Syntheses, crystal structures, and DNA binding and catalytic properties of two transition metal coordination polymers constructed from 5-aminoisophthalic acid and bis-benzimidazole ligands

Article abstract of DOI:10.1007/s11243-016-0068-x

Two mixed-ligand transition metal coordination polymers, {[Co(aip)(bbp)]·(H₂O)}_n (1) and {[Ni₂(aip)(Hbbop)₂]·(H₂O)₂}_n (2) (H₂aip?=?5-aminoisophthalic acid, bbp?=?1,3-bis(benzoimidazol-2-yl)propane, H₂bbop?=?1,3-bis(benzimidazol-2-yl)-2-oxapropane), were synthesized and characterized by elemental analyses, IR spectra, single-crystal X-ray diffraction, and thermogravimetric analyses. Complex 1 has a 1D chain structure, while 2 has a 3-connected 2D network with (6³) topology. Both structures are further connected by hydrogen bonds and π–π stacking interactions to form the 3D supramolecular architectures. DNA binding and catalytic properties of the two complexes were investigated.

Full text of DOI:10.1007/s11243-016-0068-x

Transition Met Chem
DOI 10.1007/s11243-016-0068-x
Syntheses, crystal structures, and DNA binding and catalytic
properties of two transition metal coordination polymers
constructed from 5-aminoisophthalic acid and bis-benzimidazole
ligands
1
1
1
Yong-Hong Wen
•
Xiao-Wei Mu
•
Hui-Ling Wen
Received: 22 March 2016 / Accepted: 27 May 2016
Ó Springer International Publishing Switzerland 2016
Abstract Two mixed-ligand transition metal coordination
polymers, {[Co(aip)(bbp)]Á(H O)} (1) and {[Ni (aip)-
their potential applications as functional materials for
luminescence, catalysis, and magnetism, but also because
of their intriguing structures and topologies [1–4]. A
number of coordination polymers with promising proper-
ties have been synthesized by the rational selection of
metal centers and organic linkers [5–7]. In recent years,
particular attention has been devoted to coordination
polymers constructed from aromatic polycarboxylic acids
and bis(nitrogen-containing heterocycles) as mixed organic
building blocks [8–11]. These two types of organic ligand
possess a variety of coordination modes suitable for the
construction of polymeric structures. The degree of
deprotonation or protonation of these compounds depends
greatly on the pH of the reaction system, and they can act
as both H-bond acceptors and donors to assemble
supramolecular structures [12, 13]. Most of the transition
metal coordination polymers reported to date use pyridyl-
or imidazol-containing compounds as auxiliary ligands in
metal–polycarboxylate systems [14–18]. To the best of our
knowledge, studies on the mixed-ligand transition metal
coordination polymers containing 5-aminoisophthalic acid
2
n
2
(
Hbbop) ]Á(H O) } (2) (H aip = 5-aminoisophthalic acid,
2
2
2 n
2
bbp = 1,3-bis(benzoimidazol-2-yl)propane,
H bbop =
2
1
,3-bis(benzimidazol-2-yl)-2-oxapropane), were synthe-
sized and characterized by elemental analyses, IR spectra,
single-crystal X-ray diffraction, and thermogravimetric
analyses. Complex 1 has a 1D chain structure, while 2 has a
3
3
-connected 2D network with (6 ) topology. Both struc-
tures are further connected by hydrogen bonds and p–p
stacking interactions to form the 3D supramolecular
architectures. DNA binding and catalytic properties of the
two complexes were investigated.
Introduction
There is increasing interest in the design and synthesis of
transition metal coordination polymers, not only because of
(H aip) and bis-benzimidazole ligands have been scarcely
2
reported [19]. To explore the use of mixed ligands to
fabricate new architectures, we selected two structurally
similar bis-benzimidazole compounds, 1,3-bis(benzoimi-
dazol-2-yl)propane (bbp) and 1,3-bis(benzimidazol-2-yl)-
Electronic supplementary material The online version of this
article (doi:10.1007/s11243-016-0068-x) contains supplementary
material, which is available to authorized users.
2-oxapropane (H bbop) (Scheme 1), as auxiliary ligands
2
and synthesized two transition metal coordination
polymers, namely {[Co(aip)(bbp)]Á(H O)} (1) and
2
n
&
Yong-Hong Wen
yonghwen@163.com
{
[Ni (aip)(Hbbop) ]Á(H O) } (2). Both complexes have
2
2
2
2 n
been characterized by elemental analyses, IR spectra, sin-
gle-crystal X-ray diffraction, and thermogravimetric anal-
yses. The DNA binding and catalytic properties of the
complexes for the degradation of methyl orange by sodium
persulfate in a Fenton-like process have been investigated.
1
State Key Laboratory Base of Eco-chemical Engineering,
Laboratory of Inorganic Synthesis and Applied Chemistry,
College of Chemistry and Molecular Engineering, Qingdao
University of Science and Technology, Qingdao 266042,
China
123

Transition Met Chem
obtained. Yield 67 % (based on CoCl Á6H O). Anal. Calcd
2
2
NH2
NH
NH
HN
HN
for C H N O Ni (%): C, 54.2; H, 4.0; N, 14.2. Found:
8
4
0
35
9
2
-
1
N
N
N
N
C, 54.2; H, 3.9; N, 14.1. IR (KBr, cm ): 3640 (m), 3610
(m), 3400 (s), 1626 (m), 1609 (w), 1560 (s), 1530 (m),1490
bbp
O
O
O
(m), 1474 (m), 1458 (s), 1445 (m), 1421 (m), 1398 (s),
OH
OH
1320 (m), 1272 (m), 1236 (w), 1221 (m) 1112 (s), 1044
(w), 1003 (m), 785 (w), 759 (m) 737 (s), 710 (w) 631 (w),
H aip
2
550 (m), 528 (w), 496 (w), 436 (w).
H bbop
2
Catalytic experiments
Scheme 1 Structural formulas of the ligands
The catalytic behaviors of the complexes were investigated
for the degradation of methyl orange using a standard
process, as described in reference [21].
Experimental
Materials and methods
X-ray crystallography
All commercially available reagents and chemicals were of
analytical-grade purity and used without further purifica-
tion. The bis-benzimidazole compounds were prepared by
literature procedures [20]. The C, H, and N contents were
determined using an Elementar Vario EL III analyzer.
Infrared spectra were recorded from KBr pellets on a
Nicolet 510P FT-IR spectrometer. Thermogravimetric
analyses (TGA) were performed on a Perkin-Elmer TG-7
analyzer heated from room temperature to 900 °C under air
Single-crystal X-ray diffraction data of two complexes
were collected on a Bruker SMART 1000 CCD diffrac-
tometer with graphite-monochromated MoKa radiation
˚
(
k = 0.71073 A) using x scan mode at room temperature.
Intensity data were corrected for Lp factors, and an
empirical absorption correction was applied. The structures
of both complexes were solved by direct methods and
expanded using Fourier differential techniques with
SHELXTL [22]. All non-hydrogen atoms were located
with successive difference Fourier syntheses. The struc-
tures were refined by full-matrix least squares methods on
-
1
.
at heating rate of 10 °C min
Synthesis of complex 1
2
F with anisotropic thermal parameters for all non-hydro-
A mixture of CoCl Á6H O (0.238 g, 1 mmol), 5-aminoisoph-
2
2
gen atoms. The hydrogen atoms of water molecules in both
complexes were located from the E-maps. The NH
hydrogens involved in hydrogen bonding were also located
from the difference Fourier maps and refined freely. The
other hydrogen atoms were geometrically fixed and
allowed to ride on their parent atoms. A summary of the
key crystallographic data and structural refinements for the
complexes is presented in Table 1. Selected bond distances
and angles and the hydrogen bond data for both complexes
are listed in Tables 2 and 3.
thalic acid (0.181 g, 1 mmol), 1,3-bis(benzoimidazol-2-
-
1
yl)propane (0.276 g, 1 mmol), 2 mL of 1 mol L NaOH,
and 8 mL of H O was placed in a Parr Teflon-lined stainless
2
steel vessel (25 mL). The vessel was sealed and heated to
1
90 °C for 72 h and then cooled to room temperature, leading
to the formation of block purple crystals of complex 1. Yield
1 % (based on CoCl Á6H O). Anal. Calcd for C H N O
7
2
2
25 23 5 5
Co (%): C, 56.4; H, 4.4; N, 13.2. Found: 56.5; H, 4.4; N, 13.1.
-1
IR (KBr, cm ): 3630 (s), 3440 (m), 3179 (w), 3058 (w), 2937
w), 1625 (w), 1603 (w), 1453 (s), 1414 (s), 1344 (m), 1293
s), 1271 (m), 1220 (w), 1165 (w), 1150 (w), 1037 (w), 988
w), 917 (w), 893 (w), 851 (w), 834 (w), 763 (w), 750 (s), 740
s), 726 (m), 644 (w), 507 (m).
(
(
(
Results and discussion
(
Structure of {[Co(aip)(bbp)]Á(H O)} (1)
2
n
Synthesis of complex 2
Single-crystal X-ray diffraction analysis reveals that com-
plex 1 crystallizes in the orthorhombic crystal system of
space group P2 2 2 . The asymmetric unit contains one
A
mixture of NiCl Á6H O (0.475 g, 2 mmol),
2
2
5
-aminoisophthalic acid (0.181 g, 1 mmol), 1,3-bis(benz-
1
1 1
2
-
imidazol-2-yl)-2-oxapropane (0.557 g, 2 mmol), 4 mL of
1
1
Co(II) center, one anionic aip ligand, one bbp ligand, and
one crystal water molecule. The central Co(II) is five-co-
ordinated by two nitrogen atoms from one bbp ligand, two
-
mol L NaOH, and 6 mL of H O was placed in a Parr
2
Teflon-lined stainless steel vessel (25 mL). The vessel was
sealed and heated to 180 °C for 72 h. Upon cooling to
room temperature, bronze-colored block crystals of 2 were
2
-
oxygen atoms from one aip ligand, and one oxygen atom
2
-
from another aip
ligand (Fig. 1). The coordination
1
23

Transition Met Chem
Table 1 Crystal data and
structure refinement information
of complexes 1 and 2
Compounds
1
2
Formula
C
25 23
H N
5 5
O Co
C
40 35 9 8 2
H N O Ni
Formula weight
Crystal system
Space group
532.41
Orthorhombic
P2
887.15
Monoclinic
C2/c
1 1 1
2 2
˚
a(A)
10.0078(2)
14.0948(4)
17.8140(5)
90
25.667(3)
9.4615(3)
20.467(2)
90
˚
b(A)
˚
c(A)
a(°)
b(°)
c(°)
90
132.08(2)
90
90
3
˚
V(A )
2512.81(11)
4
3688.6(2)
4
Z
-
3
)
D (g cm
1.407
1.597
-1
)
l (mm
0.728
1.091
Crystal size (mm)
Total reflections
Unique reflections
0.24 9 0.25 9 0.31
6587
0.27 9 0.34 9 0.42
6970
4111
3261
R(int)
a
0.028
0.036
R
1
(all data)
0.0426
0.0378
0.0844
0.0807
1.04
0.0480
a
1
R
[I [ 2r(I)]
0.0397
b
wR
wR
2
(all data)
0.1082
b
2
[I [ 2r(I)]
0.1001
2
GOF on F
1.06
-3
)
˚
Max/min. residual (e A
0.29/-0.31
0.51/-0.49
ꢀ
P
wR ¼
P
a
R ¼
jjFoj À jFcjj
jFoj
ꢁ
ꢀ
ꢂ
1=2
P
À
Á
P
À
Á2
b
2
2
2
w Fo À Fc
w Fo
˚
geometry of the cobalt is between trigonal bipyramidal and
H16B_O2 [C16_O2 3.215(4) A], and C18–H18B_O3
˚
square pyramidal, with a t value of 0.49 [23]. The Co1–
˚
O3A gives a relatively long distance [2.390(2) A] and the
[C18_O3 3.260(5) A] hydrogen bonds.
O3A–Co1–O4A shows a relatively small angle [58.44(9)8]
due to the chelating coordination of the carboxylate group.
Structure of {[Ni (aip)(Hbbop) ]Á(H O) } (2)
2
2
2
2 n
The other coordinated bond lengths [Co–O 1.976(2) and
˚
Substitution of the methylene group in bbp by an oxygen
atom gives bbop. Complex 2 has a two-dimensional
structure, and crystallizes in the monoclinic crystal system
of space group C2/c. As shown in Fig. 3, complex 2 con-
2
.038(2), Co–N 2.023(3) and 2.034(3) A] and angles
[
91.18(9) –120.14(11)8] fall in the normal ranges found in
the structurally related complexes [24–26]. Each aip
2-
2
-
ligand bridges two metal centers to form a 1D chain in the
˚
a direction, with Co–Co distances of 10.008 A (Fig. 2a).
sists of two Ni(II) centers, one anionic aip ligand, two
-
anionic Hbbop ligands, and two water molecules. The
˚
Intermolecular N3–H3_O4 [2.827(4) A] and N1–
asymmetric unit of 2 contains half the molecule, which is
related to the other half by a crystallographic twofold axis.
The Ni(II) center is five-coordinated by two oxygen atoms,
˚
H1B_O3 [3.217(4) A] hydrogen bonds connect the 1D
chain into a 2D net structure (Fig. 2b). The 2D networks
2
-
-
are further connected by intermolecular hydrogen bonds,
˚
one from an aip ligand and another from a Hbbop
-
O1W–H1WB_N1 [O1W_N1 2.988(7) A], O1W–
ligand, plus three nitrogen atoms, two from one Hbbop
-
˚
H1WB_O2 [O1W_O2 2.840(5) A], and N4–H4_O1W
N4_O1W 2.737(5) A] to form a 3D supramolecular
structure (Fig. S1 in Supporting Information). In addition,
ligand and one from another Hbbop ligand. The coordi-
nation geometry of the metal is between trigonal bipyra-
midal and square pyramidal, with a t value of 0.51 [23].
The axial positions are occupied by O1 and O3 with an
˚
[
˚
there are C2–H2_O3 [C2_O3 2.766(4) A], C16–
123

Transition Met Chem
˚
Table 2 Selected bond lengths (A) and angles (8) for complexes 1
and 2
Complex 1
a
Co1–O1
Co1–N2
1.976(2)
2.034(3)
Co1–O3A
Co1–O4A
2.390(2)
2.038(2)
a
Co1–N5
2.023(3)
O1–Co1–N2
O1–Co1–N5
O1–Co1–O4A
Complex 2
Ni1–O1
108.42(11)
109.28(11)
91.18(9)
N2–Co1–N5
a
O4A –Co1–N2
a
O4A –Co1–N5
110.57(11)
114.89(11)
120.14(11)
a
2.013(3)
2.169(3)
Ni1–N4
2.021(2)
2.036(3)
b
Ni1–O3
Ni1–N5C
Ni1–N2
2.049(3)
Fig. 1 The molecular structure and coordination environment of 1.
Hydrogen atoms are omitted for clarity. Symmetry codes: A = 1 ? x,
y, z
O1–Ni1–O3
O1–Ni1–N2
O1–Ni1–N4
170.30(12)
97.85(12)
104.20(11)
92.70(12)
76.26(11)
O3–Ni1–N4
76.76(10)
96.20(12)
140.05(9)
104.17(11)
107.55(12)
b
O3–Ni1–N5C
N2–Ni1–N4
b
b
O1–Ni1–N5C
O3–Ni1–N2
N2–Ni1–N5C
-
deprotonated Hbbop anion, acting as both chelating-tri-
b
N4–Ni1–N5C
dentate and bridging-monodentate ligand, connects metal
a
Symmetry codes: 1 ? x, y, z; 3/2 - x, -1/2 ? y, 3/2 - z
b
centers to form a 1D chain (Fig. 4). The two benzimidazole
-
rings in Hbbop are nearly coplanar such that the dihedral
angle between them is 39.4(2)°. The 1D chains are further
linked by aip ligands to form a 2D layer (Fig. 5). In the
2
-
˚
Table 3 Hydrogen bond data (A) and (8) for complexes 1 and 2
2
D layer, the distances between Ni atoms connected by
-
2-
˚
Hbbop and aip ligands are 5.928(2) and 10.266(2) A,
respectively. From a topological point of view, both
-
Hbbop and aip
D–H…A
d(D–H) d(H…A) d(D…A) \DHA
Complex 1
2-
ligands can be regarded as linkers
a
O1W–H1WB_N1
O1W–H1WB_O2
0.80(5)
0.80(5)
0.84(3)
0.86(3)
0.84(3)
0.93
2.45(5)
2.39(7)
1.99(3)
2.69
2.988(7)
2.840(5)
2.827(4)
3.217(4)
2.737(5)
2.766(4)
3.215(4)
3.260(5)
126(6)
117(6)
177
between the Ni(II) centers. Therefore, the framework of 2
3
can be described as a 3-connected network with (6 )
b
c
N3–H3_O4
topology (Fig. 5). Four types of hydrogen bonds are found
˚
N1–H1B_O3
N4–H4_O1 W
C2–H2_O3
125
in 2: specifically O–H_O (O_O = 2.863(6) A), N–
1.96(4)
2.44
155(4)
100
˚
H_O
3
(N_O = 2.698(4) A),
O–H_N
(O_N =
˚
.074(8) A), and C–H_O (C_O = 3. 029(5), 3.410
˚
8) A) contacts (Table 3). The 2D networks are connected
C16–H16B_O2
0.97
2.43
138
(
d
C18–H18B_O3
0.97
2.43
144
by intermolecular hydrogen bonds and short aromatic ring
p–p stacking interactions to form a 3D supramolecular
structure (Fig. S2 in Supporting Information). The cen-
troid–centroid distance between the imidazole rings of the
Complex 2
O1W–H1WA_O2
0.85(7)
0.85(9)
0.80(5)
0.97
2.01(7)
2.23(10)
2.03(5)
2.59
2.863(6)
3.074(8)
2.698(4)
3.410(8)
3.029(5)
177(9)
175(6)
141
e
O1W–H1WB_N1
f
˚
neighboring layers is 3.528(2) A.
N3–H3_O2
g
C13–H13B_O1W
146
h
C14–H14A_O1
0.97
2.45
118
Coordination modes of organic ligands in complexes
1 and 2
a
b
Symmetry codes: 3/2 - x,1 - y, ‘ ? z; ‘ ? x, 3/2 - y, 1 - z;
c
d
e
f
1
- x, -1/2 ? y, ‘ – z; 1 ? x, y, z; x, 1 ? y, z; 3/2 - x,
g
h
‘
- y, 2 - z; ‘ ? x, ‘ - y, ‘ ? z; 3/2 - x, ‘ ? y, 3/2 - z
It can be seen from the structure descriptions above that the
three organic ligands adopt different coordination modes.
2
Although aip anions bridge two mental centers in both
-
O1–Ni1–O3 angle of 170.30(12)°, and the equatorial
positions are occupied by N2, N4, and N5C with the sum of
the angles N2–Ni1–N4, N2–Ni1–N5C, and N4–Ni1–N5C
being 351.77°. All coordinated bond lengths (Ni–O
complexes 1 and 2, in complex 1, one carboxylate group of
2
-
0
1
aip
adopts a l
- g :g mode, and the other adopts
- g :g coordination (mode I, Scheme S1 in Supporting
Information). In complex 2, both carboxylate groups of
1
1
1
l
1
2
-
1
0
˚
˚
2
.013(3)–2.169(3) A, Ni–N 2.021(2)–2.049(3) A) are
aip adopt l - g :g coordination (mode II, Scheme SI).
1
comparable with those in related Ni(II) complexes [27, 28].
-
Atom N5 of the Hbbop ligand is deprotonated. The
The two structurally similar bis-benzimidazole ligands
also reveal different coordination modes. The neutral bbp
1
23

Transition Met Chem
Fig. 2 a The 1D chain structure
of 1 viewing along b axis. b The
2
D net structure of 1 formed by
hydrogen bonds (dash lines).
The imidazole rings in bbp
ligands are shown only for
clarity
ligand in complex 1 shows chelating coordination modes
mode III, Scheme S1). In complex 2, the deprotonated
(
-
Hbbop anion exhibits chelating-tridentate and bridging-
monodentate coordination modes (mode IV, Scheme S1).
Thermal analysis
Thermogravimetric analyses were carried out for both
complexes (Fig. S3 in Supporting Information). Complex 1
shows a 3.33 % weight loss from 140 to 335 °C, corre-
sponding to the loss of one lattice water molecule (calcd
3
.38 %). The second weight loss from 335 to 520 °C cor-
responds to decomposition of the organic components
obsd 81.90 %, calcd 82.53 %). The residual mass of
5.31 % corresponds to the formation of Co O (calcd
(
1
2
3
Fig. 3 The molecular structure and coordination environment of 2.
The hydrogen atoms are omitted for clarity. Symmetry codes:
A = 1 - x, y, 3/2 - z; C = 3/2 - x, -1/2 ? y, 3/2 - z
14.07 %). Complex 2 shows a 4.22 % weight loss from 100
to 310 °C, corresponding to the loss of two water mole-
cules (calcd 4.06 %). The second weight loss from 310 to
123

Transition Met Chem
Fig. 4 The 1D chain structure of 2 along b axis
DNA. Electronic absorption spectra of both complexes
were recorded in the range of 200–600 nm (Figs. 6, 7). The
lower wavelength peaks (255 nm for both 1 and 2) can be
assigned to intraligand p ? p* transitions of the benzene
2
-
ring in the aip ligand, while the higher wavelength peaks
can be assigned to intraligand p ? p* transitions of ben-
zimidazole in the bbp or Hbbop ligands, respectively. In
Fig. 6, only a single peak is observed at 271 nm, while in
Fig. 7, two absorption peaks are seen at 271 and 275 nm.
This indicates that both benzimidazole rings are in the
same chemical environment in complex 1, whereas the two
benzimidazole rings are in different chemical environments
in complex 2, in agreement with the single-crystal structure
analysis.
It can be seen from Figs. 6 and 7 that the absorption
spectra of both 1 and 2 show decreases after adding ssDNA
or dsDNA to the solutions of the complexes, but none of
the absorptions show red shifts 2. This suggests that the
interaction between these complexes and DNA might be
electrostatic in nature [29].
DNA binding properties of complexes 1 and 2 were
studied by UV–vis titration experiments. In these experi-
3
Fig. 5 The 2D layer and simplified (6 ) topology structure of 2. The
-
only bridging benzimidazoles in Hbbop ligands are shown for clarity
-5
-1
ments, 20-lL solutions of DNA (6.551 9 10 mol L
for 1, and 4.397 9 10 mol L for 2) were each added
-
5
-1
-
4
5
50 °C can be assigned to decomposition of the organic
to 3.0 mL of a solution of the complex (2.831 9 10
-
1
-4
-1
-1
components (obsd 76.81 %, calcd 79.09 %). The remain-
ing residue of 15.97 % corresponds to the formation of
NiO (calcd 16.86 %).
mol L for 1, and 1.702 9 10 mol L mol L for 2)
by a micropipette. Because of the limited solubility of these
complexes in water, the titration experiments were carried
out in the presence of a small amount of DMSO. The
intrinsic binding constants K were determined from the
b
DNA binding studies
resulting absorbance data at the specified wavelength using
the following equation [30]:
Electronic absorption spectroscopy is an effective method
to examine the binding modes of metal complexes with
½DNAŠ=ðe À e Þ ¼ ½DNAŠ=ðe À e Þ þ 1=K ðe À e Þ
a
f
b
f
b
b
f
1
23

Transition Met Chem
-
4
Fig. 7 a UV–vis absorption spectra of complex 2 (1.702 9 10
-1
-5
-1
-
4
mol L ) and 2 ? DNA (4.397 9 10 mol L ). b Plot of [DNA]/
- e ) versus [DNA] for absorption titration of dsDNA with
complex 2
Fig. 6 a UV–vis absorption spectra of complex 1 (2.831 9 10
-1
-5
-1
mol L ) and 1 ? DNA (6.551 9 10 mol L ). b Plot of [DNA]/
(
e
a
f
(
complex 1
e
a
- e ) versus [DNA] for absorption titration of dsDNA with
f
-
1
L mol for [Co(HL)(bbe)] (bbe = 1,2-bis(benzoimida-
n
zol-2-yl)ethane)} [26], but smaller than those of non-ben-
-1
for
where [DNA] is the concentration of DNA and e , e , and e
f
a
b
5
zimidazole Cd(II) complexes {7.62 9 10 L mol
refer to the extinction coefficients for the free complex,
after each addition of DNA to the complex, and for the
complex in the fully bound form, respectively. Plots of
[
Cd(5-Br-salo) (CH OH)] (5-Br-salo = 5-bromo-salicy-
2
3
2
5
laldehyde), 1.36 9 10 L mol
-1
for [Cd(5-Br-salo)
2
6
(phen)]2 (phen = 1,10-phenanthroline), and 3.83 9 10
-1
[
DNA]/(e - e ) versus [DNA] gave straight lines. The
a
f
0
L mol
for [Cd(5-Br-salo) (dpamH)] (dpamH = 2,2 -
2
5
binding constants K obtained from the ratio of slope to
b
3
intercept were 7.77 9 10 L mol
-1
for 1 (Fig. 6) and
.69 9 10 L mol for 2 (Fig. 7). These K values are
dipyridylamine)} [34]. The choice of organic ligands,
metal ions, and the resulting structures of the complexes
may all affect the resulting binding affinities with DNA.
3
-1
3
b
comparable to those of bis-benzimidazole Cd(II) com-
4
-1
plexes {2.3 9 10 L mol for [Cd(bbtp) ]Á(pic) (bbtp =
2
2
1
2
,3-bis((1-ethylbenzimidazol-2-yl)-2-thiapropane)) [31],
-1
Catalytic degradation of methyl orange
4
.19 9 10 L mol
for [Cd(bbmt) (CH OH) ]Á(NO )
2
3
2
3 2
(
bbmt = 2,5-bis((benzoimidazol-2-yl)methylthio)-1,3,4-
Transition metal coordination polymers constructed from
aromatic polycarboxylic acids and bis(nitrogen-containing
heterocycles) have the potential to act as catalysts for the
degradation of organic pollutants such as azo dyes [27, 28].
Therefore, the catalytic activities of these complexes for
the degradation of methyl orange by sodium persulfate are
4 -1
thiadiazole)) [32], and 9.06 9 10 L mol for [Cd(bbp)2]
(
[
pic) Á2DMF (bbp = 2,6-bis(2-benzimidazolyl)pyridine)
2
33]}, and also similar to those of bis-benzimidazole Co(II)
4
-1
complexes {1.48 9 10 L mol for [Co(HL)(bbop)] (H L =
n
3
4
5
-(carboxymethoxy)isophthalic acid) and 4.03 9 10
123

Transition Met Chem
Supplementary material
Crystallographic data for the structural analysis of the
compounds have been deposited with the Cambridge
Crystallographic Data Centre. CCDC reference numbers
1449760 for 1 and 1449763 for 2 contain the supplemen-
tary crystallographic data for this paper. These data can be
obtained free of charge from the Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
Acknowledgments This work was supported by the National Natural
Science Foundation of China (No. 20971076).
Fig. 8 The catalytic degradation of methyl orange with complexes 1
and 2
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