Self assembly of a novel mixed-ligand hydrogen bonding three dimensional supramolecular network [Co(Phmal)(Him)4]

Article abstract of DOI:10.1016/j.molstruc.2006.07.033

A novel supramolecular mixed ligand complex of formula [Co(Phmal)(Him)₄] (Phmal = phenylmalonate, Him = imidazole) has been synthesized and characterized by FT-IR spectroscopy, thermogravimetric analysis (TG), UV-Vis spectra. X-ray crystallographic studies of the complex reveal that the cobalt atom exhibits a distorted octahedral geometry being coordinated by four nitrogen atoms of Him ligands, two oxygen atoms from the phenylmalonate ligand. The intramolecular C-H?π interaction exists in the title complex. The three dimensional supramolecular network is constructed from the strong intermolecular N-H?O hydrogen bonds.

Full text of DOI:10.1016/j.molstruc.2006.07.033

Journal of Molecular Structure 831 (2007) 114–118
www.elsevier.com/locate/molstruc
Self assembly of a novel mixed-ligand hydrogen bonding three
dimensional supramolecular network [Co(Phmal)(Him)4]
Kou-Lin Zhang ¤, Hai-Wei Kuai, Wen-Long Liu, Guo-Wang Diao
College of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225002, PR China
Received 23 April 2006; received in revised form 20 July 2006; accepted 22 July 2006
Available online 8 September 2006
Abstract
A novel supramolecular mixed ligand complex of formula [Co(Phmal)(Him)4] (Phmal D phenylmalonate, HimD imidazole) has been
synthesized and characterized by FT-IR spectroscopy, thermogravimetric analysis (TG), UV-Vis spectra. X-ray crystallographic studies
of the complex reveal that the cobalt atom exhibits a distorted octahedral geometry being coordinated by four nitrogen atoms of Him
ligands, two oxygen atoms from the phenylmalonate ligand. The intramolecular C–H,ꢀ interaction exists in the title complex. The three
dimensional supramolecular network is constructed from the strong intermolecular N–H,O hydrogen bonds.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Cobalt complex; Crystal structure; Mixed-ligand; Supramolecular network; Infrared spectra
1. Introduction
great eVect on the formation of desirable networks.
[10,21,22]. Use of Xexible ligands may oVer a greater degree
of structural diversity and often be regarded as an eVective
strategy for the design and synthesis of new functional
materials. Recently, we have started a systematic study on
metal(II) coordination with phenylmalonate ligand (dian-
ion of phenylmalonic acid, H2Phmal) in the presence of
other N-containing ligands. One of the aims of this project
is to analyze the inXuence that factors such as the rigidity
and the possibility of speciWc attractive interactions
between phenyl rings can exert on the structure and func-
tional properties of phenylmalonate – containing metal(II)
complexes. Phmal is a suitable candidate for assembling
such complexes due to its two interesting structural fea-
tures. At Wrst, it can adopt several kinds of coordination
modes in metal complexes, which may provide abundant
structural motifs [23,24]. Second, it can act as hydrogen-
bond acceptors and provide the pyridyl ring which may
cause the aromatic ꢀ–ꢀ stacking interactions. To the best of
our knowledge, the supramolecular complexes with Phmal
ligand have not been extensively studied so far [23,24].
Furthermore, the introduction of Him ligand may induce
new structural evolution. The Him ligand is important in
Recently, the design and synthesis of supramolecular
networks that provide new shapes, sizes and chemical envi-
ronments as well as the searches for new functional materi-
als causes an incessant interest in supramolecular chemistry
[1–10]. This is not only due to their complicated structural
diversity, but also they are fundamental steps to discover
and fabricate various fundamental supramolecular devices
or technologically useful materials [11–15]. The use of
noncovalent interactions (such as the hydrogen bonds and
aromatic ꢀ–ꢀ stacking interactions) to arrange molecular
building blocks has evolved into one of the most useful and
Xexible strategies for the crystal engineering design of
extended supramolecular networks that have versatile
functions [16–20]. The current interest is focused on the
controlled assembly of donor and acceptor building blocks
in order to generate an entirely supramolecular polymer. In
this context, the rational design of organic ligands and judi-
cious selection of coordination geometry of metal ions have
*
Corresponding author. Tel./fax: +86 514 7695171.
E-mail address: koulinzhang2002@yahoo.com (K.-L. Zhang).
0022-2860/$ - see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2006.07.033

K.-L. Zhang et al. / Journal of Molecular Structure 831 (2007) 114–118
115
Table 1
maintaining the desired low dimensional coordination
Crystallographic data and structure reWnement for the title complex
polymer and may provide potential supramolecular recog-
nition sites for ꢀ–ꢀ aromatic stacking and hydrogen bond-
ing interactions. So, we assumed that Phmal ligand could be
useful in the formation of supramolecular networks with
some important features in the presence of Him ligand. In
the present paper, we report a novel supramolecular coor-
dination polymer [Co(Phmal)(Him)4] based on the mixed
Phmal and Him ligand. The complex exhibits a 3D supra-
molecular network which is constructed from the intense
intermolecular N–H,O hydrogen bonds.
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
ꢂ (°)
C21H22CoN8O4
509.39
293(2)
0.71073
Orthorhombic
P2(1)2(1)2(1)
8.569(6)
13.411(10)
20.795(16)
90
ꢃ (°)
90
ꢄ (°)
Volume
Z
Calculated density
Absorption coeYcient
F (0 0 0)
90
2389.5(3) Å3
2
2. Experimental
1.405 Mg/m3
0.762 mm¡1
1036
2.1. Materials and characterization
All reagents were reagent grade and used without fur-
ther puriWcation. Elemental analyses (C, H and N) were
carried out on a 240 C Elemental analyzer. FT-IR spectrum
(400–4000 cm¡1) was recorded from KBr pellet in Magna
750 FT-IR spectrophotometer and UV-Vis spectra on a
Shimadzu UV-3100 spectrophotometer. Thermogravimet-
ric analysis (TG) was taken on NETZSCH STA 409 PG/
PC instrument.
Theta range for data collection (°) 1.81–25.02
Limiting indices
¡10 6 h 6 9, ¡15 6 k 6 15,
¡19 6 l 6 24
ReXections collected/unique
Completeness to ꢁ D 25.06°
Absorption correction
Max. and min. transmission
ReWnement method
13112/4216 [R (int) D 0.0382]
100%
Semi-empirical from equivalents
1.0000 and 0.5469
Full-matrix least-squares on F2
4216/0/307
Data/restraints/parameters
Goodness-of-Wt on F2
1.091
Final R indices [I > 2ꢅ(I)]
R indices (all data)
R1 D 0.0378, wR2 D 0.0936
R1 D 0.0500, wR2 D 0.0989
0.395 and ¡0.202
2.2. Synthesis
Largest diV. peak and hole (e Å¡3
)
Imidazole (0.339 g, 0.555 mmol) was dissolved in metha-
nol (10 ml) and then an aqueous solution of
Co(NO3)2·6H2O (0.485g, 1.65 mmol) in water (5ml) was
added whilst stirring. To this solution a mixture of phen-
ylmalonic acid (0.300 g, 1.65 mmol) and NaOH (0.120g,
3.30 mmol) in water (10ml) was added and stirred for
10 min and then Wltered. The Wltrate was kept at ambient
temperature for several days and block red crystals were
formed. They were Wltered and washed thoroughly with
methanol and dried in vacuum (yield: 42.0% based on
phenylmalonic acid). Anal. Calcd for C21H22CoN8O4: C,
49.51; H, 4.35; N, 21.99. Found: C, 49.58%; H, 4.62%; N,
21.85%.
The contribution of these hydrogen atoms was included in
the structure factor calculations. All calculations were car-
ried out on a PC computer using SHELXL-97 program
[25]. Details of crystal data, collection and reWnement are
listed in Table 1.
3. Results and discussion
3.1. Structural description
Determination of the structure of [Co(Phmal)(Him)4] by
X-ray crystallography reveals that the complex consists of
2.3. X-ray crystallography study
C12
A
red crystal having approximated dimensions
N8
0.22 £ 0.20 £ 0.14mm was used for data collection. DiVrac-
tion data were collected at 293(2) K with a Siemens
SMART CCD diVractometer using graphite-monochro-
mated (Mo–Kꢁ) radiation (ꢀ D 0.71073Å), ꢂ and ꢃ
scans mode. The cell constants were determined from the
Full-matrix least-squares Wt of 2597 reXections with ꢁ in the
range 2.48° and 21.57°. The structure was solved by direct
methods and reWned by Full-matrix least-squares on F2
method. Intensity data were corrected for Lorenz and
polarization eVects and an empirical absorption correction
was performed. All non-hydrogen atoms were reWned
anisotropically. The hydrogen atoms were added geometri-
cally and allowed to ride on their respective parent atoms.
C11
C10
H14
O3
N7
N6
N5
C14
O4
O1
Co
N1
N2
O2
N3
N4
Fig. 1. Molecular structure of the title complex. The dashed line indicates
the intramolecular C–H,ꢀ interaction. Hydrogen atom participating in
C–H,ꢀ interactions is indicated as ball.

116
K.-L. Zhang et al. / Journal of Molecular Structure 831 (2007) 114–118
one Co atom, one phmal ligand and four imidazole ligands
in each independent crystallographic unit (Fig. 1). The Co
atom, which is in a distorted octahedral environment, is
coordinated by four nitrogen atoms from four Him ligands
[Co(1)–N(1) 2.130(3)Å; Co(1)–N(5) 2.151(3)Å; Co(1)–N(3)
2.152(3)Å; Co(1)–N(7) 2.167(3) Å] and two carboxylate
oxygen atoms from the Phmal ligand [Co(1)–O(4)
2.084(2)Å; Co(1)–O(1) 2.122(2)Å]. Selected bond distances
and angles are listed in Table 2. The angles subtended
the Co atom ranges from 84.99(9)° to 175. 86(10)°. The
Phmal group in the title complex adopts a bidentate coordi-
nation mode and exhibits the same boat conformation as in
the reported complex [Cu(2,2Ј-bipy)(Phmal)(H2O)]·2H2O]
[23]. Whereas the Phmal group in the reported complex
{[Cu(H2O)3][Cu(Phmal)2]}n simultaneously exhibits both
bidentate (through two oxygen atoms of the two
carboxylate groups) and bis(monodentate) (through two
trans carboxylate oxygen atoms from two Phmal ligands)
coordination mode. Furthermore, the two Phmal ligands
have diVerent conformation: one has the boat conforma-
tion while the other exhibits the envelope one [24].
The distance, 2.770 Å, between the H(14) atom attached
to the C(14) atom and the centroid of Him [N(8)–
C(12)–C(11)–N(7)–C(10)] shows that there is intramolecu-
lar C(14)–H(14),ꢀ interactions in the title complex
[d (C–H,Cg) D3.672Å; \(C–H,Cg)D153.38°]. This kind
of contact further stabilizes the molecule. There are Wve
strong hydrogen bonds in the present supramolecular com-
plex. The system of hydrogen bonds, which includes car-
boxylate oxygen atoms [O(1), O(2) and O(3)] and nitrogen
atoms [N(2), N(4), N(6) and N(8)] from Him ligands, is very
complicated. This system of hydrogen bridges can be
regarded as a superposition of two diVerent layers. The
layer parallel to (010) plane is deWned by the N(2)–
H(2A),O(4)#1 and N(6)–H(6A),O(2)#3 hydrogen
bonds (Fig. 2), while that parallel to (001) plane is deWned
by the N(8)–H(8A),O(1)#4 and N(4)–H(4A),O(3)#2
hydrogen bonds (Fig. 3) [N(2)–H(2A),O(4)#1D2.836(3)Å
#1: 1+x,y,z; N(4)–H(4A),O(3)#2D2.775(4)Å #2: ¡x,¡1/
2+y,3/2¡z; N(6)–H(6A),O(2)#3 D 2.725(4) Å #3:1/2¡x,
1 ¡ y,1/2 + z; N(8)–H(8A),O(1)#4D2.929(4)Å #4: 1¡x,
Table 2
Selected bond lengths (Å) and angles (°) for the title complex
Bond distances
Co(1)–O(4)
Co(1)–O(1)
Co(1)–N(1)
Co(1)–N(5)
Co(1)–N(3)
Co(1)–N(7)
2.084(2)
2.122(2)
2.130(3)
2.151(3)
2.152(3)
2.167(3)
Bond angles
O(4)–Co(1)–O(1)
O(4)–Co(1)–N(1)
O(1)–Co(1)–N(1)
O(4)–Co(1)–N(5)
O(1)–Co(1)–N(5)
N(1)–Co(1)–N(5)
O(4)–Co(1)–N(3)
O(1)–Co(1)–N(3)
N(1)–Co(1)–N(3)
N(5)–Co(1)–N(3)
O(4)–Co(1)–N(7)
O(1)–Co(1)–N(7)
N(1)–Co(1)–N(7)
N(5)–Co(1)–N(7)
N(3)–Co(1)–N(7)
84.99(9)
175.86(10)
90.87(10)
92.58(9)
175.66(11)
91.56(10)
88.06(11)
86.13(10)
91.90(12)
90.19(12)
88.03(11)
91.95(10)
91.89(12)
91.57(12)
175.78(11)
Fig. 2. View of the layer parallel to the (0 1 0) plane linked by strong intermolecular N(2),O(4) and O(2),N(6) hydrogen bonds.

K.-L. Zhang et al. / Journal of Molecular Structure 831 (2007) 114–118
117
Fig. 3. View of the layer parallel to the (0 0 1) plane formed by strong intermolecular N(3),O(4) and O(1),N(8) hydrogen bonds.
1/2 + y,3/2¡ z]. The details of the hydrogen bonds are listed
in Table 3. Thus, a novel three dimensional supramolecular
network was formed as a result of strong intermolecular
hydrogen bonding. Hydrogen bonding interactions are very
important in the preparation of supramolecular architec-
tures [26]. Undoubtedly, the hydrogen bonding plays
important roles in the stabilization of the title coordination
compound.
the coordinated Him molecule and the carboxylate oxy-
gen atom has been found (Table 3). Such low values of ꢆ
have been reported for other monodentate carboxylates
with C D O group involved in strong hydrogen bonding
[29]. In all these cases, the results of the X-ray analysis
allowed to assign unambiguously the binding mode of
carboxylate group. The broad band around 3135 cm¡1
may be assigned to the stretching vibrations of N–H
group in the Him ring with intermolecular hydrogen
bonds.
3.2. FT-IR spectra
The FT-IR spectra of the title compound show
characteristic bands of carboxylate groups at 1614 cm¡1
for asymmetric stretching and that at 1410 cm¡1 for
symmetric stretching, respectively [27]. The value of
ꢆ (COO) D as(COO) ¡ s(COO), which is usually used in
determining the coordination mode of carboxylate, fol-
3.3. UV-Vis spectra
In the UV-Vis spectra in methanol, three absorption
bands centered at 202, 204 and 208nm were observed. They
may be due to the ꢀ–ꢀ¤ and n-ꢀ¤ transitions of the ligands.
No d–d transition bands were observed. This indicates that
the concentration of methanolic solution is quite low.
While in the UV-Vis spectra of the present complex in solid
state, two absorption bands centered at 222 and 507nm
were observed. The band around 222 nm may arise from
the ꢀ–ꢀ and n-ꢀ¤ transitions of the ligands and that cen-
tered at 507nm may be due to the d–d transition band of
the Co2+ ion.
lows the order ꢆ monodentate > ꢆ ionic > ꢆ bridging > ꢆ
chelate
[28]. However, it is known that strong hydrogen bonding
with monodentate carboxylate group can decrease the ꢆ
value. The ꢆ value corresponding to the monodentate
carboxylate group in the title complex, which equals to
204 cm¡1, is signiWcantly smaller than expected. In the title
complex, strong intermolecular hydrogen bond between
3.4. Thermogravimetric analysis
Table 3
The details of the hydrogen bonds for the title complex
The thermal behavior of the title coordination
compound has been deduced from the TG analysis. The
weight loss of 57.80% in the temperature range 169–
403 °C can be attributed to the removal of four Him
ligands. The total weight loss of 85.20% in the temperature
range 169–505 °C, which is in agreement with the weight
loss calculated for the loss of all organic moieties leading
to the formation of CoO as Wnal residuals above 505 °C
(Calcd 85.29%).
D–H,A
d(D–H)
d(H,A)
d(D,A)
<DHA
N(2)–H(2A),O(4)#1
N(4)–H(4A),O(3)#2
N(6)–H(6A),O(2)#3
N(8)–H(8A),O(1)#4
N(8)–H(8A),O(2)#4
0.8600
0.8600
0.8600
0.8600
0.8600
1.9900
1.9200
1.8700
2.0700
2.5200
2.836(3)
2.775(4)
2.725(4)
2.929(4)
3.083(5)
168.00
173.00
171.00
176.00
124.00
Symmetry transformations used to generate equivalent atoms: #1
1 + x, y, z; #2 ¡x, ¡1/2 + y, 3/2 ¡ z; #3 1/2 ¡ x, 1 ¡ y, 1/2 + z; #4 1 ¡ x, 1/
2 + y, 3/2 ¡ z.

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K.-L. Zhang et al. / Journal of Molecular Structure 831 (2007) 114–118
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In conclusion, the mixed ligand complex of cobalt has
been obtained by self assembly. The Phmal ligand and
imidazole molecules complete the distorted octahedral
coordination sphere around Co2+. It has been shown that
the determination of the coordination mode of the
carboxylate group can not be made on the basis of its IR
spectra only. Strong hydrogen bonds severely inXuence the
vibrational characteristics of the carboxylate group. The
intramolecular C–H,ꢀ contacts exists in the title complex.
The complex forms a novel 3D supramolecular structure
due to the strong intermolecular hydrogen bonds.
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We gratefully acknowledge the Foundation of Jiangsu
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Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.mol-
struc.2006.07.033.
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