Aromatic carboxylic acid effect on the architectures of Co(II) coordination polymers based on a flexible double imidazole derivative

Article abstract of DOI:10.1134/S1070328411120050

Two new Co(II) coordination polymers, namely, [Co(BBA)₂(L)] (I) and [Co(NIPA)(L)] (II) have been obtained from hydrothermal reactions of Co(II) chloride with two kinds of aromatic carboxylic acids: 4-bromobenzoic acid (HBBA), 5-nitroisophthalic acid (H₂NIPA), and a flexible double imidazole derivative 1,1'-(1,3-propanediyl)bis(5,6-dimethylbenzimidazole) (L). Single-crystal X-ray diffraction analysis reveals that compound I is 1D "zigzag" coordination polymer constructed by [Co(BBA)₂] subunits and L linkers. Compound II exhibits 2D (4,4) network based on double nuclear [Co₂N₄O₈] units and (L) ₂/(NIPA)₂ double linkers. The different organic carboxylic acids influence on the coordination modes of metal ions and conformations of L ligands and thus determine the final structures of the title compounds. In addition, photoluminescence properties of the title compounds and the cyclic voltammetry behavior of compound II as a modified carbon paste electrode were investigated in this paper.

Full text of DOI:10.1134/S1070328411120050

ISSN 1070ꢀ3284, Russian Journal of Coordination Chemistry, 2012, Vol. 38, No. 1, pp. 55–60. © Pleiades Publishing, Ltd., 2012.
Aromatic Carboxylic Acid Effect on the Architectures of Co(II)
Coordination Polymers Based on a Flexible Double Imidazole
Derivative1
G. C. Liu, S. Yang, X. L. Wang*, H. Y. Lin, A. X. Tian, and J. W. Zhang
Department of Chemistry, Bohai University, Jinzhou 121000, P.R. China
*eꢀmail: wangxiuli@bhu.edu.cn
Received January 29, 2011
Abstract—Two new Co(II) coordination polymers, namely, [Co(BBA)2(L)] (I) and [Co(NIPA)(L)] (II) have
been obtained from hydrothermal reactions of Co(II) chloride with two kinds of aromatic carboxylic acids:
4ꢀbromobenzoic acid (HBBA), 5ꢀnitroisophthalic acid (H2NIPA), and a flexible double imidazole derivative
1,1'ꢀ(1,3ꢀpropanediyl)bis(5,6ꢀdimethylbenzimidazole) (L). Singleꢀcrystal Xꢀray diffraction analysis reveals
that compound I is 1D “zigzag” coordination polymer constructed by [Co(BBA)2] subunits and L linkers.
Compound II exhibits 2D (4,4) network based on double nuclear [Co2N4O8] units and (L)2/(NIPA)2 double
linkers. The different organic carboxylic acids influence on the coordination modes of metal ions and conꢀ
formations of L ligands and thus determine the final structures of the title compounds. In addition, photoluꢀ
minescence properties of the title compounds and the cyclic voltammetry behavior of compound II as a modꢀ
ified carbon paste electrode were investigated in this paper.
DOI: 10.1134/S1070328411120050
1
INTRODUCTION
acid (H2NIPA) as the anion ligands based on the folꢀ
lowing considerations:
In the past decades, the use transition metal and
organic multidentate ligands to construct metalꢀ
organic coordination polymers has attracted a great
deal of interest not only because of their structural
diversities, but also owing to their promising applicaꢀ
tions in gas storage, luminescence, magnetic materiꢀ
als, and catalysis [1–6]. In this case, a large number of
coordination polymers with various structures have
been prepared under hydrothermal conditions with
the development of crystal engineering principles [7,
8]. The rational design of prospective structures with
specific properties can be obtained by a careful selecꢀ
tion of the properties of the ligands, such as flexibility,
substituent group, and the number of donor atom [9–
13]. Among the large numbers of multidentate N/Oꢀ
donor ligands, flexible multiimidazole derivatives and
aromatic carboxylic acids seem to be excellent buildꢀ
ing blocks with versatile coordination modes, as well as
the remarkable coordination ability and stability, have
been widely used in constructing novel functional
transition metal coordination polymers by Bu, Ma,
Lang, Hou, and our group [14–17]. However, the
investigation of the influence of the aromatic carboxyꢀ
lic acids on the formation of coordination polymers is
not enough so far [18, 19].
Br
Br
NO2
M
O
O
M
O
O
O
O
O
O
M
M
M
N
N
N
N
N
N
N
N
TG
TG'
(i) comparing with double imidazole derivative
ligands, L not only possesses multi –CH2– groups for
free twist, but also has the larger aromatic ring system
and may provide potential supramolecular recognition
sites for
π
– ꢀstacking interactions; (ii) as multifuncꢀ
π
tional Oꢀdonor ligands, BBA and NIPA with different
coordination modes both have remarkable coordinaꢀ
tion ability and may induce different polymer network.
In this paper, we report a crossꢀlink supramolecular
doubleꢀchain architecture [Co(BBA)2(L)] (I) conꢀ
structed from 1D zigzag coordination polymers and
Here we chose 1,1’ꢀ(1,3ꢀpropanediyl)bis(5,6ꢀdimꢀ
ethylbenzimidazole) (L) as the neutral organic linkers,
4ꢀbromobenzoic acid (HBBA) and 5ꢀnitroisophthalic
1
The article is published in the original.
2D (4,4) network [Co(NIPA)(L)] (II) with two kinds
55

56
LIU et al.
Table 1. Crystal data and structure refinement details for
compounds and II
Synthesis of I. A mixture of CoCl2
0.1 mmol), L (0.0338 g, 0.1 mmol), HBBA (0.04 g,
0.2 mmol), NaOH (2 ml, 0.1 mol/l), and H2O (10 ml)
was sealed in a 25ꢀml Teflon reactor at 150 C for 3 days.
After slow cooling to room temperature, purple block
⋅
6H2O (0.0238 g,
I
Value
°
Parameter
Formula weight
I
II
crystals of
Co(II).
I
were obtained. The yield was 35% based on
791
600
Crystal system
Space group
Triclinic
Triclinic
IR (KBr;
ν
, cm–1): 3340 w, 3103 m, 2928 m, 1589 s,
P1
P1
1541 s, 1506 s, 1475 m, 1398 s, 1272 m, 1213 s, 1010 s,
850 s, 771 s.
a
, Å
, Å
, Å
, deg
, deg
, deg
10.541(5)
12.281(5)
14.784(5)
10.157(3)
10.552(3)
13.195(4)
75.792(4)
89.533(4)
85.630(4)
1366.9(7)
2
b
For C35H32Br2CoN4O4
c
anal. calcd., %:
Found, %:
C, 53.12;
C, 53.62;
H, 4.08;
H, 4.11;
N, 7.08.
N, 7.15.
α
93.293(5)
109.308(5)
109.581(5)
1671.0(12)
2
β
γ
Synthesis of II was similar to that of
that H2NIPA (0.0211 g, 0.1 mmol) was used instead of
I except
V
Z
, Å 3
HBBA. The yield was 40% based on Co(II).
IR (KBr;
, cm–1): 3105 s, 2858 w, 1620 s, 1585 m,
ν
ρcalcd, g cm–3
, mm–1
(000)
1.573
1.459
1566 s, 1523 m, 1456 s, 1373 s, 1344 s, 1269 m,
1213 m, 1078 m, 848 s, 731 s, 711 m.
μ
2.949
0.681
F
798
622
θmax, deg
25.10
25.0
For C29H27CoN5O6
Ranges of indices
–12
–14
–17
≤
h
≤
≤
6
–12
≤
h ≤ 6
anal. calcd., %: C, 58.00;
Found, %: C, 58.11;
H, 4.53;
H, 4.47;
N, 11.66.
N, 11.52.
≤
k
14 –12
17 –15
≤
k
≤ l ≤
≤
12
15
≤
l
≤
Reflections collected/unique 8640/5963
6939/4821
0.024
Preparation of IIꢀCPE. Compound II as bulkꢀ
modified carbon paste electrode (II CPE) was fabriꢀ
ꢀ
Rint
0.05
0.98
cated as follows: 0.06 g of compound II and 0.54 g of
graphite powder were mixed and ground together in an
agate mortar with a pestle for approximately 25 min to
achieve an even, dry mixture; 0.25 ml of paraffin oil
was added to the mixture and stirred with a glass rod;
then the homogenized mixture was used to pack 3 mm
inner diameter glass tubes to a length of 0.8 cm. The
electrical contact was established with the copper
stick, and the surface of the IIꢀCPE was wiped with
weighing paper.
GOOF
1.00
R
1* (
wR2* (all data)
Δρmax Δρmin
I
> 2
σ
(
I
))
0.0635
0.1973
0.0433
0.0976
/
,
e
Å–3
0.65/–0.88 0.39/–0.30
Fo2
–
Fc2) ]/
Σ
[
w(
Fo2) ]
2 1/2
.
2
*
R
=
Σ
||F
| – |F
||/
Σ
|F
|; wR =
2
Σ
[
w(
1
o
c
o
of double linkers. The differences of coordination
modes of metal ions, conformations of L ligand, and
the final structures of the title compounds reveal that
the organic carboxylic acids play an important role in
the synthesis of transition metal coordination polyꢀ
mers.
Xꢀray crystallographic study. Diffraction data for
compounds
1000 CCD area detector diffractometer (Mo
tion, graphite monochromator,
I
and II were collected on a Bruker Smart
radiaꢀ
K
α
λ
= 0.71069 Å for I and
λ
= 0.71073 Å for II). The crystal structures of I and II
were solved by the direct method and refined on F2 by
the fullꢀmatrix leastꢀsquares technique with the
SHELXLꢀ97 software package [21, 22]. All nonꢀ
hydrogen atoms were refined anisotropically, and all
hydrogen atoms were placed in geometrically idealized
positions and refined isotropically. The details of crysꢀ
EXPERIMENTAL
Materials and measurements. All chemicals were
used as supplied from commercial sources without
further purification. The L ligand was synthesized by
the literature method [20] and characterized by FTꢀIR
spectra and elemental analyses. FTꢀIR spectra (KBr
pellets) were taken on a Magna FTꢀIR 560 spectromꢀ
tallographic information for compounds I and II are
summarized in Table 1. Selected bond lengths and
angles are listed in Table 2.
Supplementary material for the complxes I and II
eter. Elemental analyses were performed on a Perkiꢀ has been deposited with the Cambridge Crystalloꢀ
nElmer 240CHN analyzer. The luminescence spectra graphic Data Centre (nos. 808191 (I), 808192 (II);
for the samples were measured on a HITACHI Fꢀ4500 deposit@ccdc.cam.ac.uk
fluorescence spectrophotometer. cam.ac.uk).
or
http://www.ccdc.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
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2012

AROMATIC CARBOXYLIC ACID EFFECT ON THE ARCHITECTURES
57
Table 2. Selected bond lengths (Å) and angles (deg) for
RESULTS AND DISCUSSION
compounds
Bond
I and II*
The Xꢀray structure analysis reveals that the asymꢀ
metric unit of compound I contains one Co(II) center,
d, Å
Bond
d, Å
one L ligand, and two BBA anions (Fig. 1). Each
Co(II) center is a trigonal bipyramid coordinated
environment with two nitrogen atoms of two L ligands,
two oxygen atoms of one chelating BBA, and one oxyꢀ
I
Co(1)–O(2)
Co(1)–O(4)
Co(1)–O(5)
2.014(6) Co(1)–N(4)
2.223(6) Co(1)–N(1)#1
2.086(6)
2.068(7)
2.095(6)
gen atom of one monodentate BBA to form [CoN2O3
]
subunit, showing bond distances of Co–N at 2.069(7),
Co–O at 2.015(6), 2.086(6), and 2.224(6) Å, respecꢀ
II
Co(1)–O(1)
Co(1)–O(2)
Co(1)–N(3)
2.100(2) Co(1)–N(4)
2.285(2) Co(1)–O(4)#2
2.153(2) Co(1)–O(3)#3
2.172(2)
2.026(2)
2.123(2)
tively. The NCoN angle is 104.9(2)
°
. The adjacent
[
CoN2O3] subunits are extended by L ligands to form
a 1D –L–Co–L–Co– zigzag chain, owing to the free
twist of L ligands. Thc torsion angle of aromatic ring
Angle
ω
, deg
Angle
ω
, deg
from L is 75.22
(Fig. 2a). The adjacent chains are further interlinked
through ꢀstacking interactions between the aroꢀ
°
and the Co⋅⋅⋅Co distance is 10.541 Å
I
O(2)Co(1)O(4) 107.4(2) O(4)Co(1)N(1)#1 89.4(2)
π π
–
matic rings of L and BBA with chelated coordination
mode to form a crossꢀlink doubleꢀchain supramolecꢀ
ular structure (Cg–Cg is 3.641(2) Å, and the dihedral
O(2)Co(1)O(5) 163.4(2) O(4)Co(1)N(4)
148.1(2)
O(2)Co(1)N(4) 99.4(2) O(5)Co(1)N(4)
O(2)Co(1)N(1)#1 96.0(2) O(5)Co(1)N(1)#1 95.2(2)
O(4)Co(1)O(5) 60.5(2) N(1)#1Co(1)N(4) 104.9(2)
89.6(2)
angels is 5.91(2) ) (Figs. 2a–2c).
°
Xꢀray structural determination reveals that comꢀ
pound II is a 2D coordination polymer network with
two kinds of double linkers. As shown in Fig. 3, comꢀ
pound II consists of one Co(II), one L ligand and one
NIPA anion. Each Co(II) center is a distorted octaheꢀ
dral geometry coordinated by two nitrogen atoms from
two L ligands, two chelating carboxylate oxygen atoms
from NIPA, and two oxygen atoms of bridged carboxꢀ
ylate groups from two NIPA anions. The distances of
Co–N and Co–O are in the range of 2.125(11)–
2.191(11), 2.045(9)–2.298(10) Å, respectively. The
II
O(1)Co(1)O(2) 59.85(8) O(2)Co(1)N(4)
94.29(8)
O(1)Co(1)N(3) 95.26(8) O(2)Co(1)O(4)#2 98.68(8)
O(1)Co(1)N(4) 87.07(8) O(2)Co(1)O(3)#3 86.71(8)
O(1)Co(1)O(4)#2 157.93(8) O(4)#2Co(1)N(4) 89.83(8)
O(1)Co(1)O(3)#3 91.55(8) O(3)#3Co(1)N(4) 177.60(8)
O(2)Co(1)N(3) 154.50(8) O(3)#3Co(1)O(4)#2 92.18(8)
N(3)Co(1)N(4) 89.45(9)
#1
#2
#3
NCoN angle is 89.45(9) . The bridged carboxylate
°
*
Symmetry codes: 1 +
x,
y,
z
;
–1 +
x,
y,
z
;
1 – x, –y, 1 – z.
groups of NIPA connect two adjacent Co(II) centers,
forming a binuclear second building unit (SBU) with
the Co⋅⋅⋅Co distance of 4.544 Å (Fig. 4a). The two
adjacent SBUs are connected by two NIPA to conꢀ
struct 1D infinite (–NIPA–Co–)2 double chains
coordination mode and forms a single metal node;
while in compound II, Co(II) adopts a hexa coordinaꢀ
tion mode and constructs a binuclear [Co2N4O8] SBU.
extended along the x direction (Fig. 4b). The distance
In compound
with a ⋅⋅⋅ distance of 7.393 Å and acts as a single
linker. However, it exhibits a TG’ conformation with a
⋅⋅⋅
distance of 7.226 Å and acts as a double spacer
I, L ligand shows a TG conformation
between the cores of SBUs is 10.157 Å. The 1D douꢀ
bleꢀchains are linked by pairs of L ligands with TG’
conformation (the torsion angle of aromatic rings
N
N
N
N
from L ligand is 75.47
the distance between the cores of SBUs is 10.552
°
) to generate a 2D network and
in II. BBA only has one carboxylic group, so the 1D
zigzag (–L–Co–)n chain cannot be extended into
Å
(Figs. 4c, 4d). Considering the binuclear SBU as a
node, keeping the (L)2 and (NIPA)2 as the double
spacers, compound II exhibits a interesting (4,4) netꢀ
highꢀdimensional network in
ylic groups with a 120 angle and shows excellent abilꢀ
ity in linking the (–L2–Co2–)n doubleꢀchain subunits
into 2D layer in II
I. NIPA has two carboxꢀ
°
work stabilized by intramolecular
π
– ꢀstacking interꢀ
π
.
actions between the aromatic rings of L and NIPA
(Cg–Cg is 3.652(2) Å, and the dihedral angels is
9.09(2)°) (Figs. 3 and 4e).
The main features in the IR spectra of
I and II
mainly concern the carboxylate groups and L. The
bands at 850, 1475, 1506, 1541 cm–1 for
1456, 1523 cm–1 for II can be attributed to
I
, and 848,
(C–N) of
From the structure description above, the effects of
the organicꢀacid ligands with different numbers of
carboxylic groups on the coordination polymer strucꢀ
tures have clearly been demonstrated. Co(II) metal
centers exhibit different coordination modes and neuꢀ
tral organic linkers L display various conformations in
ν
Nꢀheterocyclic rings of L ligand [14–17]. The bands
at 3103 cm–1 for and 3105 cm–1 for II can be attribꢀ
uted to (C–H) of –CH3 and –CH2– of L ligand [23].
The bands at 1589 cm–1 for , (1620 cm–1 for II) can be
I
ν
I
compounds I and II. In I
, Co(II) cation shows a penta attributed to COO– of organic carboxylic acids anions
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
No. 1
2012

58
LIU et al.
Br(1)
z
y
x
N(4)
x
y
z
O(1)
Co(1)
O(2)
O(4
O(4)
O(5)
A)
N(3)
O(3B)
O(3)
N(4)
Co(1)
N(1
A)
Co(1C)
O(2)
Fig. 3. Coordination environment of Co(II) in compound II
.
Hydrogen atoms were omitted for clarity.
Br(2)
boxylate ligands show very weak π*–n transitions and
contribute a little to the photoluminescence of the
title compounds [27]. Therefore, the solid state phoꢀ
Fig. 1. The coordination environment of Co(II) in comꢀ
pound . Hydrogen atoms were omitted for clarity.
I
toluminescence of compounds
I
and II may be
[24]. The bands at 1344 cm–1 can be attributed to attributed to ligandꢀtoꢀmetal chargeꢀtransfer transiꢀ
vibration of –NO2 groups from NIPA in II [25].
tions [28]. The different emission bands of and II
may be due to the difference between their topologiꢀ
cal structures [29].
I
Photoluminescence properties of L ligand and
compounds I–II at their solid state were investigated
at room temperature as shown in Fig. 5. L ligand
To investigate the redox property of the Co(II)
coordination polymer, compound II was selected as
representative. Due to the insolubility of II in water
and common organic solvents, II as bulkꢀmodified
carbon paste electrode (IIꢀCPE) was fabricated as the
working electrode. The electrochemical behavior of
shows an emission peak at 465 nm with λex = 380 nm,
which can be attributed to
π
*– transitions [26]. The
π
title compounds exhibit a blue/green photoluminesꢀ
cence with the emission maximum at ca. 410 nm (for I)
and 426 nm (for II) upon excitation at 260 nm. Comꢀ
paring with the emission of L, blue shifts of ca. 55 nm
and ca. 39 nm have been observed, respectively. Comꢀ
pared with the
π
*–
π
transitions of L ligand, the carꢀ
(a)
=
=
(a)
(b)
(c)
y
z
x
(d)
(e)
y
z
x
(b)
(c)
y
y
L
x
z
x
z
NIPA
NIPA
[Co]2SBU
Fig. 2. 1D doubleꢀchain structure in
zigzag coordination polymers through
teractions viewed along (a) and (b) axes; the schematic
view of the doubleꢀchain (c).
I
constructed by 1D
π
–
π
ꢀstacking inꢀ
Fig. 4. View of binuclear [Co N O ] SBU in II (a); view of
2 4 8
z
x
the (NIPA) (b) and (L) (c) double linkers; view of the 2D
2
2
(4,4) network (d); schematic view of the 2D network (e)
.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
No. 1
2012

AROMATIC CARBOXYLIC ACID EFFECT ON THE ARCHITECTURES
59
anodic and cathodic peak currents were proportional
to the scan rates, suggesting that the redox process for
IIꢀCPE was surfaceꢀconfined [17, 32, 33].
7000
6000
5000
4000
3000
2000
1000
0
I
II
ACKNOWLEDGMENTS
L
This work was supported by the NCETꢀ09ꢀ0853,
the National Natural Science Foundation of China
(no. 20871022), and the Foundation of Liaoning
Province (nos. 2009R03 and 2009402007).
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