Multinuclear coordination polymers based on Ag...Ag interaction: Syntheses, structures, and luminescence properties

Article abstract of DOI:10.1039/c4ce00236a

A series of coordination polymers based on Ag...Ag interactions, namely, [Ag₂(hpyb)_0.5(L1)_0.5(NO ₃)]·H₂O (1), [Ag₄(hpyb)(HL2)(NO ₃)₂]·2H₂O (2), [Ag₃(hpyb) _0.5(L3)(NO₃)] (3), [Ag₆(hpyb)(L4) ₂(NO₃)]·NO₃·2H₂O (4), [Ag₅(hpyb)_0.5(L5)₂(NO₃)] ·H₂O (5), {Ag₄(hpyb)[L6(CH₃) ₂]₂} (6), {Ag₆(hpyb)(HL7) ₂[L7(CH₃)]} (7) and [Ag₃(hpyb) _0.5(HL8)]·H₂O (8) (H₂L1 = p-phthalic acid, H₃L2 = 1,2,3-benzenetricarboxylic acid, H₂L3 = cis-2-butenedioic acid, H₂L4 = 2,3-pyridinedicarboxylic acid, H ₂L5 = m-phthalic acid, H₄L6 = 1,2,4,5- benzenetetracarboxylic acid, H₃L7 = 1,2,4-benzenetricarboxylic acid and H₄L8 = 4,4′-oxydiphthalic acid) has been synthesized. For compounds 1-4, the polycarboxylate anions bridge multinuclear Ag(i) units to form 1D chains, respectively. The chains are extended by π-π interactions into a 2D supramolecular layer for compound 3 and 3D supramolecular architectures for compounds 1, 2 and 4. Compound 5 displays a 3D (4,8)-connected (3⁴·4²)(3⁴·4 ¹²·5⁸·6⁴)₂ framework. Compounds 6-8 exhibit 2D layers, where the layers of 6 and 8 are further linked by π-π interactions to yield 3D supramolecular architectures. In the solid state, compounds 1-8 exhibit strong fluorescence emission bands at room temperature.

Full text of DOI:10.1039/c4ce00236a

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Multinuclear coordination polymers based on
Ag⋯Ag interaction: syntheses, structures, and
Cite this: CrystEngComm, 2014, 16,
luminescence properties†
5110
*
*
Hua-Yu Shi, Yun-Bo Dong, Ying-Ying Liu and Jian-Fang Ma
A series of coordination polymers based on Ag⋯Ag interactions, namely, [Ag2(hpyb)0.5(L1)0.5(NO3)]·H2O
(1), [Ag4(hpyb)(HL2)(NO3)2]·2H2O (2), [Ag3(hpyb)0.5(L3)(NO3)] (3), [Ag6(hpyb)(L4)2(NO3)]·NO3·2H2O (4),
[Ag5(hpyb)0.5(L5)2(NO3)]·H2O (5), {Ag4(hpyb)[L6(CH3)2]2} (6), {Ag6(hpyb)(HL7)2[L7(CH3)]} (7) and
[Ag3(hpyb)0.5(HL8)]·H2O (8) (H2L1 = p-phthalic acid, H3L2 = 1,2,3-benzenetricarboxylic acid, H2L3 =
cis-2-butenedioic acid, H2L4 = 2,3-pyridinedicarboxylic acid, H2L5 = m-phthalic acid, H4L6 = 1,2,4,5-
benzenetetracarboxylic acid, H3L7 = 1,2,4-benzenetricarboxylic acid and H4L8 = 4,4′-oxydiphthalic acid)
has been synthesized. For compounds 1–4, the polycarboxylate anions bridge multinuclear Ag(I) units to
form 1D chains, respectively. The chains are extended by π–π interactions into a 2D supramolecular layer
for compound 3 and 3D supramolecular architectures for compounds 1, 2 and 4. Compound 5 displays a
3D (4,8)-connected (34·42)(34·412·58·64)2 framework. Compounds 6–8 exhibit 2D layers, where the layers
of 6 and 8 are further linked by π–π interactions to yield 3D supramolecular architectures. In the solid
state, compounds 1–8 exhibit strong fluorescence emission bands at room temperature.
Received 30th January 2014,
Accepted 1st April 2014
DOI: 10.1039/c4ce00236a
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These ligands can provide multiple coordination sites, which
result in structural diversities of the compounds.
Introduction
Recently, the research of silver complexes has been the sub-
ject of considerable interest owing to their fascinating struc-
tures and photoluminescence properties.1 In this regard, the
silver clusters are one of the most important factors because
of their potential applications in the regions of catalysis,
pharmacy and luminescence.2 An insight into the silver clus-
ter comes from the forces associated with Ag⋯Ag interac-
tions. It is well known that polycarboxylic acids with various
spacers can influence the final structures of the silver
complexes.3 Especially, their carboxylate groups usually
exhibit the coordination capability to display diverse binding
modes with Ag(I) ions, which may create bi-, tri-, or tetra-nuclear
Ag(I) clusters.4 On the other hand, it is known that well
designed neutral ligands, such as various binding sites,
with appropriate shapes, are key factors for constructing
Ag(I)-containing coordination polymers.5 So far, a number of
silver compounds modified by, e.g., pyridine-, imidazole-,
triazole- and tetrazole-based ligands have been reported.6,7
Based on the aforementioned consideration, we selected a
N-donor neutral ligand hexakis[2-(1H-pyrazol-3-yl)pyridine-
ylmethyl]benzene (hpyb, Chart 1).8 As a multidentate ligand,
hpyb affords twelve potential coordination sites. Also, its
flexible methylenes can twist and rotate freely to conform to
the requirements of metal cations.9 Although some coordina-
tion polymers based on the single 3-(2-pyridyl)pyrazole ligand
have been reported,10 the coordination polymer constructed
by both hpyb and polycarboxylates has never been systemati-
cally studied to the best of our knowledge.8 In order to
investigate the structural varieties of the Ag(I)-containing
coordination polymers, we selected a series of polycarboxylate
ligands by retaining the N-donor ligand and inorganic salt
invariant.
In this work, eight new silver cluster-based complexes,
[Ag2(hpyb)0.5(L1)0.5(NO3)]·H2O (1), [Ag4(hpyb)(HL2)(NO3)2]·2H2O
(2), [Ag3(hpyb)0.5(L3)(NO3)] (3), [Ag6(hpyb)(L4)2(NO3)]·NO3·2H2O
(4), [Ag5(hpyb)0.5(L5)2(NO3)]·H2O (5), {Ag4(hpyb)[L6(CH3)2]2} (6),
{Ag6(hpyb)(HL7)2[L7(CH3)]} (7) and [Ag6(hpyb)(HL8)2]·2H2O (8)
(H2L1 = p-phthalic acid, H3L2 = 1,2,3-benzenetricarboxylic,
H2L3 = cis-2-butenedioic acid, H2L4 = 2,3-pyridinedicarboxylic
acid, H2L5 = m-phthalic acid, H4L6 = 1,2,4,5-benzenetetracarboxylic
acid, H3L7 = 1,2,4-benzenetricarboxylic acid and H4L8 =
4,4′-oxydiphthalic acid, Chart 1) have been prepared. The
photoluminescence properties of these complexes at room
temperature have been investigated.
Key Lab of Polyoxometalate Science, Department of Chemistry, Northeast Normal
University, Changchun 130024, People's Republic of China.
E-mail: liuyy147@nenu.edu.cn, majf247@yahoo.com; Fax: +86 431 85098620
† Electronic supplementary information (ESI) available: Selected bond
distances and angles, structure illustrations for compounds 1–8 and the
simulated and experimental PXRD patterns. CCDC 984125–984133. For ESI
and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c4ce00236a
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C60H48N18 (Mr = 1021.14): C, 70.57; H, 4.74; N, 24.69. Found:
C, 69.97; H, 4.50; N, 25.53.
Synthesis of [Ag2(hpyb)0.5(L1)0.5(NO3)]·H2O (1). H2L1
(0.10 mM, 17 mg) was deprotonated in methanol solution
using NaOH (0.20 mM, 8 mg). Then hpyb (0.02 mM, 20 mg)
and AgNO3 (0.50 mM, 85 mg) were added to the solution.
The total volume of the mixture was maintained at 8 mL
utilizing methanol as solvent. Then the mixture was sealed in
a Teflon-lined stainless steel autoclave reactor (15 mL) and
heated at 110 °C for 3 days. After allowing the reaction to
cool gradually to room temperature, colorless block crystals
of 1 were isolated in 61% yield based on Ag(I). Anal. calcd for
C34H28N10O6Ag2 (Mr = 888.39): C, 45.97; H, 3.18; N, 15.77.
Found: C, 45.89; H, 3.12; N, 15.83. IR data (KBr, cm−1):
3735(w), 3394(w), 3100(w), 1748(w), 1599(m), 1523(w), 1497(m),
1434(m), 1366(s), 1231(m), 1156(m), 1096(m), 1060(m), 1000(m),
957(w), 830(w), 776(m), 687(w), 630(w), 518(w).
Synthesis of [Ag4(hpyb)(HL2)(NO3)2]·2H2O (2). Compound
2 was made by following the same procedure as that for 1
except that H3L2 (0.10 mM, 21 mg) was used instead of H2L1.
Colorless block crystals of 2 were separated in 46% yield
based on Ag(I). Anal. calcd for C69H56N20O14Ag4 (Mr = 1820.78):
C, 45.52; H, 3.10; N, 15.39. Found: C, 46.43; H, 3.21; N, 15.49.
IR data (KBr, cm−1): 3835(w), 3739(w), 3433(w), 3088(w),
1716(w), 1594(m), 1506(w), 1367(s), 1279(m), 1227(m), 1098(w),
1003(w), 756(m), 692(w), 431(w).
Synthesis of [Ag3(hpyb)0.5(L3)(NO3)] (3). The preparation of
compound 3 was similar to that of compound 1 except
that H2L1 was replaced by H2L3 (0.20 mM, 23.2 mg) and
the weight of NaOH was changed to 16.0 mg (0.40 mM).
Colorless block crystals of 3 were obtained in 58% yield
based on Ag(I). Anal. calcd for C34H26N10O7Ag3 (Mr = 1010.24):
C, 40.42; H, 2.59; N, 13.86. Found: C, 40.33; H, 2.71; N, 13.74.
IR data (KBr, cm−1): 3419(w), 3104(w), 2982(w), 1633(w),
1572(m), 1557(s), 1430(s), 1355(m), 1305(s), 1232(m), 1157(m),
1063(m), 957(w), 844(m), 780(m), 686(m), 541(m).
Synthesis of [Ag6(hpyb)(L4)2(NO3)]·NO3·2H2O (4). The
preparation of compound 4 was similar to that of compound
3 except that H2L3 was replaced by H2L4 (0.20 mM, 33 mg).
Colorless block crystals of 4 were isolated in 43% yield based
on Ag(I). Anal. calcd for C74H58N22O16Ag6 (Mr = 2158.60):
C, 41.17; H, 2.71; N, 14.28. Found: C, 40.09; H, 2.73; N, 14.19.
IR data (KBr, cm−1):3307(w), 3078(w), 2823(w), 1573(s), 1453(m),
1381(s), 1229(w), 1093(w), 991(w), 826(m), 744(w), 649(w),
528(w), 426(w).
Chart 1 Structures of the hpyb ligand and polycarboxylic acids.
Experimental
Materials and instruments
The 3-(2-pyridyl)pyrazole and hexakis(bromomethyl)benzene
were synthesized according to the known method.11 All other
chemicals were commercially available without further purifi-
cation. Elemental analyses (C, H, N) were performed on a
Perkin-Elmer 240 analyzer. Powder X-ray diffraction (PXRD)
data were collected by a Rigaku Dmax 2000 X-ray diffrac-
tometer. A Mattson Alpha Centauri spectrometer and a
Perkin-Elmer FLS-920 spectrometer were used to obtain the
FT-IR spectra and fluorescence spectra, respectively. The
photoluminescence properties were measured on a FLSP920
Edinburgh fluorescence spectrometer.
Synthesis of hpyb.
A mixture of 3-(2-pyridyl)pyrazole
(15 mM, 2.18 g), NaOH (15 mM, 0.60 g) and DMSO (40 mL)
was stirred at 80 °C for 1 h. Then hexakis(bromomethyl)-
benzene (2.5 mM, 1.59 g) was added, and the mixture was
stirred at 100 °C for another 10 h. The crude product was
obtained when DMSO was removed by vacuum distillation;
after purification with methanol, the desired product was
obtained as a white powder (1.74 g, 68%).12 X-ray quality crys-
tals of hpyb were grown by solvothermal synthesis in methanol
at 100 °C. 1HNMR (500 MHz; (CD3)2SO): δ 5.97 (12H, s,
CH2), 8.51 (6H, d, py6), 7.25 (6H, t, py5), 7.70 (6H, t, py4), 7.59
(6H, t, py3), 7.23 (6H, d, pz5), 6.66 (6H, d, pz4). Anal. calcd for
Synthesis of [Ag5(hpyb)0.5(L5)2(NO3)]·H2O (5). The
preparation of compound 5 was similar to that of compound 1
except that H2L1 was replaced by H2L5 (0.40 mM, 66 mg) and
the weight of NaOH was changed to 32 mg (0.80 mM). Colorless
block crystals of 5 were isolated in 36% yield based on Ag(I).
Anal. calcd for C46H34N10O12Ag5 (Mr = 1458.16): C, 37.89;
H, 2.35; N, 9.61. Found: C, 38.01; H, 2.34; N, 9.59. IR data
(KBr, cm−1): 3421(w), 3105(w), 1599(s), 1502(m), 1436(s), 1375(s),
1267(m), 1230(s), 1096(w), 1000(w), 764(m), 688(w), 442(w).
Synthesis of {Ag4(hpyb)[L6(CH3)2]2} (6). The preparation of
compound 6 was similar to that of compound 3 except that
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H2L3 was replaced by H4L6 (0.20 mM, 55 mg). Colorless
block crystals of 6 were isolated in 53% yield based on Ag(I).
Anal. calcd for C42H32N9O8Ag2 (Mr = 1006.50): C, 50.12;
H, 3.20; N, 12.52. Found: C, 50.24; H, 3.18; N, 12.43. IR data
(KBr, cm−1): 3845(w), 3743(w), 3438(m), 3106(w), 1724(s),
1598(s), 1486(m), 1433(s), 1386(m), 1338(s), 1254(m), 1100(m),
959(w), 845(w), 751(m), 613(w).
The six 3-(2-pyridyl)pyrazole groups of the hpyb ligand take
up–down arrangements at intervals as shown in Fig. 1. The
flexible methylene spacers allow the six 3-(2-pyridyl)pyrazole
groups to rotate, with their coordination sites adopting four
inward and two outward fashions.
Structure of [Ag2(hpyb)0.5(L1)0.5(NO3)]·H2O (1)
Synthesis of {Ag6(hpyb)(HL7)2[L7(CH3)]} (7). The
preparation of compound 7 was similar to that of compound
1 except that H2L1 was replaced by 1,2,4-benzenetricarboxylic
anhydride (0.30 mM, 61 mg), the weight of NaOH was
changed to 24 mg (0.60 mM), and the solvent was replaced
by water/methanol (V1 : 7). Colorless block crystals of 7 were
isolated in 60% yield based on Ag(I). Anal. calcd for
C88H62N18O18Ag6 (Mr = 2306.75): C, 45.82; H, 2.71; N, 10.93.
Found: C, 45.75; H, 2.61; N, 10.98. IR data (KBr, cm−1):
3379(m), 3118(w), 1684(m), 1556(s), 1492(s), 1436(s), 1360(s),
1226(m), 1163(m), 1061(m), 856(w), 752(m), 688(w), 558(w).
Synthesis of [Ag3(hpyb)0.5(HL8)]·H2O (8). The preparation
of compound 8 was similar to that of 7 except that 1,2,4-
benzenetricarboxylic anhydride was replaced by 4,4′-oxydiphthalic
anhydride (0.20 mM, 62 mg). Colorless block crystals of
8 were isolated in 54% yield based on Ag(I). Anal. calcd for
C46H33N9O10Ag3 (Mr = 1195.41): C, 46.22; H, 2.78; N, 10.55.
Found: C, 46.27; H, 2.82; N, 10.46. IR data (KBr, cm−1):
3113(w), 2899(w), 2811(w), 1684(w), 1557(s), 1432(s), 1353(s),
1304(m), 1260(s), 1228(s), 1153(m), 1065(m), 959(m), 849(m),
758(s), 686(w), 650(w), 606(w), 439(w).
The asymmetric unit of compound 1 is formed by two Ag(I)
ions, half hpyb ligand, half L1 anion, one nitrate anion and
one free water molecule. As shown in Fig. 2a, the coordina-
tion environments of Ag1 and Ag2 are entirely different. Ag1
is five-coordinated in a tetragonal pyramid coordination
geometry by four N atoms from one hpyb ligand (Ag–N
2.451(5) to 2.554(3) Å) and one O atom from an L1 anion
(Ag–O 2.274(4) Å). Ag2 is three-coordinated in a T-shaped
coordination geometry by two N atoms from one hpyb ligand
(Ag–N 2.347(3) and 2.348(5) Å) and one O atom from an L1
anion (Ag–O 2.151(5) Å). Each hpyb ligand links with four
Ag(I) ions, with its six 3-(2-pyridyl)pyrazole groups displaying
a 1,2,3-up/4,5,6-down fashion. The L1 anion lies at an inver-
sion center, which supported Ag1 and Ag2 ions to form a
binuclear unit with the hpyb ligand. The distance of
Ag1⋯Ag2 is 3.055(3) Å, smaller than twice the van der Waals
radius for silver atoms (3.44 Å), indicating the existence of a
Ag⋯Ag interaction (Fig. S1†). The binuclear Ag(I) units are
generated by L1 anions to constitute a 1D chain (Fig. 2b).
The chains are further extended via intermolecular π–π
stackings between the pyrazole and pyridine rings of the
hpyb ligands (centroid-to-centroid distance: 3.940 Å) to yield
a 2D supramolecular layer (Fig. 2c). The layers are linked by
another double π–π interactions between the pyrazole and
pyridine rings of the hpyb ligands (centroid-to-centroid dis-
tances: 3.645 Å and 3.610 Å, respectively) to form a 3D supra-
molecular architecture (Fig. 2d).
X-ray crystallography
X-ray single-crystal diffraction data for complexes 1–8 were
collected on an Oxford Diffraction Gemini R Ultra diffractom-
eter with graphite-monochromated Mo Kα radiation (λ =
0.71073 Å) at 293 K. All the structures were solved by direct
methods using the SHELXS program and refined by full-
matrix least-squares methods with the SHELXL program,
respectively. The Fourier difference maps determined all non-
hydrogen atoms of the complexes, which were optimized with
anisotropic temperature parameters. The disordered atoms
(O3 and C36 in 2, O7 in 3, O13, O1W and O2W in 4, C12 and
O9 in 5, C41, C45, O9 and O10 in 7, O1W in 8) were divided
over two sites with the total occupancy of 1. The free water
molecules in complexes 1, 2 and 5 couldn't identify hydrogen
atoms from suitable residual peaks. The topological research
of complex 5 was analyzed by using the OLEX program. The
detailed crystallographic data and structure refinement
parameters for 1–8 are summarized in Table 1. Selected bond
distances and angles for compounds are given in the ESI†
(Tables S1–S8).
Structure of [Ag4(hpyb)(HL2)(NO3)2]·2H2O (2)
When the ligand H2L1 in compound 1 was replaced by H3L2,
a similar structure of 2 was obtained. The spatial configura-
tions of Ag1 and Ag2 in 2 are identical to those of 1 (Fig. 3a).
An HL2 anion is located at an inversion center, and its pro-
tonated middle carboxyl group is kept uncoordinated. Ag1
and Ag2 ions are gathered by the HL2 anion and the hpyb
ligand together to form a binuclear unit, with the distance of
2.926(7) Å (Fig. S2†). The HL2 anion bridges the binuclear
Ag(I) units to form a 1D chain along the c-axis (Fig. 3b). The
chains are sequentially joined by π–π interactions (centroid-
to-centroid distance: 3.789 Å) to generate a 3D supramolecu-
lar architecture (Fig. 3c).
Structure of [Ag3(hpyb)0.5(L3)(NO3)] (3)
Results and discussion
Structure of hpyb
The asymmetric unit of compound 3 contains three Ag(I)
ions, half hpyb ligand, one L3 anion and one nitrate anion.
As shown in Fig. 4a, Ag1 is five-coordinated by two N atoms
from one hpyb ligand and three O atoms from two L3 anions
The free hpyb ligand crystallizes in the monoclinic space
group P21/c, and its asymmetric unit contains half molecule.
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Fig. 1 ORTEP diagram of a hpyb ligand.
in a distorted tetragonal pyramid geometry. Ag2 is three-
coordinated in a T-shaped geometry by two N atoms from
one hpyb ligand and one O atom from an L3 anion. Ag3 is
four-coordinated by two N atoms from one hpyb ligand and
two O atoms from L3 and nitrate anions in a distorted tetra-
hedral geometry. Each hpyb ligand coordinates with six Ag(I)
ions. The Ag(I) ions are linked to each other by an L3 anion
and a hpyb ligand to yield a trinuclear Ag(I) cluster, with
Ag⋯Ag distances of 2.981 and 3.461 Å (Fig. S3†). These Ag(I)
clusters are linked by L3 anions to form a chain (Fig. 4b),
which are further constructed by π–π interactions between
the pyrazole and pyridine rings (centroid-to-centroid dis-
tance: 3.645 Å) to form a supramolecular layer (Fig. 4c).
Structure of [Ag6(hpyb)(L4)2(NO3)]·NO3·2H2O (4)
The asymmetric unit of compound 4 is composed of six Ag(I)
ions, one hpyb ligand, two L4 anions, two nitrate anions and
two free water molecules. Ag1–Ag3 display distorted tetrahe-
dral geometries, in which Ag1 is coordinated by one hpyb
ligand and one L4 anion in a [AgN3O] fashion, Ag2 is
surrounded by one hpyb and one L4 anion in a [AgN3O] fash-
ion, while Ag3 is environed by one hpyb ligand and two L4
anions in a [AgNO3] mode. Ag4 and Ag6 are five-coordinated
in anomalistic tetragonal pyramid coordination geometries,
in which Ag4 is surrounded by one hpyb ligand, one L4 anion
and one nitrate anion in a [AgN3O2] fashion and Ag6 is coor-
dinated by one hpyb and two L4 anions in a [AgN2O3] fash-
ion. Ag5 is three-coordinated in a T-shaped geometry by the
hpyb ligand and the L4 anion in a [AgN2O] mode. Each hypb
coordinates to six Ag(I) ions. Two binuclear Ag(I) units are
formed by the hpyb ligand and two kinds of L4 anions
together (with Ag2⋯Ag3 and Ag5⋯Ag6 distances of 3.027
and 3.053 Å, Fig. S4†). Each L4 anion coordinates to four
Ag(I) ions, which connects the Ag(I) ions and hpyb ligands to
Fig. 2 (a) Coordination environments of the Ag(I) cations in 1. (b) View
of the 1D chain. (c) View of the 2D supramolecular layer formed via
π–π interactions. (d) View of the 3D supramolecular architecture
formed by π–π interactions.
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Fig. 4 (a) Coordination environments of the Ag(I) cations in 3. (b) View
of the 1D chain. (c) View of the 2D supramolecular layer formed via
π–π interactions.
Fig. 3 (a) Coordination environments of the Ag(I) cations in 2. (b) View
of the 1D chain. (c) View of the 3D supramolecular architecture
formed by π–π interactions.
Structure of [Ag5(hpyb)0.5(L5)2(NO3)]·H2O (5)
When H2L5 was introduced to this system, a novel 3D frame-
work of 5 was obtained. Single-crystal X-ray analysis indicates
that the asymmetric unit of 5 contains five Ag(I) ions, half
hpyb ligand, two L5 anions, one nitrate anion and one free
water molecule. As shown in Fig. 6a, Ag1 is three-coordinated
in a T-shaped coordination geometry by two N atoms from
one hpyb ligand and one O atom from an L5 anion. The
other Ag(I) ions are four-coordinated, displaying distorted tet-
rahedral geometries with distinct coordination environments.
In which Ag2 bonds to two N atoms from one hpyb ligand
and two O atoms from different L5 anions, Ag3 and Ag4 are
form a 1D chain (Fig. 5b). Due to the double π–π interactions
between the pyrazole rings and pyridine rings of the hpyb
ligands (centroid-to-centroid distances: 3.937 Å and 3.588 Å,
respectively), the chains are linked into a 2D supramolecular
layer. These layers are further connected by another type of
π–π interactions between the pyridine rings of the hpyb
ligands (centroid-to-centroid distance: 3.720 Å) to generate
the final 3D supramolecular architecture.
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both surrounded by four O atoms from L5 anions and nitrate
ions, while Ag5 connects one N atom from the hpyb ligand
and three O atoms from two L5 and one nitrate anions.
Significantly, there exist two kinds of Ag⋯Ag interactions
supported by the hpyb ligand and L5 anions, in which Ag1,
Ag2 and Ag3 are gathered to a hexanuclear cluster, while Ag4
and Ag5 are connected into a tetranuclear cluster (Fig. S5a†).
These two types of clusters are interlinked by the hpyb
ligands and L5 anions to form a 2D layer. The nitrate anions
further connect the layers into a 3D framework (Fig. 6b).
Fig. 5 (a) Coordination environments of the Ag(I) cations in 4. (b) View
of the 1D chain. (c) View of the 2D supramolecular layer formed via
π–π interactions. (d) View of the 3D supramolecular architecture
formed by π–π interactions.
Fig. 6 (a) Coordination environments of the Ag(I) cations in 5. (b) View
of the 3D framework. (c) View of the 3D trinodal (4,8)-connected net.
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From a topological perspective, compound 5 is a 3D
trinodal (4,8)-connected net with a (34·42)(34·412·58·64)2 topol-
ogy (Fig. 6c), where the hpyb ligands, the tetranuclear
clusters and the hexanuclear clusters are defined as 4-, 8- and
8-connected nodes, respectively (Fig. S5b†).
Structure of {Ag4(hpyb)[L6(CH3)2]2} (6)
When H4L6 was introduced into the reaction system, an
esterified anion L6(CH3)2 appeared. The asymmetric unit of
compound 6 contains two Ag(I) ions, half hpyb ligand and
one L6(CH3)2 anion. As illustrated in Fig. 7a, Ag1 is four-
coordinated by two N atoms from the hpyb ligand and two O
atoms from two L6(CH3)2 anions in a distorted tetrahedral
geometry. Ag2 displays a T-shaped coordination geometry by
two N atoms from one hpyb ligand and one O atom from an
L6(CH3)2 anion. Unlike the hpyb in previous compounds,
only four 3-(2-pyridyl)pyrazole arms of the hpyb ligand in 6
coordinate with Ag(I) cations, while the other two arms
are kept free. Ag1 and Ag2 are assembled into a binuclear
Ag(I) unit by the hpyb ligand and the carboxylate group of
L6(CH3)2 anion together (Fig. S6†). The adjacent binuclear
units are further linked by L6(CH3)2 anions in different direc-
tions to form a 2D sheet (Fig. 7b). Two types of π–π inter-
actions between the hpyb ligands (centroid-to-centroid
distances: 3.657 and 3.900 Å) integrate these sheets to form a
3D supramolecular architecture (Fig. 7c).
Structure of {Ag6(hpyb)(HL7)2[L7(CH3)]} (7)
Somewhat similar to compound 6, the H3L7 is partially esteri-
fied by methanol to form L7(CH3) anions. So the asymmetric
unit of compound 7 contains three Ag(I) ions, half hpyb
ligand, one HL7 anion and half L7(CH3) anion. As shown in
Fig. 8a, Ag1 is five-coordinated by two N atoms from one
hpyb ligand and three O atoms from two HL7 anions in a
distorted tetragonal pyramid geometry. Ag2 and Ag3 are both
three-coordinated, displaying T-shaped [AgN2O] coordination
geometries, in which Ag2 connects by one hpyb and one HL7
anion and Ag3 links to one hpyb ligand and one L7(CH3)
anion. A trinuclear cluster is formed by Ag1, Ag2 and Ag3
ions. Unlike previous compounds, the trinuclear Ag(I) cluster
in compound 7 is supported by the hpyb ligand only without
any organic anions (Fig. S7a†). Each of the HL7 and L7(CH3)
anions links with two Ag(I) ions. In this fashion, the
trinuclear Ag(I) clusters are interlinked through organic
ligands to afford a wave-like layer (Fig. S7b†). The layers are
further stabilized by π–π interactions (centroid-to-centroid
distance: 3.984 Å) between the benzene rings of HL7 and
L7(CH3) anions (Fig. 8b).
Fig. 7 (a) Coordination environments of the Ag(I) cations in 6. (b) View
of the 2D sheet. (c) View of the 3D supramolecular architecture
formed by π–π interactions.
network. The asymmetric unit of compound 8 contains three
Ag(I) ions, half hpyb ligand, one HL8 anion and one free
water molecule. As depicted in Fig. 9a, Ag1 and Ag3 are both
four-coordinated, displaying distorted [AgN2O2] tetrahedral
geometries, in which Ag1 coordinates to one hpyb ligand and
two HL8 anions, while Ag3 connects with one hpyb ligand
and one HL8 anion. Ag2 is five-coordinated in a distorted
[AgN2O3] tetragonal pyramid geometry by one hpyb ligand
Structure of [Ag3(hpyb)0.5(HL8)]·H2O (8)
H4L8 is a relatively flexible ligand because of its rotatable
ether bond. This flexibility affords it the potential to con-
struct a more extensive Ag(I) cluster and to sustain a novel
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Fig. 8 (a) Coordination environments of the Ag(I) cations in 7. (b) View
of the 2D layer of 7.
and two HL8 anions. Each HL8 anion links to five Ag(I) ions.
In this manner, a hexanuclear Ag(I) cluster is formed by HL8
anions and hpyb ligands together (Fig. S8†). These clusters
are connected by HL8 anions to generate a 2D layer (Fig. 9b).
The existence of π–π interactions (centroid-to-centroid dis-
tance: 3.925 Å) between the pyrazole rings and pyridine rings
further extend the layers into a 3D supramolecular architec-
ture (Fig. 9c).
Fig. 9 (a) Coordination environments of the Ag(I) cations in 8. (b) View
of the 2D network. (c) View of the 3D supramolecular architecture
formed by π–π interactions.
Influence of polycarboxylate anions
Compounds 1–8 were synthesized under similar conditions
with an unchanging N-donor ligand and an inorganic salt.
Their diverse structures are primarily ascribed to the differ-
ence in polycarboxylic acids. In this series, polycarboxylic
anions have different spacers, flexibilities and number of car-
boxylate groups. These factors can influence the motifs of the
complexes. Compounds 1 and 5 exhibit the effects of car-
boxylate positions on their structures. Although both L1 and
L5 act as dicarboxylate anions with benzene rings, the posi-
tions of the carboxylate groups are different ( p-phenyl and
m-phenyl). Different lengths of spacers influence the num-
bers of the coordinated Ag(I) ions. As a result, Ag(I) ions are
bridged by polycarboxylic anions to form binuclear units in 1
and tetranuclear and hexanuclear clusters in 5, respectively.
This difference is magnified further by the extension of
the final structures, where 1 shows a 1D chain, but 5 displays
a 3D framework. Generally, increasing the number of carbox-
ylate groups can result in a higher dimensionality of the
structures.13 However, the coordination modes of the poly-
carboxylates play more important roles in the final structures
of complexes 2 and 6–8. The tri- and tetra-basic carboxylic
acids H3L2 and H4L8 in 2 and 8 are partly deprotonated to
HL2 and HL8, respectively. The H4L6 and H3L7 in 6 and 7
are esterified by methanol molecules to form L6(CH3)2
and L7(CH3) anions, respectively. As a result, instead of the
3D expanded framework, these compounds only display 1D
chain or 2D layers.
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Chart 2 The coordination modes of hpyb in 1–8.
Coordination modes of the hpyb ligand
In this work, the hpyb ligand exhibits five types of coordina-
tion patterns during the self-assembly process (Chart 2).
Different from the 1,3,5-above/2,4,6-below fashion of the
free hpyb ligand, these five patterns all show a 1,2,3-above/
4,5,6-below fashion. The change of the fashion indicates that
the coordinated Ag(I) ions influence the configuration of the
hpyb ligand. The hpyb ligand in these compounds can con-
nect four or six Ag(I) ions. Different coordination numbers of
the ligand lead to the distinction of the Ag⋯Ag subunits.
Each hpyb in compounds 1 (pattern I), 2 (pattern I) and 6
(pattern V) links with four Ag(I) ions using its six
3-(2-pyridyl)pyrazole arms chelating to Ag(I) ions or is kept
free. Binuclear Ag(I) units were formed in these compounds.
When a highly connected hpyb ligand (connected to six Ag
ions) appeared in structures 3 (pattern II), 5 (pattern IV),
7 (pattern II) and 8 (pattern II), tri-, tetra- or hexanuclear
Ag(I) clusters were generated. The hpyb ligand in compound
4 also links six metal ions (in pattern III), and the generation
of the binuclear Ag(I) units may be attributed to the synergis-
tic coordination effect of the 2,3-pyridinedicarboxylate (L4)
anion.
Fig. 10 Emission spectra of the hpyb ligand and compounds 1–8 in
the solid state at room temperature.
shifts. Based on the previous literature, red shifts might be
attributed to the different architectures featuring different
intensities of supramolecular interactions (such as Ag⋯Ag
and π–π interactions).16 The different emission peaks of
compounds 1–8 may also be influenced by polycarboxylate
anions.17 Compared with hpyb, although free polycarboxylic
acids show relatively lower emissions due to the effects of
their electron-withdrawing carboxylate groups,18 they may
also make contributions to the emissions, because the coor-
dination of polycarboxylates to Ag(I) ions may increase the
conformational rigidity of organic anions and reduce the
nonradiative decay of their excited state.17
PXRD results
The experimental and computer-simulated PXRD patterns of
compounds 1–8 are shown in Fig. S9,† which demonstrate
that the synthesized bulk materials and the measured single
crystals are the same.
Luminescence properties
The solid-state emission spectra of the hpyb ligand and com-
pounds 1–8 were measured at ambient temperature (Fig. 10).
As a highly conjugated ligand, hpyb exhibits a strong emis-
sion band with a maximum at 529 nm upon excitation at
343 nm. The emission can be attributed to the π* → π or
π* → n transitions.14 Compounds 1–8 exhibit the emission
maximum at 514, 590, 546, 522, 516, 572, 524 and 588 nm
upon excitation at 370 nm at room temperature, respectively.
Obviously, the peak positions of compounds 1–8 are some-
what similar to those of the free hpyb ligand. This result indi-
cates that the emissions of 1–8 mainly originate from ligand-
based luminescence.15 Compared with the emission of the
free hpyb, compounds 2, 3, 6 and 8 exhibit obviously red
Conclusion
Eight coordination polymers formed by a N-donor hpyb
ligand have been synthesized by a solvothermal method. This
series of compounds exhibits diverse 1D, 2D and 3D struc-
tural motifs based on the variable hpyb ligand and the choice
of polycarboxylic acids. Numerous Ag⋯Ag and π–π interac-
tions become the most exciting features of these complexes.
It is noteworthy that such a N-donor ligand with such coordi-
nation patterns and the special metal⋯metal interactions
are rare in the past reports. Moreover, all of these complexes
exhibit broad visible light emission bands at room temperature,
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which suggests that they may be good candidates for optical
materials.
8 D. A. McMorran and P. J. Steel, Inorg. Chem. Commun.,
2003, 6, 43.
9 (a) J. Yang, J. F. Ma, Y. Y. Liu, J. C. Ma and S. R. Batten,
Inorg. Chem., 2007, 46, 6542; (b) Y. C. He, J. Yang,
G. C. Yang, W. Q. Kan and J. F. Ma, Chem. Commun.,
2012, 48, 7859; (c) S. Y. Song, X. Z. Song, S. N. Zhao, C. Qin,
S. Q. Su, M. Zhu, Z. M. Hao and H. J. Zhang, Dalton Trans.,
2012, 41, 10412.
10 (a) S. P. Argent, H. Adams, T. Riis-Johannessen, J. C. Jeffery,
L. P. Harding and M. D. Ward, J. Am. Chem. Soc., 2006, 128,
72; (b) A. Stephenson, S. P. Argent, T. Riis-Johannessen,
I. S. Tidmarsh and M. D. Ward, J. Am. Chem. Soc., 2011, 133,
858; (c) N. K. Al-Rasbi, I. S. Tidmarsh, S. P. Argent,
H. Adams, L. P. Harding and M. D. Ward, J. Am. Chem. Soc.,
2008, 130, 11641; (d) R. Q. Zou, X. H. Bu and R. H. Zhang,
Inorg. Chem., 2004, 43, 5382; (e) T. L. Hu, J. R. Li,
C. S. Liu, X. S. Shi, J. N. Zhou, X. H. Bu and J. Ribas, Inorg.
Chem., 2006, 45, 162; ( f ) R. Q. Zou, C. S. Liu, Z. Huang,
T. L. Hu and X. H. Bu, Cryst. Growth Des., 2006, 6, 99; (g)
T. L. Hu, R. Q. Zou, J. R. Li and X. H. Bu, Dalton Trans.,
2008, 1302.
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (grant no. 21071028, 21001023, 21277022,
21371030, and 21301026) and the Fundamental Research
Funds for the Central Universities of China.
References
1 (a) A. Castiñeiras and R. Pedrido, Inorg. Chem., 2008, 47,
5534; (b) J. Y. Liu, Z. Y. Liu, L. J. Zhang, Y. Y. Wang, P. Yang,
Y. Wang, B. Ding and X. J. Zhao, CrystEngComm, 2013, 15,
6413; (c) C. Yang, O. Elbjeirami, C. S. P. Gamage,
H. V. R. Dias and M. A. Omary, Chem. Commun., 2011, 47,
7434; (d) F. F. Li, J. F. Ma, S. Y. Song, J. Yang, H. Q. Jia and
N. H. Hu, Cryst. Growth Des., 2006, 6, 209.
2 (a) N. C. Kasuga, R. Yoshikawa, Y. Sakai and K. Nomiya,
Inorg. Chem., 2012, 51, 1640; (b) S. D. Bian, J. H. Jia and
Q. M. Wang, J. Am. Chem. Soc., 2009, 131, 3422; (c) J. C. Jin,
Y. Y. Wang, W. H. Zhang, A. S. Lermontov, E. K. Lermontova
and Q. Z. Shi, Dalton Trans., 2009, 10181.
11 (a) H. Brunner and T. Scheck, Chem. Ber., 1992, 125, 701; (b)
Y. Lin and S. A. Lang, J. Heterocycl. Chem., 1977, 14, 345; (c)
A. D. U. Hardy, D. D. MacNicol and D. R. Wilson, J. Chem.
Soc., Perkin Trans. 2, 1979, 1011.
12 Z. Zhang, J. F. Ma, Y. Y. Liu, W. Q. Kan and J. Yang,
CrystEngComm, 2013, 15, 2009.
3 (a) J. Hunger, H. Krautscheid and J. Sieler, Cryst. Growth
Des., 2009, 9, 4613; (b) A. Karmakar and I. Goldberg,
CrystEngComm, 2011, 13, 350.
4 (a) Y. Zhao, P. Zhang, B. Li, X. G. Meng and T. L. Zhang,
Inorg. Chem., 2011, 50, 9097; (b) K. Nomiya, S. Takahashi,
R. Noguchi, S. Nemoto, T. Takayama and M. Oda, Inorg.
Chem., 2000, 39, 3301; (c) P. R. Wei, T. C. W. Mac and
D. A. Atwood, Inorg. Chem., 1998, 37, 2605.
5 (a) K. P. Rao, M. Higuchi, J. Duan and S. Kitagawa, Cryst.
Growth Des., 2013, 13, 981; (b) G. Z. Liu, X. D. Li, X. L. Li
and L. Y. Wang, CrystEngComm, 2013, 15, 2428; (c) W. Wang,
W. Q. Kan, J. Yang and J. F. Ma, CrystEngComm, 2013, 15, 3824.
6 (a) X. Feng, L. Liu, L. Y. Wang, H. L. Song, Z. Q. Shi,
X. H. Wu and S. W. Ng, J. Solid State Chem., 2013, 206, 277;
(b) H. Wu, J. Yang, Z. M. Su, S. R. Batten and J. F. Ma, J. Am.
Chem. Soc., 2011, 133, 11406.
13 H. Y. Liu, J. F. Ma, Y. Y. Liu and J. Yang, CrystEngComm,
2013, 15, 2699.
14 J. H. Yang, S. L. Zheng, X. L. Yu and X. M. Chen, Cryst.
Growth Des., 2004, 4, 831.
15 J. F. Ma, J. Yang, S. L. Li and S. Y. Song, Cryst. Growth Des.,
2005, 5, 807.
16 (a) Y. B. Dong, H. X. Xu, J. P. Ma and R. Q. Huang, Inorg.
Chem., 2006, 45, 3325; (b) J. H. Yang, S. L. Zheng, X. L. Yu
and X. M. Chen, Cryst. Growth Des., 2004, 4, 831; (c)
K. J. Wei, Y. S. Xie, J. Ni, M. Zhang and Q. L. Liu, Inorg.
Chem. Commun., 2006, 9, 926.
17 (a) H. Y. Liu, H. Wu, J. F. Ma, J. Yang and Y. Y. Liu, Dalton
Trans., 2009, 7957; (b) Y.-Y. Liu, J.-C. Ma, L.-P. Zhang and
J.-F. Ma, J. Coord. Chem., 2008, 61, 3583.
7 C. Femoni, S. Muzzioli, A. Palazzi, S. Stagni, S. Zacchini,
F. Monti, G. Accorsi, M. Bolognesi, N. Armaroli, M. Massi,
G. Valenti and M. Marcaccio, Dalton Trans., 2012, 10, 1039.
18 Z. Zhang, J.-F. Ma, Y.-Y. Liu, W.-Q. Kan and J. Yang, Cryst.
Growth Des., 2013, 13, 4338.
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