Coordination polymers derived from pyridyl carboxylate ligands having an amide backbone: An attempt towards the selective separation of CuII cation following in situ crystallization under competitive conditions

Article abstract of DOI:10.1039/c4ce00733f

A series of coordination polymers (CPs) derived from pyridyl carboxylate ligands equipped with a hydrogen bonding backbone (amide), namely L1 [sodium 4-(nicotinamido) benzoate] and L2 [sodium 3-(nicotinamido) benzoate], has been synthesized and characterized by single crystal X-ray diffraction. The effect of the ligating topology of these two positional isomers (L1 and L2) on the resultant supramolecular architecture of the corresponding CPs was investigated. The results indicate that most of the CPs display a 1D looped chain topology. Following in situ crystallization technique, attempts were made to separate environmentally toxic metal cation Cu^II in the form of the corresponding Cu^II CPs from a complex mixture of cations (Cu ^II, Zn^II and Co^II) using both the ligands, while L1 was unsuccessful, L2 could indeed separate the Cu^II cation. The coordinating ability of the pyridyl and carboxylate moieties on the selective separation of cations was investigated. The results indicate that the selective separation of Cu^II followed the Irving-Williams series. Atomic absorption spectroscopy revealed that ～97% of Cu^II could be separated by this technique.

Full text of DOI:10.1039/c4ce00733f

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Coordination polymers derived from pyridyl
carboxylate ligands having an amide backbone:
an attempt towards the selective separation of
CuII cation following in situ crystallization under
competitive conditions†
Cite this: CrystEngComm, 2014, 16,
7815
*
Mithun Paul and Parthasarathi Dastidar
A series of coordination polymers (CPs) derived from pyridyl carboxylate ligands equipped with a hydrogen
bonding backbone (amide), namely L1 [sodium 4-(nicotinamido) benzoate] and L2 [sodium 3-(nicotinamido)
benzoate], has been synthesized and characterized by single crystal X-ray diffraction. The effect of the
ligating topology of these two positional isomers (L1 and L2) on the resultant supramolecular architecture of
the corresponding CPs was investigated. The results indicate that most of the CPs display a 1D looped chain
topology. Following in situ crystallization technique, attempts were made to separate environmentally toxic
metal cation CuII in the form of the corresponding CuII CPs from a complex mixture of cations (CuII, ZnII
and CoII) using both the ligands, while L1 was unsuccessful, L2 could indeed separate the CuII cation. The
coordinating ability of the pyridyl and carboxylate moieties on the selective separation of cations was inves-
tigated. The results indicate that the selective separation of CuII followed the Irving–Williams series. Atomic
absorption spectroscopy revealed that ~97% of CuII could be separated by this technique.
Received 8th April 2014,
Accepted 13th June 2014
DOI: 10.1039/c4ce00733f
www.rsc.org/crystengcomm
ditopic and tritopic ligands having non-innocent (hydrogen
Introduction
bond equipped) backbones.11 Thus, various bis-pyridyl
Spontaneous self-assembly1 of organic linkers (ligand) and
suitable metal centres result in highly crystalline materials
known as coordination polymers (CPs).2 The field of CPs has
rapidly grown since the early report by Robson et al.3 on the
synthesis of a CuII-diamondoid network derived from three
dimensionally linked rod-like segments, namely 4,4′,4′′,4′′′-
tetracyanotetraphenyl methane. Because of the remarkable
advancement of single crystal X-ray diffraction techniques
and the highly crystalline nature of CPs, it has been possible
to study the structures of CPs at the molecular level enabling
researchers to design a priori CPs with desired structures and
functions. Thus, CPs are a special class of supramolecular
materials offering various potential applications, such as gas
storage,4 catalysis,5 anion separation,6 magnetic properties,7
drug delivery,8 sensors,9 opto-electronics,10 etc.
ligands having amide or urea functionality were exploited in
generating intriguing structures like an all-helical 3D
network,12a diamondoid network,12b Borromean entangled
network,12c metalla-cryptand,12d etc. We have also developed
CPs capable of displaying anion separation and meta-
llogelation properties.6e
Separation of toxic metal pollutants is important in the con-
text of environmental remediation. Aqueous phase metal cat-
ion separation has been achieved by various techniques that
include precipitation,13 adsorption14 and solvent extraction.15
While chelating agents like hydroxyoximes, β-diketones, etc.,
have been used in solvent extraction,16 solid sorbent mediated
cation separation17 includes ligand grafted organic polymers,
surface modified silica gels, mesoporous and ion exchange
materials.18 Although solvent extraction offers advantages like
flexible operation, ability to handle wide ranges of concentra-
tion and selectivity, it, however, suffers from disadvantages like
toxicity and flammability of the solvents, time consuming
phase separation due to emulsion formation, etc. Solvent
extraction method also depends on the pH of the medium,
which can be considered as an additional disadvantage.
Copper plays a crucial role in biology,19 various copper
containing enzymes carry out important biological functions.
However, beyond a critical concentration, it is immensely toxic;
As a part of our ongoing research program, we have been
interested in developing intriguing CPs derived from various
Department of Organic Chemistry, Indian Association for the Cultivation of
Science, 2A & 2B Raja S. C. Mullick Road, Kolkata-700032, West Bengal, India.
E-mail: ocpd@iacs.res.in
† Electronic supplementary information (ESI) available: Molecular plots and
H-bonding parameters of coordination polymers, TGA, PXRD, elemental analysis,
AAS, CIFcheck reports. CCDC 989153–989165. For the ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c4ce00733f
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for example, drinking water containing copper concentrations
more than 2 mg L−1 is toxic. Since copper is an indispensible
element present in various industrial materials such as stain-
less steels, nonferrous alloy, metal plating, refractory materials
and thermal and electric conductors, it is no wonder that one
of the major environmental pollutants20 (industrial waste) is
copper. In a recent report, we showed that CuII was separated
selectively from a complex mixture of divalent cations (ZnII,
CoII, CuII) by exploiting the in situ crystallization of coordina-
tion polymers.21 In this technique, a suitable ligand was
allowed to react with a competitive mixture of metal cations to
crystallize out coordination polymers containing the desired
metal centre as a part of the coordination network. In this par-
ticular study, we exploited bis-pyridyl-bis-amide based chiral
ligands derived from L-amino acids to achieve the selective
separation of CuII in the form of the corresponding coordina-
tion polymers. The reasons for obtaining the selective formation
of CuII coordination polymers in this competitive conditions
were: (a) the stability constants of CuII compounds were
expected to be more than that of CoII and ZnII as per the Irving–
Williams series,22 (b) pyridyl N atoms being a soft base as per
the HSAB principle did not react to a significant extent with the
relatively harder acids, such as CoII and ZnII, compared to the
borderline CuII metal centre under competitive conditions.
In the present study, we considered the ditopic ligands L1
and L2 wherein both soft (pyridyl N) and hard (carboxylate)
coordinating sites were available.23 The reason for choosing
ligands having both hard and soft coordinating sites was to
study the driving force behind cation separation – is it mainly
governed by the hard–soft acid–base (HSAB) principle or is it
controlled by Irving–Willams series?
coordination polymers thereby enabling the selective separa-
tion of CuII from a complex mixture of cations.
Results and discussion
The pyridyl-carboxy-amide ligands L1H and L2H were synthe-
sized by reacting nicotinoyl chloride with the corresponding
amino benzoic acid in a dichloromethane (DCM)–THF mix-
ture under refluxing conditions. The corresponding precipi-
tates, thus formed, were isolated and washed with DCM–THF
to yield the pure ligands in good yield (see Experimental).
Attempts to react these ligands with various metal salts (CuII,
ZnII, CoII, CdII and FeII) in DMF/EtOH/water resulted in crys-
tallization and precipitation of L1H and L2H, respectively. In
order to synthesize coordination polymers with these ligands,
we then converted the ligands into the corresponding Na salt
by reacting the ligands with NaOH solution. The reaction of
the Na salts of these ligands with various metal salts resulted
in 12 crystalline coordination polymers (Scheme 1). Single
crystals of L1H and the coordination polymers (CP1a–CP1f
and CP2a–CP2f) were subjected to single crystal X-ray diffrac-
tion (SXRD). It may be mentioned that in the case of L1,
CdIICPs, namely CP1e and CP1d, were crystallized concomi-
tantly. The same was true for CP2a and CP2b wherein L2 was
used. Table 1 lists the crystal data. Certain crystallographic
and structural parameters are given in Table 2.
Single crystal structure of the free ligand L1H
Colorless blocked shaped crystals of L1H belong to the centro-
symmetric orthorhombic space group Pbcn. The asymmetric
unit contained a fully occupied ligand molecule. The ligand
molecules propagated into 1D hydrogen bonded polymeric
chain involving the carboxy–pyridine synthon sustained by
N–H⋯O interactions. Such 1D chains were packed in perpen-
dicular fashion sustained by N–H⋯O interactions involving
the amide –NH and carboxylic O of the neighbouring chains
resulting in an overall 3D hydrogen bonded network (Fig. 1).
Herein, we report the syntheses and single crystal structures
of two new ligands, L1H and L2H, and their corresponding
coordination polymers derived from L1 and L2 (corresponding
sodium carboxylates) with various transition metal centres
(CuII, ZnII, CoII, CdII and FeII). Competitive reactions of L2 in
the presence of a mixture of metal cations (CuII, ZnII, CoII) from
aqueous solution provided exclusive crystallization of CuII
Scheme 1
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Table 1 Crystallographic data
Crystal parameters
L1H
CP1a
CP1b
CP1c
CCDC no.
989165
989153
989154
989155
Empirical formula
Formula weight
C13H9N2O3
242.23
C26H26CuN4O10
618.05
C26H26CoN4O10
613.44
C26H26N4O10Zn
619.88
Crystal size/mm
Crystal system
Space group
0.21 × 0.08 × 0.06
Orthorhombic
Pbcn
0.28 × 0.08 × 0.05
Monoclinic
P21/n
0.30 × 0.22 × 0.08
Monoclinic
P21/n
0.50 × 0.22 × 0.16
Triclinic
P1
¯
a/Å
b/Å
c/Å
α/°
9.4072(3)
12.7350(3)
17.8919(5)
90.00
90.00
90.00
2143.46(10)
8
1.501
7.943(3)
7.7617(2)
12.4624(3)
13.3308(4)
90.00
101.2430(10)
90.00
1264.73(6)
2
1.611
9.3173(6)
10.4833(6)
14.0375(8)
97.468(2)
96.161(2)
91.980(2)
1350.01(14)
2
12.822(5)
13.509(5)
90.00
90.626(12)
90.00
1375.8(9)
2
1.492
β/°
γ/°
Volume/Å3
Z
Dcalc/g cm−3
1.525
F(000)
1008
0.109
296(2)
0.0503
638
0.858
296(2)
0.0447
634
0.748
296(2)
0.0250
640
0.975
296(2)
0.0132
μ MoKα/mm−1
Temperature/K
Rint
Range of h, k, l
θ min/max/°
Reflections collected/unique/
observed [I > 2σ(I)]
Data/restraints/parameters
Goodness of fit on F2
Final R indices [I > 2σ(I)]
−13/13, −17/17, −24/22
2.28/29.46
38 464/2967/1907
−11/11, −18/19, −17/19
2.19/32.31
20 886/4556/2825
−11/11, −18/18, −19/18
2.26/32.29
23 878/4051/3495
−12/13, −15/12, −20/20
1.47/32.33
21 168/7990/6404
2967/0/176
1.007
R1 = 0.0526
wR2 = 0.1295
R1 = 0.0965
wR2 = 0.1543
4556/0/199
1.043
R1 = 0.0456
wR2 = 0.1069
R1 = 0.0980
wR2 =0.1362
4051/0/200
0.878
R1 = 0.0320
wR2 = 0.1034
R1 = 0.0412
wR2 = 0.1170
7990/1/370
1.056
R1 = 0.0522
wR2 = 0.1759
R1 = 0.0677
wR2 =0.1944
R indices (all data)
Crystal parameters
CP1d
CP1e
989157
CP1f
CCDC no.
989156
989158
Empirical formula
Formula weight
C26H22CdN4O9
646.88
C26H26CdN4O10
666.91
C26H26FeN4O10
610.36
Crystal size/mm
Crystal system
Space group
0.14 × 0.14 × 0.06
Triclinic
P1
0.67 × 0.11 × 0.10
Monoclinic
P21/n
0.28 × 0.08 × 0.40
Monoclinic
P21/n
¯
a/Å
b/Å
c/Å
α/°
8.7935(9)
12.2071(13)
12.6146(13)
96.023(4)
103.536(4)
96.686(4)
1295.2(2)
2
7.90160(10)
12.7481(2)
13.5560(2)
90.00
101.9350(10)
90.00
1335.98(3)
2
1.658
7.7788(3)
12.5459(4)
13.3501(5)
90.00
101.4830(10)
90.00
1276.79(8)
2
1.588
β/°
γ/°
Volume/Å3
Z
Dcalc/g cm−3
1.659
F(000)
652
0.905
296(2)
0.0150
676
0.883
296(2)
0.0161
632
0.659
296(2)
0.0234
μ MoKα/mm−1
Temperature/K
Rint
Range of h, k, l
θ min/max/°
Reflections collected/unique/
observed [I > 2σ(I)]
Data/restraints/parameters
Goodness of fit on F2
Final R indices [I > 2σ(I)]
−12/11, −16/17, −17/17
1.68/30.14
23 897/7034/6319
−12/12, −18/19, −20/20
2.22/32.99
28 656/4653/3893
−10/11, −18/18, −20/19
2.25/32.18
19 371/4090/3540
7034/0/369
1.187
R1 = 0.0304
wR2 = 0.0893
R1 = 0.0365
wR2 =0.1004
4653/0/203
0.139
R1 = 0.0218
wR2 = 0.0639
R1 = 0.2980
wR2 = 0.0777
4090/0/200
1.082
R1 = 0.0323
wR2 = 0.0934
R1 = 0.0405
wR2 = 0.1048
R indices (all data)
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Table 1 (continued)
Crystal parameters
CP2a
CP2b
CP2c
CCDC no.
989159
989160
989161
Empirical formula
Formula weight
C26H30CuN4O12
654.08
C26H26CuN4O10
618.05
C26H26CoN4O10
613.44
Crystal size/mm
Crystal system
Space group
0.16 × 0.13 × 0.05
Monoclinic
P21/c
0.26 × 0.09 × 0.07
Monoclinic
P21/n
0.77 × 0.37 × 0.12
Monoclinic
P21/n
a/Å
b/Å
c/Å
α/°
8.8359(6)
19.4935(13)
8.0415(5)
90.00
9.0273(8)
9.6688(8)
15.3406(12)
90.00
8.7930(10)
9.8082(11)
15.5768(18)
90.00
β/°
96.394(2)
90.00
1376.47(16)
2
99.176(3)
90.00
1321.84(19)
2
100.664(3)
90.00
1320.2(3)
2
γ/°
Volume/Å3
Z
Dcalc/g cm−3
1.578
1.553
1.543
F(000)
678
0.867
296(2)
0.0337
638
0.892
296(2)
0.0603
634
0.716
100(2)
0.0184
μ MoKα/mm−1
Temperature/K
Rint
Range of h, k, l
θ min/max/°
Reflections collected/unique/
observed [I > 2σ(I)]
Data/restraints/parameters
Goodness of fit on F2
Final R indices [I > 2σ(I)]
−12/12, −28/26, −12/11
2.09/32.25
24 406/4462/3541
−10/11, −12/13, −21/21
2.50/30.03
16 730/3543/2501
−12/12, −12/14, −23/19
2.91/32.11
19 416/4287/4036
4462/0/212
1.126
R1 = 0.0410
wR2 = 0.1103
R1 = 0.0614
wR2 = 0.1325
3543/0/191
1.113
R1 = 0.0586
wR2 = 0.1359
R1 = 0.1039
wR2 = 0.1714
4287/0/200
1.049
R1 = 0.0252
wR2 = 0.0720
R1 = 0.0252
wR2 = 0.0710
R indices (all data)
Crystal parameters
CP2d
CP2e
CP2f
CCDC no.
989162
989163
989164
Empirical formula
Formula weight
C27H26N4O9Zn
615.89
C28H31CdN4O11
711.97
C26H28Cd2Cl2N4O11
868.22
Crystal size/mm
Crystal system
Space group
1.00 × 0.14 × 0.10
Triclinic
P1
1.00 × 0.12 × 0.08
Monoclinic
C2/c
0.24 × 0.21 × 0.16
Monoclinic
C2/c
¯
a/Å
b/Å
c/Å
α/°
10.6479(4)
11.0165(5)
12.9533(5)
106.997(2)
96.481(2)
106.063(2)
1364.96(10)
2
20.3394(16)
10.1426(7)
14.9680(9)
90.00
104.500(5)
90.00
2989.5(4)
4
1.582
16.5778(8)
16.9789(8)
21.8040(10)
90.00
94.606(2)
90.00
6117.4(5)
8
1.885
β/°
γ/°
Volume/Å3
Z
Dcalc/g cm−3
1.499
F(000)
636
0.961
293(2)
0.0144
1452
0.797
296(2)
0.0201
3440
1.631
296(2)
0.0260
μ MoKα/mm−1
Temperature/K
Rint
Range of h, k, l
θ min/max/°
Reflections collected/unique/
observed [I > 2σ(I)]
Data/restraints/parameters
Goodness of fit on F2
Final R indices [I > 2σ(I)]
−16/16, −14/17, −16/18
1.68/33.98
48 913/8582/7322
−30/31, −13/14, −20/23
2.26/34.06
33 276/5412/4925
−20/24, −25/25, −32/26
1.87/32.18
45 949/9876/7674
8582/0/391
1.014
R1 = 0.0359
wR2 = 0.1010
R1 = 0.0438
wR2 = 0.1067
5412/0/200
1.120
R1 = 0.0253
wR2 = 0.0690
R1 = 0.0300
wR2 = 0.0715
9876/0/421
1.023
R1 = 0.0443
wR2 = 0.1552
R1 = 0.0611
wR2 = 0.1746
R indices (all data)
Single crystal structures of the coordination polymers
identical space group P21/n with near identical cell dimen-
sions. It was observed that CP2a and CP2e crystallizing in
different space groups (P21/c and C2/c, respectively) were
SXRD analyses of the coordination polymers revealed that
CP1a, CP1b, CP1e and CP1f were isomorphous displaying the
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Fig. 2 Crystal structure illustration of CP1a: (a) 1D looped chain
coordination polymer formed via metal (Cu, magenta balls)–ligand
(L1, anti) coordination displaying occluded water (red balls) molecules;
(b) parallel packing of the looped chains sustained by various H-bonding
interactions.
Fig. 1 Crystal structure illustration of L1H: (a) molecular structure
of the free ligand L1H displaying the syn conformation in its single
crystal structure; (b) perpendicularly packed 1D chains via the H-bond
(N–H⋯O).
The CuII metal center displayed slightly distorted octahedral
geometry wherein the equatorial sites were occupied by the O
atoms of the carboxylate moiety and the pyridyl N atoms and
the axial sites were coordinated by the O atoms of the solvate
water molecules. The bidentate pyridyl-carboxylate ligands
coordinated to the adjacent metal centers in such a way that
a highly non-planar 2D network was formed. Such 2D sheets
were packed in parallel fashion. The amide functionality was
found to be involved in hydrogen bonding with the carboxyl-
ate O of the ligand molecule within the 2D network, whereas
the lattice occluded water molecules bridged the adjacent 2D
networks via hydrogen bonding interactions involving the
amide carbonyl and carboxylate of the interacting networks
(Fig. 3).
isostructural with the crystals of CP1a, CP1b, CP1e and CP1f.
Thus, we describe below the crystal structure of CP1a only.
The asymmetric unit of CP1a was comprised of a fully
occupied ligand L1 coordinated to a half occupied CuII metal
center (lies on an inversion centre) via the pyridyl N atom,
one fully occupied water molecule coordinated to the metal
center and a fully occupied lattice occluded water molecule.
In the crystal structure, the ligand molecule coordinated the
metal center by both ligating sites (pyridyl N and carboxylate
O) to generate a 1D looped chain topology. The CuII metal
center displayed an almost perfect octahedral geometry
wherein the equatorial sites were occupied by the O atoms of
two water molecules and the carboxylate moiety, and the axial
sites were coordinated by the pyridyl N atoms. The 1D looped
chains were packed in parallel fashion to generate an overall
3D hydrogen bonding network wherein the amide moiety of
the ligand participated in hydrogen bonding interactions with
the lattice occlude water as well as the metal bound water
molecules sustained by both N–H⋯O and O–H⋯O interac-
tions (Fig. 2).
Crystal structure of [{Zn(μ-L1)2(H2O)}·3H2O]∝CP1c
The coordination polymer CP1c crystallized in the centrosym-
metric triclinic space group P-1. In the asymmetric unit, two
ligand molecules, one ZnII metal center, one metal bound
water and three solvate water molecules were located in gen-
eral positions. One of the ligands coordinated to the metal
center via both the carboxylate and 3-pyridyl N, whereas the
other ligand coordinated to the metal center via carboxylate
keeping the 3-pyridyl N free from coordination, resulting in a
1D polymeric chain resembling comb-like structure. The
coordination environment of ZnII may be considered as a
highly distorted octahedron wherein the equatorial positions
were coordinated by the O atoms of the two carboxylates and
one water molecule, whereas the axial positions were occu-
pied by the pyridyl N and carboxylate O atoms. The 1D comb-
like polymeric chains were packed in inter-digited fashion
resulting in bilayer structures which were further packed in
parallel fashion though out of the crystal structure. The
amide functionality of the crystallographically independent
ligand molecules displayed hydrogen bonding interactions
with the lattice occluded water and carboxylate moiety of the
Crystal structures of [{Cu(μ-L2)2 (H2O)2}·H2O]∝CP2b and
[{Co(μ-L2)2 (H2O)2}·H2O]∝CP2c
SXRD data revealed that CP2b and CP2c were isomorphous
displaying the identical space group P21/n having a near iden-
tical cell dimension. Thus, we describe below the crystal
structure of CP2b.
The asymmetric unit of CP2b was comprised of one fully
occupied ligand coordinated to the half occupied CuII metal
center (lies on an inversion centre) via the pyridyl N atom,
one fully occupied water molecule coordinated to the metal
center and a fully occupied lattice occluded water molecule.
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found to be involved in hydrogen bonding with the lattice
occluded water molecules resulting in an overall 3D hydrogen
bonded network (Fig. 5).
Crystal structure of [{Zn(μ-L2)2(H2O)}·(H2O)(CH3OH)]∝CP2d
Coordination polymer CP2d crystallized in the centrosym-
metric triclinic space group P-1. The asymmetric unit was
comprised of two ligand molecules, one ZnII metal center,
one metal bound water, two lattice occluded guest molecules,
namely water and MeOH. Both the crystallographically inde-
pendent ligand molecules coordinated to the metal centers
in such a fashion that it generated a 1D polymeric tape
formed via two parallel 1D polymeric chains cross-linked by
metallamacrocycles. The coordination environment of ZnII
may be considered as a highly distorted octahedron wherein
the equatorial positions were coordinated by the O atoms
coming two carboxylate and one pyridyl N atoms, whereas
the axial positions were occupied by the pyridyl N and water
O atoms. One of the amide carbonyl O of one of the crystallo-
graphically independent ligands was found to be free from
any hydrogen bonding interactions, whereas the rest of the
atoms of the amide functionality were involved in hydrogen
bonding interactions with the lattice occluded water and
MeOH. The 1D coordination polymeric tapes were further
packed in parallel fashion and the interstitial space was occu-
pied by the lattice occluded MeOH and water sustained by
hydrogen bonding interactions as described above (Fig. 6).
Fig. 3 Crystal structure illustration of CP2b: (a) non-planar 2D sheet
network; (b) overall 3D network sustained by various H-bonding
interactions.
neighbouring chain via N–H⋯O and O–H⋯O interactions
(Fig. 4).
Crystal structure of [{Cd(μ-L1)2(μ-L1)3 (H2O)}·2H2O]∝CP1d
Single crystals of CP1d were found to be crystallized in the
centrosymmetric triclinic space group P-1. Two ligand mole-
cules, one CdII metal center, one metal bound water and two
solvate water molecules [of which one molecule was found to
be disordered over three positions having site occupancy fac-
tors (SOF) of 0.26, 0.24 and 0.50] were located in the asym-
metric unit. The topology of the coordination network in the
crystal structure may be best described as a 2D corrugated
sheet network weaved with a looped structure generated due
to the head-to-tail centrosymmetric arrangement of the
ligands coordinating the adjacent metal centers via both the
carboxylate and pyridyl N. The coordination geometry of the
CdII metal center was found to be distorted octahedral
wherein the axial positions were occupied by pyridyl N atoms
and the equatorial positions were coordinated by three car-
boxylate and one water O atoms. The amide functionality of
the two ligand molecules present in the asymmetric unit were
Crystal structure of [{(Cl)2(H2O)2Cd2(μ-L2)2}·3H2O]∝ CP2f
The coordination polymer CP2f crystallized in the centrosym-
metric monoclinic space group C2/c. The asymmetric unit
contained two ligand molecules, two CdII metal centers, two
Fig. 4 Crystal structure illustration of CP1c: 1D comb-like polymeric
chains packed in inter-digited fashion displaying occluded solvent
water molecules (red balls) sustained by hydrogen bonding.
Fig. 5 Crystal structure illustration of CP1d: (a) a non-planar 2D
network weaved with a looped structure formed via metal–ligand
coordination; (b) the 2D network represents a corrugated sheet.
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Fig. 7 Crystal structure illustration of CP2f: (a) 1D looped chain
coordination polymer propagated via the CdII(μ-Cl)2-CdII bridge; (b)
the overall 3D network sustained by H-bonding interactions displaying
lattice occluded water molecules (red balls).
appeared to be completely different than that of the simu-
lated pattern indicating the formation of a completely new
phase presumably due to solvent loss.
Fig.
6 Crystal structure illustration of CP2d; (a) 1D polymeric
tape formed from two parallel running 1D chains cross-linked by
metallamacrocycles (green); (b) the overall 3D network sustained by
H-bonding interactions displaying lattice occluded water and methanol
molecules.
The structural features enlisted in Table 2 revealed the
following. In the case of L1, because of the symmetric position
of the carboxylate, the ligating topology mainly depended on
the relative orientation of the pyridyl N with respect to the
amide >CO (here after Npy/>CO) as a result of free rota-
tion around Cpyridyl–Ccarbonyl bond. The free ligand L1H
displayed the syn conformation for Npy/>CO, whereas the
coordination polymers displaying looped architecture (CP1a,
CP1b, CP1e and CP1f) showed the anti conformation under-
standably required to attain the looped coordination mode
resulting in similar ligating angles (~101–109°) in these CPs.
Interestingly, CP1d displayed both the syn and anti Npy/>CO
conformations in the two crystallographically independent
ligand molecules. A detailed examination of the structure of
CP1d revealed that the ligand having the anti Npy/>CO con-
formation was responsible for making the loop, whereas the
other ligand displaying the syn conformation connected the
looped structure resulting in an overall 2D corrugated sheet.
The effect of the Npy/>CO conformation on the resulting
coordination architecture was clear in the case of CP1c wherein
the ligands displaying the syn conformation was unable to
form a looped structure (Scheme 2), instead it generated comb-
like 1D polymeric chain.
In the case of L2 derived coordination polymers, the coordi-
nating sites, i.e. pyridyl N and carboxylate, were in 3-positions
in the aromatic rings making the ligating topology dependent
on both the Namide–Cphenyl and Cpyridyl–Ccarbonyl bond rotation;
as a result the Npy/>CO conformation become irrelevant and
thus, both the syn and anti Npy/>CO conformations were
observed in the coordination polymers having a looped struc-
ture (CP2a, CP2e and CP2f). All the coordination polymers
incorporated water or MeOH as guest molecules presumably
because of the hydrogen bond capable amide backbone that
participated in hydrogen bonding interactions with the guest
molecules.
coordinated chloride, two metal-bound water (of which one
was found to be disordered over two positions whose SOFs
were refined to 0.48 and 0.52 using the second variable of
FVAR in SHELXL software) and three lattice occluded water
molecules (of which one was found to be disordered over two
positions with the refined SOFs 0.60 and 0.40 obtained using
the second variable of FVAR in SHELXL software). Both the
ligands coordinated to the metal centers via pyridyl N and car-
boxylate to generate M2L2 type macrocycles. The macrocycles
were further propagated in 1D via the CdII(μ-Cl)2-CdII bridge.
Both the metal centers displayed a distorted octahedral
geometry. The amide moiety of one of the ligand molecules
was involved in hydrogen bonding with the metal-bound
water of the neighbouring 1D network keeping the amide NH
free from any interactions, whereas the amide functionality in
the other ligand molecule displayed hydrogen bonding inter-
actions with the lattice occluded water molecules. The 1D
coordination networks were packed in parallel fashion and
the interstitial space thus created was occupied by the lattice
occluded water molecules (Fig. 7).
The crystalline phase purity of the coordination polymers
CP1b, CP1c, CP1f, CP2a, CP2b, CP2c, CP2e, and CP2f were
established by PXRD analyses (see the ESI†); in the case of
CP1e, there appeared to be an extra phase as a few peaks
within the region of 10–17° 2θ did not match with the simu-
lated peaks. PXRD patterns of the bulk crystalline materials
of the coordination polymers (CP1a and CP1d) did not match
with the corresponding simulated PXRD patterns obtained
from SXRD data which may be attributed to either solvent
loss during the experiment or presence of a new crystalline
phase in the bulk materials. The PXRD pattern in CP2d
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conditions namely I, II and III. In all cases, in situ crystalliza-
tion of the coordination polymers was carried out in 1 : 1
MeOH : water by slow evaporation at room temperature keep-
ing the molar ratio of the reactants, i.e. ligand : Cu-salt : other
metal salts as 2 : 1: 2, 4 : 1: 4 and 8 : 1: 8 for the conditions I, II
and III, respectively. It was observed that in the case of L1,
the mixtures of coordination polymers were obtained as crys-
talline aggregates revealed by their characteristic colors (blue
for CuII, pink for CoII and colorless for ZnII (Fig. 8a)). The
PXRD of these crystalline aggregates turned out to be weekly
diffracting. However, the major peaks of the diffraction pat-
terns matched well with that of the simulated patterns of
CP1a (CuII), CP1b (CoII) and CP1c (ZnII) but failed to display
the one to one correspondence with any of the individual
simulated patterns thereby proving it unsuccessful in the
selective separation of CuII (see the ESI†). Whereas the same
experiments using L2 resulted in light green and deep blue
colored crystals indicating the concomitant formation of CuII
coordination polymers, namely CP2a and CP2b, respectively
(Fig. 8b).The FT-IR of the crystals displayed an excellent cor-
respondence with that of the physical mixture of CP2a and
CP2b as obtained concomitantly during their synthesis under
various conditions (condition I, II and III), thereby suggesting
the selective separation of CuII in the form of the coordina-
tion polymers CP2a and CP2b (Fig. 8c). Further support in
favour of the selective separation of CuII using L2 came from
the PXRD patterns. It was clear from Fig. 8d that the PXRD
patterns of the crystals under various conditions (I, II and III)
Scheme 2
Cation separation
For the reasons stated above (vide supra), we next explored
the possibility of separating CuII from a complex mixture of
CuII, CoII and ZnII by competitive reactions of L1 and L2 with
the corresponding metal-nitrates under three different
Fig. 8 (a) Crystalline aggregates obtained under condition I using L1; (b) crystals of CP2a and CP2b obtained under condition I using L2; (c) FT-IR
spectra and (d) PXRD patterns of the crystals of CP2a and CP2b mixture obtained under various conditions (condition I, II and III) using L2.
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were reasonably crystalline and the major peaks matched
well with that of the simulated patterns of CP2a and CP2b
indicating the separation of CuII as the crystalline coordina-
tion polymers CP2a and CP2b.
copper content in a sample was estimated using a Shimadzu
AA-6300 atomic absorption spectrometer (AAS) fitted with a
double beam monochromator.
To quantify the amount of CuII being separated during the
experiment we ran atomic absorption spectroscopy measure-
ments on the supernatant liquid after removing the crystals
of CP2a and CP2b. Interestingly, up to 97% of CuII could be
separated selectively (see the ESI†). Thus, in the case of L1,
Irving–Williams series did not seem to be operative, whereas
in the case of L2 the isolation of the CuII coordination poly-
mers (CP2a and CP2b) under competitive conditions indi-
cated that the stability of CuII coordination networks seemed
to be influencing the selective separation of CuII.
Synthetic procedure for ligand L1H and L2H
In a 250 ml 2-neck round bottom flask 100 ml DCM, 5 mmol
triethylamine (700 μl) and 5 mmol (890 mg) acid chloride
(nicotinoyl or isonicotinoyl) were mixed. The reaction mixture
was then stirred at room temperature under nitrogen atmo-
sphere. A THF solution of 5 mmol amino benzoic acid (755.5 mg)
was then added slowly. Then the mixture was allowed to react
at room temperature followed by reflux at 60 °C. The ppt. was
then filtered and washed properly with THF and DCM and
used with further purification.
Conclusions
Characterization data of L1H
Yield: 1.0 g, ~57%; m.p: >300 °C after crystallization from
DMF/EtOH/H2O (1 : 2: 2 v/v). Anal. data calcd. for C15H18O6:
C, 64.46; H, 4.16; N, 11.56. Found: C, 64.01; H, 4.24; N, 11.60.
1H NMR (400 MHz, DMSO-d6): δ = 7.57 (dd, J = 4.6, 1H); 7.91
(d, J = 8.8, 2H); 7.94 (d, J = 8.8, 2H); 8.30 (s, 1H); 8.78 (s, 1H);
9.13 (s, 1H); 10.70 (s, 1H); 12.78 (s, 1H). 13C NMR (500 MHz,
DMSO-d6): 119.51, 123.22, 130.24, 135.57, 142.88, 148.70,
164.46, 166.85 ppm. ESI-MS: calcd. For C13H10N2O3 242.23 [M]+;
found: [M + Na]+273.28. FT-IR (KBr, cm−1): 3309, 3112, 3047,
2883, 2422, 1687s, 1598s, 1531s, 1311s, 1282m, 1242m, 1174s,
1130m, 1101m, 1047s, 892s, 858m, 784s, 705, 644, 548 cm−1.
Thus, we have synthesized a series of transition metal (CuII,
CoII, CdII, ZnII and FeII) coordination polymers derived from
hydrogen bond equipped pyridyl carboxylate ligands and
characterized by single crystal X-ray diffraction. The primary
objective of the present work was to study the effect of both
hard and soft coordinating sites (pyridyl and carboxylate,
respectively) on the selective separation of CuII from a com-
plex mixture of cations following in situ crystallization of coor-
dination polymers under various competitive conditions. The
results confirmed that it was indeed possible to separate CuII
from a complex mixture of cations (CuII, CoII and ZnII) in the
form of concomitantly produced coordination polymers CP2a
and CP2b when L2 was used. The fact that such a selective
separation was unsuccessful in the case of L1 clearly indicated
that the subtle change in the position of the coordinating
sites (considering the positional isomeric relationship of L1
and L2) greatly influenced the reactivity towards metal cen-
ters. Overall, the results presented herein represent one of the
rare attempts to separate toxic metal cations such as CuII by
exploiting in situ crystallization of coordination polymers.21
Characterization data of L2H
Yield: 1.2 g, ~68%; m.p: 259 °C. Anal. data calcd. for C15H18O6:
C, 64.46; H, 4.16; N, 11.56. Found: C, 64.41; H, 4.02; N, 11.34.
1H NMR (400 MHz, DMSO-d6): δ = 7.50 (t, J = 8, 1H); 7.70 (d,
J = 7.6, 1H); 8.06 (d, J = 7.6, 1H); 8.44 (s, 1H); 8.00 (t, J = 5.6,
1H); 8.86 (s, 1H); 8.98 (d, J = 2, 1H); 9.39 (d, J = 8.8, 1H); 11.11
(s, 1H). 13C NMR (400 MHz, DMSO-d6): 121.19, 124.49, 125.04,
128.99, 131.33, 138.75, 167.00 ppm. ESI-MS: calcd. For
C13H10N2O3 242.23 [M]+; found: [M]+242.93. FT-IR (KBr, cm−1):
3244, 3072, 2638, 2069, 1699s, 1679s, 1595s, 1548s, 1450s,
1296s, 1267s, 1112m, 906m, 821s, 759s, 678s, 629m, 580 cm−1.
[{Cu(μ-L1)2 (H2O)2}·H2O]∝CP1a was synthesized by care-
fully adding an aqueous solution of L1 (40 mg, 0.15 mmol) to a
methanolic solution of Cu(NO3)2·3H2O (36.57 mg, 0.15 mmol)
and the solution was left for slow evaporation at room temper-
ature. After two weeks well formed block shaped green crys-
tals were obtained. The crystals were washed in distilled water
and finally with methanol and characterized by elemental
analysis, X-ray powder diffraction (PXRD) and FT-IR. Yield:
~36% (35 mg, 0.055 mmol). Elemental analysis calcd. for
CP1a, C26H26CuN4O10 (%): C 50.53, H 4.24, N 9.07; found:
C 50.22, H3.93, N 8.86. FT-IR (KBr pellet): 3310, 1657s, 1609s,
1565, 1525s, 1406, 1382s, 1310m, 1268m, 1177m, 1117, 1207,
909m, 856m, 814m, 780s, 705, 743m, 701m, 513m, 462m cm−1.
Thermogravimetric data analyses (Fig. S1, ESI†) revealed a
weight loss of 12.12% that occurred within a temperature
range of 29–125 °C; this was attributed to the weight loss of 1
Experimental
Materials and method
All the chemicals were commercially available and used with-
out further purification. Ligand 4-(nicotinamido) benzoicacid
(L1H) and 3-(nicotinamido) benzoicacid (L2H) were synthe-
sized by coupling nicotinoyl chloride with the corresponding
amino benzoic acids. Elemental analyses ware carried out
using a Perkin-Elmer 2400 Series-II CHN analyzer. FT-IR spec-
tra were recorded using a Perkin-Elmer Spectrum GX, and TGA
analyses were performed on a SDT Q Series 600 Universal VA.
2E TA instrument. Powder X-ray diffraction patterns were
recorded on a Bruker AXS D8 Advance Powder (Cu Kα1 radia-
tion, λ = 1.5406 Å) diffractometer. The TEM images were
recorded with a Jeol instrument using carbon coated 300 mesh
Au grids at 200 kV. The mass spectrum was recorded on a
QTOF Micro YA263. NMR spectra (1H and 13C) were recorded
using a 300 MHz BrukerAvance DPX300 spectrometer. The
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coordinated and 1 lattice occluded water molecules (calcu-
lated weight loss 11.56%); this observation was in good agree-
ment with the single crystal structure of CP1a.
1658s, 1602s, 1521, 1506, 1398s, 1326s, 1276m, 1245m, 1178s,
1126, 1056, 1029m, 902m, 858, 833, 783s, 714m, 700m, 642,
505, 428 cm−1.
[{Co(μ-L1)2 (H2O)2}·H2O]∝CP1b was synthesized by care-
fully adding an aqueous solution of L1 (40 mg, 0.15 mmol) to
a methanolic solution of Co(NO3)2·6H2O (44 mg, 0.15 mmol)
and the solution was left for slow evaporation at room tem-
perature. After two weeks well formed block shaped pink
crystals were obtained. The crystals were washed in distilled
water and finally with methanol and characterized by elemen-
tal analysis, X-ray powder diffraction (PXRD) and FT-IR.
Yield:~34.5% (32 mg, 0.052 mmol). Elemental analysis calcd.
for CP1b, C26H26CoN4O10 (%): C 50.91, H 4.27, N 9.13; found:
C 50.76, H 4.24, N 8.86. FT-IR (KBr pellet): 3487, 3047, 1643,
1622s, 1606s, 1527s, 1388s, 1344m, 1195, 1172m, 896, 831,
788m, 698, 644, 533, 507 cm−1.
Thermogravimetric data analyses (Fig. S2, ESI†) revealed a
weight loss of 13.77% that occurred within a temperature
range of 60–155 °C; this was attributed to the weight loss of 1
coordinated and 1 lattice occluded water molecules (calcu-
lated weight loss 11.73%); this observation was in good agree-
ment with the single crystal structure of CP1b.
[{Zn(μ-L1)2(H2O)}·3H2O]∝CP1c was synthesized by carefully
adding an aqueous solution of L1 (40 mg, 0.15 mmol) to a
methanolic solution of Zn(NO3)2·6H2O (45 mg, 0.15 mmol)
and the solution was left for slow evaporation at room tem-
perature. After two weeks well formed block shaped colorless
crystals were obtained. The crystals were washed in distilled
water and finally with methanol and characterized by elemen-
tal analysis, X-ray powder diffraction (PXRD) and FT-IR.
Yield:~34.5% (36 mg, 0.058 mmol). Elemental analysis calcd.
for CP1c, C26H26ZnN4O10 (%): C 50.38, H 4.23, N 9.04; found:
C 50.57, H 4.02, N 8.71. FT-IR (KBr pellet): 3444, 3249, 3076,
1658s, 1604s, 1558, 1519, 1477s, 1415s, 1326s, 1276m, 1201m,
1178s, 1122, 1056, 1029m, 904m, 871, 860, 833, 786s, 725m,
694m, 648, 516, 432 cm−1.
Thermogravimetric data analyses (Fig. S3, ESI†) revealed a
weight loss of 13.98% that occurred within a temperature
range of 48–85 °C; this was attributed to the weight loss of 1
coordinated and 3 solvated water molecules (calculated
weight loss 11.61%); this observation was in good agreement
with the single crystal structure of CP1c.
Thermogravimetric data analyses (Fig. S4, ESI†) of CP1d
revealed a weight loss of 7.66% that occurred within a tempera-
ture range of 34–85 °C; this was attributed to the weight loss of
1 coordinated and 2 lattice occluded water molecules (calcu-
lated weight loss 8.32%); this observation was in good agree-
ment with the single crystal structure of CP1d and the analysis
data (Fig. S5, ESI†) of CP1e revealed a weight loss of 12.42%
that occurred within a temperature range of 48–100 °C; this
was attributed to the weight loss of 1 coordinated and 1 lattice
occluded water molecules (calculated weight loss 10.79%); this
observation was in good agreement with the single crystal
structure of CP1e.
[{Fe(μ-L1)2(H2O)2}·H2O]∝CP1f was synthesized by carefully
adding an aqueous solution of L1 (40 mg, 0.15 mmol) to a
methanolic solution of Fe(ClO4)2·xH2O (36.3 mg, 0.15 mmol)
and the solution was left for slow evaporation at room tem-
perature. After two weeks well formed block shaped yellow
crystals were obtained. The crystals were washed in distilled
water and finally with methanol and characterized by elemen-
tal analysis, X-ray powder diffraction (PXRD) and FT-IR.
Yield:~30.5% (28 mg, 0.045 mmol). Elemental analysis calcd.
for CP1f, C26H26FeN4O10 (%): C 51.16, H 4.29, N 9.18; found:
C 50.87, H 4.02, N 8.71. FT-IR (KBr pellet): 3487, 3058, 1602,
1558, 1527s, 1334m, 1245, 788s cm−1.
Thermogravimetric data analyses (Fig. S6, ESI†) revealed a
weight loss of 11.93% that occurred within a temperature
range of 30–142 °C; this was attributed to the weight loss of 2
water molecules (calculated weight loss 11.79%); this obser-
vation was in good agreement with the single crystal struc-
ture of CP1f.
[{Cu(μ-L2)2
(H2O)2}·2H2O]∝CP2a
and
[{Cu(μ-L2)2
(H2O)2}·H2O]∝CP2b were synthesized by carefully adding an
aqueous solution of L2 (40 mg, 0.15 mmol) to a methanolic
solution of Cu(NO3)2·3H2O (36.57 mg, 0.15 mmol) and the
solution was left for slow evaporation at room temperature.
After two weeks two types of crystals (green CP2a and deep
blue CP2b) were obtained. The crystals were washed in dis-
tilled water and finally with methanol and characterized by
elemental analysis, X-ray powder diffraction (PXRD) and FT-
IR. Yield: 38.5 mg (including both the polymorph). Elemental
analysis calcd. for CP2a, C26H30CuN4O12 (%): C 47.74, H 4.62,
N 8.57; found: C 48.32, H 4.42, N 8.66 and CP2b, C26H26CuN4O10
(%): C 50.53, H 4.24, N 9.07; found: C 50.74, H 4.22, N 9.07. FT-
IR (KBr pellet) for both the polymorphs: 3414, 3314, 3065,
1655s, 1610, 1550s, 1476, 1421, 1387s, 1311, 1269m, 1200,
775s, 689, 675, 669 cm−1.
Thermogravimetric data analyses (Fig. S7, ESI†) of CP2a
revealed a weight loss of 17.51% that occurred within a tem-
perature range of 28–91 °C; this was attributed to the weight
loss of 1 coordinated and 2 lattice occluded water molecules
(calculated weight loss 16.51%); this observation was in good
agreement with the single crystal structure of CP2a and the
analysis data (Fig. S8, ESI†) of CP2b revealed a weight loss of
[{Cd(μ-L1)2(μ-L1)3(H2O)}·2H2O]∝CP1d
and
[{Cd(μ-
L1)2(H2O)2}·H2O]∝CP1e were synthesized by carefully adding
an aqueous solution of L1 (40 mg, 0.15 mmol) to a methanolic
solution of Cd(NO3)2·4H2O (46.7 mg, 0.15 mmol) and the
solution was left for slow evaporation at room temperature.
After two weeks two types of block shaped crystals were
obtained. The crystals were washed in distilled water and
finally with methanol and separately characterized by elemen-
tal analysis, X-ray powder diffraction (PXRD) and FT-IR. Yield:
~36 mg (including both the polymorph). Elemental analysis
calcd. for CP1d, C26H22CdN4O9·2H2O (%): C 46.82, H 3.93,
N 8.40; found: C 46.33, H 3.29, N 8.34 and for CP1e. H2O,
C
26H26CdN4O10·H2O (%): C 45.59, H 4.12, N 8.18; found:
C 45.73, H 3.85, N 8.03. FT-IR (KBr pellet): 3380, 3272, 3072,
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10.94% that occurred within a temperature range of 24–99 °C;
this was attributed to the weight loss of 1 coordinated and 1
lattice occluded water molecules (calculated weight loss
11.65%); this observation was in good agreement with the sin-
gle crystal structure of CP2b.
[{Co(μ-L2)2 (H2O)2}·H2O]∝CP2c was synthesized by care-
fully adding an aqueous solution of L2 (40 mg, 0.15 mmol) to a
methanolic solution of Co(NO3)2·6H2O (44 mg, 0.15 mmol) and
the solution was left for slow evaporation at room temperature.
After two weeks well formed block shaped pink crystals were
obtained. The crystals were washed in distilled water and
finally with methanol and characterized by elemental analysis,
X-ray powder diffraction (PXRD) and FT-IR. Yield: ~36.9%
(34 mg, 0.055 mmol). Elemental analysis calcd. for CP2c,
Thermogravimetric data analyses (Fig. S11, ESI†) of CP2e
revealed a weight loss of 16.84% that occurred within a tem-
perature range of 28–181 °C; this was attributed to the weight
loss of 0.5 coordinated, 1 solvated water and 1 methanol mol-
ecules (calculated weight loss 16.55%); this observation was
in good agreement with the single crystal structure of CP2e.
[{(Cl)2(H2O)2Cd2(μ-L2)2}·3H2O]∝CP2f was synthesized by care-
fully adding an aqueous solution of L2 (40 mg, 0.15 mmol) to a
methanolic solution of CdCl2 (27.5 mg, 0.15 mmol) and the
solution was left for slow evaporation at room temperature.
After two weeks well formed block shaped crystals were
obtained. The crystals were washed in distilled water and finally
with methanol and separately characterized by elemental analy-
sis, X-ray powder diffraction (PXRD) and FT-IR. Yield: ~29%
(38 mg, 0.043 mmol). Elemental analysis calcd. for CP2f,
C26H28Cd2Cl2N4O11 (%): C 35.97, H 3.25, N 6.45; found: C 36.49,
H 3.02, N 6.48.FT-IR (KBr pellet): 3298, 3261, 3058, 1685s,
1604s, 1552m, 1521m, 1508m, 1400, 1325s, 1274, 1178, 1107,
1029m, 835, 898, 864, 833, 784s, 730m, 717, 649, 432 cm−1.
Thermogravimetric data analyses (Fig. S12, ESI†) of CP2f
revealed a weight loss of 11.78% that occurred within a tem-
perature range of 28–100 °C; this was attributed to the weight
loss of 2 coordinated and 3 occluded water molecules (calcu-
lated weight loss 11.90%); this observation was in good agree-
ment with the single crystal structure of CP2f.
C
26H26CoN4O10 (%): C 50.91, H 4.27, N 9.13; found: C 51.02,
H 4.21, N 9.11. FT-IR (KBr pellet): 3382, 3296, 1652s, 1610, 1598,
1541s, 1473s, 1419s, 1388s, 1317, 1269, 1199, 1164, 1110, 1080,
1051, 1031, 950, 896, 885, 835, 784m, 740, 673, 590, 451 cm−1.
Thermogravimetric data analyses (Fig. S9, ESI†) revealed a
weight loss of 11.35% that occurred within a temperature
range of 38–150 °C; this was attributed to the weight loss of 1
coordinated and 1 lattice occluded water molecules (calcu-
lated weight loss 11.73%); this observation was in good agree-
ment with the single crystal structure of CP2c.
[{Zn(μ-L2)2(H2O)}·(H2O)(CH3OH)]∝CP2d was synthesized by
carefully adding an aqueous solution of L2 (40 mg, 0.15 mmol)
to a methanolic solution of Zn(NO3)2·6H2O (45 mg, 0.15 mmol)
and the solution was left for slow evaporation at room tempera-
ture. After two weeks two colorless block shaped crystals were
obtained. The crystals were washed in distilled water and
finally with methanol and separately characterized by elemen-
tal analysis, X-ray powder diffraction (PXRD) and FT-IR. Yield:
~37.8% (35 mg, 0.056 mmol). Elemental analysis calcd. for
CP2d, C27H26ZnN4O9 (%): C 52.65, H 4.25, N 9.10; found: C
52.29, H 3.89, N 8.79. FT-IR (KBr pellet): 3473, 3328, 3269,
1685s, 1667s, 1613s, 1577s, 1541s, 1434s, 1395s, 1323, 1292,
1262, 1203, 1177, 827, 768, 730, 701, 674 cm−1.
Thermogravimetric data analyses (Fig. S10, ESI†) of CP2d
revealed a weight loss of 10.54% that occurred within a tempera-
ture range of 45–112 °C; this was attributed to the weight loss of
1 coordinated and 1 lattice occluded water and 1 methanol mol-
ecules (calculated weight loss 11.04%); this observation was in
good agreement with the single crystal structure of CP2d.
[{Cd(μ-L2)2(H2O)}·(H2O)(CH3OH)]∝CP2e was synthesized
by carefully adding an aqueous solution of L2 (40 mg, 0.15 mmol)
to a methanolic solution of Cd(NO3)2·4H2O (46.7 mg, 0.15 mmol)
and the solution was left for slow evaporation at room tempera-
ture. After two weeks well formed block shaped crystals were
obtained. The crystals were washed in distilled water and
finally with methanol and separately characterized by elemen-
tal analysis, X-ray powder diffraction (PXRD) and FT-IR. Yield:
~34.6% (37 mg, 0.051 mmol). Elemental analysis calcd. for
CP2e, C28H32CdN4O11 (%): C 47.17, H 4.52, N 7.86; found: C
47.21, H 3.95, N 7.56. FT-IR (KBr pellet): 3458, 3368, 3254,
3075, 1666s, 1614s, 1541s, 1485, 1395s, 1327s, 1246, 1190m,
1049, 1023m, 835, 813, 767s, 742m, 703, 671 cm−1.
Cation separation
The experiments for CuII separation were performed under
different conditions, namely I, II and III, as described below.
Condition I. In a typical experiment, a methanolic solution
(15 ml) containing Cu(NO3)2 (18.28 mg, 0.07 mmol), Co(NO3)2
(44.06 mg, 0.15 mmol) and Zn(NO3)2 (45.03 mg, 0.15 mmol)
was layered over an aqueous solution (10 ml) of L2 (40 mg,
0.15 mmol) in a 25 ml beaker and the resulting solution was
allowed to undergo slow evaporation at room temperature.
After two weeks, good quality crystals of CP2a and CP2b
appeared concomitantly in the beaker. When the volume of
the solution became ~5 ml, the crystals were separated and
washed with methanol. The filtrate along with the washings
was evaporated to dryness and subjected to atomic absorption
spectroscopy (AAS).
Condition II. In a typical experiment, a methanolic solution
(15 ml) containing Cu(NO3)2 (9.14 mg, 0.035 mmol), Co(NO3)2
(44.06 mg, 0.15 mmol) and Zn(NO3)2 (45.03 mg, 0.15 mmol)
was layered over an aqueous solution (10 ml) of L2 (40 mg,
0.15 mmol) in a 25 ml beaker and the resulting solution was
allowed to undergo slow evaporation at room temperature.
After two weeks, good quality crystals of CP2a and CP2b
appeared concomitantly in the beaker. When the volume of the
solution became ~5 ml, the crystals were separated and washed
with methanol. The filtrate along with the washings was
evaporated to dryness and subjected to atomic absorption
spectroscopy (AAS).
Condition III. In a typical experiment, a methanolic
solution (15 ml) containing Cu(NO3)2 (4.5 mg, 0.017 mmol),
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Co(NO3)2 (44.06 mg, 0.15 mmol) and Zn(NO3)2 (45.03 mg,
0.15 mmol) was layered over an aqueous solution (10 ml) of
L2 (40 mg, 0.15 mmol) in a 25 ml beaker and the resulting
solution was allowed to undergo slow evaporation at room
temperature. After two weeks, good quality crystals of CP2a
and CP2b appeared concomitantly in the beaker. When the
volume of the solution became ~5 ml, the crystals were
separated and washed with methanol. The filtrate along with
the washings was evaporated to dryness and subjected to
atomic absorption spectroscopy (AAS).
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Single crystal X-ray crystallography
Single crystal X-ray diffraction data were collected using
MoKα (λ = 0.7107 Å) radiation on a BRUKER APEX II diffrac-
tometer equipped with a CCD area detector. Data collection,
data reduction, structure solution/refinement were carried
out using the software package of APEX II. All the structures
(L1H, CP1a–CP1f and CP2a–CP2f) were solved by direct
methods and refined in a routine manner. In all cases, non-
hydrogen atoms were treated anisotropically. Whenever pos-
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rier map and refined. In other cases, the hydrogen atoms
were geometrically fixed. CCDC no. 989153–989165 contain
the supplementary crystallographic data for this paper. These
data can be obtained free of charge via www.ccdc.cam.ac.uk/
conts/retrieving.html (or from the Cambridge Crystallographic
Data Centre, 12 Union Road, 95 Cambridge CB21EZ, UK; fax:
(+44) 1223-336-033; or deposit@ccdc.cam.ac.uk).
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Powder X-ray diffraction
PXRD data were collected using a Bruker AXS D8 Advance
Powder (Cu Kα1 radiation, λ = 1.5406 Å) diffractometer
equipped with a super speed LYNXEYE detector. The sample
was prepared by making a thin film from the finely powdered
sample (~30 mg) over a glass slide. The experiment was car-
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Acknowledgements
PD thanks the Department of Science & Technology (DST),
New Delhi, India for financial support. M.P thanks CSIR,
New Delhi (grant no. 09/080(0693)/2010-EMR-I) for SRF.
SXRD data were collected at the DBT-funded X-ray Diffraction
Facility under the CEIB program in the Department of
Organic Chemistry, IACS, Kolkata
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