Cobalt(II)/silver(I) coordination polymers with bis(2-methylbenzimidazole) and polycarboxylate ligands

Article abstract of DOI:10.1080/00958972.2016.1177823

Three coordination polymers, [Co(L)(tbta)]_n (1), [Ag(L)(H₂O)·(Hhpht)]_n (2) and [Ag₂(L)_1.5(oba)]_n (3) (L?=?1,4-bis(2-methylbenzimidazol-1-ylmethyl)benzene, H₂tbta?=?tetrabromoterephthalic acid, H₂hpht?=?homophthalic acid, H₂oba?=?4,4′-oxybis(benzoic acid)), have been hydrothermally synthesized and structurally characterized. Complex 1 displays a 2-D uninodal 4-connected sql network, 2 and 3 feature chain structures, which further generate 2D supramolecular networks through hydrogen bonding interactions. The thermal and fluorescence properties of 1–3 have been carried out and discussed.

Full text of DOI:10.1080/00958972.2016.1177823

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Cobalt(II)/silver(I) coordination polymers with
bis(2-methylbenzimidazole) and polycarboxylate
ligands
Xu Zhang, Yong Guang Liu, Zeng Chuan Hao & Guang Hua Cui
To cite this article: Xu Zhang, Yong Guang Liu, Zeng Chuan Hao & Guang Hua Cui (2016):
Cobalt(II)/silver(I) coordination polymers with bis(2-methylbenzimidazole) and polycarboxylate
ligands, Journal of Coordination Chemistry, DOI: 10.1080/00958972.2016.1177823
To link to this article: http://dx.doi.org/10.1080/00958972.2016.1177823
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Date: 07 May 2016, At: 12:03

Journal of Coordination Chemistry, 2016
http://dx.doi.org/10.1080/00958972.2016.1177823
Cobalt(II)/silver(I) coordination polymers with bis(2-
methylbenzimidazole) and polycarboxylate ligands
Xu Zhang, Yong Guang Liu, Zeng Chuan Hao and Guang Hua Cui
College of Chemical engineering, north China university of science and technology, tangshan, China
ARTICLE HISTORY
ABSTRACT
received 2 december 2015
accepted 3 march 2016
Three coordination polymers, [Co(L)(tbta)]n (1), [Ag(L)(H2O)·(Hhpht)]n (2)
and [Ag2(L)1.5(oba)]n (3) (L = 1,4-bis(2-methylbenzimidazol-1-ylmethyl)
benzene, H2tbta = tetrabromoterephthalic acid, H2hpht = homophthalic
acid, H2oba = 4,4′-oxybis(benzoic acid)), have been hydrothermally
synthesized and structurally characterized. Complex 1 displays a 2-D
uninodal 4-connected sql network, 2 and 3 feature chain structures, which
further generate 2D supramolecular networks through hydrogen bonding
interactions. The thermal and fluorescence properties of 1–3 have been
carried out and discussed.
KEYWORDS
Bis(2-methylbenzimidazole);
crystal structure;
fluorescence property
1. Introduction
Interest in coordination polymers (CPs) rapidly expanded owing to their applications and options
for tailoring structures and properties. Judicious choice of bridging ligands is most important for the
assembly of functional CPs [1–4]. Multidentate O-donor ligands, such as dicarboxylates are structure-
directing tools to generate multidimensional networks. Multiple bridging modes of carboxylates control
structures and packing arrangements, with diverse coordination modes and ability to act as hydrogen
bond acceptors/donors [5–7].
Derivatives of bis(2-methylbenzimidazole) are useful candidates for the construction of diverse
structures and topologies. The semi-rigid 1,4-bis(2-methylbenzimidazol-1ylmethyl)benzene (L) with
a rigid spacer of phenyl ring and two freely rotating benzimidazole arms can adopt different confor-
mations to coordinate with metal centers, beneficial to assemble extended architectures [8–11]. Hou
and our group have reported several 2-D and 3-D Co(II)/Zn(II)/Cd(II)-based CPs incorporating the
CONTACT Guang hua Cui
tscghua@ncst.edu.cn
© 2016 informa uK limited, trading as taylor & francis Group

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X. ZHAnG eT AL.
derivatives of bis(2-methylbenzimidazole). A number of topology architectures were successfully
obtained, such as dia, pcu, and ins [12–14]. More recently, our group has presented two Ag(I)
coordination complexes derived from L; both of them exhibit significantly catalytic activities to
degrade organic azo dyes [15, 16].
In continuation of our previous work, we have hydrothermally synthesized three new CoII/
AgI CPs based on mixed ligands, [Co(L)(tbta)]n (1), [Ag(L)(H2O)·Hhpht]n (2), and [Ag2(L)1.5(oba)]n (3)
(L = 1,4-bis(2-methylbenzimidazol-1-ylmethyl)benzene, H2tbta = tetrabromoterephthalic acid,
H2hpht = homophthalic acid, H2oba = 4,4′-oxybis(benzoic acid)). The structures of these ligands are
shown in scheme 1. Structures and relevant properties of the three CPs were investigated.
2. Experimental
2.1. Materials and physical measurements
All chemicals and reagents employed were purchased from Sinopharm Chemical Reagent Co.,
Ltd. and used as received. L was synthesized according to the literature procedure [17]. elemental
analyses (C, H and n) were performed on a Perkin-elmer 240C elemental Analyzer. IR spectra (KBr
pellets) were recorded on an Avatar 360 (nicolet) spectrophotometer from 4000 to 400 cm−1. X-ray
powder diffraction (XRPD) investigations were carried out on a Rigaku D/Max-2500PC X-ray diffrac-
tometer at 40 kV, 40 mA with Cu-Kα radiation (λ = 1.542 Å) in the 2θ range of 5–50° with a step size
of 0.02°, and a scanning rate of 10° min−1. Thermogravimetric analyses (TGA) were carried out on a
neTZSCH TG 209 thermal analyzer in flowing n2 with a heating rate of 10 °C/min. A Hitachi F-7000
fluorescence spectrophotometer was used for powdered solid samples at room temperature to
obtain luminescence spectra.
2.2. Synthesis of [Co(L)(tbta)]n (1)
A mixture of Co(OAc)2·4H2O (24.9 mg, 0.1 mmol), L (36.6 mg, 0.1 mmol), H2tbta (96.3 mg, 0.2 mmol), naOH
(8 mg, 0.2 mmol), and distilled H2O (10 mL) was sealed in a 25 mL Teflon-lined stainless steel container
and heated at 140 °C for 3 days. The mixture was then cooled to room temperature at 5 °C/h. Purple
crystals suitable for single-crystal X-ray diffraction were obtained by filtration and washed with distilled
Scheme 1. ligands used in this study.

JOuRnAL OF COORDInATIOn CHeMISTRY
3
water with a yield of 62% (based on Co(OAc)2·4H2O). Calcd for C32H22Br4Con4O4 (Fw = 905.11): C, 42.5; H,
2.5; n, 6.2%. Found: C, 42.3; H, 2.7; n, 6.1%. IR (KBr, cm−1): 1560 s, 1510 m, 1400 s, 1300 s, 746 m, 575 m.
2.3. Synthesis of [Ag(L)(H2O)·(Hhpht)]n (2)
A mixture of Ag(OAc) (16.7 mg, 0.1 mmol), L (36.6 mg, 0.1 mmol), H2hpht (36.0 mg, 0.2 mmol), naOH
(8 mg, 0.2 mmol), and distilled H2O (10 mL) was sealed in a 25 mL Teflon-lined stainless steel container
and heated at 140 °C for 3 days. The mixture was then cooled to room temperature at 5 °C/h. Colorless
crystals suitable for single-crystal X-ray diffraction were obtained by filtration and washed with distilled
water with a yield of 51% based on Ag(OAc). Calcd for C33H31Agn4O5 (Fw = 671.49): C, 59.0; H, 4.6; n,
8.3%. Found: C, 59.1; H, 4.4; n, 8.6%. IR (KBr, cm−1): 3415 m, 1685 m, 1615 m, 1516 m, 1458 s, 1406 s,
1353 m, 752 s.
2.4. Synthesis of [Ag2(L)1.5(oba)]n (3)
Complex 3 was obtained in 56% yield (based on Ag(OAc)) by a procedure similar to the synthesis
of 2 except that H2hpht was replaced by H2oba (51.6 mg, 0.2 mmol). Colorless crystals suitable for
single-crystal X-ray diffraction were obtained by filtration and washed with distilled water. Calcd for
C50H41Ag2n6O5 (Fw = 1021.63): C, 58.8; H, 4.0; n, 8.2%. Found: C, 60.0; H, 3.7; n, 8.3%. IR (KBr, cm–1): 1600 s,
1507 s, 1460 s, 697 m, 519 m.
2.5. Single-crystal X-ray diffraction determination
Single crystals of 1–3 were subjected to single-crystal X-ray diffraction using an Agilent Supernova
Dual diffractometer. Reflection data were acquired using mirror-monochromated Cu-Kα radiation
(λ = 1.54178 Å) at room temperature with an Atlas detector ω scan mode at 293(2) K. The structures were
solved by direct methods and refined on F2 by full-matrix least-squares procedures with SHeLXTL [18].
Atoms were located from iterative examination of difference F-maps following least-squares refinements
of the earlier models. All non-hydrogen atoms were refined anisotropically; hydrogens of water were
located on a difference Fourier map, while other hydrogens were placed in calculated positions and
isotropically refined with a riding model. Supramolecular contacts (hydrogen bonding) were probed
and calculated using PLATOn [19]. Relevant crystallographic data are listed in table 1 and selected
length and angle values for 1–3 are presented in table 2.
3. Results and discussion
3.1. Description of the crystal structures
3.1.1. [Co(L)(tbta)]n (1)
Single-crystal X-ray diffraction analysis reveals that 1 crystallizes in the monoclinic space group P21/n
and features a 2-D CP. The crystal structure of 1 contains one Co(II), one L, and one tbta2−. As shown in
figure 1(a), each CoII center with a {Con2O2} distorted tetrahedral coordination geometry is four-coor-
dinate by two oxygens from two anionic tbta2− ligands (Co–O(4) = 1.974(2) Å, Co–O(1)i = 1.987(2) Å) and
two nitrogens from two L with Co–n(2) = 2.022(3) Å, Co–n(3)ii = 2.021(3) Å (symmetry codes: i: x−1/2,
−y + 3/2, z + 1/2; ii: x + 1, y, z). The bond angles around Co are 95.88(10) to 119.95(11)°; all distances
and angles are within the normal range [20]. The τ4 value is 0.868, in which the value of 1.00 stands for
a perfect tetrahedral geometry and zero for a perfect square planar geometry [21]. The tbta2− ligands
as bis(monodentate) bridging ligands attach to adjacent CoII centers to shape a 1-D linear [Co(tbta2−)]n
chain. The neighboring chains are further linked by L to produce a 2-D layer with the grid type through
the coordination along the ac plane, in which the L ligands in 1 adopt trans-confirmation and the
dihedral angle formed by the two benzimidazole rings is 58.215(60)°. Such 2-D layer structure can

4
X. ZHAnG eT AL.
Table 1. Crystallographic data and structure refinement for 1–3.
Complex
1
2
3
Chemical formula
formula weight
C
32h22Br4Con4o4
C33h31agn4o5
671.49
C50h41ag2n6o5
1021.63
905.11
Wavelength/Å
Crystal system
space group
a (Å)
b (Å)
c (Å)
0.71073
monoclinic
P21/n
12.9207(4)
18.1193(5)
13.2092(5)
90
95.361(3)
90
3078.93(17)
4
0.71073
triclinic
Pī
0.71073
triclinic
Pī
9.7287(3)
11.7759(3)
13.2357(3)
88.641(2)
70.183(2)
82.704(2)
1414.69(7)
2
11.9731(12)
13.0500(13)
14.9551(14)
74.5180(10)
76.839(2)
87.7160(10)
2192.2(4)
2
α (°)
β (°)
γ (°)
V (Å3)
Z
Dcalcd (g cm−3
F(0 0 0)
)
1.953
1764
1.576
688
1.548
1034
Crystal size (mm)
θ range/°
0.22 × 0.21 × 0.19
0.26 × 0.23 × 0.23
2.37–27.10
27,840
0.22 × 0.21 × 0.18
1.62–26.37
12,449
2.73–26.37
25,372
6286
0.0523
5.794
293(2)
1.023
reflections collected
independent reflections
Rint
6199
0.0571
0.763
293(2)
8757
0.0326
0.949
293(2)
absorption coefficient/mm−1
T/K
Goodness-of-fit on F 2
final R indices [I > 2σ(I)]
R (all data)
1.120
1.072
R1 = 0.0365, wR2 = 0.0765
R1 = 0.0546, wR2 = 0.0845
0.836
R1 = 0.0331, wR2 = 0.0816
R1 = 0.0415, wR2 = 0.1010
0.831
R1 = 0.0601, wR2 = 0.1199
R1 = 0.1417, wR2 = 0.1435
0.628
Δρmax/e·Å−3
Δρmin/e·Å−3
−0.947
−0.581
−0.583
Table 2. selected bond lengths [Å] and angles [°] for 1–3.
Parameter
Value
Parameter
Value
Complex 1
Co–o(4)
Co–n(2)
1.974(2)
2.022(3)
95.88(10)
107.34(11)
110.17(11)
Co–o(1)i
Co–n(3)ii
o(4)–Co–n(2)
o(4)–Co–n(3)ii
n(2)–Co–n(3)ii
1.987(2)
2.021(3)
117.62(11)
103.23(11)
119.95(11)
o(4)–Co–o(1)i
o(1)i–Co–n(2)
o(1)i–Co–n(3)#2
Complex 2
ag(1)–n(1)
2.091(3)
2.836(3)
170.69(9)
102.55(9)
ag(1)–n(3)i
2.097(3)
85.23(9)
ag(1)–o(1W)
n(1)–ag(1)–n(3)i
n(3)i–ag(1)–o(1W)
n(1)–ag(1)–o(1 W)
Complex 3
ag(1)–n(3)
ag(1)–o(4)
2.238(5)
2.443(5)
2.129(5)
133.69(17)
109.7(2)
ag(1)–n(1)i
ag(2)–o(1)
2.221(5)
2.079(4)
ag(2)–n(5)
n(1)i–ag(1)–n(3)
n(3)–ag(1)–o(4)
n(1)i–ag(1)–o(4)
o(1)–ag(2)–n(5)
105.34(19)
176.3(2)
symmetry codes for 1: i: x−1/2, −y + 3/2, z + 1/2; ii: x + 1, y, z; for 2: i: x−1, y + 1, z; for 3: i: −x, −y, −z.
be simplified to a 44-sql net with mesh size of 12.921(1) × 11.038(1) Å (figure 1(b)). There exist weak
hydrogen bonding interactions [C(20)–H(20)⋯O(1)iii = 3.306(5) Å, symmetry code: iii: x−3/2, −y + 3/2,
z + 1/2] between carboxylate oxygens among the tbta2− anions and C–H from the benzimidazole rings
in L, which stabilize the supramolecular network (figure 1(c)).

JOuRnAL OF COORDInATIOn CHeMISTRY
5
Figure 1a. the coordination environment of Co(ii) in 1. hydrogens are omitted for clarity (symmetry codes: x−11/2, −y + 3/2, z + 1/2;
ii: x + 1, y, z).
Figure 1b. the 2-d (4,4) layer structure of 1.
Figure 1c. the 2-d supramolecular network of 1 extended by hydrogen bonding interactions.
3.1.2. [Ag(L)(H2O)·(Hhpht)]n (2)
X-ray diffraction analysis reveals that 2 crystallizes in the triclinic space group Pī. Complex 2 consists of
one Ag(I), one L, one water ligand, and one free Hhpht−. As shown in figure 2(a), each Ag(I) is three-coor-
dinate by two nitrogens from two individual L ligands (Ag(1)–n(1) = 2.091(3) Å, Ag(1)–n(3)i = 2.097(3) Å)
and one oxygen from water (Ag(1)–O(1 W) = 2.836(3) Å). The sum of the bond angles around silver is
nearly 360°, forming a distorted trigonal planar geometry (symmetry code: i: x−1, y + 1, z). L as a bridg-
ing ligand links neighboring Ag(I) ions into a 1-D zigzag chain with Ag⋯Ag distance of 14.290(5) Å,
in which L exhibits trans-configuration with a dihedral angle of 2.355(6)° between the pairs of imida-
zole rings (figure 2(b)). In addition, the structure is further extended by O–H⋯O hydrogen bonding
interactions between the carboxylic oxygens from Hhpht− and the O–H from the coordinated water

6
X. ZHAnG eT AL.
Figure 2a. Coordination environment around ag(i) in 2. hydrogens are omitted for clarity (symmetry code: i: x−1, y + 1, z).
Figure 2b. the 1-d linear chain structure of 2.
Figure 2c. the 2-d supramolecular network of 2 constructed by o–h⋯o hydrogen bonding interactions. the dashed lines indicate
o–h⋯o bonds.
(O(1 W)–H(1)i⋯O(4)iii: 2.932(3) Å, O(1 W)–H(1)ii⋯O(1)iiii: 2.923(3) Å) to afford a 1-D supramolecular dou-
ble-chain structure, as depicted in figure 2(c) (symmetry codes: ii: x + 1, y−1, z; iii: x, y + 1, z; iiii: −x + 1,
−y + 1, −z).
3.1.3. [Ag2(L)1.5(oba)]n (3)
X-ray crystallographic analysis reveals that 3 crystallizes in the triclinic space group Pī. In the asymmetric
unit of 3, there exist two crystallographically independent Ag(I) ions, one and a half L and one oba2−. As
shown in figure 3(a), Ag1 sits in a distorted trigonal planar geometry defined by one O4 from one oba−2
ligand and n1i and n3 from two individual L; Ag2 is two-coordinate by O2 from oba−2, and n5 from a
different L, composing a linear geometry (symmetry code: i: −x, −y, −z). The Ag–O/n bond lengths are
2.079(4)–2.443(5) and 2.129(5)–2.238(5) Å, respectively, and the bond angles around Ag1 and Ag2 are
105.34(19) to 176.3(2)°, in conformity with the corresponding bond lengths and angles reported [22].
Two μ2-bridging L have cis-conformation linking two symmetry-related Ag1 ions to form a 26-mem-
bered [Ag2L2] macrocycle, and the internuclear Ag⋯Ag separation is 10.609(1) Å; the dihedral angle
between the two benzimidazole rings is 49.05(1)°. [Ag2L2] macrocycles are connected by oba−2 and L in
an ABA sequence to give a 1-D infinite chain (figure 3(b)), in which L ligands employ trans-conformation
with the Ag⋯Ag distance of 14.330(14) Å, and the two imidazole rings are parallel to each other. The
oba−2 ligands in 3 bridge two Ag(I) ions by two carboxyl groups with bis(monodentate) coordination,

JOuRnAL OF COORDInATIOn CHeMISTRY
7
Figure 3a. Coordination environment around ag(i) in 3. hydrogens are omitted for clarity (symmetry code: i: −x, −y, −z).
Figure 3b. View of the 1-d chain structure in 3.
Figure 3c. the 2-d supramolecular network of 3 constructed by C–h⋯o hydrogen bonding interactions. the dashed lines indicate
C–h⋯o bonds.
similar to that in 1. There exist hydrogen bonding reactions during the benzimidazole rings and oba−2
ligands, such that adjacent 1-D chains are further extended by the C–H⋯O reactions to shape a 2-D
supramolecular architecture, as described in figure 3(c) [C(19)–H(19)⋯O(2)ii = 3.220(10) Å, symmetry
code: ii: −x, −y + 1, −z + 1].
3.1.4. Structural comparison of 1–3
Although the synthetic methods of 1–3 are similar, their overall structures are quite different, which
reveals that the mixed ligands with diverse metal centers can induce various structures. Complex 1
employs a 2-D uninodal 4-connected sql network; 2 and 3 are 1-D infinite chains. The tbta2− in 1 and
oba2− in 3 both adopt bis(momodentate) coordination and Hhpht− is not coordinated in 2, which
could balance the charge. The distinction between the 1-D structures of 2 and 3 is due to the various
conformations of μ2-bridging ligand L (trans-conformation in 2, trans/cis-conformation in 3), resulting
in different Ag⋯Ag distances. Comparing with 2 and 3, 1 exhibits a 2-D layer, attributed to coordination
environments of Co(II) from four-coordinate in 1, to two and three-coordinate in 2 and 3 based on Ag(I).

8
X. ZHAnG eT AL.
In the three complexes, extensive hydrogen bonding interactions (C–H⋯O for 1 and 3, O–H⋯O for 2)
play an important role in the supramolecular assembly and stability of the final networks.
3.2. XRPD and thermal properties
The XRPD patterns of 1–3 (figure 4) indicate that the synthesized complexes match with simulated
ones, indicating that the bulk synthesized material and the crystals are homogeneous.
TGA were performed to ascertain the stability and decomposition pathways of 1–3. As depicted
in figure 5, 1 shows high stability and there is no mass loss to 380 °C. The one-weight loss of 91.9% is
attributed to the loss of all moieties, leading to the formation of CoO (obsd: 8.1%, Calcd: 8.3%) as final
residuals. Complex 2 undergoes slow partial dehydration between 150 and 180 °C (2.8% mass loss,
Figure 4. X-ray powder diffraction pattern of 1–3.

JOuRnAL OF COORDInATIOn CHeMISTRY
9
2.7% Calcd for one water). The mass loss of 25.6% between 220 and 310 °C indicates the removal of
free Hhpht− except for partial oxygens, which were used for the residual (Calcd: 25.5%). The following
loss can be treated as the decomposition of L (obsd: 54.7%, Calcd: 54.6%) and the mass remnant of
16.9% at 530 °C corresponds with that predicted for Ag2O (Calcd: 17.2%). The thermal stability of 3 is
lower than 1; the loss of 77.5% between 260 and 400 °C indicates loss of all organic ligands, leading to
the formation of Ag2O (obsd: 22.5%, Calcd: 22.7%).
3.3. Luminescence properties
The solid-state photoluminescence properties of CoII/AgI complexes 1–3, together with free L, were
investigated at room temperature under the same experimental conditions (figure 6). L exhibits emission
at 394 nm upon excitation at 250 nm, which is probably attributed to π* → n or π* → π transition. under
the same experimental conditions, the emission intensities of H2tbta, H2hpht, and H2oba are much
weaker than L, so it is considered that it has no significant contribution to the fluorescent emission of
the CPs with the presence of L [23]. notably, 2 and 3 show emission at 384 and 320 nm (λex = 300 nm
Figure 5. the tGa curves of 1–3.
Figure 6. emission spectra of 1–3 and the free ligands.

10
X. ZHAnG eT AL.
for 2, λex = 270 nm for 3), respectively, the blue-shift of 10 nm in 2 and 74 nm in 3 should be attributed
to a mixture of characteristics of intraligand and ligand-to-ligand charge transfer [24]. For 1, an emis-
sion at 396 nm (λex = 260 nm) is observed and the slight red-shift is probably caused by metal–ligand
coordination interactions when comparing with free L [25].
4. Conclusion
We have synthesized three networks under hydrothermal conditions by reaction of bis(benzimida-
zole) ligand and carboxylic acids with Co(II)/Ag(I) salts. Complexes 1–3 exhibit various structures; all
three complexes are further packed by hydrogen bonding interactions to generate supramolecular
architectures. Moreover, 1–3 display specific fluorescent properties, which are potential photosensitive
materials.
Supplementary material
CCDC 1436528-1436530 contain the supplementary crystallographic data for 1–3. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Center, 12
union Road, Cambridge CB2 1eZ, uK; Fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Disclosure statement
no potential conflict of interest was reported by the authors.
Funding
The project was supported by the national natural Science Foundation of China [grant number 51474086]; natural Science
Foundation-Steel and Iron Foundation of Hebei Province [grant number B2015209299]; the Graduate Student Innovation
Fund of north China university of Science and Technology [grant number 2015S13].
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