (FT-IR) spectroscopy, and thermogravimetric analysis
(TGA). After activation, all these compounds exhibit significant
porosity, as confirmed by N2-, H2-, and CO2-sorption experi-
ments. The N2-adsorption capacity of these compounds
depends on the size of the attached alkyl groups, while the H2-
uptake values tend to increase for the alkyl-functionalized MOFs
relative to the unfunctionalized parent MOFs and exhibit a
maximum value for Pr2-MOF-5.
Introduction
properties can be attained through functionalization of the
well-known MOF-5 with alkyl-ether groups.[27] Recently, we
have reported the controlled synthesis of non-interpenetrated
and interpenetrated methyl-modified MOF-5 derivatives, which
exhibit different pore structures.[28] These compounds were
prepared via a hydrothermal synthesis using 2,5-dimethyl-1,4-
benzenedicarboxylic acid and Zn(NO3)2 ·6H2O, in which the
choice of solvent (N,N-dimethylformamide or N,N-diethylforma-
mide) is of critical importance. Our results suggest that the
suppression of framework interpenetration and control over the
pore architecture is not only the result of simple steric criteria
regarding the ligand but may be governed by other mecha-
nisms such as solvent templating. In the present study, we
further investigated this system by varying the chemical
substituents at the 2- and 5-positions of the phenylene unit in
the MOF-5 framework (R2-MOF-5; R=Me, Et, Pr, or Bu). The
total N2 uptake of the obtained jungle-gym-type MOFs
decreased with the increasing length of the incorporated alkyl
chain. The highest H2 adsorption was observed for jungle-gym-
type Pr2-MOF-5 rather than the jungle-gym-type H-substituted
MOF (MOF-5), demonstrating that the H2 adsorption showed a
different trend than the N2 adsorption. We have also reported
the CO2/N2 selectivity of these MOFs, which can be related to
the increasing chain length of the alkyl substituents.
MetalÀ organic frameworks (MOFs) are porous and crystalline
materials with infinite network structures constructed from
metal ions and organic ligands.[1–6] Their efficient adsorption of
small molecules has led to applications in e.g. gas
adsorption,[7–9] catalysis,[10–14] as well as energy storage and
conversion.[15–18] The interest in porous MOFs stems from their
desirable physical and chemical properties, such as high surface
area, tuneable pore size, modularity, as well as high micro- and
mesoporous volume. The zinc terephthalate MOF MOF-5
currently represents the area of highest interest within the field
of MOFs. MOF-5 has a zeolite-like framework in which inorganic
[Zn4O] clusters are joined in an octahedral array of 1,4-
benzenedicarboxylate (BDC) groups to form a robust and highly
porous cubic framework.[19] MOF-5, which has a large surface
area, high thermal and chemical stability, as well as very high
pore volume, exhibits excellent gas-adsorption properties.
Functionalization and modification of the organic ligands to
construct new MOFs is a fascinating and significant area in
crystal engineering owing to the potential applications of the
resulting materials. Consequently, the number of functionalized
MOFs that has been synthesized and reported is steadily
increasing.[20–27] Functionalizing the organic ligands of MOFs is
an effective method to adjust the performance of MOFs, as the
attachment of functional groups can lead to considerable
enhancement in their adsorption properties. Likewise,
enhancement of the frameworks and tuning of the sorption
Using reported procedures,[29,30] 2,5-dialkyl-1,4-benzenedi-
carboxylic acids (R2BDC; R=Et, Pr, Bu) were synthesized in three
steps from commercially available 1,4-dialkylbenzene as shown
in Scheme 1. High yields of the 2,5-dialkyl-1,4-benzenedicarbox-
1
ylic acids were obtained, and their purity was confirmed by H
NMR spectroscopy (Figures S1–S3). MOF-5 and Me2-MOF-5
[a] Dr. K. Sugamata, Dr. S. Kobayashi, T. Iihama, Prof. Dr. M. Minoura
Department of Chemistry, College of Science
Rikkyo University
were synthesized via
a previously reported solvothermal
reaction between Zn(NO3)2 ·6H2O and terephthalic acid in N,N-
dimethylformamide (DMF) or N,N-diethylformamide (DEF).[28]
The chosen synthetic route to the difunctionalized R2-MOF-5
(R=Et, Pr, or Bu) is similar to that of MOF-5. Colorless
microcrystalline powders were obtained following slow cooling
3-34-1, Nishi-Ikebukuro, Toshima-ku, Tokyo 171-8501, Japan
E-mail: sugamata@rikkyo.ac.jp
minoura@rikkyo.ac.jp
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/ejic.202100466
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ure S5).[31] When DEF was used as the reaction solvent (Fig-
ure 1b), the main peak positions of all resulting R2-MOF-5
°
patterns (R=Me, Et, Pr, or Bu; diffraction peaks at 6.8 and
°
13.8 ) were consistent with those of MOF-5. These results
suggest that the ligand functionalization does not affect the
crystallinity of the MOFs. In the cases of Et2-MOF-5, Pr2-MOF-5,
and Bu2-MOF-5, interpenetrating MOFs were not observed,
suggesting that the solvent-dependent structural change
during synthesis is probably due to steric hindrance. In other
words, the PXRD analysis revealed that the same jungle-gym-
type MOFs are generated for Et2-MOF-5, Pr2-MOF-5, and Bu2-
MOF-5 regardless of whether DMF or DEF is used in the
solvothermal synthesis.
Scheme 1. Synthetic route to R2-MOF-5 (R=Me, Et, Pr, or Bu).
FT-IR analysis was employed to confirm the formation of
covalent bonds in R2-MOF-5 (R=Me, Et, Pr, or Bu). As shown in
Figure 2, all spectra include the characteristic bands of MOF-5,
which confirms the successful formation of the framework for
all samples. The sharp peaks at approximately 1360, 1410, and
1580 cmÀ 1 are related to the COÀ O group of the dicarboxylate
linker, while the band near 750 cmÀ 1 corresponds to the CH
vibrations of the aromatic ring, and the characteristic band at
520 cmÀ 1 to the ZnÀ O bonds in the MOF-5 structure. The IR
bands related to the alkyl groups are observable near
2900 cmÀ 1 in R2-MOF-5 (R=Me, Et, Pr, or Bu), thus corroborat-
ing the successful functionalization of the aromatic ring with
alkyl groups.
of the reaction mixtures to room temperature, and their
structures were subsequently analyzed using powder X-ray
diffraction (PXRD) analysis, Fourier-transform infrared (FT-IR)
spectroscopy, thermogravimetric analysis (Figure S4), and gas-
adsorption analysis.
Results and Discussion
The PXRD spectra of MOF-5 and R2-MOF-5 (R=Me, Et, Pr, or Bu)
are shown in Figure 1a, Figure 1b, and Figures S5–S14). In our
previous report, we investigated the effect of the solvent (DMF
of DEF) on the solvothermal synthesis of Me2-MOF-5. Under
otherwise identical reaction conditions, non-interpenetrated or
interpenetrated Me2-MOF-5 were obtained using DEF or DMF,
respectively. As shown in Figure 1a, MOF-5 and Me2-MOF-5 are
considered to be interpenetrated MOFs due to a splitting of the
Bulk samples of MOF-5 and R2-MOF-5 (R=Me, Et, Pr, or Bu)
were used for this study, and any changes to their structures
were tracked using PXRD and thermogravimetric analyses
(TGA). The TGA measurements were conducted from room
°
temperature to 500 C after the MOFs had been completely
°
dried under reduced pressure at 150 C. All MOFs were
°
°
diffraction peak near 10 and the ratio of the intensity of the
thermally stable up to 400 C (Figure S4). To investigate the
°
°
peak at 13.8 relative to that at 6.8 , while Et2-MOF-5, Pr2-MOF-
5, and Bu2-MOF-5 exhibit jungle-gym-type patterns (Fig-
porosity of the structures of MOF-5 and R2-MOF-5 (R=Me, Et,
Pr, or Bu), their N2-adsorption/desorption isotherms were
Figure 1. Experimental PXRD patterns of R2-MOF-5 (R=Me, Et, Pr, or Bu) synthesized in DMF (a) and in DEF (b).
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to the N2-adsorption measurements, an almost opposite trend
is obtained for the CO2 uptake in the R2-MOF-5 (R=Me, Et, Pr,
or Bu) structures, which clearly does not coincide with the
surface area trend. Pr2-MOF-5 has a maximum CO2 uptake of
3.84, 2.37, and 1.12 mmolgÀ 1 at 258, 273, and 298 K (1 bar),
respectively. This is a moderate amount of CO2 adsorption,
comparable to that of MIL-101(Cr) (1.17 mmolgÀ 1 at 1 bar and
298 K) and UiO-66 (2.20 mmolgÀ 1 at 1 bar and 273 K).[32–34] It
should be noted here that the amount of CO2 adsorbed by Pr2-
MOF-5 is nearly double that of its parent structure MOF-5 at
258 K. The isosteric heat of adsorption (Qst) is the heat
generated during the adsorption of CO2 and represents the
force between CO2 and the adsorbent surface. MOFs with
higher Qst for CO2 tend to exhibit better capture performance.
The Qst values of R2-MOF-5 were calculated based on the raw
adsorption data collected at 273, and 298 K with virial fitting
(Figure 3d, Figures S18–S22).[35] The modest adsorption enthalpy
of R2-MOF-5 highlights the absence of strong binding centers
in R2-MOF-5, with open metal sites and active amines reported
to increase the Qst to 35–45 and 50–100 kJ·molÀ 1,
respectively.[32] The slightly higher adsorption enthalpies of CO2
in the R2-MOF-5 (R=Me, Et, Pr, or Bu) structures with
functionalized BDC ligands compared to those of the parent
structure MOF-5 suggest weak interactions between the
functionalized frameworks and CO2. At zero CO2 loading, a
reduction in pore size of the MOFs was observed to increase
the CO2 uptake through an increase in the enthalpy of
adsorption at low pressure.[36] CO2 bound preferentially to the
strong sites until saturation, and then adsorbed on the weak
sites, resulting in a decrease in Qst. The enthalpy of R2-MOF-5
(R=Me, Et, Pr, or Bu) did not decrease more than that of MOF-5
because the introduced functional groups act as adsorption
sites. Similarly, the smaller pores of the MOFs were found to be
effective for CO2 capture.[37] Therefore, the enhancement of the
CO2 uptake found in the R2-MOF-5 (R=Me, Et, Pr, or Bu)
structures prompted us to further investigate their selectivity
toward CO2 over N2. The adsorption isotherms of CO2 and N2 on
activated R2-MOF-5 (R=Me, Et, Pr, or Bu) samples were
performed under the same conditions (298 K, up to 1 bar). To
predict their selectivity towards a CO2/N2 binary mixture, ideal
adsorbed solution theory (IAST) calculations with Henry’s law
simulation were employed based on the single-component R2-
MOF-5 (R=Me, Et, Pr, or Bu) isotherms (Figures S23 and S24).[38]
Table 1 and Figure S25 show the predicated CO2/N2 selectivity
as a function of the pressure when the gas-phase mole fraction
Figure 2. FTIR spectra of MOF-5 and R2-MOF-5 (R=Me, Et, Pr, or Bu).
°
measured at 77 K after degassing for 6 h at 135 C (Figure 3a).
Each isotherm showed Type-I isotherm features, indicating a
microporous nature of MOF-5 and R2-MOF-5 (R=Me, Et, Pr, or
Bu). The SBET values determined by N2 adsorption for the
interpenetrated
MOF-5
(985 m2 gÀ 1)
and
Me2-MOF-5
(663 m2 gÀ 1) are much lower than those of the non-inter-
penetrated MOFs. The SBET values (m2 gÀ 1) of the jungle-gym-
type R2-MOF-5 structures decrease in the order MOF-5 (3,483)>
Me2-MOF-5 (2,340)>Et2-MOF-5 (1,931)>Pr2-MOF-5 (1,723)>
Bu2-MOF-5 (1,339), which corresponds to the increasing size of
the attached alkyl groups. The H2-adsorption measurements
were carried out with the activated R2-MOF-5 (R=Me, Et, Pr, or
Bu) samples at 77 K and pressures of up to 1 bar. As shown in
Figure 3b, the H2 adsorption isotherms of all the samples follow
type-I behavior in the pressure range from 0 to 1 bar. The H2-
uptake values (wt%) of R2-MOF-5 decrease in the order Pr2-
MOF-5 (1.50)>Et2-MOF-5 (1.49)>Me2-MOF-5 (1.42)>MOF-5
(1.27)>Bu2-MOF-5 (1.26) (cf. Table 1). Based on the reduced
surface area of the R2-MOF-5 (R=Me, Et, Pr, or Bu) with
increasing alkyl-group length, it is certain that the introduced
functional groups contribute to the enhanced H2 uptake. The
CO2-adsorption isotherms for activated R2-MOF-5 (R=Me, Et, Pr,
or Bu) samples were collected at 258, 273, and 298 K, and the
results are plotted in Figure 3c, Figures S16, and S17. Compared
Table 1. Temperature-dependent N2-, H2-, and CO2-uptake capacity of MOF-5 and R2-MOF-5 (R=Me, Et, Pr, or Bu) and the corresponding isosteric heat of
adsorption (Qst) of CO2.
R
N2 at 1 bar
BET
H2 at 1 bar
[wt%]
77 K
CO2 at 1 bar
Selectivity
CO2/N2
[298 K]
[cm3 gÀ 1
77 K
]
surface area
[cm3 gÀ 1 (mmol gÀ 1)]
[m2 gÀ 1
]
258 K
273 K
298 K
Qst
[kJ molÀ 1
]
H
Me
Et
Pr
Bu
860
606
511
457
356
3483
2340
1931
1723
1339
1.27
1.43
1.49
1.50
1.26
45.2 (2.02)
63.7 (2.84)
69.2 (3.09)
86.0 (3.84)
80.2 (3.58)
30.5 (1.36)
41.5 (1.85)
44.0 (1.96)
53.0 (2.37)
50.0 (2.23)
16.3 (0.738)
21.0 (0.938)
21.3 (0.951)
25.1 (1.12)
24.3 (1.08)
17.3
18.3
19.1
19.1
19.3
4.7
6.1
7.2
8.8
9.8
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Figure 3. a) N2-sorption isotherms at 77 K, b) H2-adsorption isotherms at 77 K, c) CO2-adsorption isotherms at 273 K, and d) heat of adsorption for CO2 for
MOF-5 and R2-MOF-5 (R=Me, Et, Pr, or Bu).
is 15/85, which is a typical feed composition for flue gas. The
IAST selectivities of R2-MOF-5 (R=Me, Et, Pr, or Bu) toward CO2
in the presence of N2 are 4.7, 6.1, 7.2, 8.8, and 9.8 for MOF-5,
Me2-MOF-5, Et2-MOF-5, Pr2-MOF-5, and Bu2-MOF-5 at 298 K
and 1 bar, respectively (Figure S25). The most remarkable point
of the CO2/N2 selectivity of R2-MOF-5 (R=Me, Et, Pr, Bu) is
enhanced according to the size of the alkyl group. For this
condition, the selectivities of R2- MOF-5 (R=Me, Et, Pr, Bu) are
not particularly high, but comparable to those of ZIF-8 (5–7)
and MOF-508b (4–6).[39,40]
Pr, or Bu) materials. These compounds, along with the
previously reported MOF-5, were prepared via a solvothermal
synthesis using 2,5-dialkyl-1,4-benzenedicarboxylic acids
(R2BDC) and zinc nitrite in N,N-dimethylformamide (DMF) or
N,N-diethylformamide (DEF). When 1,4-benzenedicarboxylic
acid (H2BDC) or Me2BDC were used, specific solvent effects were
observed in the interpenetrated or non-interpenetrated struc-
tures of MOF-5 and Me2-MOF-5, while Et2, Pr2, and Bu2BDC
produced only non-interpenetrated R2-MOF-5 (R=Et, Pr, or Bu).
All the non-interpenetrated MOFs exhibit significant porosity, as
revealed by the N2- (SBET: 1339–3483 m2/g) and H2- (uptake:
1.26–1.50 wt%) adsorption analyses. The N2-adsorption capacity
of these MOFs depends on the size of the attached alkyl groups.
Moreover, their CO2/N2 selectivity at 1 bar is higher than those
of the parent structure MOF-5, indicating that R2-MOF-5 (R=
Conclusion
In conclusion, we have demonstrated the synthesis and gas-
adsorption properties of functionalized R2-MOF-5 (R=Me, Et,
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reaction mixture to room temperature, the colorless precipitate was
Me, Et, Pr, or Bu) adsorb CO2 more selectively upon introduction
of the alkyl groups.
separated by centrifugation and washed with DMF. The solid was
further washed with CHCl3 to remove any remaining DMF and
subsequently immersed in CHCl3 overnight. The precipitate was
°
separated by centrifugation and treated at 150 C for 6 h under
high vacuum to afford MOF-5 and R2-MOF-5 (R=Me, Et, Pr, or Bu)
in the form of colorless crystals.
Experimental Section
General considerations: H NMR (400 MHz) spectra were measured
1
in CDCl3 and dimethylsulfoxide-d6 using a JEOL JNM ECS-400SS
spectrometer. The signals arising from the residual CHCl3
(7.26 ppm) in CDCl3 and C2D5HSO (2.50 ppm) in DMSO-d6 were used
as the internal standard. High-resolution mass spectra (HRMS) were
recorded using a JEOL JMSÀ T100LP (ESI and DART) mass spectrom-
eter. All melting points were measured on a SMP-300CT capillary
melting point apparatus and are uncorrected. 2,5-Dialkyl-1,4-
benzenedicarboxylic acids were synthesized in three steps from the
commercially available 1,4-dialkylbenzenes.
Acknowledgements
The authors acknowledge financial support from Nippon Soda Co.
Ltd.
1,4-Dialkyl-2,5-dibromobenzenes (2R); general procedure: Bromine
(6.39 g, 40.0 mmol) was added to a mixture of 1,4-diethylbenzene
Conflict of Interest
°
(2.68 g, 20.0 mmol) and iodine (0.51 g, 2.00 mmol) in CHCl3 at 0 C,
and the reaction mixture was then allowed to warm to room
temperature. After stirring the mixture overnight, 20% NaOH aq.
and a small amount of potassium iodide were added before the
reaction mixture was extracted with CHCl3. The organic layer was
dried over MgSO4, filtered, and all volatiles were removed in vacuo
to give 1,4-diethyl-2,5-dibromobenezene (2Et) (5.78 g, 19.8 mmol,
The authors declare no conflict of interest.
Keywords: Functionalization
storage · Metal-organic frameworks · Microporous materials
· Gas adsorption · Hydrogen
1
99%): H NMR (400 MHz, CDCl3): δ 7.38 (s, 2H), 2.68 (q, J=7.5 Hz,
4H), 1.21 (t, J=7.5 Hz, 6H); 1,4-dipropyl-2,5-dibromobenzene (2Pr):
96%, 1H NMR (400 MHz, CDCl3): δ 7.36 (s, 2H), 2.63 (t, J=7.9 Hz, 4H),
1.62 (m, 4H), 0.97 (t, J=7.9 Hz, 6H); 1,4-dibutyl-2,5-dibromobenzene
(2Bu): 86%, 1H NMR (400 MHz, CDCl3): δ 7.35 (s, 2H), 2.65 (t, J=
7.9 Hz, 4H), 1.62 (m, 4H), 1.40 (m, 4H), 0.95 (t, J=7.9 Hz, 6H).
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2,5-Dicyano-1,4-dialkylbenzenes (3R); general procedure: 2Et (1.00 g,
3.42 mmol) and CuCN (0.92 g, 10.3 mmol) were stirred in refluxing
DMF for 1 day, before the reaction mixture was poured into NH4OH
aq. The thus obtained precipitate was washed with H2O and
dissolved in CHCl3. The resulting solution was washed with brine
and the organic layer was dried over MgSO4, filtered, and all
volatiles were removed in vacuo to give 1,4-dicyano-2,5-diethylbe-
1
nezene (3Et; 0.56 g, 3.06 mmol, 90%). H NMR (400 MHz, CDCl3): δ
7.58 (s, 2H), 2.88 (q, J=7.5 Hz, 4H), 1.32 (t, J=7.5 Hz, 6H); 1,4-
1
dicyano-2,5-dipropylbenzene (3Pr): 75%, H NMR (400 MHz, CDCl3):
δ 7.55 (s, 2H), 2.82 (t, J=7.5 Hz, 4H), 1.69 (m, 4H), 1.0 (t, J=7.1 Hz,
1
6H); 1,4-dicyano-2,5-dibutylbenzene (3Bu): 95%, H NMR (400 MHz,
CDCl3): δ 7.35 (s, 2H), 2.65 (t, J=7.5 Hz, 4H), 1.56 (m, 4H), 1.37 (m,
4H), 0.95 (t, J=7.5 Hz, 6H).
2,5-Dialkyl-1,4-benzenedicarboxylic acids (4R); general procedure: A
mixture of 3Et (1.10 g, 6.00 mmol) and 10 M NaOH aq. (7.5 mL,
75.0 mmol) was stirred for 1 day in refluxing ethylene glycol
(100 mL). After cooling to room temperature, the reaction mixture
was poured into HCl aq. The resulting precipitate was filtered,
washed with H2O, and dried in vacuo to give 2,5-diethyl-1,4-
benzenedicarboxylic acid (4Et ; 1.25 g, 5.63 mmol, 94%): 1H NMR
(400 MHz, DMSO-d6): δ 7.61 (s, 2H), 2.85 (q, J=7.5 Hz, 4H), 1.11 (t,
J=7.5 Hz, 6H); 2,5-dipropyl-1,4-benzenedicarboxylic acid (4Pr): 89%,
1H NMR (400 MHz, DMSO-d6): δ 7.62 (s, 2H), 2.85 (t, J=7.5 Hz, 4H),
1.53 (m, 4H), 0.88 (t, J=7.5 Hz, 6H); 2,5-dibutyl-1,4-benzenedicar-
1
boxylic acid (4Bu): 94%, H NMR (400 MHz, DMSO-d6): δ 7.61 (s, 2H),
2.87 (t, J=7.5 Hz, 4H), 1.49 (m, 4H), 1.31 (m, 4H), 0.88 (t, J=7.1 Hz,
6H).
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a
solvothermal method: Zn(NO3)2 ·6H2O
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These are not the final page numbers!

FULL PAPERS
Dr. K. Sugamata*, Dr. S. Kobayashi,
T. Iihama, Prof. Dr. M. Minoura*
1 – 7
Gas Adsorption in R2-MOF-5 Di-
functionalized with Alkyl Groups
2,5-Difunctionalization of 1,4-benze-
nedicarboxylic acids with alkyl groups
(Me, Et, Pr, or Bu) leads to significant
changes of the adsorption properties
of their Zn-based metal-organic
MOF-5 (R=H) and R2-MOF-5 (R=Me,
Et, Pr, or Bu) depends on the size of
the attached alkyl groups. The H2-
storage value is higher for all R2-MOF-
5 (R=Me, Et, Pr, or Bu) relative to
MOF-5, and a maximum value was
observed for Pr2-MOF-5.
frameworks (MOFs) of the MOF-5
type. The N2-adsorption capacity of