Hydrothermal synthesis, crystal structures, and properties of CoII and NiII supramolecular complexes with 2,4,6-trimethyl benzoate and 4,4′-bipyridyl

Article abstract of DOI:10.1016/j.poly.2008.09.003

Two new coordination complexes, viz. [Co(tmb)₂(4,4′-bpy)₂(H₂O)₂](Htmb)₂ (1) and {[Ni(tmb)₂(μ-4,4′-bpy)₂(H₂O)₂](4,4′-bpy)}_n (2), have been hydrothermally synthesized by reaction of the corresponding metal acetate with 2,4,6-trimethylbenzoic acid (Htmb) and 4,4′-bipyridyl (4,4′-bpy). X-ray single-crystal diffraction suggests that complex 1 represents a discrete mononuclear species in which the central metal ion is coordinated by the terminal carboxylate moiety and the 4,4′-bipyridyl ligand. The crystal structure of complex 2 reveals a 1D chain coordination polymer in which the Ni(II) ions are connected by the bridging 4,4′-bipyridyl ligands. In both cases, the coordination arrays are further extended via hydrogen bonding interactions to generate 3D supramolecular networks. Complexes 1 and 2 have also been characterized by spectroscopic (IR and UV/Vis), thermal (TGA) and magnetic susceptibility measurements. In addition, both complexes exhibit antimicrobial activity.

Full text of DOI:10.1016/j.poly.2008.09.003

Polyhedron 27 (2008) 3593–3600
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Polyhedron
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Hydrothermal synthesis, crystal structures, and properties of CoII and NiII
supramolecular complexes with 2,4,6-trimethyl benzoate and 4,40-bipyridyl
a
a
b
Murugan Indrani a, , Ramasamy Ramasubramanian , Sudalaiandi Kumaresan , Sung Kwon Kang ,
*
Min Chen c, Miao Du c
a Department of Chemistry, Manonmaniam Sundaranar University, Tirunelveli 627 012, Tamil Nadu, India
b Department of Chemistry, Chungnam National University, Daejeon 305-764, South Korea
c College of Chemistry and Life Science, Tianjin Normal University, Tianjin 300387, PR China
a r t i c l e i n f o
a b s t r a c t
Two new coordination complexes, viz. [Co(tmb)2(4,40-bpy)2(H2O)2](Htmb)2 (1) and {[Ni(tmb)2( -4,40-
l
Article history:
bpy)2(H2O)2](4,40-bpy)}n (2), have been hydrothermally synthesized by reaction of the corresponding
metal acetate with 2,4,6-trimethylbenzoic acid (Htmb) and 4,40-bipyridyl (4,40-bpy). X-ray single-crystal
diffraction suggests that complex 1 represents a discrete mononuclear species in which the central metal
ion is coordinated by the terminal carboxylate moiety and the 4,40-bipyridyl ligand. The crystal structure
of complex 2 reveals a 1D chain coordination polymer in which the Ni(II) ions are connected by the bridg-
ing 4,40-bipyridyl ligands. In both cases, the coordination arrays are further extended via hydrogen bond-
Received 17 May 2008
Accepted 8 September 2008
Available online 22 October 2008
Keywords:
CoII and NiII complexes
2,4,6-Trimethylbenzoate
4,40-Bipyridyl
ing interactions to generate 3D supramolecular networks. Complexes
1 and 2 have also been
characterized by spectroscopic (IR and UV/Vis), thermal (TGA) and magnetic susceptibility measure-
ments. In addition, both complexes exhibit antimicrobial activity.
Ó 2008 Elsevier Ltd. All rights reserved.
Hydrogen bonding, structures and
properties
1. Introduction
the predictability of network geometries; the length of the ligand
is suitable to create the cavities of molecular dimensions upon the
Recently, supramolecular coordination complexes with diverse
organic bridging ligands have attracted extensive attention be-
cause they not only possess potential applications in catalysis,
magnetism, optical material and adsorption [1–4], but also display
intriguing architectures in virtue of coordination and/or secondary
interactions. Till now, a number of complexes containing transition
metal ions and bridging multi-functional ligands with N- and O-
donors have been reported [5].
Ligands with particular symmetry and stereochemistry may
lead to the formation of various specific architectures. For exam-
ple, exo-bidentate building blocks such as 4,40-bipyridyl (4,40-
bpy), pyrazine, 1,2-bis-(4-pyridyl)ethylene, and 1,2-bis(4-pyri-
dyl)ethane, have widely been used for constructing polymeric
chains [6,7]. Focusing only on 4,40-bipyridyl as ligand, a survey
of the recent literature reveals a number of homopolymetallic
complexes with interesting supramolecular architectures [8–11].
This ligand is an ideal connector between the transition metal ions
for the propagation of coordination networks due to the following
features: it has two potential binding sites which are arranged in a
divergent (exo) fashion; it has a rigid backbone which will help in
formation of networks with metal ions. In principle, the pyridyl
groups of 4,40-bipyridyl can rotate along the central C–C bond,
which, however, does not affect the mutual orientation of the
two terminal lone pairs. Therefore, it can be regarded as a rigid
and prototypical bridging ligand. Curiously enough, 4,40-bipyridyl
has been shown to form a variety of coordination networks rang-
ing from 1D to 3D with the familiar transition metal salts. The
resultant framework architectures depend on several factors such
as coordination geometry of the metal ion, counter anions, guest
molecules, and the ligand/metal ratio used in the reaction etc.
[12].
Although 4,40-bipyridyl has been extensively used for con-
structing numerous types of compounds [13], the employ of
2,4,6-trimethylbenzoic acid (Htmb) in crystallographic investiga-
tion appears to be scarce [14]. In this work, we will present the
hydrothermal synthesis and crystal structures of two new CoII
and NiII supramolecular complexes assembled from 4,40-bipyridyl
in conjunction with such a aromatic carboxylate species as the
anionic co-ligand. The 4,40-bipyridyl component may serve as
both terminal and bridging building block in the complexes,
and the discrete or 1D coordination entities can be extended to
interesting 3D hydrogen-bonding architectures. The thermal,
magnetic and antimicrobial properties of the complexes have also
been investigated.
* Corresponding author.
E-mail address: indrani_dec14@yahoo.co.in (M. Indrani).
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.09.003

3594
M. Indrani et al. / Polyhedron 27 (2008) 3593–3600
presented in Table 1, and selected bond distances and angles are
in Tables 2 and 3.
2. Experimental
2.1. General consideration
3. Results and discussion
All starting materials were obtained commercially from Aldrich.
IR spectra were recorded on a JASCO FTIR-410 spectrometer using
KBr pellets. UV/Vis spectra were recorded on a Perkin–Elmer
Lambda25 UV/Vis spectrophotometer. Thermogravimetric analysis
was performed on a Mettler Toledo Star system from room temper-
ature to 700ꢀC with a heating rate of 10ꢀC/min. Elemental analysis
was carried out using a Perkin–Elmer 1400 C analyzer. Magnetic
susceptibility measurements were performed on a George Associ-
ate Faraday Force Magnetometer.
3.1. Structural description of [Co(tmb)2(4,40-bpy)2(H2O)2](Htmb)2
Compound 1 crystallizes in the monoclinic space group P21/n.
The cobalt center locates on the inversion center and coordinates
to two nitrogen atoms from two 4,40-bipyridyl, two oxygen atoms
from two 2,4,6-trimethylbenzoate groups, and two oxygen atoms
from a pair of water molecules to form an octahedral geometry.
In this complex, there exist two unique 2,4,6-trimethylbenzoic acid
moieties (see Fig. 1), one in anionic form to constitute the
[Co(tmb)2(4,40-bpy)2(H2O)2] monomer via coordination with car-
2.2. Preparation of [Co(tmb)2(4,40-bpy)2(H2O)2](Htmb)2 (1)
A mixture of cobalt acetate tetrahydrate (0.0311 g, 0.125 mmol),
Htmb (0.041 g, 0.250 mmol), 4,40-bpy (0.039 g, 0.250 mmol) and
water (2.5 mL) was stirred for 30 min, sealed in a 23 mL polyflu-
oroethylene-lined stainless steel bomb, and kept at 100 °C under
autogenous pressure for 72 h. After cooling at a ramp of 10 °C/h
to room temperature, pink colored crystals of 1 were collected by
filtration, washed with deionized water followed by diethyl ether,
and then dried (0.0858 g, 65% yield).
Table 1
Crystal data and structure refinement for 1 and 2
Complex
1
2
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
C60H66N4O10Co
1062.1
293(2)
0.71073
monoclinic
P121/n1
C40H42N4O6Ni
733.49
294(2)
0.71073
orthorhombic
Ccca
For 1: Anal. Calc. for C60H66N4O10Co: C, 67.85; H, 6.26; N, 5.28.
Found: C, 68.25; H, 6.02; N, 5.60%.
Unit cell dimensions
a (Å)
b (Å)
c (Å)
V (Å3)
Z
10.4363(8)
13.0223(9)
20.6962(12)
2812.0(3)
2
1.254
0.366
1122
0.38 ꢁ 0.28 ꢁ 0.23
1.85–28.31
ꢀ13 6 h 6 13
ꢀ17 6 k 6 17
ꢀ27 6 l 6 26
30218/6982
0.0474
12.992(2)
26.101(4)
22.618(4)
7670(2)
2.3. Preparation of {[Ni(tmb)2(l
-4,40-bpy)2(H2O)2] (4,40-bpy)}n (2)
A mixture of nickel acetate tetrahydrate (0.0311 g, 0.125 mmol),
Htmb (0.041 g, 0.250 mmol), 4,40-bpy (0.039 g, 0.250 mmol) and
water (2.5 mL) was stirred for 30 min, sealed in a 23 mL polyflu-
oroethylene-lined stainless steel bomb, and kept at 75 °C under
autogenous pressure for 72 h. After cooling at a ramp of 10 °C/h
to room temperature, green colored crystals of 2 were collected
by filtration, washed with de-ionized water followed by diethyl
ether, and then dried (0.0641 g, 70% yield).
8
Dcalc (mg mꢀ3
)
1.270
0.556
3088
0.40 ꢁ 0.32 ꢁ 0.20
1.56–27.85
ꢀ17 6 h 6 16
ꢀ33 6 k 6 32
ꢀ21 6 l 6 29
22765/4564
0.0336
Absorption coefficient (mmꢀ1
F(000)
Crystal size (mm)
h Range for data collection ꢀ()
Limiting indices
)
Reflections collected/unique
Rint
Completeness to h (%)
Absorption correction
Refinement method
For 2: Anal. Calc. for C40H42N4O6Ni: C, 65.50; H, 5.77; N, 7.64.
Found: C, 66.23; H, 5.49; N, 7.51%.
100.0
none
100.0
none
full-matrix least-squares
2.4. X-ray data collection and structure refinement of 1 and 2
on F2
Data/restraints/parameters
6982/0/357
1.017
4564/0/236
1.025
Goodness-of-fit on F2
X-ray single-crystal diffraction data for compound 1 was col-
lected on a CAD-4 diffractometer equipped with graphite mono-
R1 and wR2 [I > 2
R1 and wR2 (all data)
Largest difference in peak and
hole (e Å3)
r
(I)]
0.0479, 0.1148
0.0828, 0.1340
0.541 and ꢀ0.350
0.0354, 0.0878
0.0629, 0.1016
0.278 and ꢀ0.326
chromated Mo Ka radiation at 293 K. The data was collected by
the /2h scan mode. The standard direct method was used to posi-
x
tion the heavy atoms. The remaining non-H atoms were located
from the subsequent difference Fourier synthesis. All non-H atoms
were refined anisotropically. All H atoms were calculated in ideal
positions and were riding on their respective carbon atoms (Bi-
so = 1.2 Beq and 1.5 Beq). The structure was refined in a full matrix
least-squares calculation on F2. Programs used to solve and refine
the structure: SHELXS97 and SHELXL97 [15]. Molecular graphics:
ORTEP-3 for windows [16].
X-ray single-crystal diffraction data for compound 2 was col-
lected on a Bruker Apex II CCD diffractometer at 293(2) K. A
semi-empirical absorption correction was applied using SADABS
[17] and the SAINT program [18] was utilized for integration of the
diffraction profiles. The structure was solved by direct methods
using the SHELXS program of the SHELXTL package [19] and refined
with SHELXL. The final refinement was implemented by full-matrix
least-squares methods on F2 with anisotropic thermal parameters
for all the non-H atoms. In general, H atoms attached to the ligands
were placed geometrically and allowed to ride during the subse-
quent refinement. The crystal data for both complexes are
Table 2
Selected bond lengths (Å) and angles ꢀ() for 1
Co–O(1)#1
Co–O(1)
Co–O(21)#1
Co–O(21)
Co–N(2)#1
Co–N(2)
2.0749(16)
2.0749(16)
2.1338(14)
2.1338(14)
2.1787(16)
2.1787(16)
C(10)–N(11)
C(20)–O(21)
C(20)–O(22)
C(32)–O(34)
C(32)–O(33)
O(33)–H(33)
1.318(4)
1.248(3)
1.261(3)
1.194(3)
1.306(3)
0.9300(4)
O(1)#1–Co–O(1)
O(1)#1–Co–O(21)
O(1)–Co–O(21)
O(1)#1–Co–O(21)#1
O(1)–Co–O(21)#1
O(21)–Co–O(21)#1
O(1)#1–Co–N(2)
O(34)–C(32)–O(33)
O(21)–C(20)–O(22)
180.00(11)
93.25(6)
86.75(6)
86.75(6)
93.25(6)
180.00(11)
89.34(6)
122.3(3)
123.6(2)
O(21)–Co–N(2)
88.19(6)
91.81(6)
90.66(6)
89.34(6)
91.81(6)
88.19(6)
180.00(12)
90.66(6)
O(21)#1–Co–N(2)
O(1)#1–Co–N(2)#1
O(1)–Co–N(2)#1
O(21)–Co–N(2)#1
O(21)#1–Co–N(2)#1
N(2)–Co–N(2)#1
O(1)–Co–N(2)
Symmetry transformation used to generate equivalent atoms: #1 ꢀx + 1, ꢀy, ꢀz.

M. Indrani et al. / Polyhedron 27 (2008) 3593–3600
3595
Table 3
Selected bond lengths (Å) and angles (ꢀ) for 2
Ni(1)–O(1)
Ni(1)–O(1)#1
Ni(1)–O(3)
Ni(1)–O(3)#1
Ni(1)–N(1)
2.0419(14)
2.0419(14)
2.0835(13)
2.0835(13)
2.1041(18)
Ni(1)–N(2)#2
O(1)–C(7)
O(2)–C(7)
2.105(2)
1.259(2)
1.248(2)
2.105(2)
N(2)–Ni(1)#3
O(1)–Ni(1)–O(1)#1
O(1)–Ni(1)–O(3)
177.04(7)
90.39(5)
89.54(5)
89.54(5)
90.39(5)
177.55(7)
88.52(3)
O(1)#1–Ni(1)–N(1)
O(3)–Ni(1)–N(1)
88.52(3)
88.77(3)
88.77(3)
91.48(3)
91.48(3)
91.23(3)
125.32(18)
O(1)#1–Ni(1)–O(3)
O(1)–Ni(1)–O(3)#1
O(1)#1–Ni(1)–O(3)#1
O(3)–Ni(1)–O(3)#1
O(1)–Ni(1)–N(1)
O(3)#1–Ni(1)–N(1)
O(1)–Ni(1)–N(2)#2
O(1)#1–Ni(1)–N(2)#2
O(3)–Ni(1)–N(2)#2
O(2)–C(7)–O(1)
Symmetry transformations used to generate equivalent atoms: #1 ꢀx + 1/2, ꢀy, z;
#2 x, ꢀy, z ꢀ 1/2; #3 x, ꢀy, z + 1/2.
Fig. 2. A perspective view of the 2D H-bonding layer in 1 along the [100] direction.
(H-bonds are shown in red, blue, and green broken lines). (For interpretation of the
references to colour in this figure legend, the reader is referred to the web version of
this article.)
From the least square plane calculations, the phenyl rings of
two 2,4,6-trimethylbenzoate anions and the two 4,40-bipyridyl li-
gands are located in the parallel planes and separated by the dis-
tances of 1.914 and 0.264 Å, respectively.
Fig. 1. A portion view of 1 with atom labeling of the asymmetry unit and metal
coordination sphere. Symmetry code (A) ꢀx + 1, ꢀy, ꢀz.
The dihedral angle between the 4,40-bipyridyl ring and a phenyl
ring of 2,4,6-trimethyl benzoate anion is 63.79ꢀfor the planes con-
taining (C14, C15, C16, C17, C18, and C19) and (N2, C3-C10, N11,
C12, and C13), and the dihedral angle between the phenyl rings
of coordinated and uncoordinated acids is 63.20ꢀfor the planes con-
taining (C14, C15, C16, C17, C18, and C19) and (C26, C27, C28, C29,
C30, and C31) [22].
boxylate and the other in the free acid form that is involved in
hydrogen bonding linkage.
The bond lengths involving 4,40-bipyridyl and 2,4,6-trimethyl
benzoate ligands, Co(1)–N(2) [2.1787(16) Å], Co(1)–O(1)
[2.0749(16) Å] and Co(1)–O(21) [2.1338(14) Å], are comparable
to those found in similar cobalt complexes [20]. The cis-O–Co–O/
N angles are in the range of 86.75(6)–91.81(6ꢀ) and the O–C–O an-
gle is 123.6(2ꢀ).
The group of atoms (N2, C3-C10, N11, C12, and C13) in the 4,40-
bipyridyl unit deviate significantly from planarity. Among all, C4
has the highest deviation of 0.0877 Å. The group of atoms (C14–
C20 and C23–C25) of the trimethyl benzoate moiety also deviate
significantly from planarity and C24 has the highest deviation of
0.1668 Å.
The group of atoms (C20, O21, and O22) in the carboxylate moi-
ety are coplanar but, almost perpendicular (dihedral angle 88.84°)
to its phenyl ring (C14–C19). The group of atoms (C26–C32 and
C35–C37) deviates significantly from planarity, and C32 has the
higher deviation of 0.0182 Å. From the puckering parameters (u2,
h2, and Q) [23,24] the conformation for ring 1 (C14–C19) is boat
conformation 1,4B, for ring 2 (C26–C31) is twist conformation 4T2,
for ring 3 (N2 and C3–C7) is twist conformation 3T1, and for ring
4 (C8–C9, N11, C12, and C13) is sofa conformation 3S4.
Due to the trans-disposition of the aqua molecules and both
types of organic ligands at each metal center, a square grid layer
network is propagated along the crystallographic bc plane with
the adjacent Co–Co distance of 13.022 Å via intermolecular O–
Hꢂ ꢂ ꢂN interactions, as shown in Fig. 2 [21]. The bridging role of
4,40-bipyridyl ligand via both coordination and H-bonded contacts
leads to the formation of a (4,4) sheet, in which the ligated 2,4,6-
trimethyl benzoate moieties lie along the shorter diagonals within
each subunit and the unligated 2,4,6-trimethyl benzoic acid mole-
cules recline the length of the longer diagonal by virtue of hydro-
gen bonds (Scheme 1).
In detail, the water ligands form strong intermolecular hydro-
gen bonds to the uncoordinating carboxylate oxygen atoms
with d O1–H1Aꢂ ꢂ ꢂO22
also to the uncoordinating
ꢀz) = 2.660(2) Å and \ = 158(3ꢀ), and
3.2. Structural description of {[Ni(tmb)2(
(4,40-bpy)}n
l
-4,40-bpy)(H2O)2]
(ꢀx + 1, ꢀy,
N
atoms of 4,40-bipyridyl, with
dO1–H1Bꢂ ꢂ ꢂN11 (ꢀx+3/2, y+1/2, ꢀz+1/2) = 2.767(3) Å and \ = 179(4ꢀ). In addi-
tion, there exist strong hydrogen bonds between the 2,4,6-tri-
methyl benzoic acid guests and the unligated O atoms of the
2,4,6-trimethyl benzoate ligands with dO33–H33ꢂ ꢂ ꢂO22 = 2.586(3) Å
and \ = 175(4ꢀ).
Compound 2 crystallizes in the orthorhombic space group Ccca.
It is a 1:1:2 complex with Ni ion, 2,4,6-trimethylbenzoic acid
(Htmb), and 4,40-bipyridyl. The Ni atom lies on a diad axis and
has a trans-N2O4 octahedral coordination through bonds to two
4,40-bpy N atoms, two equivalent water O atoms and two equiva-
lent carboxylate-O atoms. In the asymmetric unit, both COOH
group of Htmb and 4,40-bpy interact with Ni(II). Thus, each Ni(II)
is connected to two 4,40-bpy molecules that lie at the axial posi-
tions and two Htmb to complete the six coordination sites with
the aid of two water molecules (Fig. 4). As a result, in this case,
infinite linear polymeric chains of –Ni–bpy–Ni–bpy– are formed
Also, there are C–Hꢂ ꢂ ꢂO interactions present in the structure
[dC36–H36Bꢂ ꢂ ꢂO21
zꢀ1/2) = 3.594(4) Å and \ = 163.86(2ꢀ)],
z +1/2) = 3.333(4) Å and \ = 154.77(20ꢀ)],
ꢀz) = 3.630(4) Å and \ = 152.04(15ꢀ)], and
(x+1/2, ꢀy+1/2,
[dC10–H10ꢂ ꢂ ꢂO34
(x+1/2, ꢀyꢀ1/2,
[dC7–H7ꢂ ꢂ ꢂO34(ꢀx+1,
ꢀy,
[dC3–H3ꢂ ꢂ ꢂO22 = 3.721(3) Å and \ = 143.81(16ꢀ)], which play a signifi-
cant role in stabilizing the overall 3D structure (see Fig. 3). The
parameters of hydrogen bonds are given in Table 4.

3596
M. Indrani et al. / Polyhedron 27 (2008) 3593–3600
Scheme 1.
Fig. 3. 3D packing diagram of 1, in which the interlayer aromatic interactions are indicated by pink. (For interpretation of the references to colour in this figure legend, the
reader is referred to the web version of this article.)
running parallel to the c-axis by repeated operations of c-glide (see
Fig. 5), with the 4,40-bpy connectors joining the adjacent NiII octa-
hedrons using their typical bridging role. In each chain, the basal
plane of carboxylate and water O atoms is stabilized by O3–
Hꢂ ꢂ ꢂO2 hydrogen bonding from water to the uncoordinated car-
boxylate O.
These polymeric chains are further held together by O3–
Hꢂ ꢂ ꢂN(bpy)Nꢂ ꢂ ꢂH–O3 bridges. In short, there is much symmetry
including glide planes and 2-fold rotation axes in all three direc-
tions, 2-fold screw axes in two directions, inversion centers, and
lattice centering in this structure.
In the structure of 2, two unique 4,40-bipyridyl molecules are
found, one of which coordinates to the nickel center via its nitro-
gen atoms, whereas the other is involved only in hydrogen bonded
linkage. Both types of 4,40-bipyridyl units are nonplanar, having
torsional twists about their central linking bonds of ca. 16.3ꢀand
43.1ꢀ, respectively. Notably, the non-coordinated 4,40-bipyridyl
guest is positioned over a crystallographic inversion center, and

M. Indrani et al. / Polyhedron 27 (2008) 3593–3600
3597
Table 4
range of 89.54(5)–177.55(7ꢀ) with the average value of 118.99ꢀ
and the O–C–O angle is 125.32(18ꢀ).
Hydrogen bonds exhibited by 1 and 2
Each coordinated water molecule provides one H atom to the
coordinating carboxylate O atom and the other to the N atom of
uncoordinated 4,40-bpy [dO3–H3Aꢂ ꢂ ꢂN3 (xꢀ1/2,y,ꢀz+1) = 2.799(0) Å and
D–H
d(D–H)
d(Hꢂ ꢂ ꢂA)
\D–Hꢂ ꢂ ꢂA
d(Dꢂ ꢂ ꢂA)
A [symmetry]
Complex 1
O33–H33
O1–H1B
0.93(4)
0.78(4)
1.66(4)
1.98(4)
175(4)
179(4)
2.586(3)
2.767(2)
O22 [x,y,z]
N11 [ꢀx + 3/2, y + 1/2,
\ = 167.30(1ꢀ)] and [dO3–H3Bꢂ ꢂ ꢂO2
z) = 2.650(0) Å and
(ꢀx+1/2, ꢀy,
ꢀz + 1/2]
\ = 164.76(1ꢀ)]. The strong hydrogen bonds are apparently responsi-
ble for the supramolecular assembly of the 1D coordination chains
to generate 3D networks. In fact, considering these H-bonds, each
O1– H1A
0.86(3)
1.84(4)
158(3)
2.660(2)
O22 [ꢀx + 1, ꢀy, ꢀz]
Complex 2
O3–H3A
O3–H3B
C5–H5
0.85
0.85
0.93
0.93
1.964
1.82
2.514
2.299
167.30(1)
164.76(1)
178.34(1)
163.25(1)
2.799
2.65
3.444
3.201
N3 [x ꢀ 1/2, y, ꢀz + 1]
O2 [ꢀx + 1/2, ꢀy, +z]
O2 [ꢀx + 1, ꢀy, ꢀz + 1]
O1 [x + 1/2, y, ꢀz + 1]
metal center behaves as
a planar four-connected node to
constitute 3D CdSO4 topological frameworks [25], which are inter-
estingly of 2-fold interpenetration in the crystalline lattice (see Figs.
C21–H21
6–8). Intermolecular C–Hꢂ ꢂ ꢂO interactions [dC5–H5ꢂ ꢂ ꢂO2 (ꢀx+1,ꢀy,ꢀz+1)
=
3.444 Å and \ = 178.34(1ꢀ)] and [dC21–H21ꢂꢂꢂO1 (x+1/2, y, ꢀz+1) = 3.201 Å
and \ = 163.25(1ꢀ)] are also found, which play a significant role in
stabilizing this structure. The vibrational frequencies [26] of 1 and
2 are given in Table 5.
3.3. Magnetic properties
Temperature-dependent magnetic susceptibility measurements
for complexes 1 and 2 were performed on polycrystalline samples.
The effective magnetic moments of 1 and 2 are 5.68 and 3.42 lB
,
being close to the expected values (5.2 and 3.9 B) for the isolated
l
high-spin Co(II) and Ni(II) (S = 5/2). A vM versus T plot for 1 over
the temperature range of 23.7–291.8 K (Fig. 9), in which vM is the
corrected magnetic susceptibility per Co(II) unit, could be fitted
according to the Curie–Weiss law
v
M = C/(T ꢀ h), giving a Curie con-
stant C = 4.03 cm3 molꢀ1 K, and a Weiss constant h = ꢀ22.51 K. The
negative value of h indicates weak antiferromagnetic interactions
between Co(II), since the adjacent Co(II) ions are separated with
distance of 13.022 Å as revealed by X-ray crystal structure. The
vM value of 1.2 ꢁ 10ꢀ2 cm3 molꢀ1 at room temperature increases
as the temperature decreases, attaining 9.8 ꢁ 10ꢀ2 cm3 molꢀ1 at
23.7 K. A vM versus T plot for 2 over the temperature range of
Fig. 4. A molecular diagram showing the coordination geometry of NiII in 2.
Symmetry codes (A) ꢀx + 1/2, ꢀy, z; (B) ꢀx + 1/2, y, z ꢀ 1/2.
therefore, there is a statistical reversal of the N–N axis throughout
the structure, which however does not change the crosslinking
hydrogen bonding role of it.
The least square plane calculations show that the dihedral angle
between the phenyl rings of two 2,4,6-trimethylbenzoate anions is
8.32ꢀfor the planes containing (C8, C9, C10, C11, C12, and C13) and
(C8a, C9a, C10a, C11a, C12a, and C13a), and the dihedral angle be-
tween the two 4,40-bipyridyl units is 73.51ꢀfor the planes contain-
ing (N1, C1–C6, N2, and C10–C60) and (N1a, C1a–C6a, N2a, and
C1a0–C6a0), and the dihedral angle between the 4,40-bipyridyl ring
and a phenyl ring of 2,4,6-trimethyl benzoate anion is 48.41ꢀfor the
planes containing (C8, C9, C10, C11, C12 and C13) and (N1, C1–C6,
N2 and C10–C60).
8.4–296.7 K (Fig. 10), in which vM is the corrected magnetic suscep-
tibility per Ni(II) unit, could be fitted according to the Curie–Weiss
law
v
M = C/(T ꢀ h), giving a Curie constant C = 1.46 cm3 molꢀ1 K,
and a Weiss constant h = ꢀ34.92 K. Similarly, the negative value
of h indicates antiferromagnetic interactions between Ni(II), since
the adjacent Ni(II) ions are separated by 4,40-bpy ligands with dis-
tance of 11.3 Å. The vM value of 4.91 ꢁ 10ꢀ3 cm3 molꢀ1 at room
temperature increases as the temperature decreases, attaining
6.8 ꢁ 10ꢀ2 cm3 molꢀ1 at 8.4 K.
The bond lengths involving 4,40-bipyridyl and 2,4,6-trimethyl
benzoate ligands are Ni–O(carboxyl) [2.042(1) Å], Ni–O(water)
[2.0084(1) Å], and Ni–N [2.104(1) and 2.105(2) Å], being virtually
similar to the mean database values for these bonds [2.061,
2.087, and 2.103 Å, respectively]. The O–Ni–O angles are in the
3.4. Thermal properties
Thermal analysis (TGA) of complexes 1 and 2 were performed
between room temperature and 700ꢀC under the nitrogen atmo-
Fig. 5. The polymeric single chain in 2.

3598
M. Indrani et al. / Polyhedron 27 (2008) 3593–3600
Fig. 6. A single 3D network in 2 (left). A schematic representation of the cds (CdSO4) topology (right). The 4,40-bipy molecules involving in H-bonds are shown in violet and
orange, respectively, and the 2,4,6-trimethyl benzencarboxylic acid ligands are omitted for clarity. (For interpretation of the references to colour in this figure legend, the
reader is referred to the web version of this article.)
Table 5
Infrared spectral data of 1 and 2
Frequency range (cmꢀ1
)
Mode of vibration
Compound 1
Compound 2
3388
3415
O–Hstr (water)
3133
3061
inter molecular H-bonding
aromatic C–Hstr
3059
2919 and
2857
1604 and
1544
2929 and
2863
1609 and
1531
aliphatic C–Hstr
COOꢀ asymmetric and COOꢀ symmetric stretching
[26]
1439–1004
764 and 806
Below 600
1450–946
754 and 846
below 600
C@C and C–N stretching vibrations
C–H out of plane bending
M–N and M–O stretching vibrations
Fig. 7. 2-Fold interpenetrating structure of 2. The two cds arrays are shown in green
and rose, respectively. (For interpretation of the references to colour in this figure
legend, the reader is referred to the web version of this article.)
Fig. 9.
vM and vMT vs. T plots for complex 1. The solid lines represent the best fit of
the experimental data.
Fig. 8. A schematic view of two interpenetrating networks.
to the loss of coordinated water molecules. The second stage in-
volves the loss of 85.7% (Calc. 87.0%) of its mass in the temperature
range of 290–395ꢀC, corresponding to the loss of two 4,40-bpy and
two tmb components. The third stage occurs with the gradual
decomposition of the remaining species, leading to the formation
of nickel oxide. The saturation temperature above which there is
no obvious weight loss occurs at ꢃ530ꢀC.
sphere. The TGA results indicate that 1 undergoes a weight loss of
3.7% (Calc. 3.3%) in the temperature range of 85–106ꢀC, corre-
sponding to the removal of two coordinated water molecules.
The second stage has the weight loss of 52.2% (Calc. 51.5%) in the
temperature range of 146–274ꢀC, corresponding to removal of
two 4,40-bpy moieties and an unligated Htmb. The third stage oc-
curs with the gradual decomposition of the remaining species,
leading to the formation of cobalt oxide. The saturation tempera-
ture above which there is no obvious weight loss occurs at ꢃ425ꢀC.
The TGA results indicate that complex 2 loses 5.1% (Calc. 4.9%)
of its mass in the temperature range of 92–108ꢀC, corresponding
3.5. Electronic absorption spectra
In the electronic spectrum for complex 1, the ligand 4,40-bipyr-
idyl exhibits a low energy band at 320 nm region, which is gener-

M. Indrani et al. / Polyhedron 27 (2008) 3593–3600
3599
Table 6
Antibacterial activity of the complexes 1 and 2
Complex
Bacterial species
a
b
c
d
e
[Co(tmb)2 (4,40-bpy)2](Htmb)2
[Ni(tmb)2
(4,40-bpy)
+++
+++
++
++
++
++
+++
+++
+++
+++
(l
-4,40-bpy) (H2O)2]n
a: Escherichia coli, b: Staphylococcus aureus, c: Pseudomonas aeruginosa, d: Bacillus
subtilis; e: Klebsiella pneumoniae. Inhibition zone diameter mm (% inhibition): +, 6–
10 (27–45%); ++, 10–14 (45–64%); +++, 14–18 (64–82%); ++++, 18–22 (82–100%).
Percent inhibition values were relative to inhibition zone (22 mm) of standard
antibacterials (sulfadiazine, sulfathiazole), considered as 100% inhibition, tested
under the same conditions as the new compounds reported here.
Table 7
Antifungal activity of the complexes 1 and 2
Complex
Fungal species
Fig. 10.
vM and vMT vs. T plots for complex 2. The solid lines represent the best fit
of the experimental data.
a
b
c
[Co(tmb)2 (bpy)2](Htmb)2
[Ni(tmb)2 (l
-4,40-bpy) (H2O)2]n (4,40-bpy)
+++
+++
++
++
++
++
ally assigned to
p–
p* transition of the benzenoid and/or (C@N)
a: Aspergillus niger, b: Aspergillus flavus, c: Rhizoctonia bataicola. Inhibition zone
diameter mm (% inhibition): +, 6–10 (27–45%); ++, 10–14 (45–64%); +++, 14–18
(64–82%); ++++, 18–20 (82–100%), (–) = no inhibition zone. Percent inhibition val-
ues were relative to inhibition zone (20 mm) of standard antifungal (Bavistin),
considered as 100% inhibition, tested under the same conditions as the new com-
pounds reported here.
chromophore of the ligand. As a rule, the longer wavelength bands
in the spectra of metal complexes may be considered as evidence
for the complex formation. The absorption band at 535 nm due
to the 4T1g ? 4T1g (P) transition, suggests a high-spin octahedral
sphere. However, the presence of an additional absorption band
as a shoulder in the 680 nm region, assigned to the 4T1g ? 4A2g
transition, suggests a distorted-octahedral configuration due to
the Jahn–Teller effect.
microorganisms. The complexes may also disturb the respiration
process of the cell and thus block the synthesis of proteins, which
restricts further growth of the organism [29].
The electronic spectrum of the Ni(II) complex 2 shows two
absorption bands at 390 and 700 nm due to the MLCT transitions,
as generally observed for octahedral Ni(II) complexes.
4. Conclusion
3.6. Antibacterial and antifungal activity
In summary, two new supramolecular complexes of CoII and NiII
using 2,4,6-trimethyl benzoic acid and 4,40-bipyridyl as ligands
have been synthesized by hydrothermal reaction and characterized
by X-ray crystallography, IR, UV/Vis spectra, elemental analysis
and magnetic susceptibility measurements. Both complexes dis-
play interesting 3D hydrogen-bonded assemblies from the funda-
mental discrete or 1D coordination arrays. Weak intermolecular
antiferromagnetic interactions are found in 1 and 2, which also
show good antibacterial and antifungal activity.
The in vitro biological screening effects of both complexes were
tested against the bacteria: Escherichia coli, Staphylococcus aureus,
Pseudomonas aeruginosa, and Bacillus subtilis by the well-diffusion
method [27] using agar nutrient as the medium. The antifungal
activities were also evaluated by the well-diffusion method against
the fungi viz., Aspergillus niger, Aspergillus flavus and Rhizoctonia
bataicola cultured on potato dextrose agar as medium. The com-
pounds were tested at a concentration of 50 lg/0.01 mL in aqueous
solution. In a typical procedure [28], a well was made on the agar
medium inoculated with microorganisms. The well was filled with
the test solution using a micropipette and the plate was incubated
for 24 h for bacteria and 72 h for fungi at 35 °C. During this period,
the test solution diffused and the growth of the inoculated micro-
organisms was affected. The inhibition zone was developed, at
which the concentration was noted. The percentage inhibition
was calculated as 100(C ꢀ T)/C, where C is the average diameter
of bacteria or fungal growth on the control plate (water) and T is
the average diameter of bacteria or fungal growth on the test plate.
The susceptibility zones were measured in diameter (mm) and
the results are shown in Tables 6 and 7. The susceptibility zones
measured are the clear zones around the discs killing the bacteria.
The complexes individually exhibit varying degrees of inhibitory
effect on the growth of the tested bacterial species. On complexa-
tion, the polarity of the metal ion will be reduced to a greater ex-
tent due to the overlap of the ligand orbital and partial sharing
of the positive charge of the metal ion with the donor groups. Fur-
Acknowledgement
The authors (MI and RR) acknowledge CSIR, New Delhi for pro-
viding financial support through Senior Research Fellowship. The
authors greatly acknowledge Dr. H.N. Vasan, Principal Research
Scientist, SSCU, Indian Institute of Science, Bangalore-12 for his
constant encouragement and moral support. M.D. also acknowl-
edges the financial support from Tianjin Normal University.
Appendix A. Supplementary data
CCDC 680843 and 680844 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.poly.2008.09.003.
ther, it increases the delocalization of
p-electrons over the whole
ligand and enhances the penetration of complexes into lipid mem-
branes and blocking of the metal binding sites in the enzymes of

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M. Indrani et al. / Polyhedron 27 (2008) 3593–3600
[12] K. Biradha, M. Sarkar, L. Rajput, Chem. Commun. (2006) 4169.
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