Two-dimensional flexible Ni(II)-based porous coordination polymer showing single-crystal to single-crystal transformation, selective gas adsorption and catalytic properties

Article abstract of DOI:10.1016/j.poly.2015.12.008

A novel two dimensional (2D) porous coordination polymer {[Ni₃(TBIB)₂(BTC)₂(H₂O)₆]·5C₂H₅OH·9H₂O}_n (1) [TBIB = 1,3,5-tri(1H-benzo[d]imidazol-1-yl)benzene, H<

Full text of DOI:10.1016/j.poly.2015.12.008

Accepted Manuscript
Two-Dimensional Flexible Ni(II)-based Porous Coordination Polymer Showing
Single-Crystal to Single-Crystal Transformation, Selective Gas Adsorption and
Catalytic Properties
Rashmi A. Agarwal, Soumya Mukherjee
PII:
S0277-5387(15)00756-1
DOI:
http://dx.doi.org/10.1016/j.poly.2015.12.008
POLY 11705
Reference:
To appear in:
Polyhedron
Received Date:
Accepted Date:
15 October 2015
5 December 2015
Please cite this article as: R.A. Agarwal, S. Mukherjee, Two-Dimensional Flexible Ni(II)-based Porous Coordination
Polymer Showing Single-Crystal to Single-Crystal Transformation, Selective Gas Adsorption and Catalytic
Properties, Polyhedron (2015), doi: http://dx.doi.org/10.1016/j.poly.2015.12.008
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Two-Dimensional Flexible Ni(II)-based Porous Coordination Polymer
Showing Single-Crystal to Single-Crystal Transformation, Selective Gas
Adsorption and Catalytic Properties
a
b
Rashmi A. Agarwal, * Soumya Mukherjee
a
Department of Chemistry, Indian Institute of Technology Kanpur, 208016, India
Email:rashmi.a.agarwal@gmail.com
b
Department of Chemistry, Indian Institute of Science Education and Research (IISER), Dr.
Homi Bhabha Road, Pashan, Pune, Maharashtra 411008, India
*
Corresponding Author’s email: rashmi.a.agarwal@gmail.com
Abstract
A
Novel
(TBIB) (BTC)
yl)benzene, H BTC = 1,3,5-benzenetricarboxylic acid) has been synthesized solvothermally. In 1
two
dimensional
(2D)
porous
coordination
polymer
{
[Ni
3
2
2
(H
2
O)
6
]·5C OH·9H
2
H
5
2
O} (1) [TBIB = 1,3,5-tri(1H-benzo[d]imidazol-1-
n
3
layers are stacked in ABAB··· fashion by virtue of strong intermolecular hydrogen bonding
interactions, to generate an overall 3D supramolecular framework, consisting of isolated pockets
accommodated solvent molecules inside. These lattice-constituent solvent molecules are replaced
by dichloromethane (DCM), after immersing complex 1 in DCM for seven days at room
temperature, providing {[Ni
3
(TBIB)
2
(BTC)
2
2
(H O)
6
]·6CH
2
Cl
2
·6H
2
O}
n
(2). Arrangement of
layers is slightly changed in compound 2 wherein, small pockets are completely absent.
Characterization of these two compounds 1 and 2 has been performed employing, single crystal
X-ray diffraction, IR spectroscopy, thermogravimetry and elemental analysis. Importantly,
complex 1 shows selective sorption of CO gas at low temperature and pressure, and
2

simultaneously displays high heterogeneous catalytic activity for Knoevenagel condensation at
high temperature.
Keywords: Supramolecular Chemistry; Coordination Polymer; Gas Adsorption; Catalysis;
Hydrothermal.
1
. Introduction
Recently, the assembly of coordination polymers (CPs) with desired structures and functions has
emerged as a very hot research topic for their intriguing structural features and potential
applications in a wide range of research fields such as gas storage/separation [1], heterogeneous
catalysis [2], sensor [3], and external stimuli (heat, pressure, light or guest) induced structural
transformation [4]. Diverse range of dynamic behaviours e.g., breathing of three dimensional
(
3D) networks, sliding motion of constituent layers and, rotation or distortion of organic linkers
coupled with changes in geometry around metal centres can be precisely manifested in guest-
induced structural transformations [5]. For a dynamic coordination framework, various non-
covalent interactions (e.g. π···π stacking, hydrogen bonding etc.) are considered as the major
responsible factors involved in guest-induced structural transformations [6]. Flexible host
frameworks are anticipated to possess a superior selectivity for guest inclusion, to exhibit
structural transformation on effective adsorption or desorption phenomenon of guest molecules,
since these frameworks are based on coordination bonds as well as associated with
supramolecular interactions [7]. Greater degree of flexibility has been exhibited by coordination
polymers made up of two dimensional structures, because of the possible movement of the 2D
layers in addition to the concomitant alteration in local bond lengths and angles, during the
removal or accommodation of guest molecules.

Global climate change, caused mainly due to discharge of CO
2
into the atmosphere has surfaced
as the focal point of scientific communities’ prime concern [8]. The efficient separation of CO
2
from air under atmospheric pressure has become a pressing issue for academic researchers as
well as from industrial standpoint [9]. Physisorption phenomena existent between certain
adsorbent materials and CO
lesser amount of energy, as compared to other conventional energy-intensive methods to remove
CO gas [10]. Adsorption properties of a particular material depend on its structural
2
molecules is an expediently reversible process and it requires much
2
dimensionality (1D, 2D or 3D) in combination with porosity, pore size and surface area.
Porous coordination polymers (PCPs) can be used as heterogeneous catalysts, as these polymers
have several advantages such as, easy crystallization in high yields, high thermal stability,
insolubility in common organic solvents, fine tuning of the pores by appropriate ligand design
and dynamic behaviour in response to guest species etc. To functionalize channel surface, two
distinct strategies have been adopted: coordinatively unsaturated/open metal sites (OMS) [11],
and introduction of functional organic sites (FOS) [12] by which basic catalyst is generated as a
obvious strategic outcome [13]. Hence, PCPs having specific interaction sites in their channels
have been envisioned for catalytic applications in organic syntheses, because of several
advantages: 1) controlled reaction (stereo and regiocontrols); 2) fast reaction. However, use of
these channels in PCPs with such remarkable effects has been very limited [14]. Herein we have
reported a new layered coordination polymer {[Ni
1), which upon immersing in DCM
[Ni (TBIB) (BTC) (H O) ]·6CH Cl ·6H O}
3
(TBIB)
at
2
(BTC)
2
(H
2
O)
6
]·5C
2
H
5
OH·9H
2
O}
n
(
room
temperature
provides
{
3
2
2
2
6
2
2
2
n
(2), wherein ethanol molecules present in cavities
of 1 are replaced by DCM molecules in 2. Compound 1 proves to be an efficient heterogeneous
catalyst at 60 ºC for Knoevenagel condensation reaction and selective adsorbent material for

carbon dioxide (CO
2
) over the other flue gas components at low temperature and ambient
pressure.
2
. Experimental Section
.1. Materials and Physical measurements
2
Reagent grade 1,3,5-tifluorobenzene and metal salt Ni(NO
and used as received. All solvents, benzimidazole and K
Chemicals, India. Solvents were purified prior to use, following standard procedures. Fourier
3
)
2
·6H
2
O were acquired from Aldrich
2
CO were procured from S. D. Fine
3
–
1
Transform Infrared spectra (FTIR) were obtained (KBr disk, 400-4000 cm ) using a Perkin-
1
13
Elmer model 1320 spectrometer. H NMR and C NMR spectra were recorded using a JEOL-
ECX 500 FT (500 MHz and 125 MHz, respectively) instrument in CDCl with Me Si as the
3
4
internal standard. ESI mass spectra were recorded using a WATERS Q-TOF premier mass
◦
spectrometer. Thermograms were recorded on a Mettler Toledo (heating rate of 10 C/min) TGA
instrument. Microanalyses for the compounds were obtained using a CE-440 elemental analyzer
(
Exeter Analytical Inc.). Powder X-ray diffraction (PXRD) patterns were recorded using a
Rigaku Rint 2000 X-ray diffractometer, with CuK radiation (λ= 1.5406 Å). Low pressure gas
α
sorption measurements were performed using BelSorpmax (Bel Japan). All the gases used were
of 99.999% purity. As-synthesized compound 1 was heated at 100 °C under vacuum for 10 h, to
obtain the guest free compound. Prior to adsorption measurement, the guest-free sample was pre-
treated at 160 °C under vacuum for 4 h, using BelPrepvacII, and purged with He on cooling. For
low temperature measurements, N
CO gas adsorption isotherm was monitored at 195 K. Additionally, CO
were also monitored at 298 K and 273 K. Surface area and pore size distribution were calculated
2
and H
2
adsorption isotherms were monitored at 77 K, while
2
2
adsorption isotherms

using BelMaster analysis software package. Gas chromatography (GC) analyses have been
recorded on a LingHua GC 9890E instrument, equipped with a flame ionization detector (FID).
2
.2. Synthesis of 1,3,5-tri(1H-benzo[d]imidazol-1-yl)benzene (TBIB)
This ligand TBIB was synthesized as recently reported [15].
2
.3. Synthesis of complex 1 {[Ni
A mixture of Ni(NO ·6H O (0.055 g, 0.19 mmol), TBIB (0.04 g, 0.094 mmol) and H
0.02 g, 0.094 mmol) was taken in EtOH:H O (6 mL, 2:1 v/v), and heated to 180 °C under
3 2 2 2 6 2 5 2 n
(TBIB) (BTC) (H O) ]·5C H OH·9H O}
3
)
2
2
3
BTC
(
2
autogenous pressure in a Teflon-lined steel bomb for 3 days, followed by slow cooling (1
o
C/min) to room temperature. The green colored needle-shaped crystals were collected, washed
with ethanol. Yield: ~50%. Anal. calcd. for C82
H
102
N
12
O
32Ni
3
: C, 50.63; H, 5.25; N, 8.64%.
–
1
Found: C, 50.7; H, 5.28; N, 8.72%. IR (cm , KBr pellet): 3633(m), 3596(m), 3387(m), 1607(s),
1
556(s), 1502(s), 1475(s), 1433(s), 1370(s), 1232(s), 773(s), 752(s), 719(s) (Fig. S1).
2
3 2 2 2 6 2 2 2 n
.4. Synthesis of complex 2 {[Ni (TBIB) (BTC) (H O) ]·3CH Cl ·12H O}
Crystals of 1 were immersed in DCM (dichloromethane) for 4 days at room temperature,
whereupon compound 2 is obtained via SC-SC transformations. Anal. calcd. (%) for
–
1
C
75
H
52
N
12
O
30Ni
3
Cl
KBr pellet): 3388(m), 1611(s), 1554(m), 1500(s), 1429(m), 1366(s), 1231(m), 770(m), 717(m)
Fig. S2).
6
: C, 44.66; H, 2.6; N, 8.33%. Found: C, 44.8; H, 2.9; N, 8.35%. IR (cm ,
(
2
.5. X-ray crystallography
Single crystal X-ray data were collected at 100 K on a Bruker Smart APEX CCD diffractometer,
using graphite-monochromated MoKα radiation (λ = 0.71073 Å). Linear absorption coefficients,
scattering factors for the atoms, and the anomalous dispersion corrections were taken from

International Tables for X-ray Crystallography. Data integration and reduction were processed
16] with SAINT software. An empirical absorption correction factor was applied to the
[
collected reflections with SADABS, [17] and the space group was determined using XPREP
2
[
18]. The structure was solved by direct method, using SHELXTL-97 [19] and refined on F by
full matrix least square technique using the SHELXTL-97 [20] package. Several DFIX and
DANG commands were included for compound 1, to fix bond angles and bond distances in one
distorted ethanol molecule and for compound 2, to fix the C-Cl bond in dichloromethane. All the
non-hydrogen atoms were refined anisotropically, except O3W and O8W in 1 while for
compound 2, most of the atoms have been refined isotropically including metal atoms. The
hydrogen atoms attached to carbon atoms were positioned geometrically, and treated as riding
atoms using SHELXL default parameters. Hydrogen atoms could not be located at all water
molecules for both these compounds in the difference Fourier maps. Contribution of all hydrogen
atoms from the solvent molecules has been incorporated in both the empirical formulae and
formula weights in crystal and structure refinement data table. Because of the poor crystal
quality of compound 2, the maximum residual electron density value has remained high. We
tried the data collection with several crystals from different batches, but each of the crystals
came up with similar data. Compound 2 did not diffract well at high angles, and as a result the
data completeness was found to be 0.638. The crystal and structure refinement data are tabulated
in Table S1, while selective bond lengths and bond angles are provided in Table S2.
2
.6. General procedure for Knoevenagel condensation
The catalytic reactions are carried out in DCM medium. In a typical reaction, a solution (10 ml)
containing an aromatic aldehyde and malononitrile (1:1 molar ratio) is stirred for 5 min, followed

by the addition of 5 wt% of 1. The suspension is allowed to stir at 60 ºC temperature, under
nitrogen atmosphere for 2 h. The progress of the reaction is steadily monitored by TLC. On
completion of reaction, the catalyst is removed by filtration, washed with DCM and recovered.
The solid catalyst is in fact, reused for the same reaction later. The filtrate is evaporated to
dryness under reduced pressure, and the residue is recrystallized from EtOAc:hexane mixture to
obtain the pure products.
3
. Results and discussion
3
.1. X-ray structural description of compound 1.
X-ray crystallographic analysis of 1 reveals that this complex crystallizes in the triclinic space
3
–
group P-1 and its asymmetric unit contains three Ni(II) ion, two TBIB, two BTC ligands, six
coordinated water molecules besides five ethanol and nine water molecules in the lattice. Each
Ni(II) ion has distorted octahedral NiN
2
O
4
coordination [21], with ligation from two
benzimidazole N atoms of two different TBIB ligands (Ni–N = 2.063(7)–2.113(6) Å), two
3
–
carboxylates from two BTC ions (Ni–O = 2.004(5)–2.084(5) Å) (both in monodentate fashion),
and two coordinated water molecules (Ni–O = 2.004(5)–2.084(5) Å) (Fig. 1). Both Ni–N and
Ni–O bond distances are within normal statistical range [22].

Fig. 1. A perspective view of the metal coordination environment in complex 1.
Two types of Ni(II) ions are present in complex 1, one type (Ni1 and Ni3) is participating in
macrocyclic ring formation, while the second type (Ni2) is extending the chain along b axis via
3
–
extended bridging with BTC ligand, as shown in the Fig. 2. Distance between Ni1 and Ni3 in
the macrocyclic ring is 7.95 Å. These chains are further connected by benzimidazole N atoms of
TBIB ligand to provide a typical layered structure along crystallographic c axis (Fig. 3).
Fig. 2. Metal running chain along crystallographic b axis (TBIB ligand has been omitted) in
complex 1

Fig. 3. Showing, chains are connected through TBIB ligands forming layered structure in 1. H-
atoms are omitted for clarity
It is quite noteworthy, that the framework layers stack in an ···ABAB··· fashion and further
reinforce to give rise an overall 3D supramolecular architecture, through intricate H-bonding
interactions, involving metal coordinated water and benzene rings of benzimidazole (Fig. 4).
These interactions between layers lead to formation of isolated pockets consisting four ethanol
and six lattice water molecules and other small pockets containing one ethanol and one water
molecule, while macrocyclic ring within the layer possesses two non-coordinated water
molecules along a axis (Fig. 5). The solvent-accessible volume is ~36% of the unit cell volume,
as calculated from the crystal structure using the PLATON analysis [23] (Fig. 6).

Fig. 4. H-bonding interactions between layers in coordination polymer 1 involving oxygen of
coordinated water molecule and hydrogen atom of benzene ring of benzimidazole.
Macrocyclic ring
Large channels
Small channels

Fig. 5. Isolated pockets filled with solvent molecules in complex 1.
Fig. 6. Space-filled model of compound 1 showing isolated pockets, and connections between
layers.
Topological analysis [24] of 1 shows that, it has a (3,3,4,4)-connected 3,3,4,4L10 net by
3
–
considering TBIB and BTC as 3-connected, metal ions as 4-connected nodes in which Ni1, Ni3
take part in the formation of macrocyclic ring (Fig. 7). The point symbol for this net is
2
2
3
2
2
3
{
4.8 }
2
{4 .6.8 }
2
{4 .6} {4 . 8 .10}.
2

(c)
(
b)
(a)
(d)
3–
Fig. 7. (a) 3-connected TBIB node, (b) 3-connected BTC node, (c) 4-connected metal node
and, (d) topological view of (3,3,4,4)-connected 3,3,4,4L10 net present in compound 1.
3
2
.2. Single crystal to single crystal transformation studies and structural description of complex
Upon immersion of complex 1 in DCM solvent at room temperature for seven days, compound 2
gets formed in single crystal to single crystal manner (Fig. S3), maintaining crystallinity. In IR
spectra there is no OH- stretching for ethanol at 3635 and 3596 cm–1 which clearly indicates that
exchange has been completed (Fig. S2). Complex 2 also crystallizes in triclinic space group P-1
and its asymmetric unit consists of one Ni(II) ion with full occupancy, alongside a second Ni(II)
3
–
ion with half occupancy factor, one TBIB, one BTC , three coordinated water molecules;

besides it three DCM molecules and three lattice water molecules. In this case, Ni(II) ion has
similar distorted octahedron coordination environment as observed for 1. But in this case, bond
distances involving metal ions which are taking part in macrocycle formation are same for both
the metal ions; on the contrary, for compound 1, these bond distances are not similar for both the
metal ions.
Fig. 8. Metal running chain along crystallographic a axis in coordination polymer 2.
In case of compound 2, only two types of metal ions (Ni1 and Ni2) are involved in chain
formation as shown in Figure 8, and form a layer similar to complex 1. Arrangement of layers is
changed in compound 2, which is slightly shifted towards crystallographic b axis after admitting
DCM molecules, as presented in Fig. 9. If we see guest removed space-filled model of structure
2
, there are no small pockets consisting of solvent molecules (Fig. 10), as observed in the case of
complex 1.

Fig. 9. Arrangement of layers in complex 2 along crystallographic b axis.
(
b)
(
a)
Fig. 10. (a) Guest free layered structure and, (b) space-filled model of complex 2.

The solvent-accessible volume is ~35% of the unit cell volume, almost same like complex 1.
PXRD pattern resemble with the as-synthesized phase showing phase purity (Fig. S4).
3
.3. Thermal stability
TGA experiments have been carried out to check the thermal stability of both the complexes 1
and 2. Weight losses of ~19% (calculated 20.19%) and ~25% (calculated 27.9%) were observed
for TGA curves of complexes 1 and 2 respectively, as shown in Figures S5 and S6. Guest
molecules were released between the temperature range ~30 to 350 °C and both frameworks
underwent collapse above 400 °C.
3
.4. Gas adsorption studies
To examine porosity of the desolvated guest-free phase of layered compound 1, sorption
measurements have been performed at low pressure with CO , CH , Ar, N and H at 77 K (Ar,
and H ) and 195 K (CO and CH ). The CO gas sorption isotherm at 195 K shows a typical
2
4
2
2
N
2
2
2
4
2
−
1
type I behavior with a maximum value of 100 mL g gas uptake at low pressure, suggesting the
microporous nature of the framework (Fig. 11) [25]. The Brunauer-Emmett-Teller (BET) surface
2
−1
area, calculated from CO
2
sorption data recorded at 195 K, is 297.63 m g . The CO
uptake capabilities, 55 and
0 cm g respectively (Fig. 12). Strikingly, there is no adsorption uptake for N and H at 77 K,
2
sorption
isotherms measured at 273 K and 298 K are showing moderate CO
2
3
−1
4
2
2
in spite of possessing adequate effective pore aperture for their entry. This may be due to the
very strong interactions occurring between the adsorbate oxygen and nitrogen gas molecules at
7
7 K with the pore windows of the adsorbent surface, which is presumably blocking the next set
of adsorptive molecules from passing into the pore, since the framework is devoid of any
additional open channels [26]. Interestingly although, compound 1 shows large amount of CO
adsorption uptake, owing to the large quadrupole moment of CO which induces electrostatic
2
2

interactions with the framework to enter inside the cavities. The blocking interactions prevalent
in the cases of gaseous molecular species like N , H etc. are sufficiently surpassed by the
thermal energy operative for CO . In fact, the host adsorbent framework with a combination of
2
2
2
Ni(II), polar moieties and π-electron clouds from the constituent ligands inside the porous
channels gives rise to an electrostatic field, which is indeed effectual behind carbon dioxide
adsorption [26]. The dipole-induced-dipole interactions, where the quadrupole moment of carbon
−
39
2
dioxide (1.34 × 10 Cm ) interacts with the electric field gradient of the adsorbent surface,
facilitate the potential energy of CO adsorption at low temperature (195K). Hence, the selective
uptake of CO by 1 can be attributed to the electrostatic interactions with free carboxylate
oxygens of the BTC linker. There is no hysteresis trend observed during CO desorption-branch,
2
2
2
suggesting that complex 1 is a potential candidate for industrial post-combustion carbon capture
and storage (CCS) technology applications. The evident release of adsorbate CO2 molecules at
reduced external pressures indicates anticipation of easy reusability/ bed regeneration attribute of
this material toward CO2 storage. This kind of selective CO adsorption phenomena is vital in
2
the domain of porous coordination polymers [27]. To check the phase purity of complex 1,
variable temperature PXRD measurements were performed (Fig. S7). PXRD pattern for the as-
synthesized phase is shifting towards higher 2θ value due to temperature effect but at very low
temperature for simulated pattern it is expanding or shifting towards lower 2θ. It means complex
is breathing at room temperature, because for the as-synthesized phase, intense hydrogen bonds
are involved between layers, by virtue of which the entire porous structure gets constructed. At
high temperature, just after the initiation of guest removal from the framework, characteristic
peaks get somewhat shifted towards lower 2θ value, referring to framework-expansion.
Sometimes the whole pattern is different due to phase transitions between single crystal data

(
probably measured at low temperatures) and powder data (often measured at room temperature).
Sometimes turbostratic disorder of a layered material may alter the pattern.
−
1
Fig. 11. Low temperature gas adsorption isotherms for complex 1; amount adsorbed (in mL g )
plotted against P/P (Filled shapes = adsorption, hollow shapes = desorption).
0

Fig. 12. CO
2
sorption isotherms at 298 and 273 K for complex 1 (filled shapes = adsorption,
hollow shapes = desorption).
3
.5. Catalytic properties
Considering the demand for new-generation improved heterogeneous catalysts and the unparallel
features of MOFs, the development of environment-friendly MOF catalyst for Knoevenagel
condensation reaction is a topic of great interest in recent years [28]. Knoevenagel condensation
reactions are well known organic reactions, largely employed in order to form C-C bonds for the
synthesis of important derivatives targeted for various applications [29]. The present MOF
3
−
compound with BTC should also behave as a potential catalyst for Knoevenagel condensation
reaction, due to the presence of guest interaction sites, specifically ─C═O moieties decorating
the channel wall. Recent years have witnessed, studies done with PCPs consisting of carbonyl
oxygen atoms as catalytic interaction sites present on the channel wall [30]. Compound 1 was
used as catalyst in its as-synthesized form, without any pre-activation. In each case, 5% by
weight of compound 1 is used as catalyst. The heterogeneous catalytic properties of complex 1
for the reactions between benzaldehyde (4-methylbenzaldehyde, 4-fluorobenzaldehyde, 4-
nitrobenzaldehyde, 1-naphthaldehyde) and malononitrile in dry DCM, under nitrogen
atmosphere at 60 °C, as shown in Table 1 were comprehensively verified. We have synthesized
the targeted organic molecule, derived from benzylidene malononitrile (BMN) because of their
reported inhibitory activity of the protein tyrosine kinase [31].
Aromatic aldehyde (10.4 mmol) is allowed to react with active methylene compound (10.4
mmol) at room temperature in DCM solvent under inert atmosphere. After 5 minutes, as-
synthesized complex 1 (5% by weight with respect to the amount of benzaldehyde) was used as a
catalyst in the reaction and temperature was raised up to 60 °C, reaction progress was monitored

through TLC, which indicated completion in 2 h. Once the reaction gets over, the reaction
mixture is filtered to recover the catalyst. Conversion was monitored by GCMS, which comes up
with 100% product formation after two hours of reaction progress time (Fig. 13). To check the
catalytic activity of 1, blank experiments have been performed without using compound 1, which
led to only 15% conversion after 2 h under similar conditions.
Fig. 13. Evidence of heterogeneous nature of catalyst in the Knoevenagel condensation reaction
of benzaldehyde with malononitrile (green curve showing catalysis reaction, and blue line
presenting blank test for the reaction).
In presence of catalyst, the reaction was completed within 2 h. Consequently, it is evident that
the reaction occurs within the channels functionalized with ─C═O groups of complex 1.
Malononitrile interacts with carbonyl oxygen centres of the catalyst, as confirmed from the
lower-wavenumber shift of the characteristic IR stretching band, and splitting of the same for
nitrile group (Fig. S8) [32]. This suggests that reaction occurs in the pores of complex 1 not on
the surface. The Knoevenagel reaction is not only a weak base-catalyzed reaction, but also it
accompanies formation of a new C─C bond [33]. The guest-selective reaction suggests that the

reaction occurs in the channels, and not on the surface of the polymer. When substrate with steric
environment is used the reaction does not proceed because this compound is not able to enter
inside the pores. So we can say that this catalyst is showing guest selectivity. The base catalyst 1
shows good recyclability, when it is used five consecutive times for further catalysis. To probe
its reusability, PXRD patterns have been recorded of the dried catalyst on completion of each
catalytic cycle after using at least five times. The PXRD pattern after the adsorption experiment
shows that some peaks are shifted toward the lower 2θ values indicating expansion of the
channels in response to entry of aldehydes and malononitrile (Fig. S9).
We have carried out the catalytic reactions with Ni(NO3)2.6H2O dissolved in DCM can poorly
promote (yield ~20%) some Knoevenagel condensation reaction in 24 h.
Table 1
Knoevenagel reaction catalyzed by compound 1
Run
R
Time (h)
Yield (%)
1
2
3
4
5
Ph
2
2
2
2
2
100
90
4-NO Ph
2
4-MePh
4-FPh
100
100
0
1-Naphthyl
This selectivity depends upon the relationship between the size of the reactants and the pore
window of the host.

Fig. 14. Time conversion plot for Knoevenagel condensation reactions of different aromatic
aldehydes catalyzed by complex 1.
4
. Conclusion
This work describes the synthesis of a new layered multifunctional coordination polymer
consisting of guest accessible Lewis basic sites, and large void volume inside the structure which
is due to strong hydrogen bonding interactions between the adjacent layers. This complex acts as
a good heterogeneous base catalyst for Knoevenagel condensation reaction. Reaction takes place
at the functionalized channel surface of the host, providing good yield of the product. Desolvated
phase of compound 1 acts as a selective adsorbent for green house CO gas at low temperature
2
and pressure. It shows single crystal to single crystal transformation on immersing in DCM for 7
days, at room temperature. This resultant DCM-exchanged coordination polymer is devoid of
any small channels.

Acknowledgement. R. A. A. gratefully acknowledges the financial support received from the
Department of Science and Technology, New Delhi, India. S. M. acknowledges IISER Pune for
research facilities and funding. Prof. Parimal K. Bharadwaj and Dr. Sujit K. Ghosh are sincerely
acknowledged for their unconditional support.
Appendix A. Supplementary material
CCDC 1418347 and 1420299 contain the supplementary crystallographic data for 1 and 2
respectively.
These
data
can
be
obtained
free
of
charge
via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
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Two-Dimensional Flexible Ni(II)-based Porous Coordination Polymer
Showing Single-Crystal to Single-Crystal Transformation, Selective Gas
Adsorption and Catalytic Properties
a
b
Rashmi A. Agarwal, * Soumya Mukherjee
a
Department of Chemistry, Indian Institute of Technology Kanpur, 208016, India
Email:rashmi.a.agarwal@gmail.com
b
Department of Chemistry, Indian Institute of Science Education and Research (IISER), Dr.
Homi Bhabha Road, Pashan, Pune, Maharashtra 411008, India
For Table of Contents

A two dimensional (2D) flexible coordination polymer of Ni(II) has been solvothermally
synthesized, which upon immersing in DCM give rise to a daughter coordination polymer of
Ni(II). Compound 1 behaves as a good selective adsorbent for CO at low temperature and
2
pressure as well as, an environment-friendly heterogeneous catalyst for Knoevenagel
condensation reaction.
DCM
48 hr
complex 1
complex 2