Cadmium Metal-Organic Frameworks Based on Ditopic Triazamacrocyclic Linkers: Unusual Structural Features and Selective CO2 Capture

Article abstract of DOI:10.1021/acs.cgd.7b00217

Two three-dimensional cadmium metal-organic frameworks with general formula [Cd₂(L¹)(H₂O)₃](NO₃)_0.7(HCOO)_0.2Br_0.1 (Cd₂L¹, L¹ = 1,4,7-tris(4-carboxybenzyl)-1,4,7-triazacyclononane) and Cd(HL²)(H₂O)₂ (CdL², L² = 1,4,7-tris(3-(4-benzoate)prop-2-yn-1-yl)-1,4,7-triazacyclononane) based on 1,4,7-triazacyclononane N-functionalized by different arylcarboxylic acids were prepared under solvothermal conditions and characterized by single crystal X-ray analysis and porosity measurements. The crystal structure of Cd₂L¹ reveals a cationic net with a bcs topology, and nodes are constituted by dinuclear cadmium complexes, in which each cadmium atom adopts a hexacoordinated environment involving both the carboxylate and the cyclic amine. In contrast, CdL² displays a 2-fold interpenetrated structure with a pcu topology. In this net, the node is a mononuclear complex in which the Cd atom exhibits a seven-coordination geometry. Both materials show a high permanent porosity and good CO₂ adsorption properties with a high selectivity over N₂ and CH₄. The adsorption capacity and selectivity for CO₂ were calculated from a multisite Langmuir isotherm model and the ideal adsorbed solution theory, which gave insights into the nature of solid-gas interactions and showed the influence of interpenetration or polarity of the charged framework on their adsorption properties.

Full text of DOI:10.1021/acs.cgd.7b00217

Subscriber access provided by Binghamton University | Libraries
Article
Cadmium Metal–Organic Frameworks Based on Ditopic Triazamacrocyclic
Linkers: Unusual Structural Features and Selective CO2 Capture
Hervé Feuchter, Guillaume Ortiz, Yoann Rousselin, Alla Lemeune, and Stéphane Brandès
Cryst. Growth Des., Just Accepted Manuscript • Publication Date (Web): 31 May 2017
Downloaded from http://pubs.acs.org on June 1, 2017
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Crystal Growth & Design is published by the American Chemical Society. 1155
Sixteenth Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 38
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
Cadmium Metal–Organic Frameworks Based on Ditopic
Triazamacrocyclic Linkers: Unusual Structural Features and
Selective CO Capture
2
†‡
†§
†
†
,†
Hervé Feuchter, Guillaume Ortiz, Yoann Rousselin, Alla Lemeune, Stéphane Brandès*
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
†
Institut de Chimie Moléculaire de l’Université de Bourgogne (ICMUB), Université de
Bourgogne Franche-Comté, UMR CNRS 6302, F-21078 Dijon, France
e-mail: stephane.brandes@u-bourgogne.fr
2
+
Two assemblies involving Cd
functionalized by different arylcarboxylic acids were envisioned for constructing metal-
organic frameworks with general formula [Cd (L )(H O) ](NO ) (HCOO) Br (Cd L ,
L = 1,4,7-tris(4-(carboxybenzyl)-1,4,7-triazacyclononane ) and Cd(HL )(H
ions and 1,4,7-triazacyclononane (TACN) N-
1
1
2
2
3
3 0.7
0.2 0.1
2
1
2
2
2
2 2
O) (CdL , L
=
1,4,7-tris(3-(4-benzoate)prop-2-yn-1-yl)-1,4,7-triazacyclononane). Materials were
prepared under solvothermal conditions and characterized by single crystal X-ray
analysis and porosity measurements. The two crystal structures show an open-framework.
Cd
each cadmium atom adopts a hexacoordinated environment involving both the carboxylate
and the cyclic amine. In contrast, CdL displays a two-fold interpenetrated structure with a
pcu topology. In this net, the node is a mononuclear complex in which the Cd atom exhibits a
seven-coordination geometry. Both materials show a high permanent porosity and interesting
CO adsorption properties with a high selectivity over N and CH . The adsorption capacities
2 2 4
and selectivities for CO were calculated from a multisite Langmuir isotherm model and IAST
theory, which gave insight into the nature of solid-gas interactions and evidenced the
influence of interpenetration or polarity of the charged framework on their adsorption
properties.
1
2
L reveals a cationic net with nodes constituted by dinuclear cadmium complexes in which
2
2
OH
O
CO N CH CO
2 2 4
O
CO N CH CO
2 2 4
n
N
N
OH
n
N
Cd2+
Cd2+
n
n = 0
n = 1
HO
O
CO
2
N2 CH4 CO
Stéphane Brandès
Institut de Chimie Moléculaire de l’Université de Bourgogne (ICMUB), Université de
Bourgogne Franche-Comté, UMR CNRS 6302, F-21078 Dijon, France
e-mail: stephane.brandes@u-bourgogne.fr - http://www.icmub.com
1
ACS Paragon Plus Environment

Crystal Growth & Design
Page 2 of 38
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Cadmium Metal–Organic Frameworks Based on Ditopic
Triazamacrocyclic Linkers: Unusual Structural Features and
Selective CO Capture
2
†‡
†§
†
†
,†
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Hervé Feuchter, Guillaume Ortiz, Yoann Rousselin, Alla Lemeune, Stéphane Brandès*
†
Institut de Chimie Moléculaire de l’Université de Bourgogne (ICMUB), Université de
Bourgogne Franche-Comté, UMR CNRS 6302, F-21078 Dijon, France
e-mail: stephane.brandes@u-bourgogne.fr
ABSTRACT: Two 3D cadmium metal-organic frameworks with general formula
1
1
1
[
Cd (L )(H O) ](NO ) (HCOO) Br (Cd L , L = 1,4,7-tris(4-(carboxybenzyl)-1,4,7-
2
2
3
3 0.7
0.2 0.1
2
2
2
2
L
triazacyclononane ) and Cd(HL )(H O) (CdL ,
= 1,4,7-tris(3-(4-benzoate)prop-2-yn-1-
2
2
yl)-1,4,7-triazacyclononane) based on 1,4,7-triazacyclononane (TACN) -functionalized
N
by different arylcarboxylic acids were prepared under solvothermal conditions and
characterized by single crystal X-ray analysis and porosity measurements. Crystal
1
structure of Cd L reveals a cationic net with a bcs topology, and nodes are constituted by
2
dinuclear cadmium complexes, in which each cadmium atom adopts a hexacoordinated
2
environment involving both the carboxylate and the cyclic amine. In contrast, CdL displays a
two-fold interpenetrated structure with a pcu topology. In this net, the node is a mononuclear
complex in which the Cd atom exhibits a seven-coordination geometry. Both materials show a
high permanent porosity and good CO adsorption properties with a high selectivity over N
2
2
and CH . The adsorption capacity and selectivity for CO were calculated from a multisite
4
2
Langmuir isotherm model and the ideal adsorbed solution theory (IAST), which gave insights
into the nature of solid-gas interactions and evidenced the influence of interpenetration or
polarity of the charged framework on their adsorption properties.
2
ACS Paragon Plus Environment

Page 3 of 38
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
INTRODUCTION
Microporous solids are among the most studied materials by chemists and physicists in
recent years. Many of them are essential in different biomimetic and industrial processes,
and are for this reason considered as multifunctional materials. Besides inorganic porous
solids such as zeolites, Metal-Organic Frameworks (MOFs) have been considered as a
new class of porous molecular materials and have been widely utilized over the last two
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1,2
decades. MOFs are crystalline materials constituted of metallic ions or polynuclear
clusters coordinated to organic linkers to form porous 2D or 3D structures. The organic
linkers, metal ions and supramolecular assembly can be tuned to control the chemical
functionalities, the porosity, the topology and the nanoscale morphology of the crystalline
structure, allowing a systematic and fine tailoring of their porous architecture and reactivity,
which represents a fundamental advance in the field of materials science. The versatility of
MOFs is based on the large choice of organic linkers and inorganic components that resulted
3
in more than 20,000 MOFs structures with single topologies. Most of them are porous with
3
-10
nanometer size of the pores, which makes such materials attractive for many applications
11,12
13-16
such as hydrogen storage,
selective adsorption and gas separation,
heterogeneous
17
18
19
catalysis, chemical sensors and nanomedicine
.
In particular, MOFs are regarded as promising candidates for the capture of
greenhouse gases and especially carbon dioxide, which is becoming a growing source of
15,16,20-23
concern nowadays.
The use of MOFs as sorbents has received great attention,
because such materials are able to outperform other benchmark porous solids like zeolites or
activated carbon. It is well-known that the postcombustion flue gas from coal-fired power
plants contains about 15% CO and 85% N , whereas the contents of CO in natural and
2
2
2
landfill gas (mixture of CO
2
4
and CH ) used for the precombustion process are about 5% and
5
0%, respectively. The separation of CO
2
from CH
4
is then required in order to increase the
3
ACS Paragon Plus Environment

Crystal Growth & Design
Page 4 of 38
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
energy density of the fuel gases and reduce pipeline corrosion concerns induced by the acidity
1
5,20
of CO2.
In these contexts, cutting edge selective adsorption processes with porous
4
from N and CH .
materials are awaited to achieve efficient capture and recovery of CO
2
2
Therefore, MOFs hold promise to address this challenging issue benefiting from their modular
synthesis and their tunable porosity and functionality.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Economically viable MOFs for CO capture require to present a high selectivity and
2
gas uptake, as well as a moderate enthalpy of adsorption for recovering and recycling
2
1
them with a low energy consumption. Although a high surface area is a prerequisite to
ensure a high accessibility of the adsorption sites, the strength of CO interactions with the
2
framework is also a key factor associated with uptake, selectivity and regeneration ability.
Thus, many efforts have been devoted to enhance the CO affinity and selectivity using
2
d
ifferent strategies, including the introduction of Lewis basic sites into the
1
5,21,24-33
framework,
the generation of coordinatively unsaturated metal sites exposed to
34-38
39
gas molecules binding,
or addition of cationic or anionic charges. Ligand
40,41
40-43
shortening
or framework interpenetration control
are also good alternatives for a
fine control of the pore size because of the presence of microcavities that endows a better
performance for selective CO capture. One interesting approach to develop innovative
2
sorbents is then to combine several of these structural features to provide a careful tuning
of gas adsorption properties.
Till now, most of porous coordination polymers were prepared from polydentate linkers
functionalized by only one type of coordination sites such as carboxylate, nitrogen or
phosphonate donors. An appealing strategy that implies the assembly of polytopic organic
ligands bearing at least two distinct coordinating groups was developed in the last years.
Actually, considerable research efforts were devoted to the preparation of materials
44-47
48,49
50-54
containing strong chelating agents such as dipyrrins,
salens,
porphyrins,
4
ACS Paragon Plus Environment

Page 5 of 38
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
5
5-59
60
bipyridine
or phenanthroline ligands. The use of such metalloligands was explored in
order to bring multifunctionality to the framework and offered the opportunity to enhance gas
38,48,49,51,59,61-66
binding properties and to introduce catalytic sites in the resulting MOFs.
Such
67,68
an approach can be used for the subsequent chemical transformation of CO
2
.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
However, the design and preparation of porous and crystalline materials based on
metalloligands still remain challenging. A fine control of their assembly can be gained by
systematically adjusting the denticity and the size of the linkers, while the overall connectivity
is determined by both the topology of the ligand and the nature of the metal ion.
Our strategy implies the utilization of azamacrocycles as strong chelators for
supramolecular assembling since their polydentate and cyclic features allow a rational control
of the coordination sphere around metal ions. Azamacrocylic ligands are still scarce in the
field of MOFs despite their original geometries, which can give rise to unusual structures
67-73
and topologies.
The presence of N-donor atoms enables the complexation of metal
74
ions, allowing the preparation of metalloligands prior to the formation of a network.
Actually, the assembly relies on the fact that the coordination sphere of the metal ion is not
saturated when using non-functionalized polyazamacrocycles like 1,4,7-triazacyclononane
(TACN), 1,4,8,11-tetraazacyclotetradecane (cyclam) or 1,4,7,10-tetraazacyclododecane
(cyclen). Consequently, the supramolecular assembly requires the utilization of a second
7
5-79
ligand capable of coordinating unoccupied sites of the metal ion.
However, a more straightforward assembling of macrocycles is favored when additional
donor atoms from carboxylate are anchored in a divergent manner on a polyazamacrocyclic
scaffold. Such polytopic and polydentate ligands can be simply obtained by functionalization
67,68,70,73,78
of the nitrogen atoms by carboxylate pendent arms.
Only rare examples of
permanently porous MOFs constructed from such N-functionalized polyazamacrocycles have
6
7,70,78,80,81
already been reported,
because of the flexibility of the cyclic chelate and the wide
5
ACS Paragon Plus Environment

Crystal Growth & Design
Page 6 of 38
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
diversity of coordination geometries adopted by transition metals. Nevertheless, this synthetic
strategy provided MOFs with new functionalities, giving rise to various applications such as
67,70
73
68
82
selective gas adsorption,
separation of isomers, catalysis or biomedical imaging.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Ligands that possess a C
geometry like TACN and its N-functionalized derivatives are
3
ideally suited to generate mono- and polynuclear metal complexes for the construction of
MOFs since TACN is a tridentate ligand that coordinates facially to a metal ion, leaving two
70
or three free coordination sites. Such derivatives are of interest in the field of selective metal
83
84
85-88
89,90
ions or anions sensors, therapy, medical imaging diagnosis
and hybrid materials,
and to our knowledge only two coordination polymers based on N-functionalized TACN were
70,80
reported so far.
2
+
Our group has previously described a stable crystalline material obtained with Zn ions
and this scaffold, and the material has shown high porosity with selective capture of CO over
2
70
N
2
. This work paves a way to prepare a new family of porous materials using the isoreticular
9
1
paradigm developed along the last two decades. This strategy enables the successful
synthesis of a large diversity of MOFs with a fine tuning of their pore size and an
3
,91-93
improvement of their specific surface area and gas storage properties.
In this work we
address the question as to whether the isoreticular concept can be a useful tool for the
construction of new porous structures with a TACN platform. In addition, the role of the
spacers length anchored on the TACN has been investigated to provide diversity both in
structures and adsorption properties.
In the pursuit of new high-performance CO gas separation materials
,
we have selected
2
1
t
wo TACN macrocycles N-functionalized by benzylcarboxylate (L ) or propynylbenzoate
2
(
L ) arms possessing different lengths, and porous materials were prepared by assembling of
2+
these ligands with Cd ions. Herein we describe the synthesis of the ligands and
1
corresponding Cd-MOFs. Structures and adsorption properties of two Cd-MOFs, Cd
2
L and
6
ACS Paragon Plus Environment

Page 7 of 38
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
2
CdL , have been thoroughly analyzed based on XRD data on single crystals and powders,
FTIR, TGA and porosity measurements as well as selective CO capture and separation
2
1
2
towards N
2
, CH
4
and CO. The materials Cd
2
L and CdL represent rare examples of
permanently porous MOFs belonging to the family of polyazamacrocycles that demonstrates
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2
interesting properties for the selective adsorption of CO .
EXPERIMENTAL SECTION
The experimental section associated to ligand, material synthesis and their
characterizations are reported in the Supporting Information.
RESULTS AND DISCUSSION
1
1
Two linkers presenting a high flexibility (H
3
L and H L , Figure 1), were used for the
3
preparation of porous architectures thanks to coordination of metallic centers: i) inside the
70
cavity of the macrocycle, thus providing a metalloligand, and ii) by the carboxylate groups
allowing 3D polymer expansion and binding on the coordinatively unsaturated metallic ions
of the metalloligand.
1
Ligand synthesis. Polytopic H
3
L linker was prepared as previously described by our
7
0
2
group. The five-steps synthetic approach to polyazamacrocycle H
3
L bearing longer
carboxylate-functionalized pendent arms is summarized in Scheme 1 (see Supporting
Information for details). Commercially available 4-bromobenzoic acid was protected as
methyl ester (1) and was introduced in the Sonogashira reaction with propargylic alcohol to
afford methyl 3-(4-benzoate)-1-hydroxyprop-2-yn-1-yl (2) in 57 % overall yield. This alcohol
4
was converted in good yield (67%) to the corresponding bromide 3 using CBr as a
brominating agent. N-alkylation of TACN by bromide 3 was achieved in DMF in the presence
7
ACS Paragon Plus Environment

Crystal Growth & Design
Page 8 of 38
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
of K CO as a base to give the expected triester 4 in 63% yield. In the final step, the
2
3
2
saponification of 4 was performed using NaOH in a THF/MeOH mixture. H L was isolated
3
in its protonated form after acidification of the reaction mixture with hydrobromic acid.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
Figure 1. Structure of polytopic ligands H L and H L studied in this work.
3
3
2
Scheme 1. Synthesis of H L .
3
2+
Synthesis and preliminary characterization of the materials. The choice of Cd was
2
+
guided by its chemical analogy with Zn ions and its propensity to adopt hexa- to octa-
coordinated environments in view to promote the growth of 3D frameworks. Crystals of Cd
materials were obtained in solvothermal conditions using Cd(NO
3
)
2
·4H
2
O as a metal salt and
8
ACS Paragon Plus Environment

Page 9 of 38
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
1
2
a 0.015 M solution of H L or H L linkers in a 10:1:1 mixture ratio of DMF, ethanol and
3
3
water at 80 °C or 100 °C, respectively, for 24 hours in a sealed Pyrex tube. Octahedral and
1
rectangular parallelepiped-shaped crystals were obtained in 62% and 49% yield for H
3
L and
2
H
3
L , respectively. The composition of the solids was inferred from ICP-AES, elemental
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
analyses, bromide titration with silver nitrate, SEM and H NMR spectroscopy. The material
1
based on H L gave a metal:ligand ratio equal to 2. SEM/EDS analysis revealed the presence
3
1
of bromine atoms in the solid. H NMR analysis of the digested solid in DMSO-d /DCl also
6
showed the presence of a formate anion resulting from the degradation of DMF in
solvothermal conditions. The presence of bromide, formate and nitrate in the solid pointed out
the formation of
a
cationic framework. Overall,
a
general formula of
1
1
[
Cd (L )(H O) ](NO ) (HCOO) Br (= Cd L ) was inferred. For material prepared from
2
2
3
3 0.7
0.2 0.1
2
2
H L , the analyses gave a metal:ligand ratio equal to 1 and revealed the absence of bromide
3
and formate anions in the solid. This result unveiled the neutral charge of the framework and
therefore the monoprotonation of the ligand in order to satisfy the charge balance. A general
2
2
2 2
formula of [Cd(HL )(H O) ] (= CdL ) was then inferred. Moreover, the FTIR spectra present
signatures of different carboxylate vibrations for both materials (Figure S2), thus indicating
several coordination modes of this donor group. Therefore, the analytical data demonstrate
2
1
that CdL and Cd
2
L do not display the expected isoreticular structures.
1
1
L
Structural studies of Cd
2
L . According to single-crystal X-ray diffraction studies, Cd
2
ꢁ
crystallizes in a cubic crystal system with a ꢀ43ꢂ space group, a cell parameter a = 26.7228(8)
3
Å and a unit cell volume of 19083.0(17) Å . This compound is isostructural to the zinc(II)
1
70
analogue Zn L described in our previous work. The asymmetric unit contains two
2
2
+
crystallographically independent Cd ions (Figure 2a), both adopting a hexacoordinated
geometry. The azamacrocycle acts as a tridentate N-donor ligand for one Cd atom. The two
9
ACS Paragon Plus Environment

Crystal Growth & Design
Page 10 of 38
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
…
Cd are located in close proximity to each other (Cd1 Cd2: 3.790(9) Å) and are
interconnected through three bridging benzenecarboxylate linkers coming from three different
3
ligands. Three oxygen atoms from the carboxylate groups and the fac-N donor atoms
surround the Cd1 atom, which then displays a distorted octahedral geometry. The deviation
from the ideal geometry is caused by steric constraints imposed by the macrocycle as
evidenced by the values of 2.417(5) Å for the Cd1–N1 bond and 76.3(2)° for the N1–Cd1–N1
angle. The distortion of the coordination polyhedron can be assigned to a large displacement
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
of Cd1 from the N
3
–mean plane. As a matter of fact, the distances between Cd1 atom and
(2) atoms, are
centroids of the two planes, defined by the three nitrogen atoms and the three O
3
…
1.701 Å and 0.953 Å respectively. It has to be noticed that Cd1–N1 and Cd1 Cd2 distances
1
are significantly higher than those observed for the isostructural Zn L (2.201 and 3.517 Å,
2
70
2+
2+
respectively), which is in accordance with the larger ionic radius of Cd vs Zn . Cd2 atom
adopts a slightly distorted trigonal prism geometry and is coordinated to three oxygen atoms
from the bridging carboxylate and three water molecules, the latter having an individual
occupancy of 1/3. Overall, the stability of the architecture is supported by the rigidity of this
dinuclear cadmium cluster.
1
Thus, a secondary building unit (SBU) for Cd L is composed of two cadmium ions, one
2
N
3
-cyclic chelate unit, three carboxylates and three water molecules, giving the formula
[
Cd (COO) (fac-N )(H O) ]. Each SBU can be seen as a 6-connected node and the framework
2
3
3
2
3
94
can be described as a bcs net according to a topological approach (Figure 2b). The view
along the unit cell axis reveals the presence of regular voids due to the presence of square-
shaped channel apertures of 7.5 Å (Figure 2c,d). Owing to the cubic symmetry of the
framework, the voids are connected to each other to form a 3D network of channels.
95,96
According to calculation with the SOLV PLATON program,
the structure has an overall
10
ACS Paragon Plus Environment

Page 11 of 38
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
3
solvent accessible void volume of 46.1% (8797 Å ), and the pore volume was estimated to
3
–1
0
.380 cm g .
1
Owing to the charge of the cation (+2) and that of the ligand (–3), [Cd (L )(H O) ]
2
2
3
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
framework is monocationic and charge-balancing anions are expected to be situated in the
channels, but cannot be located by X-ray crystallography because they don’t occupy specific
1
coordination sites. As mentioned above, the cavities of Cd
2
L are filled with solvent
–
–
–
molecules and HCOO , NO
3
and Br anions, which are present in the reaction mixture.
O3
O1
Cd2
O2
Cd1
(
a)
(b)
(
c)
(d)
1
Figure 2. (a) Representation of the SBU [Cd
2
(L )(H
2
O)
3
], (b) view of the bcs net adopted by
1
Cd L , (c) view of the open channels along the c axis showing the coordination polyhedra of
2
Cd nodes (solvent molecules and hydrogen atoms are omitted for clarity), (d) space-filling
1
model of Cd
2
L shown along the c axis (Cd: yellow, O: red, C: brown).
1
1
ACS Paragon Plus Environment

Crystal Growth & Design
Page 12 of 38
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
2
2
Structural studies of CdL . Following the isoreticular approach, H L was designed by
3
insertion of alkyne spacers between the aryl moieties and the TACN scaffold. This new ligand
1
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
was expected to behave similarly to H
L and to form isoreticular nets with larger pore
3
apertures and a higher porosity. To our surprise, a new material presenting a different
topology and possessing metallic nodes with an original coordination scheme was obtained.
2
Single-crystal X-ray diffraction analysis of CdL revealed that this MOF crystallizes in a
monoclinic crystal system with space group C2/c and cell parameters of a = 20.9966(15) Å, b
=
18.9165(14) Å, c = 29.059(2) Å and β = 92.303(3)°. Only one ligand molecule and one
cadmium atom form the asymmetric unit. The overall structure can be described as a pair of
identical nets, which are mutually interwoven to form a doubly interpenetrated framework
(Figure 3b,c).
3 4
The Cd atom (Figure 3a and S7b) is heptacoordinated and exhibits an unusual CdN O
coordination scheme. These structural moieties constitute the primary building unit (PBU) of
the framework. Each metal ion is linked to three fac-nitrogen atoms from one TACN
3
macrocycle in a
κ
-fashion and three oxygen atoms belonging to two carboxylate and one
oxygen atom from a carboxyl group, each of them belonging to three vicinal ligands. The Cd–
N(1,2,3) bond lengths (2.383, 2.422, 2.417 Å) are slightly longer compared with those found
6
7
for MMCF-1 based on cyclen (2.349 Å). These values are quite similar to those determined
1
80
for Cd L (2.417(5) Å) and other TACN derivatives (Cd–N = 2.414(9) Å). despite the
2
structural difference of the coordination environment around Cd.
One carboxylate anion acts as a monodentate donor (Cd–O6: 2.237(3) Å) whereas the
second anion coordinates the metal center in bidentate fashion with Cd–O(3,4) bond lengths
of 2.519(3) and 2.276(4) Å. Surprisingly, the third carboxylate group is protonated and
coordinates to Cd atom through the carbonyl group, and exhibits a longer Cd–O2 bond length
12
ACS Paragon Plus Environment

Page 13 of 38
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
(2.497(3) Å). The protonation is clearly evidenced by the short carbonyl C1–O2 (1.217 Å)
and longer C1–O1 (1.305 Å) bond lengths compared to the C–O bonds from two carboxylate
…
groups. This unusual coordination seems to stem from the formation of the O1–H1 O6
hydrogen bond between this carboxyl group and the adjacent monodentate carboxylate
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
…
(
Figure 3a and S7b), which is evidenced by the short H1 O6 distance (1.676 Å) and a large
…
angle O1–H1 O6 (170°). This hydrogen bond is suspected to improve the stability of the
supramolecular assembly.
2
FTIR analysis of the activated CdL (dried in vacuum) provides additional data to point
out the coordination modes of O-donor ligands (Figure S2). In the spectrum, the C=O
−1
stretching band for the carboxylic group was observed at 1676 cm , and two additional
–1
vibrations at 1583 and 1538 cm were assigned to the carboxylate group coordinated in a
−1
bidentate fashion. Two other bands at 1652 and 1404 cm were attributed to the monodentate
97
carboxylate.
Bond lengths for Cd–N(1,2,3) and those of Cd–oxygen atoms reflect a distorted geometry
of the CdN coordination polyhedron. This distortion is clearly indicated by the difference
in the distances between the Cd atom and two centroids defined for the N and O mean
3
O
4
3
4
planes (1.727 Å and 1.367 Å, respectively). This distorted geometry is similar to that
1
observed in Cd
2
L and is mainly due to the shift of the metal atom above the mean plane of
the macrocycle, thus lying closer to oxygen donors. The geometry around Cd atom was
9
8,99
assessed using the method of the continuous shape measure (CShM).
A pentagonal
bipyramid (PBPY-7) and a capped trigonal prism (CTPR-7) geometry were assumed as the
most representative polyhedra. The calculations were in favour of a distorted PBPY-7
environment (S
Q
(PBPY-7) = 2.68 (D5h) and S
Q
(CTPR-7) = 4.06 (C2v)). In such a geometry,
the equatorial plane is defined by two nitrogen atoms (N2, N3) of the macrocycle and three
13
ACS Paragon Plus Environment

Crystal Growth & Design
Page 14 of 38
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
oxygen atoms (O2, O3, O4) while N1 and O6 constitute the two apical donor atoms (Figure
S7b).
Cadmium atoms can be described as 6-connecting nodes adopting a near octahedral
geometry. These nodes are linked to the closest cadmium atom through carboxylates and the
TACN macrocycle to produce a pcu net (Figure 3b). The network exhibits a slight distortion
as indicated by the difference in edge lengths of the parallelogram (14.131 and 14.585 Å) and
the deviation of the inside angle (89.0°) from a right angle.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
a)
(b)
(
c)
(d)
2
Figure 3. View of the CdL structures: (a) Representation of the 6-connected Cd node, (b)
view of the interpenetrated pcu topology, (c) view along the c axis showing the
interpenetrated framework and the coordination polyhedral of the Cd nodes (solvent
1
4
ACS Paragon Plus Environment

Page 15 of 38
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
2
molecules and hydrogen atoms are omitted for clarity, (d) space-filled model of CdL shown
along the c axis (Cd: yellow, O: red, C: black).
The network is twofold interpenetrated and the closest distance between two adjacent
aryles from two different nets is 3.8 Å (Figure S7c,d). Interestingly, these interpenetrated
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
networks exhibit multiple
π
-
π
interactions (Figures S8 and S9) between two adjacent alkynes
…
…
…
(
C8 C19 = 3.39(1) Å, C8 C18 = 3.46(1) Å), one alkyne and one aromatic ring (C20 C4
…
…
…
= 3.64(1) Å, C19 C5 = 3.44(1) Å, C6 C18 = 3.65(1) Å, C5 C18 = 3.61(1) Å) and two
…
phenylene moieties (C4 C22 = 3.72(1) Å). We can assume that the two-fold interpenetrated
framework is thermodynamically more stable than the expected isoreticular non-
interpenetrated one due to enhanced stabilization by multiple weak stacking interactions.
These results provide further evidence of the importance of controlling such interactions to
2
3,42,100-104
design interpenetrated assemblies
and show limitations of the isoreticular approach.
2
Despite interpenetration, CdL is highly porous and displays a solvent accessible volume
3
3
–1
of 54.7% (6308 Å ) and an accessible pore volume estimated to 0.633 cm g . These values
1
outperform those of the non-interpenetrated Cd
2
L . The view along the c axis reveals square
open channels with an aperture between 8.0 and 11.5 Å for the smallest and largest one,
respectively (Figure 3b,c and S8). Furthermore, the space-filling model clearly shows that the
pore accessibility is not restricted (Figure 3d).
2
It has to be noted that all attempts to obtain a non-interpenetrated analogue of CdL using
solvothermal synthetic conditions by varying the temperature and the concentration of the
reagents were unsuccessful.
Powder X-ray diffraction
15
ACS Paragon Plus Environment

Crystal Growth & Design
Page 16 of 38
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Powder X-Ray diffraction (PXRD) measurements were carried out to further investigate
the crystallinity of the two materials and their phase purity (Figures S10 and S11). The
positions of the sharp peaks in the experimental PXRD patterns for the as-synthesized solids
are in good agreement with the simulated diffractograms calculated from single-crystal data,
thus demonstrating the high phase purity and homogeneity of both solids. The structural
robustness of both frameworks was also evaluated after immersing the as-synthesized solids
in common solvents such as methanol, THF, dichloromethane (CH Cl ) and acetone. Crystals
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
2
1
of Cd L show good stability in methanol, THF and acetone. However, the material does not
2
2 2
retain its crystallinity after immersion in CH Cl since the structure partially collapses.
2
Compound CdL exhibits small structural deformations after solvent exchange with methanol,
THF, CH Cl and acetone but retains its crystallinity. Cell parameters calculated in each
2
2
solvent condition according to the Lebail refinement are reported in Table S18. A slight
2
flexibility of the interpenetrated CdL framework can be rationalized by the displacement of
the two networks with respect to each other, triggered by the introduction of solvent
molecules inside the pores and between the interwoven nets.
1
2
Special attention was made to analyse the crystallinity of Cd L and CdL after complete
2
removal of the solvent molecules. At least 3 exchanges with THF were performed before
1
drying the solids under vacuum at 298 K. For Cd
2
L , PXRD patterns of the desolvated
framework match well with those of the as-synthesized compound and indicate that this
1
material retained its crystallinity (Figure S11 and Table S19). However, Cd
2
L becomes
amorphous after heating at 80 °C for 1 h. Interestingly, the structure can be totally recovered
after soaking the activated material in DMF. This behavior can be viewed as intermediate
st
rd
between the 1 and the 3 generation of porous coordination polymer according to Kitagawa's
105
2
classification. After THF exchange and activation of CdL under vacuum at 298 K, a
broadening of the diffraction peaks was observed, which suggests some structural
16
ACS Paragon Plus Environment

Page 17 of 38
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
modifications or a partial collapse of the framework during desolvation. The lower structural
2
1
stability of CdL compared with Cd L is quite unexpected since interpenetrated frameworks
2
106-108
often provide materials with higher structural stability.
This result can probably be
2
assigned to the presence of a mononuclear primary building unit (uninode) for CdL in
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
contrast to Cd
2
L that is built from dinuclear SBUs.
TGA analysis
Thermal stabilities of the two materials were studied by TGA between 25 and 1000 °C
Figure S4). Values of the weight loss and those of the residues enable us to confirm the
(
composition of the solids suggested from the elemental analysis, ICP-AES and X-ray data.
1
2
Crystals of Cd L and CdL were analyzed after thorough exchange of the solvent used for
2
their synthesis (DMF) by THF and drying under vacuum at room temperature for 48 h.
Thermal behavior of both compounds shows a small weight loss (3%) around 400 – 420 K,
which can be due to the loss of residual solvent or water molecules adsorbed in the pores.
After a plateau until 570 K, a dramatic weight loss is observed between 600 and 780 K that
corresponds to decomposition of the networks leading to the formation of CdO. The residual
1
2
weights of each sample (Cd
2
L : 30.5%; CdL : 17.5%) are in good agreement with the
1
2
expected values (Cd
2
L : 29.8%; CdL : 17.1%). Therefore, the frameworks show a similar
thermal stability despite their different structures.
Adsorption properties
17
ACS Paragon Plus Environment

Crystal Growth & Design
Page 18 of 38
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
The porosity of the two materials was evaluated by recording N adsorption isotherms at
2
7
7 K (Figure S12). Before analysis, DMF-soaked samples were activated under reduced
pressure as described above. The absence of residual solvent trapped in the pores was checked
1
by H NMR spectroscopy after the decomposition of both samples in acidic media (Figure
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
S3). The permanent porosity of the solids was confirmed by the typical type-I shape of
109
adsorption isotherms, characteristic of microporous solids with a nitrogen uptake of 163
3
–1
1
2
and 97 cm g at saturation, respectively for Cd L and CdL . The BET surface areas were
2
2
−1
2
−1
calculated to 625 and 343 m g , and the Langmuir surface areas were 730 and 414 m g ,
respectively. Since the materials are exclusively microporous, the single data point at relative
3
–1
pressure close to 0.95 gave microporous volumes equal to 0.253 and 0.150 cm g . The
1
2
higher porosity of Cd L compared with CdL shows a discrepancy with the solvent
2
accessible volume calculated from the single crystal X-ray data and gives evidence of a partial
2
collapse of the framework during desolvation for the interpenetrated CdL as shown by
1
2
PXRD analyses (see supra). Hence, Cd L is a more opened framework than CdL . These
2
2
−1
values are in the same range (350–800 m g ) as those obtained with other MOFs based on
67,69,78,110
cyclam, cyclen or other polyazacycloalkane,
but significantly smaller than those of
1
2
−1
1 70
the previously described Zn L (1100 m g ) which is isostructural to Cd L . A mean pore
2
2
size diameter was calculated using the Horvath-Kawazoe method that gave a value around 8
Å for both solids (Figure S13) in agreement with the two crystal structures.
2
The permanent porosity was also studied by CO adsorption measurements at 195 K.
Actually, pore accessibility or re-opening can be promoted by CO at low temperature. As
2
shown in Figure S14, both materials show no gate phenomenon, usually characterized by an
inflection point disclosing a delayed adsorption induced by a structurally dynamic
111-113
behavior.
Such behaviour is in agreement with the rigidity of both frameworks.
18
ACS Paragon Plus Environment

Page 19 of 38
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
2
For CdL , the isotherm displays a type-I morphology and the progressive pore-filling is
observed with saturation profile nearly reached for 1 atm pressure. In addition, the CO2
3
–1
isotherm displays a small hysteresis loop. The adsorption capacity at 1 atm (99 cm g ) and
2
−1
the calculated Langmuir surface area (408 m g ) are very close to values found from N
2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
3
–1
2
−1
1
uptake (97 cm g and 414 m g , respectively). Cd
2
L exhibits a similar isotherm of CO
2
at
3
–1
195 K but the gas uptake at 1 atm is significantly lower (66 cm g ) and the Langmuir surface
2
−1
is only 348 m g . It has to be noted that the initial slope in the low-pressure range is more
2
pronounced, indicating a higher affinity for CO
2
than CdL .
2
Overall, the CO capacities at 195 K for both materials are in the same order than for MIL-
114
115
67,70,75,110
9
6(Al), MIL-102(Cr) or MOFs formed by the assembly of polyazamacrocycles
but for the latter, most of them are flexible and show gate-opening or breathing effects upon
CO adsorption.76,77,79 Therefore, Cd L and CdL represent one of the first example of
1
2
2
2
permanently porous MOFs based upon a N-functionalized and flexible polyazamacrocyclic
ligand and only few reports have described porous structures constructed from platforms like
116-119
70,80
67,73,78
di-,
tri-,
or tetra-azamacrocycles.
CO adsorption in non-condensing conditions (273 – 298 K) was also explored in order to
2
study the selective binding of CO and its interactions with the surface of the materials. First,
2
gas adsorption isotherms for CO
As shown in Figure 4, both materials show a significant CO
and an overall low affinity for CO and N , with values of N adsorption equal to 1.6 cm g
2
, CO, N
2
, and CH
4
at 298 K were recorded.
2
and moderate CH uptake,
4
3
–1
2
2
3
–1
3
–1
3
–1
1
2
and 1.0 cm g and CO uptake close to 1.0 cm g and 3.0 cm g for Cd L and CdL
2
2
3
−1
respectively. CdL adsorbs 26.7 cm g (5.2 % w/w) of CO at 1 atm, whereas the uptake for
2
1
3
−1
Cd
– 1 atm pressure range, indicating that the samples can adsorb a greater volume of CO
higher pressure or lower temperatures. The difference in CO capacity at 1 atm between these
2
L is 42.9 cm g (8.4 % w/w). No distinct plateau was observed for both isotherms in the
0
2
at
2
19
ACS Paragon Plus Environment

Crystal Growth & Design
Page 20 of 38
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
materials is in part ascribed to a pore blocking effect a partial collapse of the framework of the
2
desolvated CdL that limits the accessibility of the porosity.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
a)
(b)
Figure 4. Adsorption isotherms of CO
2
(298 K: blue filled circles, 285 K: blue hollow circles,
273 K: blue filled squares), CO (pink square), CH
4
2
(green triangle) and N (brown square)
1
2
recorded at 298 K for (a) Cd
2
L and (b) CdL . Solid (298 K), dashed (285 K) and dotted (273
K) lines represent the CO -fitting curves using a single or a dual-site Langmuir model for
2
1
2
Cd L and CdL respectively (see Tables S20, S21 and S22).
2
CH
4
uptake is significantly lower than CO
2
but still higher than N
over N is expected and is
(26 x 10 cm ) vs. N (17.6 x 10 cm ) and CO
2
under the same
conditions for both materials. The higher adsorption of CH
4
2
–25
3
–25
3
ascribed to the higher polarizability of CH
4
2
–25
3 120
(
19.5 x 10 cm ). Consequently, CH is preferentially adsorbed than N and CO in most of
4
2
reported sorbents.
1
2
At ambient conditions, the CO
2
capture for Cd L and CdL are in the same range than
2
67,121
other Cd-MOFs
and are also comparable to well-known IRMOF-1, IRMOF-3, MOF-
1
22
122
123
124
125
177, imidazolate frameworks ZIF-8, ZIF-20, ZIF-69, ZIF-78 and other MOFs
presenting a high porosity (see Table S23 for additional details). Nevertheless, CO2
1
adsorption is lower than the one we have obtained in our previous work for Zn
2
L (88.0
3
−1 70
cm g ).
2
0
ACS Paragon Plus Environment

Page 21 of 38
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
2
1
The porous nature of the interpenetrated (CdL ) or the charged frameworks (Cd L )
2
prompted us to explore their CO capture at lower temperatures than 298 K to get more
2
1
information on gas-surface interactions. CO
2
uptakes at 1 atm for Cd
2
L are 52.3 and 62.5
3
–1
2
cm g at 285 and 273 K, respectively (Figure 4). For CdL , these values are significantly
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
3
–1
1
lower, 34.9 and 42.9 cm g , respectively. Accordingly, Cd L presents higher uptakes
2
whatever the temperature, which can be explained by its higher porosity and polarity induced
1
by the charged framework. The isotherm curves for Cd L show a steeper slope for CO
2
2
2
2
uptake in the initial stage, which demonstrates more favorable interactions between CO
1
molecules and the host framework. In other words, Cd
2
L offers a higher affinity for CO
2
than CdL .
The isosteric heats of adsorption (
interactions, since the coverage dependent enthalpies allows a better understanding of the
adsorption selectivity for CO over other components in a mixed gas stream, in particular
CO /N and CO /CH . As a result, a high magnitude of |Qst| for CO contributes to an
improvement of such selectivities. The |Qst| values less than 30 kJ mol are indicative of non-
st
IQ I = –ꢀH) were then determined to estimate solid–gas
2
2
2
2
4
2
–1
–1
selective physisorption interactions, values between 30 and 50 kJ mol are typical of
moderately strong gas-sorbent interactions involving polar functional groups, and values
−1
above 50 kJ mol arise from stronger interactions. Moreover, isosteric heats at zero coverage
provide a quantifiable estimation of binding strengths with the most energetic sites.
The isosteric heats of adsorption were calculated from CO
2
isotherms at three different
temperatures (273, 285 and 298 K, Figure S19) using the Clausius-Clapeyron equation. The
1
–1
heat of adsorption for Cd L lies in the range of 25.1 to 28.0 kJ mol whatever the volume
2
adsorbed. This result is consistent with the single-site Langmuir model used to fit the
2
isotherms (see below and Table S21). The porous solid CdL displays more heterogeneous
2
adsorption energy sites because the enthalpy for CdL is higher at low gas loadings and
21
ACS Paragon Plus Environment

Crystal Growth & Design
Page 22 of 38
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
–
1
3
−1
decreases from 30.7 to 24.3 kJ mol for a 30 cm g uptake. The higher heat of adsorption
2
for CdL probably originates from the interpenetration of the net, which gives rise to smaller
pore size and stronger interactions between the network and CO
2
molecules in the low
coverage domain. Nevertheless, the values of the adsorption heats are characteristic of CO
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
physisorption for both materials, and low
energy consumption.
st
IQ I values enable their total recovery with a low
These enthalpy values are similar to those of benchmark porous materials with polar
–
1
126
–1 127
functional moieties such as HKUST-1 (35 kJ mol ), bio-MOF-1 (35 kJ mol ), PCN-6
–
1 128
(
35 kJ mol ) and the two-fold interpenetrating Cd-MOF based on a cyclen macrocycle
–1 67
1
2
(
MMCF-1, 26 kJ mol ). Overall, Cd
2
L and CdL show a significant porosity and CO
2
uptake, despite the difference of porosity and topology between the two structures.
2
CO adsorption selectivity calculations
The relatively high CO
to calculate the selectively for CO
performance. In a first glance, the adsorption selectivity for CO /CH and CO /N was
2
and marginal N
2
and CH
4
uptakes at 298 K and 1 atm prompted us
2
2 2 2 4
to evaluate the CO /N and CO /CH separation
2
4
2
2
estimated according to Henry’s law by the ratio of the initial slope for both isotherms (Table
1
2
S22). These calculations gave CO
2
/CH
4
selectivities for Cd
2
L and CdL equal to 12.0 and
(BTC)
7.7) or with other nitrogen linker-based MOFs including ZIF-204 (4.6), ZIF-68 (5.5), and
6
.6 at 298 K, respectively. These values compete with those of the well-studied Cu
3
2
129
(
22,130
ZIF-78 (10.5).
In addition, the CO /N selectivities at low coverage are close to 19.5 and
2 2
1
2
109, respectively for Cd
2
L and CdL , and these values make these materials promising for
applications in gas separation.
22
ACS Paragon Plus Environment

Page 23 of 38
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
More reliable information is required to evaluate the efficiency of the two materials for gas
separation. In terms of prediction, the ideal adsorbed solution theory (IAST) is a powerful
131
method to give a close approximation of the selectivity in a binary gas mixtures from the
15,22,40,132-136
experimental single-component isotherms.
CO /N binary mixture at a molar ratio of 15:85 to mimic the composition of the flue gas in
postcombustion processes, and with a 50:50 molar ratio for CO /CH mixtures typical of
The calculations were run assuming a
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2
2
2
4
general feed compositions of landfill gas. For such calculations, a deeper insight into
adsorption process is required, using equilibrium isotherm models based on the Langmuir
1
isotherm. While all isotherm data for Cd
2
L can be adequately fitted by a single-site
2
Langmuir equation, the CO
2
isotherms for CdL required a dual-site Langmuir model that
indicates the presence of adsorption sites with different energies (Tables S21 and S22). These
data were then used in order to give reliable IAST calculations and the results are shown in
Figures S20 to S23.
The results demonstrate high selectivities for the studied CO
98 K whatever the pressure. The CO /N selectivities are equal to 286.0 and 88.4 at 1 atm for
Cd L and CdL , respectively. In the same way, the CO /CH selectivity is equal to 19.9 and
2 2 2 4
/N and CO /CH mixtures at
2
2
2
1
2
2
2
4
4.7 at 1 atm. Interestingly, the CO /N and CO /CH selectivities increase with rising pressure
2
2
2
4
1
2
for Cd
2
L while they decrease smoothly for CdL . The most pronounced change (14-fold
1
increase) in the pressure range of 0–1 atm was observed for Cd
2
L and the CO
2
/N
2
mixture
(Figure S23). Generally, the host-guest interactions decrease with rising pressure. The unusual
1
behavior for Cd L is assigned to enhanced CO –CO interactions with increasing pressure.
2
2
2
Both materials compare favourably or even outperform many neutral, charged, amine-
functionalized or coordinatively unsaturated MOFs reported previously (Table S23 and S24).
Actually, the selectivities for the majority of MOFs lie mainly in the ranges of 5–30 and 10–
22
7
2 4 2 2
5 for CO /CH and CO /N at 298 K, respectively. It turns out that only few of them have
23
ACS Paragon Plus Environment

Crystal Growth & Design
Page 24 of 38
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
shown selectivities higher than 20 for CO /CH4 and 200 for CO /N2 at room
2
2
15,40,132
temperature.
Thus, the two present materials gave interesting CO adsorption properties
2
for separation purposes despite the absence of open metal sites or free basic amine lying in the
1
2
pores of the framework. However, Cd
2
2
L and CdL show moderated CO uptake at 1 atm due
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
5,16
to their rather small surface area compared with benchmark MOFs
that possess high
3
–1
affinities for CO in low pressure such as Mg-MOF-74 (190 cm g , CO /N at 298 K: 182),
2
2
2
3
–1
3
–1
Cu (BTC) (117 cm g , CO /N at 298 K: 22) and UTSA-16 (96 cm g , CO /N at 298 K:
3
2
2
2
2
2
16,34,132
300).
2
The selective capture of CO
2
at 298 K for CdL is ascribed to the decrease of the channel
size due to network interpenetration, which is well known to enhance the affinity for
40,137
CO2,
process since the pore size shown by X-ray single crystals analysis and HK calculation gave
pore size significantly larger than the guest size (CO , 3.3 Å over N , 3.64 Å, O , 3.46 Å and
rather than a size-exclusion effect of the framework through a molecular sieving
2
2
2
CO, 3.76 Å). In addition, there is some evidence in the literature that interpenetration allows
to increase gas uptake at low pressure or low temperature due to smaller pore size and the
40,42
presence of microdomains that do not exist in the non-interpenetrated analogues.
In fact,
the contraction of the pores allows a better overlap of the attractive potential fields between
the opposite walls and endows a significant enhancement for the adsorption of polarizable gas
–25
–3
–25
–3 40,41,138
molecule like CO
In the case of Cd
the existence of a cationic framework that enables quite strong interactions with CO , thanks
2
(CO
2
: 29.1 x 10 cm ; N
2
: 17.4 x 10 cm ).
1
2
L , the origin of the preference for CO over N
2
2 4
and CH is ascribed to
2
–35
to its high quadrupole moment (–1.4 x 10
C.m). Actually, charged frameworks have
received increasing attention and are well recognized to enhance adsorbent-adsorbate
interactions in the material, owing to the strong induced electrostatic field occurring in the
13,22,137,139
cavity.
24
ACS Paragon Plus Environment

Page 25 of 38
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
1
2
It is also evident that Cd L gives better separation properties than CdL as a result of the
2
existence of a cationic framework and a higher porosity. Accordingly, both materials
demonstrated a considerable interest for separation process such as natural gas purification or
CO
2
2 2 4
capture applications. To the best of our knowledge, the CO selectivity over N and CH
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
estimated from IAST calculations at 1 atm for Cd
2
L is one of the highest already reported for
6
7,70,76,78
MOFs based on polyazamacrocyclic ligands.
These outcomes also point out that our
strategy of employing a flexible polyazamacrocycle-based ligand as a platform represents an
appealing way to construct functional porous MOFs for various applications.
CONCLUSION
Two rare examples of Cd-MOFs based on the 1,4,7-triazacyclononane platform were
designed and synthesized. The isoreticular strategy was applied using two TACN linkers
1
2
H L and H L bearing 4-carboxybenzyl and 3-(4-carboxyphenyl)-prop-2-ynyl pendant arms
3
3
2
+
that were reacted with Cd ions in solvothermal conditions with the aim to prepare
1
2
isostructural MOFs with different porosities. Two 3D coordination polymers Cd L and CdL
2
were obtained and characterized using single crystal X-ray analysis. Unexpectedly, the solids
exhibited different topologies and crystalline organizations, indicating that the isoreticular
concept was not fulfilled with this triazamacrocyclic platform despite the small structural
2
differences of their carboxylate-functionalized arms. CdL presents an interpenetrated
framework with uninodal 6-connected node assembled into two interpenetrated pcu networks,
1
while a non-interpenetrated Cd
2
L material with a bcs net is built from 6-connected dinuclear
clusters as SBU. The difference in topology and porosity for these two materials was assigned
2
to the stabilization of interpenetrated CdL network by multiple
π-
π
bonds between two
2
adjacent nets. Despite its interpenetrated structure, CdL is highly porous and the solvent
25
ACS Paragon Plus Environment

Crystal Growth & Design
Page 26 of 38
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
1
accessible volume is about 55 %. Importantly, Cd L is positively charged and charge-
2
balancing anions are located in the channels that presents about 46% of porosity. Both
materials offered a good CO
CH at 298 K. However, Cd
the CO
2
2
uptake capacity as well as separation abilities over N , CO and
1
4
2
L displayed a higher porosity and a significant enhancement of
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
3
-1
2
capture and selectivity when compared with CdL (42.9 vs 26.7 cm g ), which was
assigned to the polarity of the cationic framework, yielding stronger electrostatic interactions
between CO molecules and the surface, and a better stability of the framework. Accordingly,
2
these materials are of interest for CO
2
separation processes in the context of flue gas streams
–N and CO –CO). This work also highlights the
from coal-fired power and steel plants (CO
2
2
2
interest of polyazamacrocycles for MOF elaboration. Being strong chelators of metal ions,
these compounds can be regarded as unusual metallolinkers to yield functional materials. The
diversity of carboxy-functionalized pendent arms that can be anchored to the cyclic amine
provides an excellent opportunity for preparing novel building blocks for MOFs construction
with well-designed and promising applications not only for gas adsorption, but also for
medical imaging and catalysis.
ASSOCIATED CONTENT
Supporting Information
The Supplementary Information is available free of charge on the ACS Publication
1
2
website. Details of synthesis and analyses of the organic linkers L and L , and their
1
2
respective materials Cd L and CdL were given, as well as TGA, single crystal and powder
2
26
ACS Paragon Plus Environment

Page 27 of 38
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
diffraction data, FTIR spectra, gas adsorption measurements with multi-site Langmuir fits and
parameters used for IAST calculations.
Accession Codes
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
2
CCDC-1529941 (Cd L ) and 1529942 (CdL ) information contain the supplementary
2
crystallographic data for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif
AUTHOR INFORMATION
Corresponding Authors
*
E-mail: stephane.brandes@u-bourgogne.fr
ORCID
Stéphane Brandès: 0000-0001-6923-1630
‡
Present address: ENSCL, CNRS, Centrale Lille, Université d'Artois, UMR 8181, UCCS,
Unité de Catalyse et Chimie du Solide, F-59000 Lille, France
§
Present address: ARKEMA, service Adsorption, Groupement de Recherches de Lacq, BP
34, 64170 Lacq, France
Notes
The authors declare no competing financial interest.
ACKNOWLEDGEMENTS
27
ACS Paragon Plus Environment

Crystal Growth & Design
Page 28 of 38
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
This work was supported by the “Centre National de la Recherche Scientifiqueˮ (CNRS),
the “Université de Bourgogne” and the “Conseil Régional de Bourgogne” (JCE program,
PARI IME SMT8 and PARI II CDEA programs). This work was carried out in the frame of
the International Associated French–Russian Laboratory of Macrocycle Systems and Related
Materials (LAMREM) of CNRS and RAS (Russian Academy of Sciences).
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
REFERENCES
(
(
(
1) Zhou, H.-C.; Long, J. R.; Yaghi, O. M. Chem. Rev. 2012, 112, 673-674.
2) Zhou, H.-C.; Kitagawa, S. Chem. Soc. Rev. 2014, 43, 5415-5418.
3) Furukawa, H.; Cordova, K. E.; O'Keeffe, M.; Yaghi, O. M. Science 2013, 341, 1230444-1-
1230444-12.
4) Eddaoudi, M.; Moler, D. B.; Li, H.; Chen, B.; Reineke, T. M.; O'Keeffe, M.; Yaghi, O. M.
Acc. Chem. Res. 2001, 34, 319-330.
5) Ockwig, N. W.; Delgado-Friedrichs, O.; O'Keeffe, M.; Yaghi, O. M. Acc. Chem. Res.
(
(
2005, 38, 176-182.
(6) Férey, G.; Serre, C.; Devic, T.; Maurin, G.; Jobic, H.; Llewellyn, P. L.; De Weireld, G.;
Vimont, A.; Daturi, M.; Chang, J.-S. Chem. Soc. Rev. 2011, 40, 550-562.
(
7) Stock, N.; Biswas, S. Chem. Rev. 2012, 112, 933-969.
(
8) Furukawa, S.; Reboul, J.; Diring, S.; Sumida, K.; Kitagawa, S. Chem. Soc. Rev. 2014, 43,
5700-5734.
9) Lu, W.; Wei, Z.; Gu, Z.-Y.; Liu, T.-F.; Park, J.; Park, J.; Tian, J.; Zhang, M.; Zhang, Q.;
Gentle Iii, T.; Bosch, M.; Zhou, H.-C. Chem. Soc. Rev. 2014, 43, 5561-5593.
10) Eddaoudi, M.; Sava, D. F.; Eubank, J. F.; Adil, K.; Guillerm, V. Chem. Soc. Rev. 2015,
(
(
44, 228-249.
(11) Murray, L. J.; Dinc
ă, M.; Long, J. R. Chem. Soc. Rev. 2009, 38, 1294-1314.
28
ACS Paragon Plus Environment

Page 29 of 38
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
(12) Suh, M. P.; Park, H. J.; Prasad, T. K.; Lim, D.-W. Chem. Rev. 2012, 112, 782-835.
(
(
(
13) Li, J.-R.; Kuppler, R. J.; Zhou, H.-C. Chem. Soc. Rev. 2009, 38, 1477-1504.
14) Li, J.-R.; Sculley, J.; Zhou, H.-C. Chem. Rev. 2012, 112, 869-932.
15) Sumida, K.; Rogow, D. L.; Mason, J. A.; McDonald, T. M.; Bloch, E. D.; Herm, Z. R.;
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Bae, T.-H.; Long, J. R. Chem. Rev. 2012, 112, 724-781.
(16) Zhang, Z.; Yao, Z.-Z.; Xiang, S.; Chen, B. Energy Environ. Sci. 2014, 7, 2868-2899.
(
17) Lee, J.; Farha, O. K.; Roberts, J.; Scheidt, K. A.; Nguyen, S. T.; Hupp, J. T. Chem. Soc.
Rev. 2009, 38, 1450-1459.
18) Kreno, L. E.; Leong, K.; Farha, O. K.; Allendorf, M.; Van Duyne, R. P.; Hupp, J. T.
Chem. Rev. 2012, 112, 1105-1125.
(
(
(
(
19) He, C.; Liu, D.; Lin, W. Chem. Rev. 2015, 115, 11079-11108.
20) Bae, Y.-S.; Snurr, R. Q. Angew. Chem. Int. Ed. 2011, 50, 11586-11596.
21) Mason, J. A.; Sumida, K.; Herm, Z. R.; Krishna, R.; Long, J. R. Energy Environ. Sci.
2011, 4, 3030-3040.
(22) Li, J.-R.; Ma, Y.; McCarthy, M. C.; Sculley, J.; Yu, J.; Jeong, H.-K.; Balbuena, P. B.;
Zhou, H.-C. Coord. Chem. Rev. 2011, 255, 1791-1823.
(23) Bhattacharya, B.; Ghoshal, D. CrystEngComm 2015, 17, 8388-8413.
(24) Demessence, A.; D'Alessandro, D. M.; Foo, M. L.; Long, J. R. J. Am. Chem. Soc. 2009,
131, 8784-8786.
(
25) Gu, J.-M.; Kwon, T.-H.; Park, J.-H.; Huh, S. Dalton Trans. 2010, 39, 5608-5610.
26) McDonald, T. M.; D'Alessandro, D. M.; Krishna, R.; Long, J. R. Chem. Sci. 2011, 2,
(
2
022-2028.
27) Lu, W.; Sculley, J. P.; Yuan, D.; Krishna, R.; Wei, Z.; Zhou, H.-C. Angew. Chem. Int.
Ed. 2012, 51, 7480-7484.
(
29
ACS Paragon Plus Environment