Isoreticular Expansion of Metal–Organic Frameworks via Pillaring of Metal Templated Tunable Building Layers: Hydrogen Storage and Selective CO2 Capture

Article abstract of DOI:10.1002/chem.201902491

The deliberate construction of isoreticular eea-metal–organic frameworks (MOFs) (Cu-eea-1, Cu-eea-2 and Cu-eea-3) and rtl-MOFs (Co-rtl-1 and Co-rtl-2) has been accomplished based on the ligand-to-axial pillaring of supermolecular building layers. The use of different metal ions resulted in two types of supermolecular building layers (SBLs): Kagome (kgm) and square lattices (sql) which further interconnect to form anticipated 3D-MOFs. The isoreticular expansion of (3,6)-connected Cu-MOFs has been achieved with desired eea-topology based on kgm building layers. In addition, two (3,6)-connected Co-rtl-MOFs were also successfully constructed based on sql building layers. The Cu-eea-MOFs were shown to act as hydrogen storage materials with appreciable amount of hydrogen uptake abilities. Moreover Cu-eea-MOFs have also exhibited remarkable CO₂ capture ability at ambient condition compared to nitrogen and methane, due to the presence of amide functionalities.

Full text of DOI:10.1002/chem.201902491

DOI: 10.1002/chem.201902491
Communication
&
Metal–Organic Frameworks
Isoreticular Expansion of Metal–Organic Frameworks via Pillaring
of Metal Templated Tunable Building Layers: Hydrogen Storage
and Selective CO Capture
2
[a]
[a]
[c]
[b]
Kartik Maity, Karabi Nath, Michael A. Sinnwell, Radha Kishan Motkuri,
[c]
[a]
Praveen K. Thallapally, and Kumar Biradha*
gidity and symmetry of the organic linkers should be main-
tained while increasing the size of the linkers. In addition, the
reaction conditions play a significant role in obtaining series of
isoreticular MOFs as the formation of the same inorganic SBUs
Abstract: The deliberate construction of isoreticular eea-
metal–organic frameworks (MOFs) (Cu-eea-1, Cu-eea-2
and Cu-eea-3) and rtl-MOFs (Co-rtl-1 and Co-rtl-2) has
been accomplished based on the ligand-to-axial pillaring
of supermolecular building layers. The use of different
metal ions resulted in two types of supermolecular build-
ing layers (SBLs): Kagome (kgm) and square lattices (sql)
which further interconnect to form anticipated 3D-MOFs.
The isoreticular expansion of (3,6)-connected Cu-MOFs has
been achieved with desired eea-topology based on kgm
building layers. In addition, two (3,6)-connected Co-rtl-
MOFs were also successfully constructed based on sql
building layers. The Cu-eea-MOFs were shown to act as
hydrogen storage materials with appreciable amount of
hydrogen uptake abilities. Moreover Cu-eea-MOFs have
[9–13]
is essential.
The first series of isoreticular MOFs were pro-
duced by connecting octahedral-shaped inorganic SBUs
through various linear di-carboxylate linkers to produce 16
compounds with identical topologies. These MOFs were found
[9]
to exhibit high methane and hydrogen storage capacity.
The paddlewheel cluster M (COO) is one of the most
2
4
common SBUs that has been observed to form with a wide
range of metal ions. This binuclear metal cluster can act as a
square building unit, as well as an octahedral building unit de-
pending upon the nature of the polytopic ligands. Kagome lat-
tice (kgm) and square lattice (sql) are the two edge transitive
2D-nets, which can be generated from a square building
[14–20]
also exhibited remarkable CO capture ability at ambient
unit.
Pillaring of these 2D-layered nets containing paddle-
2
condition compared to nitrogen and methane, due to the
presence of amide functionalities.
wheel units into a 3D-porous architecture has been studied re-
cently and the approach has been termed as supermolecular
building layers (SBLs). Pillaring methods of SBLs involve several
strategies which include linking axial-to-axial (A-A), ligand-to-
ligand (L-L) and ligand-to-axial (L-A). Recently amide and
amine functionalized 3-connected organic ligands have been
shown to form Cu-MOFs with eea and rtl topology, respective-
ly, based on the L-A pillaring strategy. These Cu-MOFs were ex-
Metal–organic frameworks (MOFs) have grown rapidly as effec-
tive porous materials in the last couple of decades due to their
[
1–8]
utility in various applications.
The MOFs provide a unique
[18]
advantage for the introduction of desired functionalities, and
therefore properties, by the judicious selection of appropriate
organic building block prior to assembly of the components.
The substantial challenge of reticular chemistry is associated
with the synthesis of crystalline materials using appropriate or-
ganic linkers for connecting symmetrical secondary building
units (SBUs) into extended frameworks with predefined topolo-
gies. For such isoreticular synthesis of series of MOFs, the ri-
plored for CO capture ability and hydrocarbon separations.
2
Design and synthesis of porous MOFs is of importance for
gas storage and separation purposes, impacting day-to-day as-
pects of society, such as environmental protection and energy
utilization. In particular, the capture of carbon dioxide from the
atmosphere is a necessity to minimize the greenhouse effect,
and the storage of hydrogen and methane gases is absolutely
[21,22]
crucial for the global utilization of clean energy.
For the
last few decades, the world’s flourishing energy demand is
[
a] Dr. K. Maity, K. Nath, Prof. K. Biradha
Department of Chemistry, Indian Institute of Technology
Kharagpur 721302 (India)
being furnished by the combustion of fossil fuels, resulting in
[23–34]
an ever increasing CO concentration in the atmosphere.
2
The combined effect of CO emission on climate, and an inade-
E-mail: kbiradha@chem.iitkgp.ernet.in
2
quate supply of fossil fuels have prompted the development
of alternative fuel sources. Hydrogen is considered as one of
the more favourable energy sources for the replacement of
coal and gasoline, due to its high gravimetric heat of combus-
tion and zero carbon emission. Therefore, the use of hydrogen
as fuel, for automobiles and various other purposes, necessi-
[
b] Dr. R. K. Motkuri
Energy and Environment Directorate
Pacific Northwest National Laboratory, Richland, WA 99352 (USA)
[
c] Dr. M. A. Sinnwell, Dr. P. K. Thallapally
Physical and Computational Sciences Directorate
Pacific Northwest National Laboratory, Richland, WA 99352 (USA)
Supporting information and the ORCID identification number(s) for the
author(s) of this article can be found under:
[35–38]
tates the exploration of hydrogen storage materials.
https://doi.org/10.1002/chem.201902491.
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In this contribution, the gradual expansion of the frame-
works has been achieved for an isoreticular series of Cu-MOFs
by maintaining the underlying eea-topology. The isophthalate
moieties of the ligands form the anticipated 2D-layers with
kgm-topology (Scheme 1) in combination with the metal pad-
green coloured single crystals of Cu-MOF. The crystal structure
of the as synthesized MOF was confirmed by single-crystal X-
ray diffraction and has been formulated as {[(PIA1) Cu ](solv.) } ,
6
6
x n
(Cu-eea-1). The structural analysis revealed that Cu-eea-1 crys-
tallised in the R 3¯ space group and the asymmetric unit con-
II
II
tains one unit each of PIA1 and Cu ions. The Cu ion was
found to exhibit a distorted square pyramidal coordination ge-
II
ometry and two such types of square pyramidal Cu centre
II
produce the Cu (COO) paddlewheel SBU. The Cu centres of
2
4
the dinuclear Cu -paddlewheel are equatorial coordinated by
2
four carboxylate oxygen atoms and the pyridyl nitrogen from
two different ligands occupied two apical positions.
The isophthalate moieties in Cu-eea-1 are involved in bridg-
ing of the square building Cu -paddlewheel in order to pro-
2
duce 2D-kgm layers. Further these 2D-kgm layers are intercon-
nected by the pyridyl moieties through the L-A pillaring
method to produce a porous 3D-framework. The PIA1 unit
with a T-shaped geometry acts as a 3-connected node, where-
Scheme 1. Two possible edge transitive 2D-nets from square building unit:
Kagome and square lattice.
as the Cu -paddlewheel serves as a 6-connected node to form
2
a (3,6)-connected framework with the desired eea-topology.
The pillaring of the kgm-layers occurs in such a way that the
six-membered ring window of a layer interconnects two three-
membered ring windows from the adjacent kgm-sheets to
generate a large and prolate-ellipsoid-shaped Cage A. Further
in between a pair of Cage A, another type of cage has been
formed by the connection between a pair of three-membered
ring windows from the adjacent two layers, which is more
spherical in nature (cage B). Cage A is encircled by six PIA1
dlewheel, whereas the pyridyl group, a second functionality,
connects the adjacent layers to lead to the formation of (3,6)-
II
II
connected 3D-MOFs. Further the use of Co salt instead of Cu
salt resulted in the formation of sql building layers. The result-
ing Cu-eea-MOFs have been explored for selective capture of
CO over nitrogen and methane. Further the Cu-MOFs were
2
also found to exhibit remarkable hydrogen storage capability.
II
However the Co -based rtl MOFs hardly showed porous nature,
possibly due to collapse of the pores in one case and the pres-
ence of interpenetration that totally occupied the voids in an-
other case.
units and twelve Cu -paddlewheel clusters (length 26 ꢁ),
2
whereas Cage B is surrounded by six Cu -paddlewheel clusters
2
and six PIA1 units (lengthꢀ16 ꢁ, widthꢀ12 ꢁ) (Figure 1).
It has been observed that size of the cavities and the separa-
tion between the kgm-layers are larger in Cu-eea-1 compared
to the previously studied Cu-based (Cu-INIA) eea-MOF, con-
structed by using INIA. As our aim was to build a series of eea-
MOFs with reticular expansion of the framework, so another
The organic building units used in this work (Scheme 2) are
the elongated version of the previously explored T-shaped
[
16,18]
ligand, 5-(isonicotinamido) isophthalic acid (H INIA).
The li-
2
gands, 5-(3-(pyridin-3-yl)acrylamido)isophthalic acid (H PIA1), 5-
2
(
(
3-(pyridin-4-yl)acrylamido)isophthalic acid (H PIA2) and 5-(4-(2-
2
pyridin-4-yl)vinyl)benzamido)isophthalic acid (H PIA3) were
2
synthesized by condensation reactions of dimethyl-5-amino-
isophthalate with 3-pyridylacrylic acid, 4-pyridylacrylic acid and
4-(2-(pyridin-4-yl)vinyl)benzoic acid, respectively, followed by
hydrolysis. The synthesized molecules were characterized by
1
H NMR spectroscopy prior to their use for MOFs synthesis.
The solvothermal reaction of copper nitrate and H PIA1 in a
2
DMF-EtOH-H O solvent mixture resulted in needle-shaped
2
Figure 1. Illustrations for Cu-eea-MOFs: a) kgm-layers formed by the iso-
phthalate moieties; b) two types of cages: cage A (yellow, prolate-ellipsoid
shaped) and cage B (pink, spherical); c) overall (3,6)-connected MOF with
eea-topology.
Scheme 2. Molecular structure of the organic building blocks.
&
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couple of ligands were designed, H PIA2 and H PIA3, by shift-
linkers, over the kgm-sheet observed in Cu-eea MOFs. In this
case the sql-layers are also interconnected through the pyridyl
coordination in an L-A pillaring mode to produce 3D-frame-
works. The overall 3D-network was found to have a (3,6)-con-
nected rtl-topology, where the ligand acted as a 3-connected
2
2
ing the position of N-donor coordination sites of the pyridine
ring, and also increasing the length of the spacer between iso-
phthalate and pyridyl moieties. The solvothermal reaction of
H PIA2 and H PIA3 with copper nitrate in DMF/acetic acid sol-
2
2
vent system afforded block-shaped green coloured single crys-
tals of the corresponding Cu-MOFs. The crystal structures were
determined by single-crystal X-ray diffraction and the formulas
were found to be {[(PIA2) Cu ](solv.) } , (Cu-eea-2) and
node and the Co -paddlewheel as 6-connected node. The
2
square windows from sql-layers are comprised of four iso-
phthalate units; the adjacent pairs of benzene moieties point
up, while the other two benzene moieties point down. The dis-
tances between two successive sql-layers was found to be
13.6 ꢁ and pillaring of the sql-layers generates a rectangular
grid-type cage with the dimension of approximately 10ꢂ10ꢂ
13.6 ꢁ (Figure 3).
6
6
x n
{
[(PIA3) Cu ](solv.) } , (Cu-eea-3).
6 6 x n
As anticipated the two expanded MOFs, Cu-eea-2 and Cu-
eea-3 were found to be isoreticular with the previous one,
having eea-topology. The sizes of the two types of cages have
also been found to increase. The crystallographic parameters
revealed a gradual increase of c-axis length compared to the
earlier synthesized eea-MOF as: 37.8 ꢁ (Cu-INIA), 42.6 ꢁ (Cu-
eea-1), 44.7 ꢁ (Cu-eea-2) and 52.2 ꢁ (Cu-eea-3). As the length
of the middle spacer for the ligands were increased, the sepa-
ration between the kgm-layers have been also found to be in-
creased (Figure 2). The inter-layer distances between the two
successive kgm-layers are 12.67 ꢁ (Cu-INIA), 14.19 ꢁ (Cu-eea-
1
), 14.89 ꢁ (Cu-eea-2) and 17.42 ꢁ (Cu-eea-3).
Figure 3. Illustrations for Co-rtl-1: a) sql-layers formed by the isophthalate
moieties; b) overall (3,6)-connected MOF with rtl-topology; side view of the
rectangular grid type cage: c) Co-rtl-1; d) Co-rtl-2.
The ligand H PIA3 was employed along with cobalt(II) salts
2
for the construction of desired rtl-MOFs, anticipating the in-
crease in size of the cages as for the Cu-eea MOFs series. The
Figure 2. Gradual expansion of the cavity sizes as well as separation be-
tween the kgm-layers in a) Cu-INIA; b) Cu-eea-1; b) Cu-eea-2; d) Cu-eea-3.
solvothermal reaction of H PIA3 and cobalt nitrate in DMF-
2
EtOH-H O resulted in deep-purple coloured block-shaped crys-
2
As discussed earlier, the square building unit has an ability
to generate sql SBL other than the kgm-sheet; these organic
building units were further employed to construct MOFs with
another transition metal in order to explore the versatility of
tals. The single-crystal X-ray diffraction analysis revealed the
space group was P2 /c and the asymmetric unit was composed
1
II
of one unit each of Co and PIA3 ions, with the formula
{[(PIA3) Co ](solv.) } , (Co-rtl-2). Further structural analysis
2
2
x n
the SBL approach. The solvothermal reaction of H PIA2 with
showed that Co-rtl-2 exhibited a (3,6)-connected two-fold in-
terpenetrated 3D-framework with rtl-topology. The desired ex-
pansion in terms of size of the cage (dimension approximately
10ꢂ10ꢂ20 ꢁ) was achieved, but the huge voids of the frame-
works were occupied by the two-fold interpenetration of the
networks. The interlayer separation of sql-layers within the rtl-
framework was found to be ꢀ20 ꢁ (Figure 3).
2
cobalt nitrate in DMA-H O solvent system afforded dark purple
2
coloured block-shaped single crystals. The crystal structure was
determined by single crystal X-ray diffraction, and the MOF has
been formulated as {[(PIA2) Co ](solv.) } , (Co-rtl-1). The struc-
2
2
x n
tural analysis revealed that Co-rtl-1 crystallised in P2 /c space
1
II
group and the asymmetric unit contains one unit each of Co
II
and PIA2 ions. Co ions exhibited a distorted square-pyramidal
The permanent porosities of Cu-eea MOFs were investigated
by nitrogen isotherms at 77 K for the activated phase of those
MOFs. The nitrogen uptake of Cu-eea-1 exhibited an adsorp-
tion isotherm with an unusual stepwise uptake, which led to
generation of a prominent hysteresis between the adsorption
and desorption curves, and which may be due to the flexibility
of the frameworks. The amount of nitrogen uptake up to the
geometry with four equatorial positions coordinated by car-
boxylates and the apical position being occupied by the pyrid-
II
yl moiety. Two such penta-coordinated Co centres produced a
Co -paddlewheel cluster in a similar fashion as in Cu-eea MOFs.
2
Interestingly, the square building unit, Co -paddlewheel clus-
2
ter preferred the formation of sql-layers through isophthalate
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3
À1
first step was found to be ꢀ219 cm g , whereas the total
Apart from the hydrogen storage ability, these materials
amount of nitrogen adsorption by the framework at 1 bar was
were explored for their CO capture ability due to the presence
2
3
À1
ꢀ
278 cm g . The Brunauer–Emmett–Teller (BET) surface area
of amide-decorated cages and channels within the network of
2
À1
for Cu-eea-1 was estimated to be 687 m g . Further the nitro-
gen adsorption isotherms for Cu-eea-2 and Cu-eea-3 were
also measured and the corresponding BET surface areas were
the MOFs. As anticipated, the Cu-eea-1, Cu-eea-2 and Cu-eea-
3 have shown remarkable CO capture ability at ambient con-
2
ditions, along with gradual increases in adsorption values as
the pore size increases. The MOF containing smaller cavities,
2
À1
found to be 873 and 922 m g respectively, with reversible
type-I isotherms. A small hysteresis was observed in the case
of Cu-eea-2, due to the presence of a slight plateau in the de-
sorption isotherm (Figure 4). We note here that the framework
of Co-rtl-1 was found to collapse during the activation process,
and it hardly showed any kind of porous behaviour. The pres-
ence of two-fold interpenetration in Co-rtl-2 makes it a non-
porous material.
3
À1
Cu-eea-1 can uptake 105 cm g of CO2 whereas Cu-eea-2
with somewhat bigger cavities showed better CO uptake ca-
2
3
À1
pacity (114 cm g ) at 273 K and 1 bar pressure. Further Cu-
eea-3, with larger cages and channels compared to the other
3
À1
two, can capture 143 cm g of CO which was found to be
2
the highest among the present Cu-eea-MOFs (Figure 4). The
CO uptake capacities for the present MOFs are comparable
2
All the MOFs, Cu-eea-1, Cu-eea-2 and Cu-eea-3, were ana-
lysed for their ability towards the storage of hydrogen at ambi-
ent pressure. Cu-eea-1 was found to be capable of storing
with some of the previously explored Cu-based MOFs for CO
2
À1
3
À1
3
capture (e.g., JUC-1000: 125 cm g ; Cu-NTTA: 115.6 cm g ;
À1
À1 [5,30,16,33]
LIFM-10: 129.5 mLg ; LIFM-11: 129.5 mLg ).
(Table S2,
3
À1
142 cm g (1.27 wt.%) of hydrogen at 77 K and one bar pres-
Supporting Information) The adsorption enthalpies (Q ) for
st
À1
sure without any sort of hysteresis in adsorption and desorp-
tion isotherms, in contrast to its nitrogen adsorption isotherm.
The other two MOFs, Cu-eea-2 and Cu-eea-3, also exhibited a
CO adsorption were found to be 27.5, 36 and 17.7 kJmol for
2
Cu-eea-1, Cu-eea-2 and Cu-eea-3, respectively, at zero cover-
age.
3
À1
significant amount of hydrogen uptake capacity of 180 cm g
The selective capture of CO over nitrogen at ambient tem-
2
3
À1
(
1.61 wt.%) and 202 cm g (1.8 wt.%), respectively, at 77 K and
perature and pressure was analysed for all the Cu-eea MOFs
given their practical importance in removal of CO2 from flue
gas (mixture of N and CO ) produced in the coal-fired power
ambient pressure. It can be concluded that the change in posi-
tion of pyridyl nitrogen, and also the expansion of the spacer,
led to the increase in the hydrogen uptake values (Figure 4).
The hydrogen storage capabilities exhibited by these MOFs are
comparable with some of the highly porous MOFs which in-
clude IRMOF-6, MOF-177 and PCN-68. (Table S3, Supporting In-
formation)
2
2
plants. All the MOFs were found to exhibit significant CO2
uptake capacity at ambient condition, whereas they hardly
adsorb nitrogen under similar conditions. Cu-eea-1 was found
3
À1
to adsorb 4 cm g of nitrogen at 298 K and 1 atm pressure,
3
À1
whereas it can capture about 66.9 cm g of CO at the same
2
Figure 4. a) Nitrogen isotherm for Cu-eea MOFs at 77 K and 1 bar pressure; b) hydrogen uptake isotherm for the Cu-eea MOFs at 77 K and 1 bar; c) CO
2
ad-
sorption isotherms for the Cu-eea MOFs at 273 K and 1 bar; Selective adsorption of CO
pressure): d) Cu-eea-1; e) Cu-eea-2; f) Cu-eea-3.
2
over nitrogen and methane at ambient conditions (298 K and 1 bar
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Communication
conditions. The other two MOFs have also exhibited similar be-
Acknowledgements
haviour as Cu-eea-2 and Cu-eea-3 were found to uptake 60
3
À1
and 81.7 cm g of CO at 298 K and 1 atm pressure, respec-
2
We acknowledge SERB (EMR/2017/001499), New Delhi, India,
for financial support and DST-FIST for the single-crystal X-ray
diffractometer. K.M. thanks UGC and IIT Kharagpur for research
fellowship.
tively, but they exhibited little nitrogen adsorption ability
3
À1
under the same conditions (3.2 and 2.4 cm g ). The adsorp-
tion selectivity was also maintained at 273 K as the Cu-eea-
MOFs adsorbed a lesser amount of nitrogen (10, 7 and
3
À1
4
1
cm g , respectively) compared to CO (105, 114 and
2
3
À1
43 cm g , respectively) (Figure 4).
Conflict of interest
Further, Cu-eea-MOFs were also analysed for their methane
adsorption propensity at ambient conditions. The methane ad-
sorption isotherm revealed that the Cu-eea MOFs have very
little tendency towards its storage. The Cu-eea MOFs were
The authors declare no conflict of interest.
3
À1
Keywords: CO capture · hydrogen storage · isoreticular ·
2
found to uptake 17, 14 and 9 cm g of methane, respectively,
at 298 K and 1 bar pressure which are much less than the
metal–organic frameworks · supermolecular building layers
3
À1
amounts of CO adsorbed (66.9, 60, and 81.7 cm g ) at the
2
same conditions. The methane adsorption studies were also
carried out at 288 and 278 K, but did not show much improve-
ment in adsorption values. At 278 K and 1 bar pressure the
amounts of methane adsorbed were found to be 25.8, 26.1
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gands utilized here for the MOFs synthesis contain larger
spacers compared to previously explored ones, and conse-
quently the gradual expansion of framework dimensions has
been achieved for the desired MOFs whilst retaining the un-
derlying eea-topology. Further the change of metal ions from
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Manuscript received: May 31, 2019
Accepted manuscript online: September 6, 2019
Version of record online: && &&, 0000
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ꢀ 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Communication
COMMUNICATION
Pillar to post: Ligand-to-axial pillaring
of supermolecular building layers leads
to a number of isoreticular metal–or-
ganic frameworks. The copper com-
pounds can act as hydrogen stores, and
show remarkable, and selective, CO2
capture.
&
Metal–Organic Frameworks
K. Maity, K. Nath, M. A. Sinnwell,
R. K. Motkuri, P. K. Thallapally, K. Biradha*
&
& – &&
Isoreticular Expansion of Metal–
Organic Frameworks via Pillaring of
Metal Templated Tunable Building
Layers: Hydrogen Storage and
Selective CO Capture
2
Chem. Eur. J. 2019, 25, 1 – 7
www.chemeurj.org
7
ꢀ 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ