Metal-dependent ribbon and self-penetrated topologies in nitroaromatic-sensing zinc and cadmium coordination polymers with terephthalate and dipyridylamide ligands

Article abstract of DOI:10.1016/j.poly.2015.10.011

Hydrothermal reaction of the requisite metal nitrate, potassium terephthalate (K₂tere) and the dipyridylamide 3-pyridylisonicotinamide (3-pina) afforded a pair of crystalline coordination polymers whose dimensionality and topology depends criti

Full text of DOI:10.1016/j.poly.2015.10.011

Polyhedron xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Metal-dependent ribbon and self-penetrated topologies
in nitroaromatic-sensing zinc and cadmium coordination
polymers with terephthalate and dipyridylamide ligands
⇑
Megan J. Wudkewych, Robert L. LaDuca
Lyman Briggs College and Department of Chemistry, Michigan State University, East Lansing, MI 48825, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Hydrothermal reaction of the requisite metal nitrate, potassium terephthalate (K2tere) and the dipyridy-
lamide 3-pyridylisonicotinamide (3-pina) afforded a pair of crystalline coordination polymers whose
dimensionality and topology depends critically on the metal coordination environment. The two new
crystalline phases were structurally characterized via single-crystal X-ray diffraction. {[Zn(tere)(3-
pina)2]ꢀ2H2O}n (1) manifests a 1-D zig-zag ribbon motif with monodentate 3-pina ligands. [Cd(tere)(3-
pina)2]n (2) displays a self-penetrated 3-D network with 446108 mab topology. Thermal and luminescent
properties of these two new materials are also presented. Both 1 and 2 show capability as sensors for
nitroaromatic compounds via luminescence quenching, with better absorption for nitrobenzene than
the more sterically bulky analyte m-nitrophenol.
Received 20 July 2015
Accepted 8 October 2015
Available online xxxx
Keywords:
Cadmium
Zinc
Coordination polymer
Crystal structure
Nitroaromatic detection
Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction
display intriguing and rare self-penetrated networks, in which
the shortest rings within the topology pass through other shortest
Over the past fifteen years, there has been an intense research
spotlight on the exploratory synthesis and structure of crystalline
coordination polymer solids. Interest remains strong due to poten-
tial of this genre of solid state materials in gas storage [1], molec-
ular separations [2], ion exchange [3], heterogeneous catalysis [4],
and as luminescent explosives trace detectors [5]. The undeniable
esthetic appeal of their underlying 1-D, 2-D, or 3-D topologies also
provides an impetus for continued research efforts [6]. Divalent
zinc or cadmium ions have proven efficacious choices as the requi-
site cationic component, predicated on their closed shell d10 elec-
tronic configurations. Full d shell population results in forbidden
visible light d–d transitions, imparting the transparent visible light
spectral window required for fluorescent sensing [7] or second har-
monic generation applications [8]. Due to the lack of crystal field
stabilization for divalent zinc and cadmium ions, coordination
polymer structure direction is ascribed to the combined effects of
ligand donor disposition, carboxylate binding mode and steric
requirements, as opposed to a specific preferred metal coordina-
tion geometry.
rings. For example, [Cd(Hpht)2(bpy)]n (pht = phthalate, bpy = 4,40-
bipyridine) manifests a self-penetrated 6-connected 3-D network
with 510647 topology [9]. Using the kinked and hydrogen bonding
capable dipyridyl ligand 4,40-dipyridylamine (dpa) afforded {[Cd
(pht)(dpa)(H2O)]ꢀ4H2O}n, which displays a unique chiral self-pene-
trated 4-connected 7482 yyz topology based on interlocked helical
subunits [10]. In other cases, this combination of ligand types has
allowed self-assembly of coordination polymers with enticing
adsorptive properties. For example, the desolvated apohost of
{[Zn2(tere)2(bpy)]ꢀH2OꢀDMF}n can separate challenging mixtures
of low molecular weight alkanes [11].
In comparison to coordination polymers containing bpy or dpa
ligands, there are fewer reports of related materials containing the
hydrogen-bonding capable dipyridylamide ligand 3-pyridylnicoti-
namide (3-pina, Scheme 1) or its isomeric dipyridylamide
congeners [15–19].
A 3-pina ligand can engage in both
supramolecular hydrogen bonding donating and accepting path-
ways due to its central amide moiety, unlike the kinked dpa or
rigid-rod bpy linkers. Different locked conformations are possible
for 3-pina ligands when entrained in a coordination polymer net-
work, including syn (with the 3-pyridyl ring nitrogen atom posi-
tioned on the same side of the molecule as the carbonyl oxygen
atom) or anti (with the 3-pyridyl ring nitrogen atom positioned
on the opposite side of the molecule as the carbonyl oxygen
atom, as depicted in Scheme 1). The isostructural phases
[M(tere)(3-pina)2]n (M = Mn, Co) display identical (4,4) grid layer
A myriad number of different topologies have been reported for
divalent zinc and cadmium coordination polymers with aromatic
dicarboxylate and neutral dipyridyl linkers [9–14]. Some of these
⇑
Corresponding author.
E-mail address: laduca@msu.edu (R.L. LaDuca).
http://dx.doi.org/10.1016/j.poly.2015.10.011
0277-5387/Ó 2015 Elsevier Ltd. All rights reserved.
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M.J. Wudkewych, R.L. LaDuca / Polyhedron xxx (2015) xxx–xxx
Table 1
Crystal and structure refinement data for 1 and 2.
Data
1
2
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C
30H26N6O8Zn
C30H22CdN6O6
674.94
monoclinic
P21/n
8.9838(15)
7.3016(12)
20.264(3)
90
101.657(3)
90
663.94
monoclinic
C/2c
21.6696(15)
9.2376(5)
15.9194(9)
90
115.921(1)
90
Scheme 1. Ligands used in this study.
topologies, with the 3-pina ligands adopting a slightly twisted syn
conformation in which their 3-pyridyl rings do not ligate [15]. {[Cu
(ip)(3-pina)]ꢀH2O}n (ip = isophthalate) exhibits dimeric units pil-
lared into a non-interpenetrated 3-D 658 cds network by tethering
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
syn
conformation
3-pina
ligands,
while
({[Cu(tbip)
V (Å3)
Z
2866.1(3)
4
1.539
1301.8(4)
2
1.722
(3-pina)2(H2O)]ꢀH2O}n (tbip = 5-tert-butylisophthalate) is a 1-D
chain coordination polymer with a ‘‘butterfly” morphology brought
about by syn conformation 3-pina ligands whose isonicotinamide
4-pyridyl rings do not ligate [16]. It is thus clear that 3-pina can
afford access to a wide variety of coordination polymer topologies
in the presence of different aromatic dicarboxylate ligands.
We have therefore attempted to extend this underdeveloped
3-pina coordination chemistry into closed-shell configuration
divalent metal systems. In this contribution we report the synthe-
sis, single-crystal structural characterization, luminescent and
nitroaromatics sensing properties, and thermal degradation behav-
ior of two new dual-ligand coordination polymers, {[Zn(tere)
(3-pina)2]ꢀ2H2O}n (1) and [Cd(tere)(3-pina)2]n (2). These phases
show a very significant change in coordination polymer dimen-
sionality and topology depending on the coordination environment
present at the closed shell divalent metal ion.
D (g cmꢁ3
l
)
(mmꢁ1
)
0.921
0.899
Crystal size (mm)
Minimum/maximum
trans.
0.21 ꢂ 0.18 ꢂ 0.16
0.24 ꢂ 0.17 ꢂ 0.04
0.9528
0.8447
hkl ranges
ꢁ25 6 h 6 25,
ꢁ11 6 k 6 11,
ꢁ19 6 l 6 19
22651
2575
0.0303
212
0.0251
0.0231
0.0585
ꢁ10 6 h 6 10,
ꢁ8 6 k 6 8,
ꢁ24 6 l 6 24
10364
2379
0.0421
196
0.0342
0.0260
0.0668
Total reflections
Unique reflections
Rint
Parameters
a
R1 (all data)
a
R1 (I > 2
r
(I))
b
wR2 (all data)
wR2 (I > 2
b
r(I))
0.0573
0.333/ꢁ0.273
0.0621
0.393/ꢁ0.507
Maximum/minimum
residual (e Åꢁ3
Goodness-of-fit
)
1.065
1.064
2. Experimental
a
R1
wR2 = {
=
R
||Fo| ꢁ |Fc||/
R|Fo|.
b
R
[w(F2o ꢁ F2c)2]/
R .
[wF2o]2}1/2
2.1. General considerations
2.3. Preparation of [Cd(tere)(3-pina)2]n (2)
Cd(NO3)2ꢀ4H2O (114 mg, 0.37 mmol),
Metal nitrates, terephthalic acid, and nitroaromatics were com-
mercially obtained. Potassium terephthalate was obtained via the
reaction of terephthalic acid with excess potassium hydroxide in
ethanolic solution. The dipyridylamide ligand 3-pyridylisonicoti-
namide (3-pina) was prepared by a literature procedure [20].
3-pina
(74 mg,
0.37 mmol), and potassium terephthalate (89 mg, 0.37 mmol) were
mixed with 10 mL of distilled H2O in a 23 mL Teflon-lined acid
digestion bomb. The bomb was sealed and heated in an oven at
120 °C for 144 h, and then was cooled slowly to 25 °C. Colorless
crystals of 2 (112 mg, 89% yield based on 3-pina) were isolated
after washing with distilled water, ethanol, and acetone and drying
in air. C30H22CdN6O6 calc. C, 53.39; H, 3.29; N, 12.45; found C,
~
Water was deionized above 3 M
X-cm in-house. Elemental analy-
sis was carried out using a Perkin Elmer 2400 Series II CHNS/O
Analyzer. IR spectra were recorded on powdered samples using a
Perkin Elmer Spectrum One instrument. The luminescence spectra
of 1 and 2 were obtained with a Hitachi F-4500 Fluorescence
Spectrometer on solid crystalline samples anchored to quartz
microscope slides with Rexon Corporation RX-22P ultraviolet-
transparent epoxy adhesive. The same Hitachi F-4500 Fluorescence
Spectrometer instrument was used for nitroaromatic absorption
studies. Thermogravimetric analysis was performed on a TA Instru-
ments Q50 thermal analyzer under flowing N2. Topological analy-
sis of coordination polymer networks was carried out using TOPOS
software [21].
52.87; H, 3.11; N, 11.98%. IR (m) = 3591 (w), 3056 (w), 2911 (w),
1677 (m), 1560 (s), 1537 (s), 1486 (w), 1424 (m), 1366 (s), 1330
(m), 1303 (s), 1008 (m), 895 (m), 840 (w), 812 (s), 746 (s), 693
(s) cmꢁ1
.
2.4. Nitroaromatic detection studies
A 5 mg sample of coordination polymer 1 or 2 was suspended in
5 mL ethanol in a volumetric flask, with immersion in an ultrasonic
bath for 60 s to ensure an even dispersion. The fluorescence spec-
trum was recorded with an excitation wavelength of 300 nm. Stock
solutions of nitrobenzene, m-nitrophenol, and benzene
(1 ꢂ 10ꢁ4 M) in dimethyl sulfoxide were prepared. Aliquots of
2.2. Preparation of {[Zn(tere)(3-pina)2]ꢀ2H2O}n (1)
Zn(NO3)2ꢀ6H2O
(113 mg,
0.38 mmol),
3-pina
(74 mg,
0.37 mmol), and potassium terephthalate (89 mg, 0.37 mmol) were
mixed with 10 mL of distilled H2O in a 23 mL Teflon-lined acid
digestion bomb. The bomb was sealed and heated in an oven at
120 °C for 50 h, and then was cooled slowly to 25 °C. Colorless
crystals of 1 (95 mg, 77% yield based on 3-pina) were isolated after
washing with distilled water, ethanol, and acetone and drying in
air. C30H26N6O8Zn 1 calc. C, 54.27; H, 3.95; N, 12.66; found C,
~
these stock solutions (10 lL) were added sequentially to coordina-
tion polymer ethanol suspensions with sonication for 30 s after
each addition. The emission spectra were measured before any
analyte addition and after each aliquot of analyte solution.
3. X-ray crystallography
54.13; H, 3.91; N, 12.43%. IR (m) = 3064 (w), 1687 (m), 1595 (s),
1556 (s), 1487 (m), 1422 (m), 1393 (m), 1359 (s), 1333 (s), 1303
Diffraction data for 1 and 2 were collected on a Bruker-AXS
(s), 1250 (m), 1200 (m), 1131 (w), 1067 (m), 1023 (w), 896 (w),
SMART-CCD X-ray diffractometer using graphite-monochromated
843 (m), 826 (m), 754 (s), 689 (s), 655 (m) cmꢁ1
.
Mo K
a radiation (k = 0.71073 Å). The data were processed via SAINT
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M.J. Wudkewych, R.L. LaDuca / Polyhedron xxx (2015) xxx–xxx
3
Table 2
Table 3
Selected bond distance (Å) and angle (°) data for 1.
Selected bond distance (Å) and angle (°) data for 2.
Zn1–O1#1
Zn1–O1
1.9713(11)
1.9713(11)
2.0429(13)
2.0429(13)
108.47(7)
O1–Zn1–N1
103.25(5)
103.25(5)
108.78(5)
108.78(5)
123.74(8)
Cd1–O2#1
Cd1–O2
2.2168(18)
2.2168(18)
2.416(2)
2.416(2)
2.393(2)
2.393(2)
180.0
86.26(7)
93.74(7)
93.74(7)
86.26(7)
O2#1–Cd1–N3#3
O2–Cd1–N3#2
O2–Cd1–N3#3
O2#1–Cd1–N3#2
N1–Cd1–N1#1
N3#2–Cd1–N1
N3#3–Cd1–N1#1
N3#2–Cd1–N1#1
N3#3–Cd1–N1
N3#3–Cd1–N3#2
97.79(7)
97.79(7)
82.21(7)
82.21(7)
180.0
85.83(7)
85.83(7)
94.17(7)
94.17(7)
180.00(11)
O1#1–Zn1–N1#1
O1#1–Zn1–N1
O1–Zn1–N1#1
N1–Zn1–N1#1
Zn1–N1#1
Zn1–N1
Cd1–N1
Cd1–N1#1
O1#1–Zn1–O1
Cd1–N3#2
Cd1–N3#3
O2#1–Cd1–O2
O2–Cd1–N1#1
O2–Cd1–N1
O2#1–Cd1–N1#1
O2#1–Cd1–N1
Symmetry transformation: #1 ꢁx + 1, y + 1, ꢁz + 1/2.
[22] and subjected to Lorentz effect, polarization effect and absorp-
tion corrections using SADABS [23]. The structures were solved using
direct methods with SHELXTL [24] using the OLEX2 software suite [25].
All non-hydrogen atoms were refined anisotropically. Hydrogen
atoms were placed in calculated positions and refined isotropically
with a riding model. Crystallographic details for 1 and 2 are given
in Table 1.
Symmetry transformations: #1 ꢁx + 2, ꢁy + 1, ꢁz; #2 ꢁx + 3/2, ꢁy ꢁ 1/2, ꢁz + 1/2;
#3 x + 1/2, ꢁy + 3/2, z ꢁ 1/2.
1537 cmꢁ1 and 1366 cmꢁ1 (2). Sharp, medium intensity bands in
the range of ꢃ1600 cmꢁ1 to ꢃ1200 cmꢁ1 are attributed to the
stretching modes of the pyridyl rings of the 3-pina ligands [26].
Features corresponding to pyridyl and aryl ring puckꢁe1ring are
observed in the region between 800 cmꢁ1 and 600 cm . Sharp,
moderate intensity bands at 1687 cmꢁ1 and 1678 cmꢁ1 denote
the C@O stretching bands within the amide moieties of the 3-pina
ligands for 1 and 2, respectively.
4. Results and discussion
4.1. Synthesis and infrared spectroscopy
Compounds 1 and 2 were prepared cleanly by hydrothermal
reaction of the requisite metal nitrate, potassium terephthalate,
and 3-pyridylisonicotinamide. Infrared spectra were consistent
with the structural components as determined by single-crystal
X-ray diffraction. Broad, weak bands at ꢃ3300 cmꢁ1 signify the
OAH bonds in the water molecules of crystallization and 3-pina
NAH bonds. Weaker, high energy bands at ꢃ3000–3200 cmꢁ1 are
attributed to CAH bond stretching modes in all cases. Asymmetric
and symmetric CAO stretching modes of the tere ligands are
marked by strong bands at 1556 cmꢁ1 and 1359 cmꢁ1 (1) and
4.2. Structural description of {[Zn(tere)(3-pina)2]ꢀ2H2O}n (1)
The asymmetric unit of compound 1 contains a divalent zinc
atom on a crystallographic 2-fold rotation axis, a complete 3-pina
ligand, and half of a tere ligand whose centroid is sited on a crys-
tallographic inversion center, and a water molecule of crystalliza-
tion. Operation of the rotation axis generates
a {ZnO2N2}
Fig. 1. (a) {ZnO2N2} tetrahedral coordination environment in 1. Thermal ellipsoids are drawn at 50% probability with symmetry codes as listed in Table 2. (b) Side view of [Zn
(tere)(3-pina)2]n ribbon motif in 1. (c) View of a single ribbon of 1 down [101].
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Fig. 2. (a) {CdO4N2} octahedral coordination environment in 2. Thermal ellipsoids are drawn at 50% probability. The symmetry codes are listed in Table 3. (b) [Cd(3-pina)2]n
(4,4) grid cationic layered motif in 2.
tetrahedral coordination environment, with the nitrogen donors
belonging to the 3-pyridyl rings of two different 3-pina ligands.
The isonicotinamide 4-pyridyl nitrogen atoms do not ligate to zinc.
The oxygen donors belong to monodentate carboxylate groups of
two different tere ligands. Bond lengths and angles within the
tetrahedral coordination environment are listed in Table 2, with
a thermal ellipsoid plot depicted in Fig. 1a.
ligands and to unligated tere carboxylate oxygen atoms in neigh-
boring ribbons. Non-classical CAHꢀ ꢀ ꢀO hydrogen bonding interac-
tions between tere aromatic carbon atoms, and the carbonyl
group within 3-pina ligands in neighboring ribbons, serve an ancil-
lary role in the inter-ribbon aggregation.
4.3. Structural description of [Cd(tere)(3-pina)2]n (2)
Bis(monodentate) tere ligands conjoin divalent zinc atoms into
neutral zig-zag [Zn(tere)]n chain motifs with a Znꢀ ꢀ ꢀZn distance of
11.098 Å. These are decorated by the monodentate anti conforma-
tion 3-pina ligands to afford neutral [Zn(tere)(3-pina)2]n ribbons
(Fig. 1b). Viewing the ribbon motif down [101] gives a perspective
of an ‘‘X” shape (Fig. 1c). Adjacent [Zn(tere)(3-pina)2]n ribbons
aggregate (Fig. S1) by hydrogen bonding patterns (Table S1) involv-
ing isolated water molecules of crystallization located in small sol-
vent-accessible pockets comprising 2.0% of the unit cell volume
according to PLATON [27]. The water molecules of crystallization
accept hydrogen bonds from NAH groups within the amide func-
tional groups of the 3-pina ligands, and donate hydrogen bonds
to unligated isonicotinamide pyridyl nitrogen atoms in 3-pina
The asymmetric unit of compound 2 contains a divalent cad-
mium atom on a crystallographic inversion center, half of a tere
ligand whose centroid rests on another inversion center, and a
complete 3-pina ligand. Operation of the crystallographic inversion
center generates a {CdO2N4} distorted octahedral coordination
environment, with trans nitrogen donor atoms belonging to the
3-pyridyl rings of two different 3-pina ligands, and another set of
trans nitrogen donor atoms belonging to the isonicotinamide pyr-
idyl rings of two additional 3-pina ligands. The oxygen atom
donors are provided by two tere ligands. Bond lengths and angles
within the octahedral coordination environment at cadmium are
listed in Table 3, and a thermal ellipsoid plot is drawn in Fig. 2a.
Fig. 3. [Cd(tere)(3-pina)2]n 3-D self-penetrated coordination polymer network in 2.
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Fig. 4. (a) Schematic perspective of a traditional straight-pillared pcu 41263 topology. (b) Schematic perspective of the 446108 mab topology cross-pillared 3-D self-penetrated
net in 2.
Cadmium atoms are connected into cationic [Cd(3-pina)2]n (4,4)
coordination polymer grid motifs (Fig. 2b) by tethering syn confor-
mation 3-pina ligands, that span a Cdꢀ ꢀ ꢀCd distance of 12.432 Å.
The grid apertures are rather pinched, with through-space Cdꢀ ꢀ ꢀCd
distances of 7.302 and 23.768 Å; the Cdꢀ ꢀ ꢀCdꢀ ꢀ ꢀCd angles around
the perimeter of all the grid windows measure 34.1° and 145.9°.
The cationic [Cd(3-pina)2]n layers in 2 are situated parallel to the
(101) crystal planes.
Parallel [Cd(3-pina)2]n layers stack along (100), with a closest
Cdꢀ ꢀ ꢀCd contact distance of 8.984 Å that matches the a lattice
parameter. However, this distance is too small to be pillared by
any charge-balancing tere ligands. Instead the bis(monodentate)
tere ligands connect cadmium atoms in neighboring layers in a
crossed fashion in order to span a Cdꢀ ꢀ ꢀCd distance of 11.577 Å in
the resulting [Cd(tere)(3-pina)2]n 3-D coordination polymer net-
work (Fig. 3). Straight pillaring would result in a standard 41263
pcu primitive-cubic like network (Fig. 4a), but the crossed pillaring
necessitated by the long span of the tere ligands in 2 affords a
6-connected 446108 mab self-penetrated network (Fig. 4b). There
have been some previous reports of this self-penetrated mab
topology [28–30]. However, most of these prior phases feature
metal dicarboxylate layers with paddlewheel dinuclear units pil-
lared by dipyridyl ligands, for example in [Cu2(glutarate)2(bpmp)]n
(bpmp = bis(4-pyridylmethyl)piperazine) [28]. Compound 2 thus
represents a rare example of a metal-dipyridyl layered coordina-
tion polymer pillared into a self-penetrated network by the dicar-
boxylate ligands. There are no solvent-accessible voids within the
self-penetrated network of 2.
4.4. Thermal properties
Compound 1 underwent dehydration between 85 and 110 °C,
with a mass loss of 5.8% corresponding well with the predicted
value for two molar equivalents of water (5.4%). Combustion of
the organic ligands occurred above 240 °C. The mass of compound
2
remained stable until 330 °C, whereupon ligand ejection
occurred. TGA traces for 1 and 2 are shown in Figs. S2 and S3.
Fig. 5. Solid-state emission spectra of 1 and 2.
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Fig. 6. Emission profiles of 1 in ethanol suspension, in the presence of varying amounts of a 1 ꢂ 10ꢁ4 M DMSO solution of nitrobenzene.
4.5. Luminescence spectra
revealing maximum excitation wavelengths of 337 nm and
320 nm, respectively. Upon excitation at this wavelength, modest
blue-violet visible light emission was observed in both cases. The
emission maxima for 1 and 2 were 467 nm and 441 nm, respec-
tively (Fig. 5). When the pure 3-pina ligand was irradiated at
Solid samples of 1 and 2 were irradiated with ultraviolet light to
examine their photoluminescent behavior. The excitation spectra
for 1 and 2 were recorded by monitoring emission at 400 nm,
Fig. 7. Emission profiles of 2 in ethanol suspension, in the presence of varying amounts of a 1 ꢂ 10ꢁ4 M DMSO solution of nitrobenzene.
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7
Fig. 8. Emission profiles of 1 in ethanol suspension, in the presence of varying amounts of a 1 ꢂ 10ꢁ4 M DMSO solution of m-nitrophenol.
Fig. 9. Emission profiles of 2 in ethanol suspension, in the presence of varying amounts of a 1 ꢂ 10ꢁ4 M DMSO solution of m-nitrophenol.
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M.J. Wudkewych, R.L. LaDuca / Polyhedron xxx (2015) xxx–xxx
265 nm, a blue emission with broad spectral profile centered at
Acknowledgements
465 nm was observed (Fig. S4). The fluorescent properties of 1
and 2 are ascribed to
the aromatic ring systems of the 3-pina and tere ligands [7].
p–
p⁄ molecular orbital transitions within
Funding for the work was provided by Lyman Briggs College of
Michigan State University. We thank Dr. Rui Huang for elemental
analysis.
Appendix A. Supplementary data
4.6. Nitroaromatic sensing
CCDC 1048725 and 1048726 contains the supplementary crys-
tallographic data for 1 and 2. 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. Supplementary data associated with this
article can be found, in the online version, at http://dx.doi.org/10.
1016/j.poly.2015.10.011.
Both compounds 1 and 2 show capability for detection of
nitrobenzene (Figs. 6 and 7, respectively) and m-nitrophenol
(Figs. 8 and 9, respectively) in ethanol suspension. Addition of
small aliquots of nitroaromatic compounds dissolved in DMSO
(1 ꢂ 10ꢁ4 M) resulted in diminution of the coordination polymer
luminescence intensity upon excitation with ultraviolet light
(kex = 300 nm). This loss of emission signal is attributed to charge
transfer from the excited states of the ligand molecular orbitals
within the coordination polymer, to those of the adsorbed elec-
tron-withdrawing nitroaromatic substrate [5]. As control experi-
ments, aliquots of a benzene solutions in DMSO (1 ꢂ 10ꢁ4 M)
were added to ethanol suspensions of both 1 and 2. Only a very
small decrease in luminescence intensity was observed in either
case (Figs. S5 and S6, respectively). Thus, it is averred that coordi-
nation polymers 1 and 2 are functional detectors for nitroaromatic
compounds. Both compounds 1 and 2 show enhanced absorption
of nitrobenzene compared to the more sterically bulky m-nitrophe-
nol. For nitrobenzene, the intensity factor (Io ꢁ I)/Io (Io = maximum
intensity in the absence of analyte) reaches a level about 13% of the
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5. Conclusions
A pair of closed-shell divalent metal terephthalate coordination
polymers with ancillary 3-pina ligands has been prepared and
structurally characterized. Although both the zinc and cadmium
derivatives have the same ratio of ligands and a similar bis(mon-
odentate)terephthalate binding mode, their structural topologies
are radically different. The smaller ionic radius of zinc affords a
4-coordinate tetrahedral arrangement of donors. As the pendant
4-pyridyl donor atoms of the 3-pina ligands cannot bind, a zig-
zag chain motif is observed in 1. Expansion of the coordination
sphere to octahedral, due to the larger ionic radius of cadmium,
results in the ability to ligate all of the 3-pina donor atoms, which
instills the generation of the 3-D net seen in 2. As the interlayer
spacing is too small for direct terephthalate bridging, an uncom-
mon 6-connected self-penetrated network is observed in the cad-
mium derivative. Ancillary structure-directing effects provided by
different 3-pina conformations (anti in 1, syn in 2) and amide group
hydrogen bonding patterns act in a synergistic fashion with the
predominating coordination environment effects. The self-penetra-
tion of the coordination polymer network in 2 resulted in added
thermal stability. Both materials show promise as sensors for the
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Please cite this article in press as: M.J. Wudkewych, R.L. LaDuca, Polyhedron (2015), http://dx.doi.org/10.1016/j.poly.2015.10.011