Self-assembly of three new coordination complexes: Formation of 2-D square grid, 1-D chain and tape structures

Article abstract of DOI:10.1016/j.molstruc.2009.05.024

Three distinct coordination complexes, viz., [Co(imi)₂(tmb)₂] (1) [where imi = imidazole], {[Ni(tmb)₂(H₂O)₃]·2H₂ O}_n (2) and [Cu₂(μ-tmb)₄(CH₃OH)<

Full text of DOI:10.1016/j.molstruc.2009.05.024

Journal of Molecular Structure 931 (2009) 35–44
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Self-assembly of three new coordination complexes: Formation of 2-D square grid,
1-D chain and tape structures
Murugan Indrani a, Ramasamy Ramasubramanian a, Frank R. Fronczek b, N.Y. Vasanthacharya c,
Sudalaiandi Kumaresan a,
*
a Department of Chemistry, Manonmaniam Sundaranar University, Tirunelveli 627 012, TamilNadu, India
b Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803 1804, USA
c Solid State and Structural Chemistry Unit, Indian Institue of Science, Bangalore 560 012, Karnataka, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Three distinct coordination complexes, viz., [Co(imi)2(tmb)2] (1) [where imi = imidazole], {[Ni(tmb)2
Received 11 January 2009
Received in revised form 11 May 2009
Accepted 11 May 2009
(H2O)3]Á2H2O}n (2) and [Cu2(
l-tmb)4(CH3OH)2] (3), have been synthesized hydrothermally by the reac-
tions of metal acetates, 2,4,6-trimethylbenzoic acid (Htmb) and with or without appropriate amine.
The Ni analogue of 1 and the Co analogue of 2 have also been synthesized. X-ray single-crystal diffraction
suggests that complex 1 represents discrete mononuclear species and complex 2 represents a 1D chain
coordination polymer in which the Ni(II) ions are connected by the bridging water molecules. Complex
3 represents a neutral dinuclear complex. In 1, the central metal ions are associated by the carboxylate
moiety and imidazole ligands, whereas the central metal atom is coordinated to the carboxylate moiety
and the respective solvent molecules in 2 and 3. In 3, the four 2,4,6-trimethylbenzoate moieties act as a
bridge connecting two copper (II) ions and the O atoms of methanol coordinate in an anti arrangement to
form a square pyramidal geometry, with the methanol molecule at the apical position. In all the three
structures the central metal atom sits on a crystallographic inversion centre. In all the cases, the coordi-
nation entities are further organized via hydrogen bonding interactions to generate multifarious supra-
molecular networks. Complexes 1, 2 and 3 have also been characterized by spectroscopic (UV/Vis and
IR) and thermal analysis (TGA). In addition, the complexes were found to exhibit antimicrobial activ-
ity.The magnetic susceptibility measurements, measured from 8 to 300 K, revealed antiferromagnetic
interactions between the Co(II) ions in compound 1 and the Ni(II) ions in 1a, respectively.
Ó 2009 Elsevier B.V. All rights reserved.
Available online 20 May 2009
Keywords:
Crystal structure
2,4,6-Trimethylbenzoate
Hydrogen-bonding
1-D chain
2-D grids
Magnetic properties
1. Introduction
distorted tetrahedral or facial octahedral geometry, conducive for
model complexes with a tridentate ligand system.
The exercise of small molecule replica complexes to study more
complex organic or life systems has long been appreciated by
chemists [1], especially given the reality that structural geometries
of model complexes are often quite comparable to those in the pro-
teins [2]. Nitrogen containing heterocyclic ligands are a subject of
much interest to those who wish to model biological systems
including histidine and its imidazole-1 type bonding [3–9]. Many
proteins and enzymes are known to contain active sites with mul-
tiple histidine residues bound to a metal center, including, among
others, the long studied carbonic anhydrase [7,10], nitrite reduc-
tase [6], dopamine b hydroxylase [11,12], superoxide dismutase
[13–17], cytochrome c oxidase [4,18,19], pirin [20], and acireduc-
tone dioxygenases [21]. These enzymes have been shown to con-
The role of imidazole as a complexing agent has been studied
for years, mainly because imidazole is involved in important bio-
logical processes [22–26]. The tertiary nitrogen atom in imidazole
is a good resource to coordinate with a metal ion and a good num-
ber of compounds based on imidazole and different metal ions
have been reported [27–33]. On the other hand, the secondary
nitrogen atom is a good hydrogen bonding donor and, multi-
dimensional supramolecular assembly can be obtained via hydro-
gen bonding interactions [34–41].
The deliberate construction of extended metal–organic net-
work systems is an area of active research in recent years [42]
and variety of organic–inorganic compounds containing ben-
zene-substituted-carboxylic acid and or N-donor ligands as the
organic part have been structurally characterized. The structures
of these compounds are held together by strong metal–ligand
bonding and further stabilized by weaker bonding forces such
tain three histidine residues bound to
a metal center in a
* Corresponding author. Tel.: +91 4622333887.
E-mail address: skumarmsu@yahoo.com (S. Kumaresan).
as hydrogen bonding and
p–p interactions. The importance of
0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2009.05.024

36
M. Indrani et al. / Journal of Molecular Structure 931 (2009) 35–44
H-bonding interactions for the assembly of supramolecular struc-
tures is well documented in the literature [43,44]. A convenient
way to build unbounded polymeric structures is by using a mul-
ti-functional ligand to link metal ions to form an infinite configu-
ration. In this perspective, substituted benzenecarboxylic acids
have been exposed to be very constructive reagents by numerous
research groups, as evidenced by the exciting array of interesting
metal–organic molecular architectures synthesized from this cat-
egory of ligands [45–49]. The benefit of using benzene based li-
gand systems is due to the fact that donor groups like –COOH,
–SH, –NH2, etc. can be anchored onto the rigid six-membered
benzene ring and the resulting supramolecular structures will lar-
gely depend on the positioning of the donor groups on the six
membered ring. Besides, the donor groups can also participate
in H-bonding interactions as well to the formation of a metal–li-
gand bond. As part of an ongoing programme, we are investigat-
ing the chemistry of metal complexes of 2,4,6-trimethylbenzoic
acid (Htmb). In continuation of this theme, we wish to present
the synthesis, spectroscopic, thermal, and structural characteriza-
tion of three new transition metal 2,4,6-trimethylbenzoates with
or without an amine [50].
2. Experimental
2.1. Materials and methods
All chemicals purchased were of analytical grade and used
without further purification. IR spectra were recorded on a JASCO
FTIR-410 spectrometer using KBr pellets. UV/Vis spectra were re-
corded on a Perkin-Elmer Lambda 25 UV/Vis spectrophotometer.
Thermogravimetric analysis was performed on a Mettler Toledo
Star system from room temperature to 700 °C with a heating rate
of 10 °C/min. Elemental analysis was carried out using a Perkin-El-
mer 1400C analyzer. Magnetic susceptibility measurements were
performed on a George Associate Faraday Force Magnetometer.
2.2. Synthesis
A
mixture of cobalt acetate tetrahydrate (0.0311 g,
0.125 mmol), 2,4,6-trimethylbenzoic acid (0.041 g, 0.250 mmol),
imidazole (0.017 g, 0.250 mmol), and water (2.5 mL) was homoge-
nized for 30 min. It was then sealed in a 23 mL polyfluoroethylene-
lined stainless steel bomb, and kept at 150 °C under autogenous
Scheme 1.

M. Indrani et al. / Journal of Molecular Structure 931 (2009) 35–44
37
pressure for 72 h. After cooling at a ramp of 10 °C per hour to room
temperature, magenta coloured crystals of Co(tmb)2(imi)2 were
collected by filtration, washed with de-ionized water followed by
diethyl ether, and then dried (0.0442 g, 68%). Anal. Calc. for
C26H30N4O4Co: C, 59.88; H, 5.80; N, 10.74%: Found: C, 60.40; H,
5.45; N, 10.93%.
drate. Anal. Calc. for C26H30N4O4Co: C, 59.88; H, 5.80; N, 10.74%:
Found: C, 60.80; H, 5.77; N, 10.94%.
Nickel acetate tetrahydrate (0.0311 g, 0.125 mmol), and 2,4,6-
trimethylbenzoic acid (0.041 g, 0.250 mmol) were dissolved in
aqueous medium (2.5 mL). The mixture was sealed in a 23 mL
Teflon-lined stainless steel bomb, and held at 70 °C for 72 h.
The bomb was cooled naturally to room temperature and pale
green coloured crystals of {[Ni(tmb)2(H2O)3]Á2H2O}n were
Similar procedure was adopted for the synthesis of 1a with
nickel acetate tetrahydrate used in place of cobalt acetate tetrahy-
Table 1
Crystal data and structure refinement summary for compounds 1–3.
Complex
1
1a
2
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C26H30N4O4Co
521.47
90
0.71073
Orthorhombic
Pbcn
C26H30N4O4Ni
521.25
90(2)
0.71073
Orthorhombic
Pbcn
C20H32O9Ni
475.15
90(2)
0.71073
Triclinic
ꢀ
P1
12.2516(12)
13.0111(14)
16.842(2)
2684.7(5)
4
1.290
0.676
1092
12.1888(14)
13.0080(15)
16.8167(16)
2666.3(5)
4
1.299
0.765
1096
7.8642(10)
9.9520(15)
15.398(3)
1158.2(3)
2
1.363
0.883
504
b (Å)
c (Å)
Volume (Å3)
Z
Dcalc (MgmÀ3
)
Absorption coefficient (mmÀ1
F(000)
)
Crystal size (mm)
h Range for data collection (°)
Limiting indices
0.20 Â 0.17 Â 0.10
0.10 Â 0.08 Â 0.07
2.59–28.26
À16 6 h 6 16
À17 6 k 6 17
À22 6 l 6 22
6216/3307
0.0439
0.22 Â 0.20 Â 0.03
2.75–27.86
À10 6 h 6 10
À13 6 k 6 13
À20 6 l 6 20
10453/5467
0.0336
2.9–27.9
À16 6 h 6 16
À17 6 k 6 17
À22 6 l 6 22
46420/3201
0.018
Reflections collected/unique
Rint
Completeness to h (%)
Absorption correction
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
99.9
0.0024(4)
99.9
None
99.1
None
Full-matrix least-squares on F2
3201/0/166
1.017
3307/0/165
1.026
5467/0/298
1.074
R1 and wR2 [I>2
r
(I)]
0.028, 0.070
0.039, 0.074
0.33 and À0.32
0.0366, 0.0709
0.0629, 0.0805
0.260 and À0.371
0.0349, 0.0802
0.0530, 0.0869
0.366 and À0.453
R1 and wR2 (all data)
Largest difference peak and hole (e ÅÀ3
)
Complex
2a
3
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C20H32O9Co
475.39
90
C42H52O10Cu2
843.92
298(2)
0.71073
Monoclinic
P121/c1
0.71073
Triclinic
ꢀ
P1
8.036(3)
9.962(3)
15.302(4)
1176.8(6)
2
1.342
0.774
502
7.5642(7)
15.2818(14)
17.4881(16)
2017.7(3)
2
1.389
1.110
884
b (Å)
c (Å)
Volume (Å3)
Z
Dcalc (MgmÀ3
)
Absorption coefficient (mmÀ1
F(000)
)
Crystal size (mm)
h Range for data collection (°)
Limiting indices
0.25 Â 0.20 Â 0.10
1.85–28.31
À11 6 h 6 11
À13 6 k 6 13
À21 6 l 6 19
21743/11380
0.070
0.34 Â 0.20 Â 0.18
1.77–25.38
À9 6 h 6 9
À18 6 k 6 18
À21 6 l 6 20
16420/3690
0.0476
Reflections collected/unique
Rint
Completeness to h (%)
Absorption correction
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
99.0
99.8
None
Semi-empirical from equivalents
Full-matrix least-squares on F2
11380/0/281
3690/1/254
0.947
1.029
R1 and wR2 [I > 2
r
(I)]
0.046, 0.106
0.084, 0.121
0.51 and À0.48
0.0359, 0.0861
0.0475, 0.0897
0.408 and À0.295
R1 and wR2 (all data)
Largest difference peak and hole (e ÅÀ3
)

38
M. Indrani et al. / Journal of Molecular Structure 931 (2009) 35–44
Table 2
Table 3
Selected bond lengths and angles for 1–3.
Possible hydrogen bond geometries in the crystal structures of 1–3.
Compound
Bond lengths (Å)
Bond angles (deg)
Compound
D–HÁÁÁA
DÁÁÁA (Å)
2.7853(15)
3.4310
HÁÁÁA (Å)
1.905(18)
2.621
D–HÁÁÁA (°)
166.2(1)
1
Co(1)–N(1)
Co(1)–O(1)
Co(1)–O(2)
O(1)–C(1)
O(2)–C(1)
N(1)–C(13)
2.0525(11)
2.1295(10)
2.2145(9)
1.2574(16)
1.2661(16)
1.3799(18)
N(1)–Co(1)–N(1)a
N(1)–Co(1)–O(1)a
O(2)–Co(1)–O(2)a
N(1)–Co(1)–O(1)
O(1)–Co(1)–O(1)a
N(1)–Co(1)–O(2)
O(2)–Co(1)–O(1)a
O(1)–C(1)–O(2)
101.81(6)
97.05(4)
81.62(5)
97.82(4)
156.33(5)
92.74(4)
100.38(4)
120.74(12)
1
N(2)–H(2 N)ÁÁÁO(2)a
C(9)–H(9C)ÁÁÁO1b
140.08(1)
1a
2
N(2)–H(2 N)ÁÁÁO(2)a
C(9)–H(9C)ÁÁÁO1b
2.796(2)
3.471(2)
1.91(2)
2.668
170(1)
139.41(1)
O(3)–H(31)ÁÁÁO(5)c
O(3)–H(32)ÁÁÁO(8)
O(4)–H(41)ÁÁÁO(2)
O(4)–H(42)ÁÁÁO(6)
O(7)–H(71)ÁÁÁO(9)
O(7)–H(72)ÁÁÁO(1)d
O(8)–H(81)ÁÁÁO(6)
O(9)–H(91)ÁÁÁO(2)
1.84(3)
1.97(3)
1.75(3)
1.71(3)
1.96(3)
1.93(3)
1.83
2.686(2)
2.762(2)
2.586(2)
2.595(2)
2.753(2)
2.694(2)
2.700(2)
2.693(2)
176(3)
166(3)
172(2)
166(2)
166(3)
176(3)
150.8
1a
Ni(1)–N(1)
Ni(1)–O(1)
Ni(1)–O(2)
O(1)–C(1)
O(2)–C(1)
N(1)–C(11)
N(1)–C(13)
N(2)–C(11)
N(2)–C(12)
2.0135(15)
2.0743(13)
2.1910(12)
1.263(2)
1.268(2)
1.319(2)
1.382(2)
1.344(2)
1.370(2)
N(1)–Ni(1)–N(1)a
N(1)–Ni(1)–O(1)
O(2)–Ni(1)–O(2)a
O(1)–Ni(1)–O(1)a
O(1)–C(1)–O(2)
N(1)–Ni(1)–O(2)a
O(1)–Ni(1)–O(2)a
O(2)–Ni(1)–N(1)a
O(1)–Ni(1)–O(2)
98.51(8)
98.06(6)
83.37(7)
156.94(7)
120.72(17)
157.38(5)
99.83(5)
157.38(5)
62.02(5)
1.86
144.6
2a
O(3)–H(31)ÁÁÁO(5)c
O(3)–H(32)ÁÁÁO(8)
O(4)–H(41)ÁÁÁO(2)
O(4)–H(42)ÁÁÁO(6)
O(7)–H(71)ÁÁÁO(9)
O(7)–H(72)ÁÁÁO(1)d
O(8)–H(81)ÁÁÁO(6)
O(9)–H(91)ÁÁÁO(2)
1.85
1.9
2.6738(19)
2.736(2)
2.616(2)
2.6288(18)
2.735(2)
2.6834(19)
2.715(2)
167.8
177.4
172.7
163.5
168.9
168.5
153
1.78
1.81
1.91
1.86
1.94
1.98
2
Ni(1)–O(3)
Ni(1)–O(1)
Ni(1)–O(4)
Ni(2)–O(7)
Ni(2)–O(5)
Ni(2)–O(4)
O(1)–C(1)
O(2)–C(1)
2.0337(15)
2.0485(13)
2.1316(13)
2.0344(15)
2.0464(14)
2.1299(13)
1.270(2)
O(3)–Ni(1)–O(1)
O(3)–Ni(1)–O(4)
O(1)–Ni(1)–O(4)
O(7)–Ni(2)–O(5)
O(2)–C(1)–O(1)
O(6)–C(11)–O(5)
O(7)–Ni(2)–O(4)
O(5)–Ni(2)–O(4)
89.18(6)
91.45(6)
92.52(5)
88.82(6)
124.29(18)
124.33(18)
91.19(6)
93.15(5)
2.725(2)
147.7
3
O(5)–H(5A)ÁÁÁO(4)d
C18–H18AÁÁÁO2
C19–H19CÁÁÁO2e
1.991(10)
2.902(2)
2.594(2)
2.830(3)
3.729(3)
3.554(4)
178(3)
144.9(2)
179.02(2)
1.250(2)
Symmetry transformations used to generate equivalent atoms: aÀx + 1/2, y À 1/2, z.
2a
Co(1)–O(3)
Co(1)–O(1)
Co(1)–O(4)
Co(2)–O(7)
O(5)–C(11)
Co(2)–O(5)
Co(2)–O(4)
O(1)–C(1)
O(2)–C(1)
O(6)–C(11)
2.0349(13)
2.0813(14)
2.1963(14)
2.0410(14)
1.271(2)
2.0795(13)
2.1883(14)
1.275(2)
O(3)–Co(1)–O(1)
O(1)–Co(1)–O(4)
O(1)–Co(1)–O(1)b
O(3)–Co(1)–O(4)
O(7)–Co(2)–O(5)
O(3)–Co(1)–O(3)b
O(5)–Co(2)–O(4)
O(2)–C(1)–O(1)
O(6)–C(11)–O(5)
O(5)–Co(2)–O(5)c
90.13(6)
92.01(5)
180.00(7)
93.08(5)
89.26(6)
180.00(1)
93.28(5)
123.94(18)
124.19(16)
180.0
b
Àx + 1/2, y + 1/2, z. cx + 1, y, z. dx À 1, y, z. ex, Ày À 1/2, z + 1/2.
1.250(2)
1.256(2)
3
Cu(1)–O(1)
Cu(1)–O(2)d
Cu(1)–O(3)
Cu(1)–O(4)d
Cu(1)–O(5)
Cu(1)–Cu(1)d
O(1)–C(7)
1.9514(17)
1.9699(17)
1.9787(17)
1.9789(16)
2.1550(19)
2.6041(6)
1.262(3)
1.263(3)
1.257(3)
1.270(3)
1.406(4)
O(1)–Cu(1)–O(2)d
O(1)–Cu(1)–O(3)
O(3)–Cu(1)–O(2)d
O(1)–Cu(1)–O(4)d
O(3)–Cu(1)–O(4)d
O(1)–Cu(1)–O(5)
O(5)–Cu(1)–O(2)d
O(3)–Cu(1)–O(5)
O(5)–Cu(1)–O(4)d
O(1)–C(7)–O(2)
168.80(7)
87.98(8)
92.87(8)
88.55(7)
168.84(7)
94.52(7)
96.55(7)
94.24(8)
96.60(8)
124.6(2)
124.3(2)
O(2)–C(7)
O(3)–C(17)
O(4)–C(17)
O(5)–C(21)
Fig. 1. Molecular structure of 1 with atom labeling of the asymmetric unit and
metal coordination. Symmetry code for A: Àx + 1, y, Àz + 1/2.
O(3)–C(17)–O(4)
a
Symmetry transformations used to generate equivalent atoms: Àx + 1, y, Àz + ½.
b
c
d
Àx + 1, Ày + 1, Àz + 1. Àx, Ày + 1, Àz + 1. Àx + 1, Ày, Àz.
obtained. Then the crystals were collected by filtration, washed
with de-ionized water followed by diethyl ether, and then dried
(0.048 g, 81.2%). Anal. Calc. for C20H32O9Ni: C, 50.56; H, 6.79%;
Found: C, 51.61; H, 6.48%.
The procedure used for the synthesis of 2 was exactly followed
for the synthesis of 2a with cobalt acetate tetrahydrate used in
place of nickel acetate tetrahydrate. Anal. Calc. for C20H32O9Ni: C,
50.53; H, 6.78%; Found: C, 51.50; H, 6.46%.
For the synthesis of 3, copper acetate tetrahydrate (0.0311 g,
0.125 mmol), 2,4,6-trimethylbenzoic acid (0.0205 g, 0.125 mmol),
and caffeine (0.0242 g, 0.125 mmol) were mixed in deionised
water (3 mL). After stirring for half an hour, the mixtures were
placed in a 23 mL Teflon-lined reactor and heated at 85 °C in an
oven for three days. Then the reactor was cooled slowly to room
temperature; dark green coloured crystals of [Cu2(l-
tmb)4(CH3OH)2]) were collected by filtration, washed with de-ion-
ized water followed by diethyl ether, and then dried (0.0460 g,
87.7%). In this synthesis caffeine serves as a mineralizer. In the ab-
Fig. 2. A perspective view of square grid network in 1.

M. Indrani et al. / Journal of Molecular Structure 931 (2009) 35–44
39
sence of caffeine, no crystals were obtained. Anal. Calc. for
3. Results and discussion
C42H52O10Cu2: C, 59.77; H, 6.21%: Found: C, 59.68; H, 6.13%. The
syntheses of all the five complexes were schematically represented
in Scheme 1.
3.1. Structure descriptions
Compound 1 crystallizes in the orthorhombic space group Pbcn.
The Co(II) atom sits on an inversion centre. The asymmetric unit in
1 (Fig. 1) consists of one cobalt, two carboxylate and two imidazole
ligands. The cobalt centre is coordinated by two nitrogens from
two imidazole groups and four oxygens from two carboxylates to
form [Co(imi)2(tmb)2] monomers with distorted octahedral
geometry.
The molecule can be viewed as a four-bladed paddle wheel
(Fig. 1), when viewed with the Co–O1 bond as axis and the four li-
gands, each nearly planar, as paddles. The bond lengths involving
imidazole and 2,4,6-trimethylbenzoate ligands Co(1)–N(1)
[2.0525(11) Å], Co(1)–O(1) [2.1295(10) Å] and Co(1)–O(2)
[2.2145(9) Å] are comparable to those found in similar reported co-
balt complexes. The difference in the bond lengths of Co–O is prob-
ably due to the effect of the chelating coordination of the
carboxylate group in the cobalt complex. The O–Co–O angles are
in the range 60.62(4)°–156.33(5)° [average = 99.73°]. The O–C–O
angle is 120.74(12)°. The N–Co–N angle is 101.81(6)°. The average
angles of O–Co–N and Co–O–C are 103.41° and 89.23°, respectively.
A view of the crystal packing of complex (1) is shown in Fig. 2. The
packing results from an extended 2D network of inter-molecular
interactions. Each [Ni(imi)2(tmb)2] complex molecule is involved
2.3. X-ray crystallography
Diffraction data for the compounds 1 and 2, were collected at
90 K on a Nonius Kappa CCD diffractometer fitted with an Oxford
Cryostream
cooler
and
graphite-monochromated
MoKa
(k = 0.71073 Å) radiation. Data reduction, including multi-scan
absorption corrections, was carried out using DENZO and HKL
SCALEPACK [51]. The structures were solved by direct methods
and refined by full-matrix least squares techniques using SHEL-
XL97 [52]. All non-hydrogen atoms were refined anisotropically.
All hydrogen atoms were visible in difference maps, but were
placed in idealized positions, except for N–H and H2O hydrogen
atoms, for which coordinates were typically refined. In cases
where H2O hydrogen atom positions did not refine well, they
were placed by difference maps and allowed to ride on the O
atoms.
Diffraction data for the compound 3, was collected at 298 K on a
Bruker Smart APEX AXS CCD diffractometer fitted with graphite-
monochromated MoKa (k = 0.71073 Å) radiation. The data was col-
lected by using SMART [53]. Cell refinement and data reduction,
including multi-scan absorption corrections, were carried out
using SAINT [53]. The structures were solved by direct methods
and refined by full-matrix least squares techniques using SHELXTL
[54]. All H atoms bonded to C were found in a difference Fourier
map and refined using a riding model, with C–H = 0.93–0.97 Å
and Uiso(H) = 1.2Ueq(C). H atom bonded to N was refined, giving
N–H distances of 0.69–0.97 Å and Uiso(H) = 1.2Ueq(N).
All H atoms other than those of water molecules in 1, 2, and 3
were positioned geometrically (C–H = 0.93–0.97 Å) and refined as
riding, with Uiso(H) = 1.2Ueq(C). The H atoms of water molecules
were located in a difference map and refined as riding in their
as-found relative positions, with Uiso(H) = 1.5Ueq(O). Crystal data
and details of measurements are summarized in Table 1. Selected
bond distances and angles are listed in Table 2, and the hydrogen
bonding geometric details are summarized in Table 3.
in N–HÁÁÁO [dN2–H2NÁÁÁO2(Àx+1/2,
z) = 2.785 Å, \ = 166.25(1)°]
yÀ1/2,
hydrogen bonds with its four nearest neighbours. The hydrogen
bonds from the four nearest neighbours when extended forms infi-
nite square grid. It is noteworthy that two CoII atoms, two imidazole
molecules and two tmb anions produce a 24 membered grid, with a
CoÁÁÁCo distance of 8.935(1) Å (through ligand), and 12.252 Å
(through space), via coordination covalent bonds and hydrogen
bonds. These grids, by sharing CoII atoms, extend to form a molecu-
lar-sieve type structure (Fig. 2). The frame work has large, 2-dimen-
sionally inter-connected voids. The ring shaped hydrogen bonded
motif can be described by Etter’s hydrogen bond notation [55] as
R44(24). Also the C9–H9CÁÁÁO1 interaction present in the structure
[dC9–H9CÁÁÁO1(Àx+1/2, y+1/2, z) = 3.431 Å, \ = 140.08(1)°] plays a significant
role in stabilizing the structure (Fig. 3).
Fig. 3. Packing diagram of 1 showing the arrangement of the mononuclear molecules.

40
M. Indrani et al. / Journal of Molecular Structure 931 (2009) 35–44
The mean plane through C2–C10 shows that C8 has a higher
polymeric chain in the crystal. Two water molecules are left unco-
ordinated in the crystal. The coordinated geometry of nickel(II)
ions can be well described as a distorted octahedron (Fig. 4).
The NiÁ Á ÁNi distance across the chain is 3.932 Å. Ni–O bond
lengths in the complex are in the range 2.0337(15)–2.1316(13) Å
which are consistent with the similar reported structure. [58]
Among the Ni–O coordinations, the Ni(1)–O(3) bond
[2.0337(15) Å] is the shortest and the Ni(1)–O(4) bond
[2.1316(13) Å] is the longest in the structure. This difference may
be attributed to the large bidentate binding of O(4) of the bridged
water molecule. The bridging O(4) atom is almost equidistant from
the two nickel atoms. The aqua ligands and the 2,4,6-trim-
ethylbenzoate ligands are at trans disposition in each metal center.
The O(2)–C(1)–O(1) and O(6)–C(11)–O(5) angles are 124.29(18)°
and 124.33(18)°, respectively. These values seem to be slightly in-
creased than that present in a free acid (122.2)°. This deviation in
the bond angle is attributed to the coordination of oxygen atoms
[O(1) and O(5)] to the metal atom. The C–O bond lengths in the
carboxylic acid moiety indicate delocalization of charge [C(1)–
O(1) = 1.270(2) Å and C(1)–O(2) = 1.250(2) Å] as they are interme-
diate between single and double bond lengths. The C(1)–
O(1) = 1.270(2) Å and C(11)–O(5) = 1.270(2) Å are quite greater
than the C(1)–O(2) = 1.250(2) Å and C(11)–O(6) = 1.251(2) Å. This
difference shows that only O(1) and O(5) are coordinated to the
metal.
deviation from the plane (0.0486 Å). The puckering parameters
(/2, h and Q) [56,57] indicate that the six membered ring C2–C7
is between envelope 2E and sofa 2S1 conformations, and the five
membered ring N1, N2/C11–C13 adopts a deformed envelope con-
formation. The /2 = 100.40(56.71) is close to the value of envelope
with 108° for /2.
The least square plane calculations to find the dihedral angles
present in complex 1 and 1a show that the dihedral angle between
the phenyl rings of two 2,4,6-trimethylbenzoate anions is 72.92°
(for 1) and 73.50° (for 1a) for the planes containing [C2, C3, C4,
C5, C6, C7] and [C2A, C3A, C4A, C5A, C6A, C7A; symmetry code:
(A) Àx + 1, y, Àz + 1/2], and the dihedral angle between the two
imidazole rings is 87.10° (1) and 86.44° (1a) for the planes contain-
ing [C11, N2, C12, N1, C13] and [C11A, N2A, C12A, N1A, C13A, sym-
metry code: (A) Àx + 1, y, Àz + 1/2], and the dihedral angle between
the imidazole ring and a phenyl ring of 2,4,6-trimethylbenzoate
anion is 47.77° (for 1) and 48.54° (for 1a) for the planes containing
(C11, N2, C12, N1, C13) and (C2, C3, C4, C5, C6, C7). The nickel com-
plex 1a is isomorphic in structure with the cobalt analogue (1) de-
scribed above.
{[Ni(tmb)2(H2O)3]Á2H2O}n, (2) crystallizes in the triclinic space
group P1. In 2 the coordination sphere of Ni2+ ion includes six oxy-
ꢀ
gen atoms two of these belonging to the carboxylate group of
2,4,6-trimethylbenzoic acid moieties, and the other four to the
water molecules. Each nickel(II) metal ion is bridged to the neigh-
bouring nickel(II) ions by a water molecule on either side of the
Each monomer unit in the coordination polymer 2 is held to-
gether by O–HÁÁÁO type hydrogen bonds between the carbonyl
groups of the 2,4,6-trimethylbenzoate of one unit with the termi-
nal and bridging water molecules of the adjacent unit, thereby
forming an indefinite chain along a-axis (Fig. 5).
An unligated carboxylate oxygen atom O(6) makes two hydro-
gen bonds, one from the oxygen atom O(4) of bridged water mol-
ecule and another from the uncoordinated water molecule O(8)
present in the lattice which in turn accepts a hydrogen bond from
the oxygen atom of a water molecule O(3) coordinated to the
neighbouring metal atom. The oxygen atom O(7) of coordinated
water molecule donates two hydrogen bonds, one to the lattice
water O(9) and the other to the ligated carboxylate oxygen atom
O(1). This hydrogen bond [O(7)–H(72)ÁÁÁO(1)] bridges the two me-
tal ions Ni(1) and Ni(2). The five oxygen atoms except O(9) form a
ring shaped hydrogen bonding pattern with the graph symbol
Fig. 4. A portion view of 2 showing the coordination spheres of NiII. Symmetry
codes for A: Àx + 1, Ày + 1, Àz + 1 and B: Àx, Ày + 1, Àz + 1.
Fig. 5. The polymeric chain of 2 extended by water bridges along [1 0 0]. The different H-bonds are shown in red (within the chain) and green (between the chain and lattice
water) broken lines, respectively, and irrelevant H atoms 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.)

M. Indrani et al. / Journal of Molecular Structure 931 (2009) 35–44
41
R33(12). This large ring consists of three smaller rings namely R23(8),
R11(6), and R11(5).
the mean plane formed by the four basal O atoms towards the api-
cal O(5) atom by 0.188 Å. The four oxygen atoms which are copla-
nar, lie at an average distance of 1.9697 Å and the fifth oxygen
atom, O(5), of a molecule of methanol, at 2.1550(19) Å. The
Cu(1)aÁÁÁCu(1)–O(5) [symmetry code: (a) Àx + 1, Ày, Àz] angle of
174.03° indicates a slight deviation from the expected value of
180° for idealized D4h symmetry [59].
All of the bridging and terminal H2O molecules are involved in
hydrogen-bonding interactions. The H2O molecules coordinating to
the terminal nickel ions of the dinuclear clusters form ‘‘moderate”
hydrogen bonds with the oxygen atoms of the carboxylate groups
in the nearest-neighbour lying in the polymeric chain. The bridging
H2O molecules afford intracluster hydrogen bonding interactions
with the oxygen atoms of the carboxylate groups. The bond dis-
tances of 2.586(2) and 2.595(2) Å are very short, indicating the for-
mation of ‘‘strong” hydrogen bonds. The bond angles of O–HÁÁÁO are
close to 180° [166(2)° and 172(2)°].
In the dinuclear cluster, neighbouring nickel ions are bridged by
the H2O molecule. The Lewis basicity of a H2O molecule is weaker
than that of a 2,4,6-trimethylbenzoic acid ligand. Therefore, to sta-
bilize the dinuclear cluster, it is necessary to improve the Lewis ba-
sicity of the bridged H2O molecule. Each nickel ion is coordinated
to the monodentate carboxylate groups in addition to the bridged
H2O molecules. Coordination-free oxygen atoms of such carboxyl-
ate groups can interact with bridged H2O molecules via ‘‘strong”
hydrogen bonds. As the protons of the bridged H2O molecules
are attracted to the oxygen atoms of the carboxylate groups, the
Lewis basicity of the bridged H2O molecule increases. Hence, it is
presumed that formation of ‘strong’ hydrogen bonds stabilize the
dinuclear clusters. The cobalt complex 2a is found isomorphic in
structure with the nickel analogue (2) described above.
The adjacent [Cu2(l-tmb)4(CH3OH)2] units are linked by the ax-
ial methanol group through an intermolecular O–HÁÁÁO hydrogen
bond. The linkage forms eight-membered rings described by the
R22(8) graph-set motif. This linkage which associates the adjacent
units can also be represented as C22(8) chains. The combination of
these motifs results in the formation of a one-dimensional ribbon
structure lying in ab-plane and running along the a-axis, as shown
in Fig. 7.
The C–O distances in all the 2,4,6-trimethylbenzoate groups are
approximately equal ranging from 1.257(3) to 1.270(3) Å, indicat-
ing the distinct delocalization of their
p electrons [60]. The planes
of the two independent bridging 2,4,6-trimethylbenzoate groups
are orthogonal within experimental error. Due the presence of mu-
tual O–HÁÁÁO interaction between the Cu2(
l-tmb)4 neighbours, the
rotation of the Cu2( -tmb)4 core is sterically restricted by the adja-
l
cent unit. The methanol ligands form strong intermolecular hydro-
gen bond to the coordinating carboxylate oxygen atom (O4) with
dO5–H5AÁÁÁO4
z) = 2.830(3) Å and \ = 178(3)°. Also, there are
(xÀ1, y,
C–HÁÁÁO interactions present in the structure [dC19–H19CÁÁÁO2 (x, ÀyÀ1/
Compound 3 consists of centrosymmetric dinuclear paddle-
wheel units in which four 2,4,6-trimethylbenzoato groups are
bridging the two copper atoms, in a syn–syn disposition, and a
methanol molecule occupies the axial position of each copper
atom, coordinated to them through the oxygen atom. Fig. 6 shows
the ORTEP view of the dimer 3 with the atomic numbering scheme
(35% probability ellipsoids).
z+1/2) = 2.594 Å and \ = 179.02°, dC18–H18AÁÁÁO2 z) = 2.902 Å
2,
(x, y,
and \ = 144.98°], which play a significant role in stabilizing the
overall 3-D structure. The CuÁÁÁCu distance of 2.604 Å is comparable
to those found in other dimeric copper(II) carboxylates. [59] The
vibrational frequencies [61] for 1–3 are given in Table 4.
3.2. Electronic absorption spectra
Compound 3, is
a dimeric copper(II) complex [Cu2(l-
tmb)4(CH3OH)2]). Since the copper(II) ion is located on a crystallo-
The electronic spectrum for complexes 1–3 is shown in Fig. 11.
In the electronic spectrum for complex 1, the imidazole and 2,4,6-
trimethylbenzoate ligands exhibit energy bands at 284 nm region,
graphic inversion centre, the asymmetric unit is composed of half
of the complex [Cu2(l
-tmb)4(CH3OH)2]. Each CuII atom has a (reg-
ular within experimental error) five-coordinate square-pyramidal
environment, with the basal plane defined by the O atoms of four
bridging bidentate carboxylate groups of 2,4,6-trimethylbenzoate
ligands. The apical position is occupied by the O atom of methanol,
coordinating in an anti arrangement. The CuII atom deviates out of
which is generally assigned to p–
p* transition of the benzenoid
and/or (C@N) chromophore of the ligands. As a rule, the longer
wavelength bands in the spectra of metal complexes may be con-
sidered as evidence for the complex formation. The absorption
band at 533 nm due to the 4T1g ? 4T1g (P) transition, suggests a
high-spin octahedral sphere [62].
The electronic spectrum of the Ni(II) complex 1a shows two
absorption bands at 284 and 398 nm due to p–p
* transition caused
by the ligands and another band at 685 nm appears due to the
MLCT transitions, as generally observed for octahedral Ni(II)
complexes.
The electronic spectra of the nickel(II) complex 2 exhibits
absorption peaks at 287 nm, 410 nm, and 712 nm showing three
3
4
spin-allowed transitions in A2g(F) ? 3T2g(F), T1g(F) ? 4A2g(F)
and T1g(F) ? 4T1g(P) regions, which clearly indicated the octahe-
4
dral stereochemistry of the complexes. The cobalt(II) complex 2a
shows absorption peaks at 287 nm and 534 nm respectively corre-
sponding to p–
p* transition effected by the ligand and d–d transi-
tions (4T1g ? 4T1g (P)).
The copper(II) complex 3 shows absorption peaks at 303 nm
and 725 nm, respectively, subsequent to
by the ligand and d–d transitions.
p–
p* transition resulted
3.3. Thermogravimetric analysis
Thermal analysis (TGA) of complex 1 was performed between
room temperature and 700 °C under the nitrogen atmosphere.
The TGA results indicate that 1 (Fig. 8) undergoes a weight loss
of 24.2% due to the decomposition of two imidazole moieties
Fig. 6. Molecular structure 3 with atom labeling of the asymmetric unit and
coordination spheres of CuII. Symmetry code for A: Àx + 1, Ày, Àz.

42
M. Indrani et al. / Journal of Molecular Structure 931 (2009) 35–44
Fig. 7. A perspective view of 3 exhibiting the 1-D hydrogen-bonded chain extended along the [0 1 0] direction. A portion of trimethylphenyl groups of the ligands are omitted
for clarity.
(calculated 26.1%) in the temperature range of 246–290 °C. The
second stage occurs with the gradual decomposition of the two
2,4,6-trimethylbenzoate moieties leading to the formation of co-
balt oxide. There is no apparent weight loss beyond 575 °C.
The TGA curve of the nickel analogue (1a) exhibits similar
weight loss stages compared with 1.
ples. The effective magnetic moments of 1 and 1a are 4.7 and 2.8
B, being close to the expected values (4.3–5.2 and 2.9–3.9 lB
for the isolated high-spin Co(II) and Ni(II) (S = 5/2). A vM versus T
plot for 1 over the temperature range of 8.3–296.5 K (Fig. 9), in
which vM is the corrected magnetic susceptibility per Co(II) unit,
l
)
could be fitted according to the Curie–Weiss law
vM = C/(T–h),
The TGA results indicate that complex 2 (Fig. 8) loses 19.2% (cal-
culated 18.9%) of its mass in the temperature range of 98–121 °C,
corresponding to the loss of three coordinated and two lattice
water molecules. The second stage occurs with the gradual decom-
position of the two 2,4,6-trimethylbenzoate moieties at 295 °C
leading to the formation of nickel oxide. The saturation tempera-
ture above which there is no obvious weight loss occurs at
ꢀ370 °C.
Complex 3 (Fig. 8) loses 8.4% (calculated 7.5%) of its mass in the
temperature range of 78–114 °C, corresponding to the loss of two
coordinated methanol molecules. The second stage involves the
loss of 38.4% (calculated 38.6%) of its mass in the temperature
range of 221–268 °C corresponding to the loss of two tmb compo-
nents. The third stage occurs with the gradual decomposition of
the remaining two 2,4,6-trimethylbenzoate species, leading to
the formation of copper oxide. No obvious weight loss occurs
above 375 °C.
3.4. Magnetic properties
Temperature-dependent magnetic susceptibility measurements
for complexes 1 and 1a were performed on polycrystalline sam-
Fig. 8. TGA curves of 1–3.
Table 4
Infrared spectral data for 1–3.
Frequency range (cmÀ1
)
Mode of vibration
1
1a
2
2a
3
–
–
36213410 and 3200
36283404 and 3216
3397
O–Hstr (water)
N–Hstr
3133
3133
3061
3061
3027
2924 and 2857
1684 (free acid) 1526 and 1448
1404–1114
–
Aromatic C–Hstr
Aliphatic C–Hstr
2925 and 2857
1613 and 1539
1455–1039
758
2929 and 2863
1609 and 1531
1450–1038
754
2923 and 2857
1533 and 1446
1401–1113
–
2924 and 2856
1600 and 1440
1440–1028
–
COOÀ asymmetric and COOÀ symmetric stretching
aromatic C@C and/or C–N stretching vibrations
N–H out of plane bending
948 and 650
Below 600
1000 and 650
Below 600
851 and 820
Below 600
853 and 822
Below 600
754 and 846
Below 600
C–H out of plane bending
M–N and M–O stretching vibrations

M. Indrani et al. / Journal of Molecular Structure 931 (2009) 35–44
43
giving a Curie constant C = 3.20 cm3 molÀ1 K, and a Weiss constant
h = À8.13 K. The negative value of h indicates weak antiferromag-
netic interactions between Co(II), since the adjacent Co(II) ions
are separated with a distance of 8.936 Å as revealed by the X-ray
crystal structure. The vM value of 9.41 Â 10À3 cm3 molÀ1 at room
temperature increases as the temperature decreases, attaining
37.4 Â 10À3 cm3 molÀ1 at 8.3 K. A vM versus T plot for 1a over
the temperature range of 9.5–294.6 K (Fig. 10), in which vM is
the corrected magnetic susceptibility per Ni(II) unit, could be fitted
according to the Curie–Weiss law
vM = C/(T–h) giving a Curie con-
stant C = 0.7956 cm3 molÀ1 K and a Weiss constant h = À51 K. Sim-
ilarly, the negative value of
h indicates antiferromagnetic
interactions between Ni(II), since the adjacent Ni(II) ions are sepa-
rated by imidazole ligands with a distance of 8.913 Å. The vM value
2.8 Â 10À3 cm3 molÀ1 at room temperature increases as the tem-
perature decreases, attaining 56.39 Â 10À3 cm3 molÀ1 at 9.5 K.
3.5. Antibacterial activity
Fig. 9.
vM and vMT versus T plots for complex 1. The solid lines represent the best fit
of the experimental data.
The in vitro biological screening effects of 1–3 were tested
against the bacteria: Escherichia coli, Staphylococcus aureus, Pseudo-
monas aeruginosa, and Bacillus subtilis by the well-diffusion method
[63] using agar nutrient as the medium. The antifungal activities of
the compounds were 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 compounds were tested at a concentration of 50 lg/0.01 mL in
aqueous solution. In a typical procedure [64], 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 24 h for bacteria and 72 h for fungi at 35 °C. During
this period, the test solution diffused and the growth of the inocu-
lated microorganisms was affected. The concentration was noted
Table 5
Antibacterial activity of the complexes 1, 1a, 2, 2a and 3.
Complex
Bacterial species
a
b
c
d
e
[Co(imi)2(tmb)2]
[Ni(imi)2(tmb)2]
+ +
+ +
+ + +
+ + +
+ + +
+ ++
+ ++
+ +
+ +
+ +
++ +
+ ++
++
++
++
+ + +
+ + +
++
++
+++
+ +
+ +
++
++
++
Fig. 10.
fit of the experimental data.
vM and vMT versus T plots for complex 1a. The solid lines represent the best
{[Ni(tmb)2(H2O)3]Á2H2O}n
{[Co(tmb)2(H2O)3]Á2H2O}n
[Cu2(l-tmb)4(CH3OH)2]
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 6
Antifungal activity of the complexes 1, 1a, 2, 2a and 3.
Complex
Fungal species
a
b
c
[Co(imi)2(tmb)2]
[Ni(imi)2(tmb)2]
+ + +
+ + +
+ +
+ +
+ + +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
{[Ni(tmb)2(H2O)3]Á2H2O}n
{[Co(tmb)2(H2O)3]Á2H2O}n
[Cu2(l-tmb)4(CH3OH)2]
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%), (À), no inhibition zone. Percent inhibition
values 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.
Fig. 11. UV–vis absorption spectra of 1–3.

Indrani et al. / Journal of Molecular Structure 931 (2009) 35–44
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age diameter of bacteria or fungal growth on the test plate. The
susceptibility zones were measured in diameter (mm) and the re-
sults are shown in Tables 5 and 6. The susceptibility zones mea-
sured were 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-
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p-electrons over the whole
ligand and enhances the penetration of complexes into lipid mem-
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4. Conclusion
In summary, three new complexes, [Co(imi)2(tmb)2] (1),
{[Ni(tmb)2(H2O)3]Á2H2O}n (2) and [Cu2(
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were synthesized by hydrothermal reactions. Their structures were
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CCDC 689650, 689651, 689652, 689653 and 695666 contain the
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The authors (M.I. and R.R.) acknowledge CSIR, New Delhi for
providing financial support through Senior Research Fellowship.
Dr. F.R.F. acknowledges the Louisiana Board of Regents for the pur-
chase of the diffractometer by Grant No. LEQSF(1999–2000)-ENH-
TR-13.
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