Tuned synthesis of two coordination polymers of Cd(II) using substituted bent 3-pyridyl linker and succinate: Structures and their applications in anion exchange and sorption properties

Article abstract of DOI:10.1039/c5dt03738g

Two new Cd(ii) coordination polymers, namely [Cd(3-bpdh)₂(ClO₄)₂]_n (1) and {[Cd(3-bpdh)(suc)(H₂O)]·3(H₂O)}_n (2), have been synthesized using a substituted bent N,N′-donor ligand 2,5-bis-(3-pyridyl)-3,4-diaza-2,4-hexadiene (3-bpdh) and aliphatic dicarboxylate disodium succinate (suc) with Cd(ii) perchlorate salts at room temperature by a slow diffusion technique for the exploration of our previous reported work. Both the structures were determined by single-crystal X-ray diffraction analysis and also by other physicochemical methods. Structure analysis revealed that complex 1 is a 1D chain structure containing coordinated perchlorate with a metal centre, and complex 2 shows a porous 3D framework with encapsulation of lattice water molecules into the void along the crystallographic a-axis. The PXRD study shows the bulk purity of both the complexes and TGA analysis of 2 exhibits that the structure is thermally stable up to 250 °C. Complex 1 shows a nice anion exchange property with replacement of weakly coordinated perchlorate with the inclusion of new anions; and the anion exchanged solids were characterised by FT-IR, PXRD and photoluminescence properties. The desolvated framework of 2 exhibits sorption of CO₂ and water vapor and surface adsorption of N₂ corroborating with the nature of the pore environment present in 2. The photoluminescence study has been also done for both complexes in the solid state which exhibits ligand based emissions at room temperature.

Full text of DOI:10.1039/c5dt03738g

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Tuned synthesis of two coordination polymers of Cd(II) using substituted bent
-pyridyl linkers and succinate: structure and their applications in anion
exchange and sorption properties
3
†
Dilip Kumar Maity, Biswajit Bhattacharya, Arijit Halder and Debajyoti Ghoshal *
Department of Chemistry, Jadavpur University, Jadavpur, Kolkata, 700 032, India
Eꢀmail: dghoshal@chemistry.jdvu.ac.in
_
_________________________________________________________________
Two new Cd(II) coordination polymers namely [Cd(3ꢀbpdh) (ClO ) ] (1) and {[Cd(3ꢀ
2
4 2 n
.
bpdh)(suc)(H O)] 3(H O)} (2) have been synthesized using substituted bent N,N´ꢀdonor ligand
2
2
n
2,5ꢀbisꢀ(3ꢀpyridyl)ꢀ3,4ꢀdiazaꢀ2,4ꢀhexadiene (3ꢀbpdh) and aliphatic dicarboxylate disodium
succinate (suc) with Cd(II) perchlorate salts at room temperature by a slow diffusion technique
for the exploration of our previous reported work. Both the structures were determined by singleꢀ
crystal Xꢀray diffraction analysis and also by other physicochemical methods. Structure analysis
revealed that complex 1 is a 1D chain structure containing coordinated perchlorate with metal
centre and complex 2 shows a porous 3D framework with encapsulation of lattice water
molecules into the void along crystallographic aꢀaxis. PXRD study shows the bulk purity of both
the complexes and TGA analysis of 2 exhibits that the structure is thermally stable up to 250 °C.
Complex 1 shows nice anion exchange property with replacement of weakly coordinated
perchlorate with the inclusion of new anions; and the anion exchanged solids were characterised
by FTꢀIR, PXRD and photoluminescence properties. The desolvated framework of 2 exhibits
sorption of CO , water vapor and a surface adsorption of N corroborating the nature of the pore
2
2
environment present in 2. The photoluminescence study has been also done for both the
complexes in solid state which exhibits ligand based emissions at room temperature.
_____________________________________________________________________________

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Introduction
Applications are one of the strongest driving forces of synthetic chemical research. This has been
reflected in enormous thirst for the design of coordination polymers (CPs) in recent years,
1
because of their multifunctional potential applications, in gas storage and separation, ion
2
3
4
5
6
exchange, heterogeneous catalysis, magnetism, conducting materials, optical materials and
7
sensors etc. To achieve such functionalities, the control over the structure is highly necessary;
and that ease of design in the synthesis of CPs, are made them extremely popular to the
contemporary researchers. The design of the structure of CPs are mostly done by tuning the
8
9
structure of the organic ligands, but there are many other crucial factors such as the metal ions,
1
0
11
12
13
nature of organic ligands, pH of the medium, reaction temperatures, solvents and counter
1
4
anions may also contributes significantly to create structural diversities in CPs. Thus it is very
crucial to understand the interplay of all possible factors which may sometime take significant
role for the formation of the structures of CPs. To explore the nonconventional factors in the
1
5
organization of the structure of CPs, a couple of years back we had reported a reaction of
Cd(II) with succinate (suc) and 1,4ꢀbisꢀ(3ꢀpyridyl)ꢀ2,3ꢀdiazaꢀ1,3ꢀbutadiene (3ꢀbpdb) which gave
three frameworks having 1D, 2D and 3D structure respectively. It is worth mentioning that in the
said 3D structure, there was an interesting emergence of chloride integrated framework, which
−
was originated by the reduction of ClO along with the oxidation of imine group of 3ꢀbpdb. To
4
explore the role of the electron supplier in the aforesaid process we have modified the linker and
−
made the same reaction which does not facilitate the formation of Cl integrated product. Here,
by the same reaction with methylated 3ꢀbpdh we got only two products; one is 1D chain and the
other is a 3D framework with water filled channels. In both the present and reported work the
1
6
perchlorate salt of Cd(II) was used. It had also been observed in our other previous report that
ꢀ
ꢀ
the slight change in the counter anion (ClO to NO ) with the same reaction as the present
4
3
report, yielded a single product with completely different structure and functionality. Therefore,
our present work is an attempt to address and correlate some crucial factors during the synthesis
of CPs which has not been explored much.
Herein
we
have
synthesized
[Cd(3ꢀbpdh) (ClO ) ]
(1)
and
{[Cd(3ꢀ
2
4 2 n
bpdh)(suc)(H O)].3(H O)} (2) by the reaction of Cd(II) perchlorate with succinate and a
2
2
n
substituted N,N´ꢀdonor ligand 3ꢀbpdh. It is interesting to note that here 1 shows excellent anion
exchange property and 2 exhibits gas and water vapor sorption properties.

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The anion exchange property has been significantly studied for CPs having coordinated
1
7
anions with metal centres. It has been revealed from such reports that the exchange of anions
with the metal centre may depends on the size, shape, and coordinating abilities of the anions and
−
here ClO being a comparatively weakly coordinated anion, can easily be exchanged with other
4
anions. On the other hand gas sorption properties of mixed ligand CPs is one of the most
important and widely explored functionality as this class of material shows their performance in
1
8
executing selective gas adsorption properties. Considering the burning issue of rise of CO
2
level in environment, the design of CPs which can uptake CO ; has become very much
2
1
9
contemporary in this particular field.
1
5
15
Scheme 1. Synthetic scheme of complexes 1ꢀ2 with our previous reported work (R1 , R2 and
1
5
R3 : previous reported complexes)

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Experimental section
Materials and methods
2,5ꢀbisꢀ(3ꢀpyridyl)ꢀ3,4ꢀdiazaꢀ2,4ꢀhexadiene (3ꢀbpdh) was synthesized by the procedure reported
2
0
earlier. High purity cadmium(II) perchchlorate hexahydrate; succinic acid; 3ꢀacetylpyridine
were purchased from SigmaꢀAldrich Chemical Co. Inc. and used as received. Na suc was
2
synthesized by the slow addition of solid Na CO to aqueous solution of H suc in a 1:1 ratio and
2
3
2
was allowed to evaporate until dryness. All other chemicals including solvents were of AR grade
and used as received. Ultrapure water obtained from a Milliopore water purification system (≥18
Mꢁ, MilliꢀQ, millipore) was used in synthesis as well as in all experiment.
Physical measurements. Microanalyses (C, H, N) were performed on a Heraeus CHNS
−
1
analyzer. Infrared spectra (4000–400 cm ) were taken on KBr pellet, using Perkin–Elmer
Spectrum BXꢀII IR spectrometer. Powder Xꢀray diffraction (PXRD) data were collected on a
Bruker D8 Discover instrument with CuꢀKα radiation. Thermogravimetric analysis (TGA) was
carried out on a METTLER TOLEDO TGA 850 thermal analyzer in the temperature range of
−
1
3
0ꢀ600 °C under N atmosphere at a heating rate of 10 °C min . The solid state emission was
2
recorded on HORIBA Jobin Yvon (Fluoromaxꢀ3) instrument. GCꢀMS analysis was performed
using a Perkin Elmer CLARUS 680 instrument. ESI mass spectra were recorded with Waters
QTOF Micro YA263 equipment.
Sorption measurements. The adsorption isotherms of N (77 K), CO (195 K) and water vapor
2
2
(298 K) were measured using the dehydrated sample of 2 in Quantachrome Autosorb iQ
instrument. In the sample tube ~40 mg sample of 2 were placed which had been prepared at
−
1
1
30°C under a 1×10 Pa vacuum for about 4 hours prior to measurement of the isotherms.
Helium gas (99.999% purity) at a certain pressure was introduced in the gas chamber and
allowed to diffuse into the sample chamber by opening the valve. The amount of gas/vapor
adsorbed was calculated from the pressure difference (Pcal − P ), where P is the calculated
e
cal
pressure with no gas adsorption and P is the observed pressure at equilibrium. All operations
e
were computerꢀcontrolled and automatic.
Synthesis
.
[
Cd(3-bpdh) (ClO ) ] (1) and {[Cd(3-bpdh)(suc)(H O)] 3(H O)} (2). Compounds 1 and 2
2
4 2 n
2
2
n
were synthesized in a same reaction. A methanolic solution (20 mL) of 2,5ꢀbisꢀ(3ꢀpyridyl)ꢀ3,4ꢀ
diazaꢀ2,4ꢀhexadiene (3ꢀbpdh) (1 mmol, 0.238 g) was mixed with an aqueous solution (20 mL) of

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disodiumsuccinate (Na suc) (1 mmol, 0.162 g) and the resulting solution was stirred for 1 hour to
2
.
mix well. Cd(ClO ) 6H O (1 mmol, 0.419 g) was dissolved in 20 mL water in a separate beaker.
4
2
2
6
mL of this mixed ligand solution was slowly and carefully layered above 3 ml of metal
solution using 5 mL buffer (1:1 MeOH of and H O) in a glass tube. After three weeks, white
2
colored block shaped single crystals of 1 (yield. 30%) and simultaneously yellowish block
shaped single crystals of 2 (yield. 42%) were obtained at the wall of the tube; they were
separated manually using microscope and washed with methanol–water (1:1) mixture and dried.
Anal. calcd for C H N O Cl Cd (1, %): C, 42.69; H, 3.58; N, 14.22. Found: C, 42.63; H, 3.62;
2
8
28
8
8
2
ꢀ1
N, 14.19. IR for 1 (KBr pellet, cm ): ν(CHꢀAr), 3089; ν(C=N), 1609; ν(C=C), 1479ꢀ1420 and
ν(ClO ), 1121ꢀ1049. Anal. Calc. for C H N O Cd (2, %): C, 40.12; H, 4.86; N, 10.4. Found: C,
4
18 26
4
8
ꢀ1
4
0.17; H, 4.91; N, 10.36. IR for 2 (KBr pellet, cm ): ν(H O), 3422; ν(CHꢀAr), 3063; ν(C=N),
2
1575; ν(C=C), 1575ꢀ1421 and ν(CꢀO), 1288ꢀ1045.
Crystallographic data collection and refinement. The single crystals of compounds 1 and 2
were mounted on the tips of glass fibers with commercially available glue. Xꢀray data collection
of two single crystals were performed at room temperature using Bruker APEX II diffractometer,
equipped with a normal focus, sealed tube Xꢀray source with graphite monochromated MoꢀKα
2
1
radiation (λ= 0.71073Å). The data are integrated using SAINT program and the absorption
2
2
23
corrections are made with SADABS. Both the structures are solved by SHELXSꢀ97 using
Patterson method and followed by successive Fourier and difference Fourier synthesis. Full
2
23
matrix leastꢀsquares refinements were performed on F using SHELXLꢀ97 with anisotropic
displacement parameters for all nonꢀhydrogen atoms. All the hydrogen atoms are fixed
geometrically by HFIX command and placed in ideal positions for both cases. Calculations are
2
3
23
24
25
carried out using SHELXS 97, SHELXL 97, PLATON v1.15, ORTEPꢀ3v2, and WinGX
2
6
system Verꢀ1.80.
Data collection and structure refinement parameters along with
crystallographic data for both the complexes are given in Table 1. The selected bond lengths and
angles are given in Table 2ꢀ3.
Results and discussion
Discussion regarding synthesis of the compounds
1
5
As mentioned before, in our earlier work we had reported an in situ perchlorate to chloride
transformation supported by the metal organic framework, where a single reaction produced
three different compounds (Scheme 1). The role of the N,N´ꢀdonor ligand has been discussed

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vividly in the previous case for the said reduction. There was a clear evidence of the oxidation of
the 3ꢀbpdb (Scheme 2), which may have facilitated the said framework assisted perchlorate to
chloride reduction. With extension of our curiosity in this particular point here we have used a
methyl substituted ligand 3ꢀbpdh which is much more difficult to oxidize to form nicotinamide
1
5
due to the presence of more stable CꢀC bond, rather than CꢀH bond in case of 3ꢀbpdb.
Following our line of thinking that occurs when we made a reaction of Cd(ClO ) and succinate
4
2
with 3ꢀbpdh. We got only two products (Scheme 1) without any chloride containing product,
which was found in case of 3ꢀbpdb. Here complex 1 exhibits a 1D chain which contains bridging
3ꢀbpdh ligand and coordinated perchlorate ions and complex 2 contains succinate and 3ꢀbpdh to
form a three dimensional structure. There is no existence of any structure with chlorides ions,
rejecting the possibility for reduction of perchlorate to chloride and oxidation for imine group
containing 3ꢀbpdh ligand to amide. This has been convincingly proved by GCꢀMS study and ESI
mass spectra (Fig. S2ꢀS5) taking the residue of reaction mixture after drying. In all studies only
the existence of 3ꢀbpdh ligand has been established whereas in our previous work with 3ꢀbpdb,
imine group of this linker was oxidized to form amide which was confirmed by GCꢀMS
experiment and ESI mass spectra. So, comparing our previous work it can be ascertained that the
reduction of perchlorate must be inspired by the use of non methylated 3ꢀbpdb linkers; which is
not possible here with a methylated 3ꢀbpdh linkers.
Scheme 2. Representing diagram to show the oxidation process favored by non methylated 3ꢀ
1
5
bpdb instead of methylated 3ꢀbpdh

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Crystal structure descriptions of [Cd(3-bpdh) (ClO ) ] (1). Compound 1 crystallizes in
2
4 2 n
monoclinic P21/n space group with Z value 2 and the structure analysis reveals that the
compound 1 exhibits one dimensional (1D) structure of Cd(II) connected by doubly bridging 3ꢀ
bpdh ligand. In asymmetric unit of 1 Cd(II) ions are in special position (1,0,1) with their half
occupancy along with one 3ꢀbpdh linker and one coordinated perchlorate ion. The hexaꢀ
coordinated Cd(II) with CdO N coordination environments shows a distorted octahedral
2
4
a
b
c
geometry (Fig. 1a) created by four nitrogen atoms (N1, N1 , N4 and N4 where a = 2ꢀx, ꢀy, 2ꢀz;
b = ꢀ1+x, y, ꢀ1+z; c = 3ꢀx, ꢀy, 3ꢀz) of four different 3ꢀbpdh linker which creates the basal plane.
a
The axial positions are occupied by two symmetry related oxygen atoms (O1, O1 where a = 2ꢀx,
ꢀ
y, 2ꢀz) of two coordinated perchlorate ion. In 1, the CdꢀN bond length varies from 2.319(3) ꢀ
.342(3) Å and the CdꢀO bond length is 2.394(3) Å (Table 2). The other selected bond lengths
and bond angles are reported in Table 2. Here two adjacent Cd(II) centers are connected by two
ꢀbpdh linkers and resulting the formation of 1D chain structure containing pendant perchlorate
2
3
2
7
ion (Fig. 1b). Structural analysis with TOPOS suggests that the overall framework exhibits a
2,4ꢀc binodal net (Fig. 1c) with stoichiometry (2ꢀc)2(4ꢀc) and the corresponding Schläfli symbol
2
for the net is {4 }{4}.
.
Crystal structure descriptions of {[Cd(3-bpdh)(suc)(H O)] 3(H O)} (2). Compound 2
2
2
n
crystallizes in the orthorhombic Pna21 space group with Z value 4 and the structure analysis
reveals that the compound 2 exhibits a porous three dimensional (3D) framework of Cd(II)
connected by bridging succinate (suc) and bent bisꢀ(3ꢀpyridyl) N,N´ꢀdonor ligand (3ꢀbpdh). The
asymmetric unit of 2 contains one Cd(II) ion, one 3ꢀbpdh linker, one succinate, one coordinated
water molecule and three lattice water molecules. The hexaꢀcoordinated Cd(II) with CdO N2
4
coordination environments shows distorted octahedral geometry (Fig. 2a) created by four oxygen
a
atoms (O1, O2, O4 and O1W where a = ꢀ1ꢀx, ꢀy, ꢀ1/2+z) of two different succinate and one
coordinated water molecule, which creates the basal plane. The axial positions are occupied by
b
two nitrogen atoms (N1, N4 where b = ꢀ1/2ꢀx, 1/2+y, 1/2+z) of two different 3ꢀbpdh ligands. In
compound 2, the CdꢀO bond length varies from 2.224(3) ꢀ 2.507(3) Å and the CdꢀN bond lengths
are in the range from 2.332(3) ꢀ 2.358(3) Å (Table 3). The other selected bond lengths and bond
angles are reported in Table 3. Here each succinate ligand bridges in between two Cd(II) centers
where one end of carboxylate binds in a monodentate fashion and another end in a chelating
fashion and resulting the formation of 1D chain along cꢀaxis (Fig. 2b). The bent 3ꢀbpdh ligands

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connects alternate Cd(II) centers in crisscross fashion to make a overall 3D framework (Fig. 2c).
The resultant 3D framework contains water filled 1D channels oriented along a axis having a
2
cannel dimension of around 4.8 × 3 Å (Fig. S6a). Without the water molecules the total solvent
3
accessible void value is estimated by PLATON is 458.2Å which is 20.57% of the total crystal
3
volume of 2228 Å . The 3D framework is also additionally stabilized through intramolecular πꢀπ
interactions in between two 3ꢀpyridyl aromatic rings of two different 3ꢀbpdh linkers (Fig. S6b
2
7
and Table S1). Structural analysis with TOPOS suggests that the overall framework exhibits a
5
4
ꢀc uninodal net (Fig. 2d) with Schläfli symbol for the net is {6 .8}.
Powder X-ray diffraction (PXRD) analysis
Powder Xꢀray diffraction (PXRD) analysis was carried out to confirm the phase purity of the
bulk materials both complexes at room temperature. The experimental PXRD patterns of
complexes 1 and 2 are in good agreement with the simulated ones from their corresponding
single crystal structures (Fig. S7), confirming the phase purity of the complexes. For 2 the PXRD
pattern has also been collected after heating the sample at 130°C which is also in agreement with
the as synthesized form of 2 (Fig. S7). This clearly indicates the thermal stability of the
framework even after the removal of volatiles (water) at 130°C.
Thermogravimetric analysis
Caution! The TGA experiment was not carried out in case of 1 because there has no solvent
molecule and it contains coordinated perchlorate ion which is explosive on heating; so for safety
reasons we have ignored this measurement.
The TGA curve of complex 2 (Fig. S8) exhibits a weight loss of ~13.11% at ~104 °C, which
reveals the presence of three lattice and one coordinated water molecules (calc. wt% 13.36) and
the dehydrated framework is stable up to 250 °C without any weight loss suggesting the
complete removal of all water molecules during activation process. After further heating the
dehydrated framework collapses and decomposed into unidentified products.
Anion exchange and luminescence studies
As revealed from the single crystal structure analysis of 1, the perchlorate anions are coordinated
with Cd(II) centre. Since complex 1 is insoluble in water and common organic solvents so it is
expected to exhibit anion exchange properties due to the presence of labile coordinated
2
8
perchlorate ion. The wellꢀground powder of complex 1 (~ 60 mg) was suspended in 5 ml

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0
.01M aqueous solution (taking ion free water) of Naꢀsalt of different anions viz. NaN , NaNCO,
3
NaSCN, NaNO and Na CrO ; separately and stirred gently for 24 hours at room temperature to
3
2
4
permit the anion exchange. After that each mixture was filtered and washed with deꢀionized
water for three times. The completion of anion exchange with the parent complex 1 was
monitored by FTꢀIR spectroscopy (Fig. 3) and PXRD measurement. In IR spectra of 1 intense
ꢀ1
−
band at ~1121 and ~1049 cm is appeared which corroborates the presence of ClO anions.
4
After the anion exchange, the IR spectra of the exchanged solids (Fig. 3) exhibit significant
−
weakening of the ClO bands present in parent complex and emergence of new characteristic
4
ꢀ1
−
ꢀ1
−
ꢀ1
−
peak at ~2033 cm for N (1@N ), ~2187 cm for NCO (1@NCO), ~2043 cm for SCN
3
3
ꢀ1
−
ꢀ1
2ꢀ
(
1@SCN), ~1429 to 1367 cm for NO3 (1@NO ) and at ~891 to 855 cm for CrO4
3
−
(
1@CrO ) respectively. The weakening of ClO bands and the generation of new characteristic
4
4
bands of respective anions used for the exchange validated the progression of anion exchange
process. Other peaks in the spectra remained virtually unchanged, which indicates that the
framework structure of the MOF remained intact after the exchange process. After completion of
anion exchange process with the corresponding foreign anions, the filtrates are collected in each
case and dried to check the IR spectra. The presence of significant amount of perchlorate in all
IR spectrums of the filtrates (Fig. S9); also support the exchange of perchlorate with the
corresponding anions. From the PXRD pattern (Fig. S10) it is noticed that 1@ NO and parent 1
3
2
9
is closely isostructural which has been confirmed by indexing with the use of TREOR program.
The indexing shows same crystal system with very close cell parameters (Fig. S11, Table S2)
between 1@NO and 1. The PXRD patterns (Fig. S10) of other anion exchanged products except
3
1
@N and 1@CrO are quite similar with the PXRD pattern of 1 which also corroborates the
3 4
retention of skeletal structures of the frameworks.
−
In case of N , the slight variation in PXRD pattern attributes probably due to the different
3
−
−
size, shape and coordinating tendency of N3 compared to the other anions. The N being a
3
−
strongly coordinating anions can easily remove the coordinated ClO from the respective parent
4
frameworks and may facilitate a structural change in the framework, after the anion exchange
2
ꢀ
process. In case of CrO4 the variation is probably due to the different charge and large size
2
ꢀ
compared to the other anions. The CrO4 being a bulky binegative anion, must attached to the
central metal atom with a different ratio than the others, resulting a structural change in the
framework after the anion exchange process. However the anion exchange could not be

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monitored by single crystal structure due to the loss of single crystalinity of the compounds
during anion exchange process.
The solid state fluorescence spectra of both complexes 1 and 2 as well as the 3ꢀbpdh
ligand has been measured at room temperature, which shown in Fig. S12. The free 3ꢀbpdh ligand
and complexes 1ꢀ2 were excited at 325 nm, 241 nm and 330 nm respectively. The fluorescent
emissions were found with a maximum at 394 nm and 391 nm for free 3ꢀbpdh ligand and both of
the complexes respectively. The emission spectrum of 3ꢀbpdh ligand with πꢀconjugated
backbones is may be due to from the lowest singlet excited state to the singlet ground state i.e.
intra ligand π*ꢀπ or π*ꢀn transition and both the complexes 1 and 2 also show the ligand based
emission may be due to the same π*ꢀπ or π*ꢀn transition. The photoluminescence spectra of its
anion exchanged products of complex 1 were also investigated in solid state at room temperature
(
Fig. 4). Like complex 1 all the anion exchanged products are excited at λ = 241 nm. For
ex
1
@NO and 1@CrO the emission maxima were obtained at 391 nm and 390 nm respectively
3 4
with a lesser emission intensity compared to 1 whereas in case of 1@NCO, 1@SCN and 1@N3
the emission maxima were at 390 nm with an enhancement of emission intensity compared to 1.
The observed emission intensity order for the anion exchanged solids and parent complex with
free 3ꢀbpdh ligand was 1@NCO> 1@SCN> 1@N > 1> 1@CrO > 1@NO > 3-bpdh. The
3
4
3
probable rationale to the difference in luminescence intensities of parent 1 with its anion
exchange solids can be ascribed to the various electronic interactions of the corresponding anions
with the framework and metal node, as well as with their different characteristic coordinating
2
8
modes, shapes, sizes, and geometries.
Gas and water vapor sorption studies
The single crystal Xꢀray diffraction analysis reveals that the 3D framework of 2 have oneꢀ
dimensional pores occupied by the guest water molecules. Prior to gas and vapor sorption
experiments, guest water molecules of 2 was removed by solvent exchange using dry acetone
o
−1
and then thermal activation at 130 C, under dynamic vacuum (1×10 Pa).
The desolvated framework of 2 was permitted to N and CO gas and water vapor
2
2
adsorption experiments. It was found nonporous with respect to N at 77 K probably due to its
2
2
pore aperture (i.e. 4.8 × 3 Å ) very close to the kinetic diameter of N (kinetic diameter = 3.6 Å).
2
Besides this the presence of unidirectional channel in the 3D structure make it unavailable for
further inclusion of the N , after blocking the pore windows by incoming N during adsorption.
2
2

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As a result, the porosity was unavailable with respect to N due to the absence of multi
2
dimensional channel (Fig. S13). Thus in complex 2, only surface adsorption for N molecules
2
has been observed (Fig. S14). The CO adsorption isotherms has been measured for 2 at 195 K
2
3
−1
show reversible uptake of 4.7 (23.87cm g ) wt % of CO , as the pressure approaches to 1 atm
2
(
Fig. 5). The CO molecules have comparatively smaller kinetic diameter (3.3 Å) than N (3.6 Å)
2
2
and it has a quadruple moment which may show a strong interaction with the Nꢀbased electron
riched polar azine moiety [ꢀ(Me)C=NꢀN=C(Me)ꢀ] of 3ꢀbpdh and uncoordinated oxygen atom of
succinate in 2. These two collective phenomena are probably responsible for the enhanced CO2
adsorption of 2. There was a hysteresis in CO adsorptionꢀdesorption isotherm of 2 which can be
2
corroborated to the strong interaction between quadrupolar CO and the basic polar azine moiety
2
present in the framework (Fig. 5).
The water vapor adsorption of 2 has also been studied at 298 K to understand the nature of
interaction of water with the pore wall of the framework. It shows a steep rise in the uptake of
3
ꢀ1
water vapor of ~36 cm g at very low pressure (P/P ≈ 0.32), which has been corroborated with
0
the high water affinity of the desolvated framework. In the crystal structure, there is a
coordinated water molecule which released in sample preparation temperature (130°C) and
creates an open metal site in the framework. This open metal site is responsible for the said rise
of water uptake in very low pressure. Thereafter, a sharp increase in the vapor adsorption profile
3
ꢀ1
was observed which reaches finally up to ~94 cm g which corresponds to around two
molecules of H O per formula unit of 2 (Fig. 6). This moderately high water uptake of 2 is
2
accountable due to the presence of open metal site in the desolvated form, presence of polar
azine moiety in the framework and also due to the presence of flexible succinate with
uncoordinated oxygen atom. Similarly in water vapor sorption profile there occurs a large
hysteresis which may be due to the flexible frameworks and the strong interaction between the
3
0
framework and the guest or diffusion barrier.
Conclusion
To explore the nonconventional factors in the organization of the structure of CPs, we have
synthesized here two Cd(II) based CPs with different topology using a substituted bent 3ꢀpyridyl
1
5
linker (3ꢀbpdh) instead of previously used non substituted 3ꢀbpdb and disodium succinate
suc). From aforesaid discussion it is revealed that in our previous work we had obtained three
different CPs including 1D, 2D and 3D framework using same reaction as present except use of
(

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3ꢀbpdb ligand instead of 3ꢀbpdh. It is note worthy that in our said previous work, there was an
−
interesting appearance of Cl integrated 3D framework, which was generated by the reduction of
−
ClO4 along with the oxidation of imine group of 3ꢀbpdb to nicotinamide. To verify the
ꢀ
formation of this Cl integrated 3D framework mentioned through electron taking reduction
process, we have used the methylated linker (3ꢀbpdh) instead nonmethylated linker (3ꢀbpdb) and
−
performed the same reaction as previous which does not lead to the formation of Cl integrated
product. At present reaction with methylated 3ꢀbpdh we have obtained only two products; one is
1D chain and the other is a 3D structure having water filled channels. Another interesting
1
6
observation had been shown in our other previous work that when we made same reaction
except taking Cd(NO ) instead of Cd(ClO ) then a totally different single product with different
3
2
4 2
functionality had been found. As a result our present work is an attempt to address and correlate
some crucial factors during the synthesis of CPs which has not explored much. Two complexes
1
ꢀ2 at present are not only interesting for their structure of formation and topology but also
applicable for their excellent anion exchange property and gas sorption properties respectively.
The one dimensional complex 1 contains coordinated perchlorate ions with Cd(II) centers and
performs well anion exchange with the inclusion of foreign anions retaining the same skeleton
structure. On the other hand, Complex 2 shows nice sorption of CO , water vapor and a surface
2
adsorption of N which is commensurate to its pore size and pore environment. In summary this
2
work is a nice example of cogent design of functional CPs by controlling such factors which are
not so conventional.
Acknowledgements
Authors gratefully acknowledge the financial assistance given by SERB [No. SB/S1/ICꢀ06/2014,
grant to DG] and CSIR [No.01(2729)/13/EMRꢀII, grant to DG], Govt. of India. BB and DKM
acknowledges UGC for the research fellowship. The Xꢀray diffractometer facility under the
DSTꢀFIST program of Department of Chemistry (JU) is also gratefully acknowledged. Authors
are grateful to Prof. S. Bhattacharya for the GCꢀMS study and Prof. K. K. Rajak for the
photoluminescence study.
Electronic supplementary information (ESI) available:
The IR, PXRD patterns, Photoluminescence spectra of complexes 1ꢀ2 and TGA of complex 2
along with different application based figures of both complexes and tables related to the crystal
structure reported in this paper are available as ESI. The structure reported in this paper having

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DOI: 10.1039/C5DT03738G
the CCDC reference numbers 1426873 and 1426874. For ESI and crystallographic data in CIF or
other electronic format see DOI:
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Figures and Tables:
Fig. 1 (a) Coordination environment around the Cd(II) ions in 1; Cd (green), N (blue), O (red), C
(black), Cl (yellow); (b) 1D chain structure constructed through 3ꢀbpdh ligand and coordinated
perchlorate ions in 1; (c) Simplified topological representation of 1D chain in 1.

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Fig. 2 (a) Coordination environment around the Cd(II) ions in 2; Cd (green), N (blue), O (red), C
(
black); (b) 1D metal carboxylate chain along cꢀaxis in 2 (3ꢀbpdh ligands are omitted for clarity);
c) 3D framework of 2 constructed by both succinate and 3ꢀbpdh ligand viewing by topos
(
diagram (green: Cd(II) metal; pink: succinate and blue: 3ꢀbpdh ligand); (d) Topological
representation of 4ꢀconnected uninodal net in 2.

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Fig. 3 Combined FTꢀIR spectra of parent complex 1 and its anionꢀexchanged solids with
highlighted bands of the corresponding anions.
Fig. 4 Combined photoluminescence spectra of complex 1 and its anion exchanged solids with
free 3ꢀbpdh ligand.

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Fig. 5 CO sorption isotherms of 2; filled and open circles represent adsorption and desorption
2
respectively.
Fig. 6 Water sorption isotherms of 2; filled and open triangles represent adsorption and
desorption respectively.

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Table 1 Crystallographic and structural refinement parameters of complexes 1ꢀ2
1
2
Formula
C H N O Cl Cd
C H N O Cd
2
8
28
8
8
2
18 26
4
8
Formula Weight
787.89
538.84
Crystal System
Space group
a/ Å
b/Å
c/ Å
α/°
Monoclinic
P21/n
8.840(5)
17.934(5)
10.458(5)
90
Orthorhombic
Pna21
7.087(5)
17.669(5)
17.793(5)
90
β/°
γ/°
V/ Å
Z
98.701(5)
90
1638.9(13)
2
1.597
0.890
90
90
3
2228.0(18)
4
1.600
1.031
1088
1.6ꢀ27.6
35046
5146
4818
0.021
–
3
D / g cm
c
–
1
ꢂ /mm
F(000)
θ range/°
Reflections collected
Unique reflections
Reflections I > 2σ(I)
Rint
796
2.3ꢀ27.6
28123
3780
3131
0.034
2
goodnessꢀofꢀfit (F )
R1 (I > 2σ(I))
1.06
1.07
[
a]
0.0387
0.1087
ꢀ0.58, 0.89
0.0204
0.0578
ꢀ0.28, 0.35
[
a]
wR2(I > 2σ(I))
ρ min / max /e Å
3
∆
[a]
2
2
c
2
2 2 ½
R = ΣF –F /ΣF , wR = [Σ (w (F – F ) )/ Σw (F ) ]
1
o
c
o
2
o
o
Table 2 Selected bond lengths (Å) and bond angles (°) for complex 1
Cd1ꢀO1
Cd1ꢀN4
2.394(3)
2.319(3)
2.342(3)
Cd1ꢀN1
Cd1ꢀO1
Cd1ꢀN4
2.342(3)
2.394(3)
2.319(3)
94.76(10)
87.73(10)
87.35(8)
180.00
b
a
c
a
Cd1 ꢀN1
O1ꢀCd1ꢀN1
b
a
b
a
92.27(10) O1ꢀCd1ꢀN4
O1ꢀCd1ꢀO1c 180.00 O1ꢀCd1ꢀN1
O1ꢀCd1ꢀN4 85.24(10) N1ꢀCd1ꢀN4
O1 ꢀCd1 ꢀN1 87.73(10) N1ꢀCd1ꢀN1
a
a
c
a
b
N1ꢀCd1ꢀN4
92.65(8)
O1 ꢀCd1ꢀN4
85.24(10)
a
b
b
c
N1 ꢀCd1ꢀN4 92.65(8)
N4 ꢀCd1 ꢀN4 180.00
a
a
a
c
O1 ꢀCd1ꢀN1 92.27(10) O1 ꢀCd1ꢀN4
94.76(10)
a
c
N1 ꢀCd1ꢀN4 87.35(8)
Symmetry code: a = 2ꢀx, ꢀy, 2ꢀz; b = ꢀ1+x, y, ꢀ1+z; c = 3ꢀx, ꢀy, 3ꢀz.

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Table 3 Selected bond lengths (Å) and bond angles (°) for complex 2
Cd1ꢀO1
Cd1ꢀO2
Cd1ꢀO4
O1ꢀCd1ꢀO1W
O1ꢀCd1ꢀN1
O1ꢀCd1ꢀN4
O1WꢀCd1ꢀN1
O1WꢀCd1ꢀN4
2.338(3) Cd1ꢀO1W
2.507(3) Cd1ꢀN1
2.224(3) Cd1ꢀN4
95.09(9) O1ꢀCd1ꢀO2
90.45(10) O1ꢀCd1ꢀO4
90.92(10) O1WꢀCd1ꢀO2 148.57(8)
2.302(3)
2.332(3)
2.358(3)
53.49(7)
139.40(10)
a
b
a
b
a
91.24(6) O1WꢀCd1ꢀO4 125.19(11)
b
83.50(7) O2ꢀCd1ꢀN1
86.09(9) O2ꢀCd1ꢀN4
93.31(9) N1ꢀCd1ꢀN4
89.01(9)
89.78(7)
95.19(7)
174.66(6)
a
b
b
O2ꢀCd1ꢀO4
a
O4 ꢀCd1ꢀN1
a
b
O4 ꢀCd1ꢀN4
Symmetry code: a = ꢀ1ꢀx, ꢀy, ꢀ1/2+z; b = ꢀ1/2ꢀx, 1/2+y, 1/2+z.

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For Table of Content Use
Tuned synthesis of two coordination polymers of Cd(II) using substituted bent
-pyridyl linkers and succinate: structure and their applications in anion
3
exchange and sorption properties
Dilip Kumar Maity, Biswajit Bhattacharya, Arijit Halder and Debajyoti Ghoshal