Synthesis and structures of ligand-dominated one-dimensional silver(I)–bis(pyridylmethyl)amine coordination chains

Article abstract of DOI:10.1016/j.jssc.2016.07.031

Reactants slow diffusion of Ag(I) salts with 3,4′-bis(pyridylmethyl)amine (3,4′-bpma), an unsymmetric bis-pyridyl ligand equipped with a non-innocent amine backbone, afforded polymeric coordination adducts 1–5 having a general formula {[Ag(3,4′-bpma)(solv)]X}_n (solv = H₂O, CH₃OH, and none; X= CF₃CO₂^–, BF₄^–, ClO₄^–, CF₃SO₃^–, and SbF₆^–). Single-crystal X-ray diffraction (SCXRD) analyses reveal that colorless crystals of Ag(I) coordination polymers (CPs) 1–5 have very similar one-dimensional (1D) non-flat chain structures, which are preferentially depicted as a “zipper-like” rather than a ladder-like or a double-stranded chain topologies. The 3,4′-bpma ligand in these Ag(I) CPs displays a μ₃-bridging mode with a gauche–trans (1,4, and 5) and a trans–trans (2 and 3) conformations. Noteworthy, anions do not show strong influence on structural modulation of Ag(I) CPs in the solid state, but really affect CP conformations and packing fashions, indicative of a ligand-dominated assembly process for such a Ag(I)–3,4′-bpma system. Thermal stabilities and solid-state photoluminescence properties of crystalline materials 1–5 were investigated.

Full text of DOI:10.1016/j.jssc.2016.07.031

Journal of Solid State Chemistry 242 (2016) 253–260
Contents lists available at ScienceDirect
Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
Synthesis and structures of ligand-dominated one-dimensional
silver(I)–bis(pyridylmethyl)amine coordination chains
Hung-Jui Lin a, Yu-Chiao Liu b, Yu-Jui Tseng a, Jing-Yun Wu a,
n
a Department of Applied Chemistry, National Chi Nan University, Nantou 545, Taiwan
b Institute of Chemistry, Academia Sinica, Taipei 115, Taiwan
a r t i c l e i n f o
a b s t r a c t
Article history:
Reactants slow diffusion of Ag(I) salts with 3,4′-bis(pyridylmethyl)amine (3,4′-bpma), an unsymmetric
Received 18 May 2016
Received in revised form
29 July 2016
Accepted 30 July 2016
Available online 31 July 2016
bis-pyridyl ligand equipped with a non-innocent amine backbone, afforded polymeric coordination
adducts 1–5 having a general formula {[Ag(3,4′-bpma)(solv)]X}n (solv
¼
H2O, CH3OH, and none;
X¼ CF3CO2–, BF4–, ClO4–, CF3SO3–, and SbF6–). Single-crystal X-ray diffraction (SCXRD) analyses reveal that
colorless crystals of Ag(I) coordination polymers (CPs) 1–5 have very similar one-dimensional (1D) non-
flat chain structures, which are preferentially depicted as a “zipper-like” rather than a ladder-like or a
Keywords:
double-stranded chain topologies. The 3,4′-bpma ligand in these Ag(I) CPs displays a 3-bridging mode
μ
Bis-pyridyl ligand
Coordination polymer
Silver
Slow diffusion
Zipper-like
with a gauche–trans (1,4, and 5) and a trans–trans (2 and 3) conformations. Noteworthy, anions do not
show strong influence on structural modulation of Ag(I) CPs in the solid state, but really affect CP con-
formations and packing fashions, indicative of a ligand-dominated assembly process for such a Ag(I)–
3,4′-bpma system. Thermal stabilities and solid-state photoluminescence properties of crystalline ma-
terials 1–5 were investigated.
& 2016 Elsevier Inc. All rights reserved.
1. Introduction
bis-pyridyl ligands, as potential candidates for building structu-
rally diverse and functionally intriguing CPs. Generally, bis-pyridyl
During the past decades, numerous examples of coordination
polymers (CPs), which are metal complexes having infinite one-,
two-, or three-dimensional (1D, 2D, 3D) architectures [1,2], have
been constructed due to the realization of their fascinating struc-
tural diversity and encouraging potential for use as functional
materials [3,4]. These materials are usually the thermodynamically
favored products constructed by the coordination-driven self-as-
sembly of inorganic (metal ions/clusters) and organic components
[5]. Generally, the structural and functional properties of these
materials would be fine-tuned by modifications in functionality,
rigidity/flexibility, or geometry/conformation of the ligand or by
changes in reaction variables such as counterion, solvent medium,
or even crystallization rate/route [6–9].
Among various factors that control the resultant structures and
functions of CPs, rational design and reasonable use of the char-
acteristic ligand, without a doubt, occupies the capital. 4,4′-Bi-
pyridine (bpy) is the most exploited neutral N-donor bridging li-
gand with rigid rodlike structure having linear ligating topology
used in the construction of CPs. Position isomerism and backbone
enlargement are two ideas to design novel bpy-derivatives, i.e.,
ligands with an innocent backbone such as alkyl chain, aryl, –
CQC–, –C≡C–, –NQN– etc, which are incapable of forming hy-
drogen bond have a tendency to augment the scale of well-defined
structures of bpy-based CPs [10,11]. On the other hand, bis-pyridyl
ligands having a non-innocent backbone such as amide, urea,
amine, sulfide, pyromellitic, oxadiazole, thiadiazole etc., may fre-
quently lead to rich and unexpected overall supramolecular
structures due to the influences of hydrogen bonding and/or co-
ordination interactions from the equipped functionalities [10,12–
14].
It is of particular note that applying bis-pyridyl ligands having
an amine-functionalized non-innocent backbone in the formation
of inorganic supramolecular architectures is rarely documented to
date [15,16]. Our group has recently working on the supramole-
cular synthesis of a simple bis-pyridyl bridging ligand, di(3-pyr-
idylmethyl)amine (dpma), with silver(I) salts of different coun-
teranions, resulting in numerous structurally diverse silver(I) CPs
[17]. The role of anions in controlling the network formation has
been noted. In terms of anion trends there is a propensity for
coordinating and weakly coordinating anions to give lower di-
mensional structures, while for noncoordinating anions to yield
higher dimensional networks.
n
Herein we continue our comprehensive study on the structural
effects brought by changes in ligand, from dpma to 3,4′-bis
Corresponding author.
E-mail address: jyunwu@ncnu.edu.tw (J.-Y. Wu).
http://dx.doi.org/10.1016/j.jssc.2016.07.031
0022-4596/& 2016 Elsevier Inc. All rights reserved.

254
H.-J. Lin et al. / Journal of Solid State Chemistry 242 (2016) 253–260
(pyridylmethyl)amine (3,4′-bpma) [18], an unsymmetrically posi-
tional isomer of dpma, and counteranions. A series of Ag(I)–3,4′-
colorless crystals. Yield: 33%. IR (ATR, cm–1): 3417br, 3332b,
3222m, 1677s, 1612m, 1477m, 1424m, 1377w, 1232w, 1198s, 1166s,
1126s, 1068w, 1044w, 1010w, 975w, 916m, 872, 826w, 795s, 709s,
643w. Anal. Calcd for C14H15AgF3N3O3: C, 38.38; H, 3.45; N, 9.59%.
Found: C, 37.98; H, 3.59; N, 9.47%.
bpma crystalline products with a general formula {[Ag(3,4′-bpma)
ꢀ
(solv)]X}n (solv¼ H2O, CH3OH, and none; X ¼ CF3CO2ꢀ, BF4
,
ClO4ꢀ, CF3SO3ꢀ, and SbF6ꢀ) have been obtained by reactants slow
diffusion synthesis and characterized by X-ray diffraction analyses.
Thermal stabilities and solid-state photoluminescence properties
of crystalline materials of silver(I) complexes were investigated.
2.4. Synthesis of {[Ag(3,4′-bpma)(CH3OH)](BF4)}n2
The synthetic procedure was almost the same as for 1 except for
the use of AgBF4 instead of AgCF3CO2. Yield: 60%. IR (ATR, cm–1):
3655w, 3557w, 3295w, 2921w, 2866w, 1611m, 1435m, 1290w,
1201w, 1031s, 928w, 800s, 709s, 608w. Anal. Calcd for
2. Experimental section
2.1. Materials and instrumentation
C13H17AgBF4N3O: C, 36.66; H, 4.02; N, 9.86%. Found: C, 36.55;
H, 3.98; N, 9.70%.
All chemical reagents and solvents were commercially available
and were used as received. NMR spectra were collected at room
temperature on a Bruker AMX-300 Solution-NMR spectrometer.
Chemical shifts are given in parts per million (ppm) and coupling
constants are given in hertz (Hz). FAB-MS were performed on a
JMS-700 double focusing mass spectrometer (JEOL, Tokyo, Japan)
using 3-nitrobenzyl alcohol (NBA) as matrix with a resolution of
3000 and 8000 for low and high resolution, respectively. Thermal
analyses were performed under a flux of nitrogen on a Thermo
Cahn VersaTherm HS TG analyzer with a heating rate of 5 °C/min
in the temperature range of 30–900 °C. XRPD patterns were ac-
quired on a Shimadzu XRD-7000 diffractometer with a graphite
2.5. Synthesis of {[Ag(3,4′-bpma)(CH3OH)](ClO4)}n3
The synthetic procedure was almost the same as for 1 except for
the use of AgClO4 instead of AgCF3CO2. Yield: 76%. IR (ATR, cm–1):
3646br, 3535br, 3276w, 2922w, 2862w, 1610m, 1433m, 1069s,
1015m, 925m, 799s, 709s, 620s. Anal. Calcd for C13H17AgClN3O5:
C, 35.60; H, 3.91; N, 9.58%. Found: C, 35.50; H, 3.97; N, 9.56%. Cau-
tion! Perchlorate metal salt and its complex in the presence of or-
ganic ligands are potentially explosive. Only a small amount of
material should be used and handled with care.
monochromatized Cu K
α
radiation (
λ¼1.5406 Å) at 40 kV and
2.6. Synthesis of {[Ag(3,4′-bpma)(CH3OH)](CF3SO3)}n4
30 mA. IR spectra were measured using attenuated total reflection
(ATR) technique on a Perkin-Elmer Frontier FT-IR spectrometer in
the range of 4000–550 cm–1; abbreviations: s ¼ strong, m ¼
medium, w ¼ weak, br ¼ broad. Room temperature solid-state
luminescence spectra were recorded using a Hitachi F4500 fluor-
escence spectrophotometer equipped with a 150 W xenon lamp as
an excitation source. Microanalyses (C, H, N) were done using an
Elementary Vario EL III microanalyzer.
A solution of 3,4′-bpma (0.20 mmol) in MeOH (3 mL) was
carefully layered on top of a mixture of MeOH and THF (4 mL,
1:1 v/v, middle) and a solution of AgCF3SO3 (0.20 mmol) in THF
(3 mL, bottom) at room temperature. The solution was allowed to
stand for approximately one week, resulting in the formation of
colorless crystals. Yield: 76%. IR (ATR, cm–1): 3478br, 3260m,
3224m, 2921w, 2854w, 1612m, 1435m, 1250s, 1160s, 1027s, 929m,
802s, 759m, 708s, 634s, 573m. Anal. Calcd for C14H17AgF3N3O4S: C,
34.44; H, 3.51; N, 8.61%. Found: C, 34.05; H, 3.78; N, 8.64%.
2.2. Synthesis of 3,4′-bis(pyridylmethyl)amine (3,4′-bpma)
Under ice bath, 4-pyridinecarboxaldehyde (2.14 g, 20.0 mmol)
in methanol (20 mL) was slowly added to a solution of 3-(ami-
nomethyl)pyridine (2.16 g, 20.0 mmol) in methanol (20 mL). After
the mixture was stirred at room temperature for approximately
10 h, excess NaBH4 was added under ice bath condition. The re-
action mixture was then allowed to stir continuously overnight at
room temperature. The reaction solvent was subsequently re-
moved under reduced pressure, and the residue was poured into
water and extracted with dichloromethane (3 ꢁ 30 mL). The
combined organic extracts were dried over MgSO4 and con-
centrated. The crude products were purified by column chroma-
tography (silica gel, dichloromethane/methanol ¼15/1 v/v) to af-
ford product 3,4′-bpma in 55% yield as yellow liquid (2.20 g,
2.7. Synthesis of {[Ag(3,4′-bpma)](SbF6)}n5
The synthetic procedure was almost the same as for 4 except
for the use of AgSbF6 instead of AgCF3SO3. Yield: 47%. IR (ATR, cm–
1): 3299w, 1618m, 1434m, 1375w, 1230w, 1204w, 1008w, 909m,
839w, 807m, 713m, 648s. Anal. Calcd for C12H13AgF6N3Sb: C,
26.55; H, 2.41; N, 7.74%. Found: C, 26.50; H, 2.74; N, 7.49%.
2.8. Single crystal X-ray diffraction
Data collections for 1 and 5 were performed on an Oxford
Diffraction Gemini S diffractometer; data for 2 and 3 were col-
lected by using a Bruker Smart 1000 CCD diffractometer; and data
for 4 were collected by using a Bruker Enraf-Nonius KappaCCD
diffractometer. All of the diffractometers were equipped with a
11.1 mmol). 1H NMR (300 MHz, DMSO-d6, ppm):
δ 8.52 (d,
J¼1.8 Hz, 1 H), 8.48 (dd, J¼4.8, 3.3 Hz, 2H), 8.43 (dd, J¼4.8, 3.3 Hz,
1H), 7.73 (dd, J¼9.3, 7.8 Hz, 1H), 7.36–7.30 (m, 3H), 3.70 (s, 2H),
3.68 (s, 2H), 2.93 (br, 1H). 13C{1H} NMR (75.5 MHz, DMSO-d6,
graphite monochromated Mo K
α
radiation (λ¼0.71073 Å). All of
the structures were solved by direct methods with SHELXS-97 [19]
for 1–3 and 5, and SIR92 for 4 [20], and refined using full-matrix
least squares treatment on F2 (WINGX [21] and SHELX-97 [19])
with atomic coordinates and anisotropic thermal parameters for
all non-hydrogen atoms. Whenever possible, the hydrogen atoms
were located on a difference Fourier map and refined. In other
cases, the hydrogen atoms were theoretically added. The hydrogen
atoms were allowed to ride on their bonded atoms with the iso-
tropic displacement factors. Crystal parameters and procedural
information corresponding to data collection and structure re-
finement were given in Table 1. CCDC 1046709-1046713 contain
the supplementary crystallographic data for this paper. These data
ppm):
δ 149.93, 149.59, 148.16, 136.08, 135.87, 123.55, 123.16, 51.13,
49.80. LR-MS (FABþ): m/z 200.12 [MþH]þ. HR-MS (FABþ): m/z
200.1184 [MþH]þ (calcd for C12H14N3: m/z 200.1188.
2.3. Synthesis of {[Ag(3,4′-bpma)(H2O)](CF3CO2)}n1
A solution of 3,4′-bpma (0.40 mmol) in MeOH (3 mL) was
carefully layered on top of a mixture of MeOH and H2O (4 mL,
1:1 v/v, middle) and a solution of AgCF3CO2 (0.40 mmol) in H2O
(3 mL, bottom) at room temperature. The solution was allowed to
stand for approximately 1–2 weeks, resulting in the formation of

H.-J. Lin et al. / Journal of Solid State Chemistry 242 (2016) 253–260
255
Table 1
Crystallographic data for Ag(I)–3,4′-bpma adducts 1–5.
1
2
3
4
5
Empirical formula
Mw
C14H15AgF3N3O3
438.16
C13H17AgBF4N3O
425.98
C13H17AgClN3O5
438.62
C14H17AgF3N3O4S
488.24
C12H13AgF6N3Sb
542.87
Crystal system
Space group
Triclinic
Monoclinic
P21/n
Monoclinic
P21/n
Monoclinic
P21/n
Monoclinic
C2/c
̅
1
P
a/Å
b/Å
c/Å
α/°
β/°
8.6052(5)
9.7332(5)
10.5973(6)
101.887(5)
108.089(5)
103.554(5)
782.02(8)
2
8.3521(17)
12.587(3)
15.387(3)
90
99.23(3)
90
8.468(3)
12.527(5)
15.414(6)
90
98.584(9)
90
8.803(5)
12.257(5)
16.752(5)
90
97.005(5)
90
14.7371(13)
9.4506(6)
23.5871(19)
90
105.890(9)
90
γ/°
V/Å3
Z
1596.7(6)
4
1616.9(11)
4
1794.0(14)
4
3159.6(4)
8
T/K
λ/Å
D
110(2)
0.71073
1.861
200(2)
0.71073
1.772
200(2)
0.71073
1.802
200(2)
0.71073
1.808
150(2)
0.71073
2.283
calc/g cm–3
F000
436
1.340
848
1.309
880
1.440
976
1.295
2064
3.012
μ/mm–1
θmin, θmax/°
refl collected
unique refl (Rint
2.86, 29.24
7096
3574 (0.0350)
3184
2.10, 25.09
8156
2809 (0.0248)
2352
2.10, 25.17
10,722
2874 (0.0318)
2288
3.58, 25.08
9011
3166 (0.0227)
2831
2.87, 29.17
7255
3644 (0.0635)
2470
)
obs refl (I 4 2s (I))
parameters
217
0.0356
0.0742
0.0432
0.0788
1.044
1.639, –0.835
210
208
237
208
0.0679
0.1486
0.1062
0.1735
a
R1 (I 4 2s (I))
0.0353
0.1010
0.0461
0.1228
1.151
0.0342
0.0836
0.0482
0.0892
1.052
0.0223
0.0496
0.0266
0.0517
1.039
b
wR2 (I 4 2s (I))
a
R1 (all data)
b
wR2 (all data)
GOF on F2
1.092
2.365, –1.829
Δρmax, Δρmin/e Å–3
1.201, –0.641
0.584, –0.377
0.496, –0.332
a
R1¼
Fo − F /∑ Fo
∑ .
c
wR2¼{Σ[w(Fo2 − F 2)2]/Σ[w(Fo2)2]}
.
b
1/2
c
–
–
–
–
can be obtained free of charge from the Cambridge Crystal-
lographic Data Center via www.ccdc.cam.ac.uk/data_request/cif.
CF3CO2 (1); solv¼ CH3OH, X ¼ BF4 (2), ClO4 (3), CF3SO3 (4);
–
solv¼ none, X ¼ SbF6 (5) (Scheme 1). Their solid state structures
were determined by single-crystal X-ray diffraction (SCXRD) ana-
lyses and further characterized by elemental analyses and infrared
(IR) spectra (Fig. S3). The IR spectra of adducts 1–5 all show the
characteristic peaks of anions CF3CO2– (1677 cm–1), BF4– (1031 cm–1),
3. Results and discussion
ClO4 (1069 cm–1), CF3SO3 (1250 and 1027 cm–1), and SbF6
–
–
–
3.1. Ligand design
(648 cm–1). The N–H stretching of the amine group of the 3,4′-bpma
ligand is clearly observed as a sharp peak at 3222, 3295, 3276, 3224,
and 3299 cm–1 in sequence for 1–5. In addition, broad bands arising
from the O–H stretching of coordinated H2O molecules for 1 are
centered at 3417/3332 cmꢀ1, and of coordinated CH3OH molecules
for 2–4 are respectively centered at 3655/3557, 3646/3535, and
3478/3260 cm–1. X-ray powder diffraction (XRPD) studies suggest
the formation of a single phase of the bulk materials for each
compound, supported by well-comparison of the observed and the
calculated diffraction patterns (Figs. S4–S8), with exception of slight
difference in intensity that can be attributed to the preferred-or-
ientation effects [23].
As a well-known fact that the nature of the ligand plays a
crucial role among the various factors that control the final out-
come of the structures and functions of CPs. In this sense, the
designed 3,4′-bpma ligand has two pyridine (Npy) and one amine
(Nam) nitrogen donors, making it being either as a ditopic bridge
with an angular ligating topology to coordination via the two Npy
donors or a tritopic bridge to coordination via all the Npy and Nam
donors in an irregular T- or Y-shape fashion. Moreover, the flexible
–CH2NHCH2– backbone of the 3,4′-bpma ligand resembling the –
CH2CH2CH2– backbone of the 1,3-bis(4-pyridyl)propane (bpp) li-
gand can lead to different ligand conformations in trans-trans (TT),
trans-gauche (TG), gauche-trans (GT), gauche-gauche (GG and
GG′) conformations [22]. As a consequence, the 3,4′-bpma ligand
can be assumed to have dynamic coordination behaviors to pos-
sibly rich the structures of CPs. Finally, it should not be neglected
that the equipped amine function can serve as both hydrogen-
bond donor and acceptor, which may make significant efforts on
the overall supramolecular structures.
3.3. Solid-state structures of 1–5
SCXRD structure analyses indicate that the Ag(I) center in the
Ag(I)–3,4′-bpma adducts 1–5 is coordinated by two Npy nitrogens
of two different 3,4′-bpma ligands, with Ag–Npy¼2.248(8)–2.397
(3) Å, and one Nam nitrogen of third 3,4′-bpma ligand, with Ag–
Nam¼2.241(8)–2.277(4) Å, forming
a three-coordinate trigonal
3.2. Synthesis and characterization
planar geometry (N–Ag–N ¼92.75(9)–149.08(9)°, Ag∙∙∙N3-basal
plane ¼0.16–0.32 Å, Figs. S9a–S13a). For 1–4, however, one water
molecule (1, Ag–O ¼2.551(2) Å) or one methanol molecule (2–4,
Ag–O ¼2.623(2)–2.661(4) Å) is also weakly involved in the co-
ordination sphere of Ag(I) center, therefore, giving rise to a 3þ1
capped trigonal planar geometry. In turn, the 3,4′-bpma ligand in
Reactants slow diffusion of a methanol solution of 3,4′-bpma
–
into an aqueous solution or a THF solution of AgX (X ¼ CF3CO2
,
BF4–, ClO4–, CF3SO3–, and SbF6–) at room temperature for approxi-
mately 1–2 weeks resulted in the formation of colorless crystals of
1:1 polymeric Ag(I)–3,4′-bpma coordination adducts with a gen-
eral formula {[Ag(3,4′-bpma)(solv)]X}n, where solv¼ H2O, X ¼
all five Ag(I) compounds presents a
μ3-bridging mode with various
conformations to bind three Ag(I) ions (Table S1). The Cpy–C–Nam
–

256
H.-J. Lin et al. / Journal of Solid State Chemistry 242 (2016) 253–260
Scheme 1. Synthesis and schematic representation of polymeric Ag(I)–3,4′-bpma coordination adducts 1–5.
C torsion angles are 65.0(3)/168.9(3)° for 1, ꢀ175.5(4)/ꢀ175.8(4)°
for 2, ꢀ174.0(3)/–173.7(3)° for 3, 85.2(2)/172.8(2)° for 4, and 72.6
(10)/172.8(8)° for 5. As a consequence, the ligand conformations
encompass a gauche–trans (1, 4, and 5) and a trans–trans (2 and 3)
conformations, where the gauche and trans conformations are
given when the Cpy–C–Nam–C torsion angles (
θ) are 0r∣θ∣r90°
and 90o∣ ∣r180°, respectively [17b]. The dihedral angle about
θ
the two pyridine rings of each ligand is in a narrow range of 80.3
(1)–87.1(1)° for the gauche–trans conformer and 76.5(1)–78.6(1)°
for the trans–trans conformer, which are compared to those
(gauche–trans conformer: 14.4–79.4°; trans–trans conformer:
55.9–77.2°) for dpma/Hdpmaþ ligand in the Ag(I) and Cu(II) co-
ordination arrays [16b,17b]. The Npy-to-Npy distance is in a range of
8.632(4)–8.845(4) Å for the gauche–trans conformer and 9.216(6)–
9.261(6) Å for the trans–trans conformer.
The Ag(I)–3,4′-bpma adducts 1–5 have very similar 1D poly-
meric chain structures (Fig. 1 and S9b–S13b), wherein the parallel
4-pyridine rings are paired in a “head-to-tail” manner and form
slipped intra-chain
π∙∙∙π stacking with a centroid∙∙∙centroid dis-
tance of 3.60–3.69 Å. Of particular interest, the 3,4′-bpma ligand
has shown chirality of either S or R configuration at the asym-
metric amine nitrogen (N1) when it coordinates to the Ag
(I) center. As shown in Fig. 1, the amine nitrogens within the chain
structures of 1–4 have shown the chiralities in a S∙∙∙R∙∙∙S∙∙∙R se-
quence. Comparably, the sequence of the chiralities of the amine
nitrogens within the chain structure of 5 is S∙∙∙S∙∙∙R∙∙∙R.
Fig. 1. (a–e) Side (left) and perspective (right) views of the 1D Ag(I)–3,4′-bpma
chain structures in 1–5. Counteranions, coordinated water/methanol molecules,
and carbon-bound hydrogen atoms are omitted for clarity. Dashed lines represent
the slipped intra-chain π∙∙∙π stacking between the parallel 4-pyridine rings that are
paired in a “head-to-tail” manner. The letters “S” and “R” are used to assign the
chiralities of the amine nitrogens.
The packing diagram of 1 reveals that when viewed down
slightly off the crystallographic a axis, the non-flat Ag(I)–3,4′-bpma
coordination chains align alternately to make cavities that are
large enough to accommodate trifluoroacetate counteranions. Two
coordinated water molecules and two trifluoroacetate counter-
anions form four sets of O–H∙∙∙O hydrogen bonds (O∙∙∙O ¼2.753
extending (from 1D coordination chain to 2D hydrogen-bonded
sheet) and network-stabilizing interactions (Fig. 3).
(4) and 2.833(3) Å, Table S2) to give a 4(12) pattern (Fig. 2a). In
R4
addition, there are also N–H∙∙∙O hydrogen bonds (N∙∙∙O ¼3.079(4)
Å) between the amine hydrogens and the trifluoroacetate coun-
teranions. These hydrogen bonds not only stitch the 1D chains into
a supramolecular 2D hydrogen-bonded sheet (Fig. 2b), but serve to
stabilize the system of extensive supramolecular network.
In 2–4, the Ag(I)–3,4′-bpma coordination chains all align in an
order of AAA along the crystallographic a axis. The counteranions
are not involved in the Ag(I) coordination sphere but are hydrogen
bonded to amine hydrogens of the 3,4′-bpma ligands through N–
H∙∙∙anion interactions (N∙∙∙F4B ¼2.992(6) Å for 2, N∙∙∙O4Cl ¼3.085
(6) Å for 3, and N∙∙∙O3SCF3¼2.992(6) Å for 4) and to the methanol
ligands through O–H∙∙∙anion interactions (O∙∙∙F4B ¼2.709(8) Å for
2, O∙∙∙O4Cl ¼2.772(6) Å for 3, and O∙∙∙O3SCF3¼2.709(8) Å for 4).
These hydrogen bonds, as observed in 1, serve as both network-
In 5, The Ag(I)–3,4′-bpma coordination chains align in an order
of AAA along the crystallographic
b axis with the hexa-
fluoroantimonate counteranions resided the inter-chain spaces.
Though the Ag∙∙∙F6Sb distances of 3.370(9) and 3.393(8) Å are
slightly longer than the sum of the van der Waals radii for Ag and F
(3.19 Å) [24], the hexafluoroantimonate counteranions have very
weak contacts with the Ag(I) centers. Moreover, the hexa-
fluoroantimonate counteranions also form pertinent N–H∙∙∙F hy-
drogen bonds (N∙∙∙F ¼3.183(10) and 3.136(10) Å) with the amine
hydrogens. Both two types of weak interactions cooperatively
stitch these 1D chains to be an extensive 2D supramolecular sheet
(Fig. 4).
Herein, though the Ag(I)–3,4′-bpma adducts 1–5 have similar
chain structures, their packing arrays are significantly different,

H.-J. Lin et al. / Journal of Solid State Chemistry 242 (2016) 253–260
257
Fig. 2. (a) Representation of the R44(12) hydrogen-bonding pattern formed by two
coordinated aqua ligands and two trifluoroacetates in 1. (b) View of the hydrogen-
bonded sheet structure in 1.
which can reasonably be attributed to the influence of anionic
counterpart showing different shape, size, and ability to co-
ordination and/or formation of hydrogen bonds, and the co-
ordinated solvent molecules. The elongated polar CF3CO2– anion in
1 forms strong hydrogen-bonding interactions with both co-
ordinated water molecule and amine group of the cationic Ag(I)–
3,4′-bpma chains, resulted in offset-stacked packing to make sig-
nificant spaces that are large enough to fill such large anions.
Compounds 2 and 3 have visual identical interdigited packing
–
–
patterns as a result of their anionic counterparts, BF4 and ClO4
anions, are nonpolar tetrahedral geometry and show non-
coordinating or weakly coordinating and hydrogen-bonding be-
–
haviors. In 4, the polar CF3SO3 anion shows similar hydrogen-
Fig. 3. (a–c) Representations of the hydrogen bonds stitched sheet structures in 2–4.
bonding behaviors with that of BF4 and ClO4–, but its elongated
–
geometry and large size induce an anti-parallel packing manner. In
ꢀ
5, the nonpolar octahedral SbF6 anion forms very weak contacts
with the Ag center, which protect Ag center from the solvent
molecule, thus leading to an interdigited packing manner which is
entirely different from those of 1–4.
3.4. Topology analysis of 1D polymeric arrays 1–5
In this work, the Ag(I)–3,4′-bpma adducts 1–5 all adopt 1D
chain structures consisting of two Ag(I)–bis-pyridyl chains inter-
connected through Ag–Nam coordination bonds. Such a structural
feature is quite similar to the topologies of [Ag(dpma)(solv)]X
(solv¼ H2O, none; X ¼ NO3–, CF3CO2–, BF4–, CF3SO3–) [17b] and [Ag
(L)NO3]n (L¼ bis(4-pyridylmethyl)sulfide) [12a], which in topol-
ogy were termed respectively as ladder-like chains and double-
stranded chains. This argument makes our interest to carefully
search the literature reports to understand the topology of 1D
polymeric chains 1–5 unambiguously, along with other similars.
As surveyed in reviews [11,25,26], even the 1D chain is the
simplest topological type of infinite coordination arrays, it shows
many fascinatingly topological patterns which, according to the
connectivity of their constituents, can be simply classified into
three categories: (1) single-stranded chains including linear, zig-
zag, wavelike/sinusoidal, helical, rotaxane, metal cluster; (2) dou-
ble-stranded chains including ladder, ribbon, fused loops; (3) other
Fig. 4. View of the extensive supramolecular sheet structure in 5.
types of chain arrays including loops and rods, tubular. Clearly, the
Ag(I)–3,4′-bpma adducts 1–5 should have a topological structure
belonging to category 2. Unlike the topological structures of ca-
tegories 1 and 3, which are very unambiguous, there are argu-
ments among these topological structures in category 2 since they
sometimes look very alike (Scheme 2a–c). Therefore clear in-
dicators that can easily distinguish the differences among these

258
H.-J. Lin et al. / Journal of Solid State Chemistry 242 (2016) 253–260
Scheme 2. Schematic representation of different types of double-stranded chain topologies: (a) ladder; (b) ribbon; (c) fused loops; (d,e) zipper-like. Balls represent metal
nodes; bold lines represent spacer ligands; dashed lines represent direct metal–ligand coordination bonds, metallophilic bonds, and π∙∙∙π interactions.
double-stranded chains are necessary.
3.5. Comparisons on silver(I)–bis(pyridylmethyl)amine coordination
To resemble a real ladder in daily life, a supramolecular ladder
structure, which is formed through linear, T-shaped, and H-shaped
building units that defined the rung and rail components, should
be in a linear, flat fashion and the most important, it must actually
form cavities/pores defined by rails and rungs with representation
by space-filling models (CPK models) [25,26]. Ribbon polymers
also called looped chains or ring polymers and can be regarded as
a result of two single-stranded wavelike/sinusoidal/zigzag chains
joined together through single metal nodes. Just like ladder
structures, these ribbon polymers should also contain cavities/
pores which may facilitate encapsulation of guest solvents/anions
[11,25]. Fused loops are a sequence of macrocycles fused together
in one dimension [11]. In the topological point of view, although
sometimes they are looked like ladders, a flat structure feature and
working cavites/pores are not necessary.
arrays
In this work, structural investigation reveals that the five Ag(I)–
3,4′-bpma coordination arrays of different anions exhibit almost
identical 1D “zipper-like” chain, with subtle differences in precise
structures. This means that anions do not deeply affect the
structural modulation of Ag(I) CPs since varying anions does not
direct to structure variations, but just slightly influence CP con-
formations and packing fashions in the solid state. Though the
3,4′-bpma ligand encompasses GT (1, 4, and 5) and TT (2 and 3)
conformations, the tridentate donating feature makes only a li-
gating orientation/topology of distorted T-shape in these Ag(I) CPs,
which narrows the possibility of network-forming in different
manners. In addition, no crystalline products or alternate struc-
tures were successfully obtained from a MeOH/THF system for
synthesizing 1–3 and from a MeOH/H2O system for synthesizing 4
and 5, meaning that solvent control may be a lack of the Ag(I)–3,4′-
bpma system. As a result, such a Ag(I)–3,4′-bpma system can be
considered a case of ligand domination .
Comparably, our previous work on the Ag(I)–dpma coordination
arrays has obviously represented an anion-dominated assembly
process [17b]. Anions with different coordinating nature, hydrogen-
bonding propensity, and templating effect have strongly influenced
the conformation of the tridentate dpma ligand from a gauche–
trans–anti to a trans–trans–anti, a trans–trans–syn, a gauche–
gauche–syn, and a trans–gauche–syn conformation. The varied
ligand conformations result in different orientations/topologies
such as distorted T- and Y-shape, leading to a variety of polymeric
structures including 1D zipper-like chain, metallamacrocycle-based
chain (loops and rods topology), and 2D honeycomb-like layer.
Therefore, the anion is being as the crucial factor in influencing the
complexity and diversity in structures for Ag(I)–dpma CPs.
Accordingly, direct chemical bonds, such as Ag–Nam coordina-
tion bonds herein and Ag∙∙∙Ag/Ag∙∙∙π/π∙∙∙π interactions elsewhere,
are not suitable to be rungs in forming supramolecular ladder as
they are not actual spacer to define working cavities/pores. On the
other hand, double-stranded chain is too simple to truly reflect the
chain topology of Ag(I)–3,4′-bpma adducts 1–5 as the Ag–Nam
coordination bonds might be ignored from the simplized structure
topology. In other words, both ladder-like chain and double-
stranded chain are failed to actually illustrate the chain topology of
Ag(I)–3,4′-bpma adducts 1–5. Therefore, we make our imagination
and favor to name this type of double-stranded chain polymer as
“zipper-like” topology that two single-stranded chains showing
geometry- and interaction-complementary are zipped up through
the connections of direct chemical bonds (Scheme 2d,e).
As the definitions, some previous examples of chemical
bonds assisted ladder structures such as [Ag(pytz)(X)(MeCN)] (X
–
–
¼
PF6
,
BF4
;
pytz ¼3,6-di(4-pyridyl)-1,2,4,5-tetrazine) [27],
[Ag2(dp)2(H2O)]NO3 (dp ¼1,2-diaminopropane) [28], [Ag(4,4′-py-
but)(X)](MeCN) (X ¼ PO2F2–, MeCO2–; 4,4′-pybut ¼1,4-bis(4-pyr-
idyl)butadiyne) [29], and others [30–32], as well as [Ag(dpma)
(solv)]X (solv¼ H2O, none; X ¼ NO3–, CF3CO2–, BF4–, CF3SO3–) [17b]
and [Ag(L)NO3]n (L¼ bis(4-pyridylmethyl)sulfide) [12a], can be re-
termed as a “zipper-like” topology rather than a ladder or a dou-
ble-stranded chain topologies. However, this topological type of
The above findings clearly indicate that such differences be-
tween the two silver(I)–bis-pyridyl systems, Ag(I)–3,4′-bpma and
Ag(I)–dpma, can be reasonably attributed to the influences of the
nature of the ligand. For the two positional isomers, the flexible
dpma ligand has essentially richer ligand conformations and li-
gating orientations/topologies than that exhibited by the flexible
3,4′-bpma ligand, making more chances to vary the network to-
pology of silver(I)–bis-pyridyl coordination arrays. Hence, this
work studied on the Ag(I)–3,4′-bpma coordination arrays, along
with our previous work on the Ag(I)–dpma system, provides sig-
nificant efforts on the supramolecular design of Ag(I)–bis-pyridyl
coordination arrays.
2þ
“zipper-like” chain is well-compared with that of [Ag(tmpb)]2
(tmpb ¼4-thiomethyl-6-(4-pyridyl)-2,2′-bipyridine), which shows
2þ
that the [Ag(tmpb)]2
binuclear metallacycles assemble into in-
finite 1D chains via chemical bonds, depicted as a row of fused
loops (Scheme 2c) [33].

H.-J. Lin et al. / Journal of Solid State Chemistry 242 (2016) 253–260
259
state excitation spectra (λem¼400 nm) of 1–5 displayed two in-
tense bands centered at 24571 and 35174 nm (Fig. S14a). The
high-energy excitation closely resembles the absorption spectrum
(λabs¼257 nm) of the free 3,4′-bpma ligand in acetonitrile solution
(Fig. S14b), suggesting a reasonable assignment of intraligand (IL)
transition. On the other hand, the low-energy band, which is ab-
sence from the absorption spectrum of the free 3,4′-bpma ligand,
is tentatively assigned to a metal-perturbed intraligand (MPIL)
transition that may have a slight metal-to-ligand charge transfer
(MLCT) characteristic [34].
At room temperature, Ag(I)–3,4′-bpma adducts 1–5 all dis-
played a broad structureless emission band with maxima at 414,
403, 410, 398, and 411 nm, respectively, upon excitation at 345 nm
in the solid state (Fig. 6). Since the free 3,4′-bpma ligand is fluor-
escence silent in acetonitrile solution, this emission is reasonably
attributed to originate from the MPIL transition, as demonstrated
by the nicely symmetrical excitation spectra at about 35174 nm
[34,35]. In addition, there is also a low-energy shoulder band in
the region of 475–600 nm (centered at 500, 491, 511, and 500 nm
for 1–3 and 5, respectively), which is believed to be originated
from MLCT transition, mixed in part with the MPIL transition [34].
In principle, photoluminescence behaviors are closely associated
with the local environments around metal ions [36], so the re-
semblance in fluorescence between these Ag(I)–3,4′-bpma adducts
indicates that the difference in coordination spheres of the Ag
(I) centers, with a strongly coordinated water molecule in 1, a
weakly coordinated methanol molecule in 2–4, and none in 5, are
not great enough to significantly influence the emission characters
of 1–5.
Fig. 5. TG diagrams of 1–5.
4. Conclusion
In this work, five Ag(I)–3,4′-bpma 1D coordination chain arrays
have been successfully assembled. Topology analysis on the poly-
meric non-flat chain structures of 1–5 have addressed a new to-
pology of “zipper-like” chain that is essentially different from the
well-known double-stranded 1D chain polymers such as ladder,
ribbon/tape-like, and fused loops topologies. The studies on the Ag
(I)–3,4′-bpma coordination arrays, a ligand-dominated assembly
system, along with our previous work on the Ag(I)–dpma co-
ordination arrays [17b], an anion-dominated assembly system,
provide significant predictability of these informations in the for-
mation of Ag(I)–bis-pyridyl coordination arrays, even for the
simple connectivity in 1D CPs.
Fig. 6. Normalized fluorescence spectra (λex¼345 nm) of 1–5 in the solid state at
room temperature.
3.6. Thermal properties
Thermogravimetric (TG) analyses of polymeric Ag(I)–3,4′-bpma
adducts 1–5 were performed on polycrystalline samples under a
flux nitrogen atmosphere in the temperature range of 30–900 °C
(Fig. 5), and the results were consistent with the results of the
X-ray crystallography and microanalyses. The TG traces for 1–4
show that the coordinated water/methanol molecules were re-
moved during heating from room temperature to ca. 76 °C for 1
(found, 3.8%; calcd, 4.1%), 135 °C for 2 (found, 7.0%; calcd, 7.5%),
142 °C for 3 (found, 7.1%; calcd, 7.3%), and 80 °C for 4 (found, 6.8%;
calcd, 6.6%), and their coordination networks begin to decompose
when the temperature was raised to near 170 °C (TE170, 170, 180,
and 185 °C for 1–4, respectively). Noteworthy, the TG curves of
these materials seem to continue still weight loss even heating to
as high as 900 °C, with exception of 1. The remaining product for 1
is reasonably assigned to Ag2O (found, 27.6% at 750 °C; calcd,
26.8%). For 5 no significant weight loss is observed until it begins
to decompose at ca. 170 °C and ended at ca. 750 °C; the final re-
sidue may be assigned to AgF (found, 22.6%; calcd, 23.4%). These
data indicate that these polymeric Ag(I)–3,4′-bpma adducts 1–5 do
not show very high thermal stability.
Acknowledgments
We are very grateful to the National Chi Nan University and the
Ministry of Science and Technology of Taiwan for financial
support.
Appendix A. Supplementary material
Supplementary data associated with this article can be found in
the online version at http://dx.doi.org/10.1016/j.jssc.2016.07.031.
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