Metallogels and Silver Nanoparticles Generated from a Series of Transition Metal-Based Coordination Polymers Derived from a New Bis-pyridyl-bis-amide Ligand and Various Carboxylates

Article abstract of DOI:10.1021/acs.cgd.5b00911

A new series of coordination polymers, namely, CP2 [{(H₂O)Co_1.5(μ-3-bpna)_1.5(μ-btc)}·3DMF·3H₂O]_α, CP3 [{Cd(μ-3-bpna)(μ-hbtc)}·CH₃OH·2H₂O]_α, CP4 [{Co(μ-3-bpna)(μ-ipa)}·DMF·2H₂O]_α, CP5 [{Co(μ-3-bpna)(μ-1,3-pda)}·DMF]_α, CP6 [Cd(μ-3-bpna)_0.5(μ-1,3-pda)]_α, CP7 [(H₂O)Co_0.5(μ-3-bpna)_0.5(μ-1,4-pda)_0.5]_α, and CP8 [{Zn(μ-3-bpna)(μ-oba)}·DMF·2H₂O]_α, has been synthesized by reacting a hydrogen-bond-functionalized bis-pyridyl ligand, namely, N′,N″-di(pyridin-3-yl)naphthalene-2,6-dicarboxamide, with various transition metal salts and different di- or tricarboxylates (as co-ligand) displaying 2D and 3D network topology and having lattice-occluded solvents in the majority of cases. A 1D coordination polymer, namely, CP1 [{Ag_0.5(μ-3-bpna)}_0.5·0.5BF₄·CH₃CN]_α, has also been isolated by reacting 3-bpna with AgBF₄ in the absence of any carboxylate co-ligand. All of the CPs were characterized by single crystal X-ray diffraction. Interestingly, two such CPs, namely, CP1 and CP2, produced metallogels, which were characterized by rheology, transmission electron microscopy, and X-ray powder diffraction. The metallogel of CP1 produced Ag nanoparticles within the gel bed upon exposure to light. (Chemical Equation Presented).

Full text of DOI:10.1021/acs.cgd.5b00911

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Crystal Growth & Design
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Metallogels and Silver Nanoparticles Generated from a Series of
Transition Metal Based Coordination Polymers Derived from a
New Bis-pyridyl-Bis-amide Ligand and various carboxylates
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Karabi Nath, Ahmad Husain and Parthasarathi Dastidar*.
Department of Organic Chemistry, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road,
Jadavpur, Kolkataꢀ700032, India.
KEYWORDS coordination polymer, metallogel, supramolecular interactions, nanoparticles.
ABSTRACT: A new series of coordination polymer namely; CP2 [{(H2O)Co1.5(ꢁꢀ3ꢀbpna)1.5(ꢁꢀbtc)}·3DMF·3H2O]α, CP3 [{Cd(ꢁꢀ
3ꢀbpna)(ꢁꢀhbtc)}·CH3OH·2H2O]α, CP4 [{Co(ꢁꢀ3ꢀbpna)(ꢁꢀipa)}·DMF·2H2O]α, CP5 [{Co(ꢁꢀ3ꢀbpna)(ꢁꢀ1,3ꢀpda)}·DMF]α, CP6
[Cd(ꢁꢀ3ꢀbpna)0.5(ꢁꢀ1,3ꢀpda)]α, CP7 [(H2O)Co0.5(ꢁꢀ3ꢀbpna)0.5(ꢁꢀ1,4ꢀpda)0.5]α and CP8 [{Zn(ꢁꢀ3ꢀbpna)(ꢁꢀoba)}·DMF·2H2O]α has
been synthesized by reacting a hydrogen bond functionalized bisꢀpyridyl ligand namely N’,N’’ꢀdi(pyridinꢀ3ꢀyl)naphthaleneꢀ2,6ꢀ
dicarboxamide with various transition metal salts and different diꢀ or triꢀcarboxylates (as coꢀligand) displaying 2D and 3D network
topology having lattice occluded solvents in the majority of the cases. A 1D coordination polymer namely CP1 [{Ag0.5(ꢁꢀ3ꢀ
bpna)}0.5ꢂ0.5BF4·CH3CN]α has also been isolated by reacting 3-bpna with AgBF4 in absence of any carboxylate coꢀligand. All the
CPs were characterized by single crystal Xꢀray diffraction. Interestingly, two such CPs namely CP1 and CP2 produced metallogels,
which were characterized by rheology, transmission electron microscopy, and Xꢀray powder diffraction. The metallogel of CP1
produced Ag nanoparticle within the gelꢀbed upon exposure to light.
Introduction
(hydrogen bonding, πꢀπ stacking, van der Waals interactions
etc.) or by polymerization via covalent bond formation.41,42
When metal ion is a part of the gel network, the resulting gel is
called metallogel.23 Supramolecular gel containing metal naꢀ
noparticle is also called metallogel.43 Discrete coordination
compounds,44–46 infinite CP,47 crossedꢀlinked CPs48 – all have
shown to be capable of immobilizing (gelling) solvent producꢀ
ing metallogels.
Coordination polymers (CPs) are an important class of metalꢀ
organic hybrid compounds that are formed spontaneously
when multidentate organic linker(s) (ligand) is allowed to reꢀ
act with an appropriate metal salt(s).1–4 The field really took
off when Robson et al. reported a CuII diamondoid network
derived from three dimensionally linked rodꢀlike segments,
namely 4,4′,4′′,4′′′ꢀ tetracyanotetraphenyl methane.5 CPs are
usually highly crystalline compounds enabling detailed strucꢀ
tural characterization at the atomic level by single crystal Xꢀ
ray diffraction (SXRD). Such subꢀmolecular level structural
information led the researchers to design wide varieties of CPs
with potential applications such as in gas storage,6,7 anion8–10
and cation11 separation, catalysis,12–14 magnetic materials,15
drug delivery,16,17 sensors,18 optoꢀelectronics,19,20 etc.
As a part of our ongoing research program on CPs,3 we are
interested in developing CPs having intriguing structures and
functions such as in situ anion and cation separation,11 metalꢀ
logelation,21 metalꢀnanoparticle synthesis and catalysis22 etc.
For this purpose, we have been focusing on pyridyl or carboxꢀ
ylate based multidentate ligands equipped with hydrogen
bonding capable backbone such as amide or urea functionality.
Among the various potential applications CPs offer, metalloꢀ
gelation23–29 is extremely important to study because of their
potential applications in catalysis,30,31 sensing,18,32,33 photoꢀ
physics,34,35 synthesis of nanomaterials,27,36–38 magnetic mateꢀ
rials,39,40 and so forth. Gel is a soft material displaying both the
properties of solid and liquid. It is usually formed by the imꢀ
mobilization of the liquid (gelling solvent) within the gel netꢀ
work that is formed either by purely noncovalent interactions
Designing CPs is a challenging task. There are several efforts
by various groups to meet such a challenge; for example, inꢀ
troducing long alkyl chain (hydrophobic group) on coordinaꢀ
tion complex,49 installing a wellꢀknown aromaticꢀlinkerꢀ
steroid (ALS) moiety (a wellꢀknown gelꢀforming moiety), on a
metallocene,50 utilizing surface modifications with mixed ligꢀ
ands of different lengths,51 slowly crystallizing CPs with flexiꢀ
ble ligands,52 exploiting the wellꢀstudied supramolecular
synthon53,54 etc. In an another approach, we55,56 and others57
have suggested that molecular solids having lattice occluded
solvents were good candidate for gelation because of the strucꢀ
tural similarity present between gels and solvent occluded
molecular solids – in both the cases, a large amount of solꢀ
vents were occluded.
With this background in mind, we set out to synthesize a new
series of CPs that are expected to generate lattice occluded
solids which, under suitable condition, might display metalloꢀ
gelation behavior. For this purpose, we synthesized a hitherto
unexplored bisꢀpyridylꢀbisꢀamide ligand namely N’,N’’ꢀ
di(pyridinꢀ3ꢀyl)naphthaleneꢀ2,6ꢀdicarboxamide (hereafter 3ꢀ
bpna). We envisaged that the amide moieties and relatively
large πꢀcloud of the central naphthyl ring would be of some
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Crystal Growth & Design
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was taken in a 25 ml torsion vial, heated at 75 °C for 60 h, and
allowed to cool slowly (5 °C per hour in 12 h). After cooling,
blockꢀshaped pink crystals were isolated. Anal. calcd. for
C40H43Co2N7O11 (%): C 52.47, H 4.73, N 10.71 Found: C
51.97, H 4.54, N 11.03. FTꢀIR (KBr, cm–1): 3334, 3056, 1662,
1606, 1541, 1485, 1436, 1384, 1301, 1280, 1240, 1134, 1099,
1051, 929, 819, 800, 729, 700, 659, 640, 630, 594, 584.
help in the selfꢀassembly process of gelation via hydrogen
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bonding and πꢀπ stacking interactions, respectively. Moreover,
the amide functionality is also expected to invite guest moleꢀ
cules as lattice occluded solvents which in turn might contribꢀ
ute to metallogelation behavior of the resulting CPs. A series
of crystalline CPs was indeed isolated when 3ꢀbpna was reꢀ
acted with various metal salts and different bisꢀ or trisꢀ
carboxylate coꢀligands (Scheme 1).
CP3: The synthetic procedure was similar to that of CP2 unꢀ
Experimental Section
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der solvothermal condition from a DMFꢀmethanolꢀwater soluꢀ
tion of
a mixture of 3ꢀbpna (30 mg, 0.08 mmol),
9
Materials and Methods: All chemicals were commercially
available and used without further purification. The elemental
analyses were carried out using a PerkinElmer 2400 Series II
CHN analyzer. FTꢀIR spectra were recorded using Perkiꢀ
nElmer Spectrum GX. The mass spectra were recorded on Qꢀ
TOF Micro YA 263 mass spectrometer. NMR spectra (1H and
13C) were recorded using a 300 MHz Bruker Avance DPX 200
spectrometer. The photoluminescence (PL) spectra were obꢀ
tained from solid films prepared by drop casting an aqueous
suspension of the 3ꢀbpna and CPs on quartz plates using a
Nanolog spectrofluorometer from HORIBA Jobin Yvon.
Cd(NO3)2·4H2O (24.6 mg, 0.08 mmol) and trimesic acid (16.8
mg, 0.08 mmol). After cooling, blockꢀshaped crystals were
isolated. Anal. calcd. for C32H30CdN4O11 (%): C 50.64, H 3.98,
N 7.38 Found: C 51.05, H 3.14, N 7.73. FTꢀIR (KBr, cm–1):
3375, 3068, 1676, 1662, 1541, 1487, 1419, 1367, 1330, 1303,
1199, 1182, 1130, 810, 757, 727, 696, 644.
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CP4: The synthetic procedure was similar to that of CP2 unꢀ
der solvothermal condition from a DMFꢀmethanolꢀwater soluꢀ
tion of
Co(NO3)2·6H2O (23.2 mg, 0.08 mmol) and isophthalic acid
(13.28 mg, 0.08 mmol). After cooling, blockꢀshaped pink
crystals were isolated. Anal. calcd. for C34H35CoN5O9 (%): C
56.99, H 4.11, N 9.77 Found: C 56.41, H 4.03, N 9.32. FTꢀIR
(KBr, cm–1): 3365, 3062, 1652, 1606, 1541, 1483, 1398, 1328,
1299, 1191, 1107, 918, 806, 742, 721, 696, 418.
a mixture of 3ꢀbpna (30 mg, 0.08 mmol),
Synthesis of the ligand 3ꢀbpna
To a solution of 2,6ꢀnapthalenedicarboxylic acid (500 mg, 2.3
mmol) in dry dichloromethane (DCM), 2 ml of oxalyl chloride
and 4 drops of DMF was added and kept stirring with a gut
tube for 12 hours to yield a yellow suspension which was
dried under vacuum. The dried powder was stirred in toluene
for two hours and the sticky mass of oxalyl chloride was reꢀ
moved by decanting the toluene solution which was further
evaporated to isolate the pure acid chloride, as a dried mass
(600 mg, 2.37 mmol, yield: 70%).
CP5: The synthetic procedure was similar to that of CP2 unꢀ
der solvothermal condition from a DMFꢀmethanolꢀwater soluꢀ
tion of
Co(NO3)2·6H2O (23.2 mg, 0.08 mmol) and 1,3ꢀphenylene
diacetic acid (15.52 mg, 0.08 mmol). After cooling, blockꢀ
shaped pink crystals were isolated. Anal. calcd. for
C35H33CoN5O7 (%): C 60.52, H 4.79, N 10.08 Found: C 59.45,
H 4.42, N 9.79. FTꢀIR (KBr, cm–1): 3296, 3064, 1670, 1608,
1581, 1544, 1485, 1421, 1299, 1267, 1236, 1191, 1134, 1095,
811, 804, 756, 723, 698, 663, 640, 476.
a mixture of 3ꢀbpna (30 mg, 0.08 mmol),
To a solution of the acid chloride (550 mg, 2.1 mmol) and 1
ml of triethylamine in dry DCM, 3ꢀamino pyridine (395 mg,
4.2 mmol) in dry THF was added drop wise. The thick white
coloured precipitate thus formed, was kept stirring with refluxꢀ
ing for 12 hours. After filtration, the precipitate was washed
with DCMꢀTHF mixture properly; air dried, and treated with
5% NaHCO3 solution and washed with distilled water, dried
and recrystallized from DMSO (yield: 650 mg, 70%). Anal.
calcd. for C22H16N4O2 (%): C, 71.73; H, 4.38; N, 15.21.
Found: C, 71.42; H, 4.14; N, 15.00. 1H NMR (500 MHz,
DMSOꢀd6): δ = 10.73 (2H, s), 8.99 (2H, s), 8.69 (2H, s), 8.35ꢀ
8.34 (2H, d, J = 5 Hz), 8.26ꢀ8.25 (4H, d, J = 5 Hz), 8.13ꢀ8.12
(2H, d, J = 5 Hz), 7.45ꢀ7.43 (2H, dd, J = 5, 5 Hz) ppm. ESIꢀ
MS: calcd for C22H16N4O 369.18 (M+1). Found: [M + Na]+
391.17. FTꢀIR (KBr, cm–1): 3346, 3265, 3047, 1670, 1596,
1541, 1479, 1413, 1328, 1307, 1234, 1184, 1134, 1105, 1024,
943, 916, 900, 811, 790, 752, 700, 632, 487, 408.
CP6: The synthetic procedure was similar to that of CP2 under
solvothermal condition from a DMFꢀmethanolꢀwater solution
of a mixture of 3ꢀbpna (30 mg, 0.08 mmol), Cd(NO3)2·4H2O
(24.6 mg, 0.08 mmol) and 1,3ꢀphenylenediacetic acid (15.52
mg, 0.08 mmol). After cooling, blockꢀshaped crystals were
isolated. Anal. calcd. for C32H26CdN4O6 (%): C 52.13, H 3.88,
N 6.44 Found: C 52.50, H 3.62, N 5.94. FTꢀIR (KBr, cm–1):
3278, 3085, 1677, 1614, 1552, 1537, 1517, 1485, 1469, 1404,
1307, 1247, 1195, 1161, 1124, 908, 804, 757, 738, 698, 659,
592, 480.
CP7: The synthetic procedure was similar to that of CP2 unꢀ
der solvothermal condition from a DMFꢀmethanolꢀwater soluꢀ
tion of
Co(NO3)2·6H2O (23.2 mg, 0.08 mmol) and 1,4ꢀ
phenylenediacetic acid (15.52 mg, 0.08 mmol). After cooling,
blockꢀshaped pink crystals were isolated. Anal. calcd. for
C32H26CoN4O6 (%): C 60.02, H 4.22, N 9.01 Found: C 59.31,
H 4.62, N 8.62. FTꢀIR (KBr, cm–1): 3321, 3028, 1670, 1606,
1539, 1487, 1390, 1338, 1303, 1257, 1182, 1134, 894, 813,
790, 757, 703, 624, 599, 584.
a mixture of 3ꢀbpna (30 mg, 0.08 mmol),
Synthesis and Characterization of CPs
CP1: CP1 was synthesized by layering carefully a CH3CN
solution of AgBF4 (31 mg, 0.16 mmol) to a DMSO solution of
3ꢀbpna (30 mg, 0.08 mmol) in a thin long glass tube and kept
for slow evaporation at room temperature. After three weeks
Xꢀray quality block shaped white crystals were obtained.
Calcd. for C24H19AgBF4N5O2 (%): C 47.72, H 3.17, N 11.59.
Found: C 47.18, H 3.63, N 10.79. FTꢀIR (KBr, cm–1): 3398,
3083, 1672, 1596, 1541, 1481, 1413, 1328, 1307, 1263, 1234,
1188, 1134, 1105, 1070, 1026, 945, 916, 790, 700, 632, 487.
CP8: The synthetic procedure was similar to that of CP2 unꢀ
der solvothermal condition from a DMFꢀmethanolꢀwater soluꢀ
tion of
Zn(NO3)2·6H2O (24.6 mg, 0.08 mmol) and oxyꢀbisbenzoic
acid (20.6 mg, 0.08 mmol). After cooling, plateꢀshaped crysꢀ
tals were isolated. Anal. calcd. for C44H46ZnN4O10 (%): C
61.72, H 4.68, N 9.13 Found: C 61.01, H 4.08, N 8.63. FTꢀIR
a mixture of 3ꢀbpna (30 mg, 0.08 mmol),
CP2: CP2 was synthesized under solvothermal condition from
a DMFꢀmethanolꢀwater solution (3:1:1) of a mixture of 3ꢀ
bpna (30 mg, 0.08 mmol), Co(NO3)2·6H2O (23.2 mg, 0.08
mmol) and trimesic acid (16.8 mg, 0.08 mmol). The mixture
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Crystal Growth & Design
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0.71073 Å) radiation. Data reduction and unit cell refinement
were performed using SAINTꢀPlus.58 The structures were
solved by direct method and refinement procedure by fullꢀ
matrix leastꢀsquares method, based on F2 values against all
reflections was performed by SHELXLꢀ2014/7.59
Scheme 1. Schematic representation for the synthesis of
CP1-CP8.
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(KBr, cm–1): 3276, 3078, 1666, 1595, 1544, 1500, 1421, 1400,
1284, 1232, 1188, 1134, 877, 808, 784, 773, 698, 663, 649,
599.
Powder Xꢀray diffraction: Powder Xꢀray diffraction (PXRD)
measurements were performed on a Bruker AXS D8 Advance
Xꢀray (Cu Kα1 radiation, λ = 1.5406 Å) diffractometer in the
5–35° 2θ range using a 0.02° step size per second. The sample
was prepared by making a thin film from the finely powdered
sample (~30 mg) over a glass slide.
Metallogelation: In a typical gelation experiment for CP1, 3ꢀ
bpna (22 mg, 0.06 mmol) was dissolved in 0.4 ml hot DMF to
get a clear solution, and mixed with 0.6 ml aqueous solution of
AgBF4 (11.7 mg, 0.06 mmol) at room temperature; so that the
metal:ligand molar ratio was 1:1 and the resulting DMF or
DMSO/water ratio was 2:3 v/v. The gel formed almost instanꢀ
taneously. Gel formation was confirmed by the test tube inverꢀ
sion method. In a typical gelation experiment for CP2, 3ꢀbpna
(17 mg, 0.046 mmol) was dissolved in 0.4 ml hot DMF to get
a clear solution and btc (9.7 mg, 0.046mmol) was added; this
solution was mixed with 0.6 ml aqueous solution of
Co(NO3)2ꢂ6H2O (13.4 mg, 0.046 mmol) at room temperature
so that the metal:3ꢀbpna:btc, molar ratio was 1:1:1 and the
resulting DMF or DMSO/water ratio was 2:3 v/v. The gel
formed almost instantaneously. Gel formation was confirmed
by test tube inversion method.
Results and Discussion
The acylamide ligand 3ꢀbpna was synthesized by reacting 2,6ꢀ
naphthalenedicarbonyl dichloride with 3ꢀaminopyridine in a
dichloromethane (DCM)–THF mixture under refluxing condiꢀ
tions. Blocked shape crystals of 3ꢀbpna were grown by slow
evaporation form a DMSO solution. CP1 was crystalized by
layering a CH3CN solution of AgBF4 to a DMSO solution
containing 3ꢀbpna at room temperature for 3 weeks to afford
xꢀray quality blocked shape crystals. Crystals for CP2ꢀCP8
were obtained by solvothermal reaction in a DMFꢀmethanolꢀ
water solution (3:1:1).We have reacted 3ꢀbpna (in separate
experiments) with various polycarboxylates and several metal
salts [AgBF4, Co(NO3)2·6H2O, Cd(NO3)2·4H2O and
Zn(NO3)2·6H2O] in a 1 : 1 : 1 (metal : 3ꢀbpna : polycarboxꢀ
ylate) molar ratio to generate CPs CP2ꢀCP8. Crystallographic
data, bond length and bond angles, and hydrogen bonding
parameters for all the crystals were listed in tables 1, S1 and
S2, respectively.
Transmission electron microscopy: TEM micrographs were
recorded using a JEOL JEMꢀ2011 instrument operating at 200
keV. Sample preparation involved drop casting a suspension
of gel in water onto a 300 mesh carbon film supported by a
copper grid, which was then dried in air.
Rheology Studies: The rheological response of both the metalꢀ
logels was studied under dynamic and steady shear measureꢀ
ment at room temperature (25 °C) on parallelꢀplate geometry
(25 mm diameter, 1 mm gap). Rheological experiments were
carried out using Anton Paar Modular Compact Rheometer
(MCR 102).
Crystal structure of N',N''ꢀbis(3ꢀpyridyl)naphthaleneꢀ2,6ꢀ
dicarboxamide (3ꢀbpna)
Singleꢀcrystal Xꢀray diffraction analysis reveals that 3ꢀbpna
crystallizes in the centrosymmetric monoclinic space group
P21/n. The asymmetric unit contains half of 3ꢀbpna as the free
ligand is located on a center of inversion. Both the amide
groups of 3ꢀbpna are in antiꢀperiplanar conformation. The
molecule is significantly nonplanar as evident from the diheꢀ
dral angle of 13.2° involving the terminal pyridyl rings and the
Single Crystal Xꢀray Diffraction Analysis: Suitable, apparently
single crystals of 3-bpna and CP1 – CP8 were selected. Data
collection was carried out on a Bruker SMART APEX II CCD
diffractometer using graphite monochromated Mo Kα (λ =
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Table 1. Crystallographic data for compounds 3-bpna and CP1 –CP8.
3-bpna
1017718
C22H16N4O2
368.39
CP1
CP2
CP3
CP4
CP5
CP6
CP7
CP8
CCDC No.
emp. formula
formula weight
Temp. (K)
λ (Å)
1017721
C26H22AgBF4N6O2
645.17
296(2)
1028834
C102H104Co3N18O32
2270.82
213(2)
1017720
C32H26CdN4O11
754.97
1028835
C33H27CoN5O9
696.52
296(2)
1028836
C35H31CoN5O7
692.58
296(2)
1017719
C21H16CdN2O5
488.76
223(2)
0.71073
monoclinic
P 21/n
1028837
C32H28CoN4O8
655.51
298(2)
1028838
C39H31N5O10Zn
795.06
296(2)
173(2)
296(2)
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0.71073
monoclinic
P 21/n
0.71073
monoclinic
C 2/c
0.71073
triclinic
P ꢀ1
0.71073
triclinic
P ꢀ1
0.71073
triclinic
P ꢀ1
0.71073
monoclinic
P 21/n
0.71073
triclinic
P ꢀ1
0.71073
triclinic
P ꢀ1
crystal system
space group
a (Å)
8.590(1)
9.162(1)
11.199(1)
90
12.595(4)
11.220(4)
19.450(7)
90
10.034(1)
15.285(1)
18.421(2)
67.73(1)
87.02(1)
77.36(1)
2549.8(5)
1
10.247(1)
11.786(1)
14.209(1)
74.78(12)
76.18(1)
69.71(1)
1532.51(18)
2
9.147(1)
10.091(1)
17.097(3)
93.39(1)
91.55(1)
99.94(1)
1550.7(5)
2
16.117(5)
8.978(2)
22.390(6)
90
14.018(1)
7.025(1)
19.466(1)
90
6.796(1)
9.143(2)
11.838(3)
100.72(1)
96.44(1)
96.51(1)
711.4(3)
1
11.394(6)
14.357(9)
14.395(8)
101.55(1)
112.43(1)
101.04(1)
2037(2)
2
b (Å)
c (Å)
α (°)
β (°)
96.91(1)
90
102.05(1)
90
110.86(1)
90
104.87(1)
90
λ
(°)
V (Å3)
875.1(3)
2
2688.1(17)
4
3027.4(15)
4
1853.06(17)
4
Z
ρcalc. (gcmꢀ3)
ꢁ (mmꢀ1)
F000
1.398
1.594
1.479
1.636
1.492
1.520
1.752
1.530
1.296
0.093
0.814
0.575
0.783
0.619
0.629
1.216
0.665
0.663
384
1296
1179
764
718
1436
976
339
820
cryst. size (mm)
θrange (°)
miller index ranges
0.26x0.06x0.06
2.83 ꢀ 25.86
0.34x0.25x0.24
2.45 ꢀ 25.70
ꢀ15≤h≤15
0.20x0.15x0.13
1.19 – 25.67
ꢀ12≤h≤12
0.25x0.25x0.20
1.50 ꢀ 25.99
ꢀ12≤h≤11
0.30x0.25x0.10
2.05 ꢀ 25.68
ꢀ11≤h≤11
0.35x0.18x0.12
1.35 ꢀ 26.00
ꢀ19≤h≤18
0.15x0.12x0.10
2.06 ꢀ 25.50
ꢀ16≤h≤16
0.70x0.36x0.26
1.76 ꢀ 25.99
ꢀ8≤h≤7
0.28x0.12x0.08
1.84 ꢀ 24.71
ꢀ13≤h≤13
ꢀ10≤h≤9
ꢀ11≤k≤11
ꢀ13≤l≤13
10902
ꢀ13≤k≤13
ꢀ18≤k≤18
ꢀ14≤k≤14
ꢀ12≤k≤12
ꢀ11≤k≤10
ꢀ8≤k≤8
ꢀ11≤k≤11
ꢀ16≤k≤16
ꢀ23≤l≤19
ꢀ22≤l≤22
ꢀ17≤l≤17
0≤l≤20
ꢀ27≤l≤27
ꢀ23≤l≤22
ꢀ14≤l≤14
ꢀ16≤l≤16
reflections collected
independent reflections
Rint
16430
65266
19780
5862
36846
19865
9138
20348
1701
2562
9679
5959
5862
5930
3447
2772
6891
0.0338
0.0214
99.90
0.0815
100
0.019
0.0574
99.70
0.1669
99.80
0.0174
100
0.0117
99.30
0.0929
completeness to θmax (%)
data / restraints /parameters
goodnessꢀofꢀfit on F2
final R indices [I>2σ(I)]
99.90%
1701 / 0 / 127
1.038
99.50
99.20
2562 / 0 / 188
1.104
9679 / 0 / 686
1.103
5959 / 3 / 442
1.202
5862 / 407 / 444
1.042
5930 / 0 / 436
0.954
3447 / 242 / 262
1.054
2772 / 8 / 225
1.165
6891 / 867 / 498
1.076
R1 = 0.0376
R1 = 0.0532
R1 = 0.0571
R1 = 0.0235
R1 = 0.0790
R1 = 0.0830
R1 = 0.018
R1 = 0.0330
R1 = 0.0979
wR2 = 0.0916
R1 = 0.0627
wR2 = 0.1547
R1 = 0.0566
wR2 = 0.1659
R1 = 0.0800
wR2 = 0.0705
R1 = 0.0278
wR2 = 0.2103
R1 = 0.0908
wR2 = 0.1837
R1 = 0.1523
wR2 = 0.0481
R1 = 0.0198
wR2 = 0.488
0.281 and ꢀ0.380
wR2 = 0.0981
R1 = 0.0354
wR2 = 0.2748
R1 = 0.1582
R indices (all data)
wR2 = 0.1009
0.148 and ꢀ0.138
wR2 = 0.1572
1.039 and ꢀ0.781
wR2 = 0.1841
0.958 and ꢀ0.876
wR2 = 0.0893
0.586 and ꢀ0.605
wR2 = 0.2240
1.756 and ꢀ1.152
wR2 = 0.2213
0.904 and ꢀ1.244
wR2 = 0.1081
0.386 and ꢀ0.419
wR2 = 0.3098
1.284 and ꢀ0.742
largest diff. peak
and hole (e Åꢀ3)
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Crystal Growth & Design
central naphthyl spacer. The N atoms of the terminal pyridyl
rings are disposed in trans conformation. In the crystal strucꢀ
ture, the amide functionality is involved in hydrogen bonding
via NꢀHꢂꢂꢂN interactions with the pyridyl N atoms of the
neighboring molecules resulting in a herringbone packing
when viewed down cꢀaxis (Fig. 1)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
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26
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29
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32
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34
35
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40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 2. Crystal structure illustration of CP1; (a) ORTEP plot
(30% probability level); (b) packing of 1Dꢀchains viewed down aꢀ
axis (CH3CN is shown in ball and stick model in pink, AgI –
green ball).
Crystal
structure
of
[{(H2O)Co1.5(ꢁꢀ3ꢀbpna)1.5(ꢁꢀ
btc)}ꢂ3DMFꢂ3H2O]α (CP2)
The CP CP2 crystallizes in the centrosymmetric triclinic space
group Pꢀ1. The asymmetric unit consists of two CoII metal
centers (one fully occupied and the other half occupied as it
sits on a center of inversion), one btc, two 3ꢀbpna ligands (one
fully occupied and the other half occupied as the central naphꢀ
thyl moiety sits on an inversion center), one coordinated aqua
ligand, three lattice occluded DMF molecules and three solvꢀ
ate water molecules. The ligand 3ꢀbpna is found to be signifiꢀ
cantly nonplanar as evident from the dihedral angles (50.8°
and 58.9°) involving the terminal pyridyl rings and the central
naphthyl moiety. Both the metal centers display octahedral
geometry; while the fully occupied CoII center displays slightꢀ
ly distorted octahedral geometry, the other one show a perfect
octahedral geometry owing to its special position (center of
inversion). The axial sites were coordinated by the pyridyl N
atoms of the ligand 3ꢀbpna, the equatorial positions are occuꢀ
pied by O atoms of the carboxylate and water molecules. The
tricarboxylate coꢀligand namely btc coordinates through its
carboxylate O atoms to CoII metal centers resulting in a 2D
sheets propagating parallel to acꢀplane. The 2D sheets are
further threaded by the 3ꢀbpna ligands via pyridyl N–Co coꢀ
ordination resulting in an overall 3D network. The void space
with the 3D network are occupied by the solvate DMF and
water molecules sustained by various hydrogen bonding of the
type N–HꢂꢂꢂO and O–HꢂꢂꢂO. Topological analysis60 reveals that
the network present in CP2 is a 3,4,6ꢀconnected net also
known as sqc130 topology (Fig. 3). A similar 3,4,6ꢀconnected
topology based on cadmium phenylenediacetate isonicotinate
CP has been reported recently.61
Figure 1. Crystal structure illustration of 3ꢀbpna; (a) ORTEP plot
(30% probability level); (b) herringbone arrangement due to N–
H···N hydrogen bonding interactions, viewing down cꢀaxis.
Crystal structure of [{Ag0.5(ꢁꢀ3ꢀbpna)}0.5ꢂ0.5BF4ꢂCH3CN]α
(CP1)
The crystal of CP1 belongs to the centrosymmetric monoclinic
space group C2/c. The asymmetric unit consists of half of AgI
located on an inversion center, half of 3ꢀbpna molecule whose
central naphthyl ring resides on an inversion center, half of
BF4‾ anion (located on a 2ꢀfold), and a fully occupied CH3CN
molecule. The angle between the planes of terminal pyridyl
moieties and the central naphthyl spacer is 5.82° indicating
that 3ꢀbpna ligand is reasonably planar. The metal center AgI
displays a linear coordination geometry wherein the coordinatꢀ
ing sites are occupied by the pyridyl N atoms of 3ꢀbpna formꢀ
ing 1D CPic chain propagating approximately along the diagꢀ
onal of ab plane. One of the fluorine atoms (F2) of BF4‾ anion
is disordered and modelled over two positions. The >C=O of
amide functionality is not involved in any intermolecular hyꢀ
drogen bonding interaction. However, the N–H of the amide is
involved in hydrogen bonding with the BF4‾ anion that bridgꢀ
es adjacent 1D polymeric chains skewed at 52.8°, and such
packing of the 1D chains results in void space occupied by the
lattice occluded solvent molecule CH3CN stabilized by weak
C–H···N hydrogen bond (table S2). In addition, the 3ꢀbpna
also experience πꢂꢂꢂπ interactions, with interplanar distances of
3.611 Å between the pyridine and naphthyl rings (Fig. 2).
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Crystal Growth & Design
Page 6 of 12
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 3. Crystal structure illustration of CP2; (a) ORTEP plot
Figure 4. Crystal structure illustration of CP3; (a) ORTEP plot
(50% probability level); (b) coordination mode of btc; (c) topologꢀ
ical representation of the 3D network found in CP2 viewing down
bꢀaxis (topological figures were drawn using XꢀSeed62).
(50% probability level); (b) coordination mode of Hbtc for CP3;
(c) packing of 2D sheets; (d) topological representation of the 2D
network found in CP3 (rods in magenta colour, topological figꢀ
ures were drawn using XꢀSeed62).
Crystal structure of [{Cd(ꢁꢀ3ꢀbpna)(ꢁꢀhbtc)}ꢂCH3OHꢂ2H2O]α
(CP3)
Crystal structure of [{Co(ꢁꢀ3ꢀbpna)(ꢁꢀipa)}ꢂDMFꢂ2H2O]α
(CP4)
The CP CP3 crystallizes in the centrosymmetric triclinic space
group Pꢀ1. The asymmetric unit consists of one CdII, one
hbtc2–, one 3ꢀbpna, two lattice occluded water molecules and
one methanol. The ligand 3ꢀbpna is found be nearly planar as
evident from the dihedral angles involving the pyridyl moieꢀ
ties and the central naphthyl ring (12.45° and 17.82°). The CdII
metal center displays distorted octahedral geometry wherein
the equatorial positions are occupied by the carboxylate O
atoms and the axial sites are coordinated by the pyridyl N atꢀ
oms. The monoprotonated Hbtc is found to coordinate to the
adjacent CdII metal centers resulting a 1D looped chain; such
chains are further bridged by the bisꢀpyridyl ligand 3ꢀbpna
resulting in an overall 2D coordination network. The 2D
sheets are packed in parallel fashion further sustained by interꢀ
sheet N–HꢂꢂꢂO interactions involving the amide N–H and
>C=O of the COOH moiety of Hbtc and πꢂꢂꢂπ stacking (3.793ꢀ
3.922 Å, between the pyridyl···pyridyl, naphthyl···naphthyl
and naphthyl···pyridyl rings). The solvate CH3OH is found be
hydrogen bonded with amide N–H and carboxylate via N–
HꢂꢂꢂO and O–HꢂꢂꢂO interactions, respectively. Two solvate
water molecules are hydrogen bonded with each other via O–
HꢂꢂꢂO interactions; one of the water molecules further forms
hydrogen bond with amide carbonyl and COOH of Hbtc. The
overall network may best described as 4ꢀconnected uninodal
framework as suggested by topological analysis60 (Fig. 4).
The CP CP4 crystallizes in the centrosymmetric triclinic space
group Pꢀ1. The asymmetric unit consists of one CoII, one
isophthalate (ipa), one 3ꢀbpna, two lattice occluded water
molecules and one unligated DMF. The ligand 3ꢀbpna is
found to be significantly nonplanar as evident from the diheꢀ
dral angles (39.7° and 44.8°) involving the terminal pyridyl
rings and the central naphthyl moiety. The CoII metal center
displays distorted octahedral geometry wherein the equatorial
positions are occupied by the carboxylate O atoms and the
axial sites are coordinated by the pyridyl N atoms.
Figure 5. Crystal structure illustration of CP4; (a) ORTEP plot
(50% probability level); (b) packing of 2D sheets viewing down
bꢀaxis; (c) topological representation of the 2D network found in
CP4 (rods in magenta colour, topological figures were drawn
using XꢀSeed62).
The fully deprotonated ipa is found to coordinate to the adjaꢀ
cent CoII metal centers resulting a 1D looped chain; such
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Crystal Growth & Design
chains are further bridged by the bisꢀpyridyl ligand 3ꢀbpna in CP5) and is involved transꢀtetradentate bridging mode with
one acetate arm chelating (ꢁ1ꢀη1:η1) to one CdII center, whilst
the other arm chelates as well as bridges (ꢁ3ꢀη2:η2) three CdII
metal centers resulting in 2D network. The bisꢀpyridyl ligand
3ꢀbpna is found to bridge the 2D sheets packed in parallel
fashion resulting in an overall 3D network. The amide N–H is
found to be involved in hydrogen bonding with the carboxꢀ
ylate O via N–H···O interactions. The overall network may
best be described as 5ꢀconnected uninodal new topology as
suggested by topological analysis60 (Fig. 7).
1
2
3
4
5
6
7
8
resulting in an overall 2D coordination network. The 2D
sheets are packed in parallel fashion resulting in voids that
were occupied by the solvate water and DMF molecules susꢀ
tained N–HꢂꢂꢂO interactions involving the amide N–H. The
overall network may best described as 4ꢀconnected uninodal
framework as suggested by topological analysis60 (Fig. 5).
Crystal structural of [{Co(ꢁꢀ3ꢀbpna)(ꢁꢀ1,3ꢀpda)}ꢂDMF]α
9
(CP5)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The CP CP5 crystallizes in the centrosymmetric monoclinic
space group P21/n. The asymmetric unit consists of a CoII, one
1,3ꢀpda, one 3ꢀbpna molecule and one occluded DMF moleꢀ
cule. The ligand 3ꢀbpna is found to be significantly deviated
from planarity as evident from the dihedral angles involving
the pyridyl moieties and the central naphthyl ring (3.6° and
20.8°). The CoII metal center displays distorted octahedral
geometry wherein the equatorial positions are occupied by the
carboxylate O atoms and the axial sites are coordinated by the
pyridyl N atoms. Remarkably, the dicarboxylate 1,3ꢀpda ligꢀ
and adopts cis conformations rather than a much more stable
and usually observed trans conformation;63,64 1,3ꢀpda displays
an tridentate bridging mode with one carboxylate chelating
(ꢁ1ꢀη1:η1) to one CoII, whilst the other carboxylate bridges two
CoII atoms with each oxygen atom acting as a monodentate
donor (ꢁ2ꢀη1:η1). Such coordination mode results in a 1D
looped chain topology that are further bridged by the bisꢀ
pyridyl ligand 3ꢀbpna producing an overall 2D coordination
network. The 2D sheets are packed in parallel fashion. The
interstitial space is occupied by the solvate DMF sustained N–
H···O and C–H···π (Cg···H–C=2.787 Å) interactions involvꢀ
ing the amide N–H and DMF >C=O, and DMF methyl and the
aromatic moiety of 1,3ꢀpda, respectively. The overall network
may best be described as 4ꢀconnected uninodal framework as
suggested by topological analysis60 (Fig. 6).
Figure 7. Crystal structure illustration of CP6; (a) ORTEP plot
(50% probability level) and polyhedral view for CdII coordination
environment; (b) coordination modes of 1,3ꢀpda; (c) 2D sheet; (d)
topological representation of the 3D network found in CP6 (topoꢀ
logical figures were drawn using XꢀSeed62)
.
Crystal structure of [(H2O)Co0.5(ꢁꢀ3ꢀbpna)0.5(ꢁꢀ1,4ꢀpda)0.5]α
(CP7)
The CP CP7 crystallizes in the centrosymmetric triclinic space
group Pꢀ1. The asymmetric unit consists of half of CoII, half of
a 1,4ꢀpda and half of a 3ꢀbpna ligand – all reside on inversion
center, and a fully occupied aqua ligand. The ligand 3ꢀbpna is
found to be almost planar as evident from the dihedral angles
involving the pyridyl moieties and the central naphthyl ring
3.7°). The CoII metal center displays a perfect octahedral geꢀ
ometry owing to its special position (center of inversion)
wherein the equatorial positions are occupied by the carboxꢀ
ylate O atoms and coordinated water molecules, and the axial
sites are coordinated by the pyridyl N atoms. 1,4ꢀpda ligand
bridges CoII atoms in trans coordination fashion to form a 1D
chain which further tethered by 3ꢀbpna ligands to form 2D
corrugated (4,4) rhomboid network. Parallel corrugated 2D
sheets64 stack in an interdigitating fashion sustained interꢀsheet
N–HꢂꢂꢂO interactions involving the amide N–H and carboxꢀ
ylate O and O–HꢂꢂꢂO interactions involving the metal bound
water and carboxylate. The overall network may best be deꢀ
scribed as 4ꢀconnected uninodal network as suggested by
topological analysis60 (Fig. 8).
Figure 6. Crystal structure illustration of CP5; (a) ORTEP plot
(30% probability level); (b) 1D looped chain generated due to Coꢀ
1,3ꢀpda coordination mode; (c) topological representation of the
2D network found in CP5 (rods in magenta colour, topological
figures were drawn using XꢀSeed62).
Crystal structural of [Cd(ꢁꢀ3ꢀbpna)0.5(ꢁꢀ1,3ꢀpda)]α (CP6)
The CP CP6 crystallizes in the centrosymmetric monoclinic
space group P21/n. The asymmetric unit consists of a CdII, one
1,3ꢀpda moiety and half of 3ꢀbpna molecule (located on an
inversion center). The ligand 3ꢀbpna is found be nonplanar as
evident from the dihedral angles involving the pyridyl moieꢀ
ties and the central naphthyl ring (20.9°). The CdII metal cenꢀ
ter displays distorted pentagonal bipyramidal geometry whereꢀ
in the equatorial positions are occupied by the carboxylate O
atoms and the axial sites are coordinated by the pyridyl N atꢀ
om and one of the carboxylate O atoms. 1,3ꢀpda displays the
usually observed trans conformation (contrary to that observed
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Crystal Growth & Design
Page 8 of 12
The foregoing structural description of the free ligand and all
1
the CPs reveals the following (Table 2): The bispyridyl ligand
displays trans ligating topology with respect to the terminal
pyridyl moieties in all the crystal structures of the CPs as well
as the free ligand (Figure S1). The amide functionality is
found to be antiꢀperiplanar in all structures except for CP6 and
CP8 (synꢀperiplanar). In most of the cases, the dihedral angle
involving the terminal pyridyl rings and the central naphthyl
moiety indicates significant nonꢀplanarity of the ligand 3ꢀ
bpna. In the mixed ligand CPs, the carboxylate coꢀligands
display various coordination modes that include bidentate,
tridentate and tetradentate depending on how the carboxylate
O takes part in coordination. Except for CP6, the metal centers
displays perfect to distorted octahedral geometry wherein the
equatorial positions are mostly occupied the carboxylate O
atoms. Threading by the pyridyl N atoms of 3ꢀbpna ligand to
the axial sites of the octahedral metal center leads mainly to
2D coordination architecture except in CP2 and CP6; these
two CPs display 3D coordination network. The most important
feature of the CPs reported herein, as envisaged, is that majoriꢀ
ty of them occluded solvent in their crystal lattice; only CP6
and CP7 did not occlude any solvent in the crystal structures.
It may be mentioned here naphthyl based bisꢀpyridylꢀbisꢀ
amide ligands having similar structural features to 3-bpna also
produced lattice occluded coordination polymers in mixed
ligand systems.65,66
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 8. Crystal structure illustration of CP7; (a) ORTEP plot
(50% probability level); (b) packing 2D sheets; (c) topological
representation of the 2D network found in CP7 (topological figꢀ
ures were drawn using XꢀSeed62).
Crystal structure of [{Zn(ꢁꢀ3ꢀbpna)(ꢁꢀoba)}ꢂDMFꢂ2H2O]α
(CP8)
The CP CP8 crystallizes in the triclinic space group Pꢀ1. The
asymmetric unit consists of a ZnII, one 4,4′ꢀoxybisꢀbenzoate
(oba), one 3ꢀbpna, two lattice occluded water molecules and
one DMF molecule. The ligand 3ꢀbpna is found be nonplanar
as evident from the dihedral angles involving the pyridyl moiꢀ
eties and the central naphthyl ring (61.57° and 35.57°). The
ZnII metal center displays square pyramidal coordination geꢀ
ometry coordinated by carboxylate O atoms and the pyridyl N
atoms. The flexible oba ligand bridges neighboring ZnII metal
center resulting in 1D chain which are further threaded by the
bispyridyl ligand 3ꢀbpna producing a corrugated 2D sheet.
The adjacent sheets are intercalated into threeꢀdimensional
layered architecture through strong aromatic π···π stacking
interactions between 3ꢀbpna ligands (Cg···Cg = 3.447 Å).
Interestingly the adjacent 2D sheets are arranged in ABABꢂꢂ
fashion. The interstitial space within the network is occupied
by the solvate water and DMF molecules sustained by hydroꢀ
gen bonding interactions; while the water molecule is involved
in hydrogen bonding with the amide N–H, the DMF takes part
in hydrogen bonding interactions with the water. The overall
network may best described as uninodal 4ꢀconnected network
as suggested by topological analysis60 (Fig. 9).
Powder Xꢀray diffraction (PXRD) patterns are provided in the
supplementary material for 3ꢀbpna and CP1-CP8 (Figure S2).
Except CP1, in all the cases, the experimental patterns agree
well with the simulated patterns indicating the phase purity of
the bulk material. The experimental PXRD pattern of CP1
does exhibit a few ‘extra’ peaks, which may indicate the presꢀ
ence of a small crystalline impurity. The lattice occluded solꢀ
vent content in the single crystal structures of all the CPs was
further verified by TGA (Figure S3ꢀS10, supporting inforꢀ
mation).
Since the ligand 3-bpna contained a naphthalene moiety
which is a known fluorophore,67 we studied the photophysical
properties of the free ligand 3-bpna and a few selected CPs
namely CP2, CP5 and CP3 in the solid state. The bisꢀpyridylꢀ
bisꢀamide ligand 3-bpna, displays a broad emission band cenꢀ
tered around ca. 415 nm (excitation wavelength, λex=330 nm),
which can be ascribed to the intraꢀligand or ligandꢀligand πꢀπ*
or nꢀπ* transitions. The emission spectrum of CP3 (excitation
wavelength, (λex=300 nm) also appeared to be of similar feaꢀ
ture as that of the free ligand displaying a broad emission band
centered around ca. 435 nm. Since the photoluminescent d10
metal center CdII is quite far away (ca. 10 Å) from the fluoroꢀ
phore core of 3-bpna in the crystal structure of CP3, it underꢀ
standably did not affect the overall fluorescence. On the other
hand, the emission spectra of CP2 and CP5 (excitation waveꢀ
length, (λex=300 nm) appeared to have sharp characteristic
displaying a peak centered around ca. 380 nm with satellite
peaks at ca. 370 and 400 nm. It is clear that in these cases, the
d7 metal center CoII was unable to quench the luminescence68
because of its far away distance (ca. 10 Å) from the naphthyl
moiety in the respective crystal structures of the CPs (Fig.
S11, supporting information).
Figure 9. Crystal structure illustration of CP8; (a) ORTEP plot
(50% probability level); (b) schematic diagram for the interdigiꢀ
tated 2d sheets in ABAB… fashion; (c) packing diagram of the
2D sheets with the voids occupied solvents; (d) topological repreꢀ
sentation of the 2D network found in CP8 (topological figures
were drawn using XꢀSeed62).
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Crystal Growth & Design
Table 2 Crystallographic and structural information
1
2
3
4
Ligand
and
Space
group
Asymmetric unit
content
Relative
Relative
orientation
of amide
group
Dihedral
angle between
the terminal
Network
topology
Hydrogen bonding involving
the amide moiety
Lattice
occluded
solvent
orientation
of pyridyl
atoms
CPs
N
pyridyl & central
naphthyl rings
molecules per
asymmetric unit
5
6
7
8
9
3ꢀbpna
P21/n
half of 3ꢀbpna
trans
trans
antiꢀperiplanar
antiꢀperiplanar
13.20°
5.82°
Namide–H···F [N···F=3.083(5)
Å; ∠N–H···F=162.1°]
Nil
1 CH3CN
CP1
C 2/c
half of 3ꢀbpna, 0.5
1D
3D
N
amide···Npy [N···N=3.021(1)
AgI, 0.5 BF4‾,
solvate CH3CN
1
Å; ∠N–H···N=172.1°]
CP2
CP3
P ꢀ1
P ꢀ1
1.5 CoII, 1.5 of 3ꢀ
bpna, 1 btc, 1 coord
H2O, 3 solvate DMF,
3 solvate H2O
trans
antiꢀperiplanar
50.71°, 58.97°
N–H⋯Osolvate
[N⋯O
=
3 DMF
3 H2O
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2.865(5)ꢀ2.879(4) Å; ∠N–H⋯O
= 144ꢀ154.9°]
O–H⋯O [O⋯O
=
2.77(4)ꢀ
2.803(6) Å; ∠O–H⋯O = 142.6ꢀ
163°]
1
CdII, one 3ꢀbpna,
trans
antiꢀperiplanar
17.82°, 12.46°
2D
N–H⋯Osolvate
2.825(3) Å; ∠N–H⋯O
[N⋯O
=
=
2 H2O
1 CH3OH
1hbtc, 2 solvate H2O,
1 solvate MeOH
141.8°]
O–H⋯O [O⋯O
= 2.556(3)ꢀ
2.729(3) Å; ∠O–H⋯O
=
170(4)ꢀ176.1°]
CP4
CP5
P ꢀ1
1 CoII, 1 of 3ꢀbpna, 1
ipa, 1 solvate DMF, 2
solvate H2O
1 CoII, 1 of 3ꢀbpna, 1
of 1,3ꢀpda, 1 solvate
DMF
trans
trans
antiꢀperiplanar
antiꢀperiplanar
39.71°, 35.11°
21.42°, 1.82°
2D
2D
N–H⋯Osolvate
[N⋯O
=
1 DMF
2 H2O
2.878(8)ꢀ2.981(16) Å; ∠N–
H⋯O = 160ꢀ161.4°]
P 21/n
N–H⋯Osolvate
[N⋯O
=
1 DMF
3.081(6) Å; ∠N–H⋯O = 157°]
N–H⋯Ocarboxy [N⋯O
3.007(7) Å; ∠N–H⋯O
162.7°]
=
=
CP6
CP7
CP8
P 21/n
P ꢀ1
1 CdII, half of 3ꢀbpna,
1 of 1,3ꢀpda,
trans
trans
trans
antiꢀperiplanar
antiꢀperiplanar
antiꢀperiplanar
20.93°
3D
2D
2D
N–H⋯Ocarboxy [N⋯O
2.934(2) Å; ∠N–H⋯O
163.6°]
=
=
Nil
0.5 CoII, 0.5 of 3ꢀ
bpna, 0.5 of 1,4ꢀpda,
1 coord H2O
1 ZnII, 1 of 3ꢀbpna, 1
oba, 1 solvate DMF, 2
solvate H2O
3.75°
N–H⋯Ocarboxy [N⋯O
3.057(2) Å; ∠N–H⋯O
155.7°]
=
=
1 H2O
P ꢀ1
61.57°, 35.57°
N–H⋯Osolvate
[N⋯O
=
1 DMF
2 H2O
2.970(12) Å; ∠N–H⋯O = 156°]
N–H⋯Ocarboxy [N⋯O
2.908(8) Å; ∠N–H⋯O
159.7°]
=
=
Gelation studies
The morphology of the gel fibers was studied by transition
electron microscopy (TEM). The dried gels prepared by drop
casting a suspension of gel in water on a TEM grid revealed
the existence of highly entangled network of 1D tape type
fibers. Understandably these fibers formed by the spontaneous
selfꢀassembly involving the organic linkers and the metal cenꢀ
ters were capable of immobilizing the solvent molecules reꢀ
sulting in the metallogels.
Since AgI is prone to photochemical reduction to produce Ag0
nanoparticle (hereafter AgNP) under suitable conditions, the
gel obtained from the reactant of CP1 was exposed to sunlight
for a day. It was observed that the color of the gel turned
brown from white indicating AgNP formation. The tiny partiꢀ
cles (3ꢀ10 nm) seen in the TEM image of the dried gel of CP1
presumably were the AgNPs. Selected area electron diffraction
(SAED) performed on the TEM machine revealed that these
particles were crystalline as they produced wellꢀordered difꢀ
fraction spots. Existence of AgNPs was finally confirmed by
the surface plasmon resonance peak at ~470 nm in the UVꢀvis
spectrum of the suspended xerogel of CP1 in DMSO. Forꢀ
mation of metal nanoparticle including AgNPs within gel bed
has earlier been reported by us22 and others.38
Since majority of the CPs turned out to be inclusion materials
as envisaged, we decided to scan all the CPs for potential
metallogelation. Before that, we scanned the ligand 3ꢀbpna for
gelation as the amide functionality is reported to be gel proꢀ
ducing moiety. However, 3ꢀbpna turned out to be a nonꢀ
gelator when scanned with various solvents (both polar and
nonpolar). Metallogelation scanning revealed that the reactants
of majority of the CPs failed to produce metallogels with the
target solvent system DMF/water. Only the reactants of CP1
and CP2 did produce metallogels with DMF/water. The miniꢀ
mum gelator concentrations (MGCs) were found to be 3.4 and
4.0 % for CP1 and CP2, respectively considering all the reacꢀ
tants. In a typical experiment, DMF solution of the ligand(s)
was mixed with aqueous solution of the metal salt at room
temperature so that the metal:ligand molar ratio was 1:1 and
the resulting DMF/water ratio was 2:3 v/v. The gel was
formed almost instantaneously, which was visually confirmed
by the tube inversion test.
The viscoꢀelastic nature of the gels was further confirmed by
rheology. The amplitude sweep experiments wherein elastic
modulus (G') and viscous modulus (G'') were plotted against
the strain applied, suggested that a strain of 0.1% was approꢀ
priate for the frequency sweep experiments. Both CP1 and
CP2 metallogels displayed expected behavior for viscoꢀelastic
materials like gels; in both the cases, G' was greater than G''
throughout the frequency range specially, in the longer time
scale – typical of viscoꢀelastic materials like gels.
Attempt to gain insights into the gel network structure by
powder Xꢀray diffraction studies was not successful because
both the concerned CPs (CP1 and CP2) were lattice occluded
molecular solids which were susceptible towards desolvation
leading to change and/or collapse of the crystal lattice. Moreoꢀ
ver, in the case CP1, Ag nanoparticles were formed which
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Page 10 of 12
meant partial degradation of the coordination network leading logical approach adopted herein to gain access to metallogels
1
to different PXRD patterns (Fig. S12).
was worthwhile.
2
3
4
ASSOCIATED CONTENT
5
6
Supporting Information
CCDC numbers 1017718ꢀ1017721 and 1028834ꢀ1028838
contains the supplementary crystallographic data for this paꢀ
per. This data can be obtained free of charge via www.
ccdc.cam.ac.uk/data_request/cif [or from the Cambridge Crysꢀ
tallographic Data Centre (CCDC), 12 Union Road, Cambridge
CB2 1EZ, U.K.; fax: +44(0)1223ꢀ336033; eꢀmail: deposꢀ
it@ccdc.cam.ac.uk]. Additional figures, crystallographic paꢀ
rameters (bond lengths and bond angles), hydrogen bonding
table is available free of charge via the Internet at
http://pubs.acs.org.
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
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27
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AUTHOR INFORMATION
Corresponding Author
*Email: ocpd@iacs.res.in.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
KN thanks CSIR, New Delhi for a Junior Research Fellowꢀ
ship. AH thanks DST for a research associate position. PD
thanks DST for financial support. SXRD data were collected
at the DBTꢀfunded Xꢀray diffraction facility under the CEIB
program (BT/01/CEIB/11/v/13) in the Department of Organic
Chemistry, IACS, Kolkata.
Figure 10. Amplitude sweep and frequency sweep experiments of
the metallogels for CP1 (a) and CP2 (c). TEM micrograph of the
xerogels; (b) for CP1 in DMSO/water (2:3 v/v); (d) for CP2 in
DMF/water (2:3 v/v). Inset: optical images of the gels. TEM imꢀ
ages were taken on freshly prepared gels after drop casting on 300
mesh carbon coated copper grid followed drying at RT. (e) Seꢀ
lected area electron diffraction (SAED) photograph of AgNPs. (f)
Characteristic surface plasmon peak in the UV/Vis spectrum of
AgNPs derived from metallogel gel CP1.
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Metallogels and Silver Nanoparticles Generated from a Series of
Transition Metal Based Coordination Polymers Derived from a
New Bis-pyridyl-Bis-amide Ligand and various carboxylates
Karabi Nath, Ahmad Husain and Parthasarathi Dastidar*.
SYNOPSIS TOC. A rational approach has been adopted to synthesize a new series of coordination polymers derived from 3ꢀbpna
under various conditions. Two such coordination polymers (CP1 and CP2) produced metallogels. Ag nanoparticles have also been
isolated from one such metallogel.
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