Coordination of a mesogenic Schiff-base with MnII, CoII, NiII, CuII and ZnII: Synthesis, spectral studies and crystal structures

Article abstract of DOI:10.1016/j.poly.2008.09.013

A novel mesogenic (nematic) Schiff-base, N,N′-di-4-(4′-pentyloxybenzoate)salicylidene diaminoethane, H₂dpbsde (abbreviated as H₂L⁵) was synthesized and its structure studied. The Schiff-base crystallizes in the non-centrosymmetric space group Pna2₁ with Z = 4, and the mesogenic isomorphous nickel and copper complexes, [NiL⁵]₂ and [CuL⁵], in the centrosymmetric space group P2₁/c with Z = 4. The (L⁵)^2- species coordinates to the metal ions through two phenolate oxygens and two azomethine nitrogens. Both the [NiL⁵]₂ and [CuL⁵] complexes involve cis-MN₂O₂ planes; the former complex has a low-spin distorted square-pyramidal geometry with a Ni-Ni bonding of 3.337 ? and the latter, a square-planar geometry.

Full text of DOI:10.1016/j.poly.2008.09.013

Polyhedron 27 (2008) 3710–3716
Contents lists available at ScienceDirect
Polyhedron
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Coordination of a mesogenic Schiff-base with MnII, CoII, NiII, CuII and ZnII:
Synthesis, spectral studies and crystal structures
Angad Kumar Singh a, Sanyucta Kumari a, T.N. Guru Row b, Jai Prakash b, K. Ravi Kumar c, B. Sridhar c,
T.R. Rao a,
*
a Department of Chemistry, Banaras Hindu University, Varanasi 221005, India
b Indian Institute of Science, Bangalore 560012, India
c Indian Institute of Chemical Technology, Tarnaka, Hyderabad 500 007, India
a r t i c l e i n f o
a b s t r a c t
A novel mesogenic (nematic) Schiff-base, N,N0-di-4-(40-pentyloxybenzoate)salicylidene diaminoethane,
H2dpbsde (abbreviated as H2L5) was synthesized and its structure studied. The Schiff-base crystallizes
in the non-centrosymmetric space group Pna21 with Z = 4, and the mesogenic isomorphous nickel and
copper complexes, [NiL5]2 and [CuL5], in the centrosymmetric space group P21/c with Z = 4. The (L5)2ꢀ
species coordinates to the metal ions through two phenolate oxygens and two azomethine nitrogens.
Both the [NiL5]2 and [CuL5] complexes involve cis-MN2O2 planes; the former complex has a low-spin
distorted square-pyramidal geometry with a Ni–Ni bonding of 3.337 Å and the latter, a square-planar
geometry.
Article history:
Received 2 July 2008
Accepted 13 September 2008
Available online 7 November 2008
Keywords:
Mesogenic Schiff-base
Low-spin distorted square-pyramidal NiII
complex
Ó 2008 Elsevier Ltd. All rights reserved.
Crystal structures
Square-planar complexes of CoII and CuII
1. Introduction
2. Experimental
2.1. Starting materials
Liquid crystals with transition-metal core groups, called metall-
omesogens, have attracted increasing attention because of the pos-
sibility of combining the physico-chemical properties of the metal
(color, magnetism, polarizability, redox behaviour etc.) with those
of the organic framework [1–8]. Thus, the synthesis and study of
metallomesogens has been a very active area of research for more
than 20 years and different approaches have been adopted in order
to accommodate different metal centres [9,10]. A major distinction
between metallomesogens and organic mesogens is the greater
tendency in the former type to exhibit intermolecular dative coor-
dination in the solid state [11]. The major part of the metallomes-
ogens extensively studied includes those complexes derived from
salicylaldimine Schiff-bases [12–14]. As a part of our systematic
investigation [15–18] on structural and spectroscopic studies of
3d metal complexes of a series of mesogenic salicylaldimine
Schiff-base derivatives, we report here the results of our investiga-
tion on the synthesis, spectroscopic studies and crystal structures
of the mesogenic Schiff-base, N,N0-di-4-(40-pentyloxybenzoate)sal-
icylidene diaminoethane (H2L5), and the corresponding 3d metal
complexes.
All reagents were purchased from commercial sources and were
used as received: 4-hydroxy benzoic acid, 1-bromopentane, 2,4-
dihydroxybenzaldehyde, N,N0-dicyclohexylcarbodiimide (DCC),
N,N-dimethylaminopyridine (DMAP) and 1,2-diaminoethane are
from Sigma–Aldrich, USA; all metal acetates and KOH are from
Merck. The solvents received were dried using standard methods
[19] when required.
2.2. Instrumentation
The 1H and 13C NMR spectra were recorded on a JEOL AL-
300 MHz FT-NMR multinuclear spectrometer. C, H and N contents
were microanalyzed on an Elemental Vario EL III Carlo Erba 1108
analyzer. Infrared spectra were recorded on a JASCO FT/IR (mod-
el-5300) spectrophotometer in the 4000–400 cmꢀ1 region. Elec-
tronic spectra of the complexes in chloroform solutions were
recorded on a Shimadzu spectrophotometer, model Pharmaspec
UV-1700. The mass spectra were recorded on JEOL SX-102 (EI/
FAB) mass spectrometers. Magnetic susceptibility measurements
were made at room temperature on a Cahn-Faraday balance.
2.3. X-ray crystallographic data collection and refinement of the structure
X-ray data for the compounds H2L5 [jpl5], [NiL5]2 [jpni1] and
[CuL5] [ac27] were collected using a Bruker AXS SMART APEX
* Corresponding author. Tel.: +91 542 2307326; fax: +91 542 2368127.
E-mail address: drtrrao@gmail.com (T.R. Rao).
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.09.013

A.K. Singh et al. / Polyhedron 27 (2008) 3710–3716
3711
CCD diffractometer using graphite monochromated Mo
(k = 0.7107 Å) radiation and the intensities were measured using
the scan method. Preliminary lattice parameters and orientation
K
a
line product was suction-filtered, thoroughly washed with cold
ethanol, recrystallized from a solution of absolute ethanol/chloro-
form (v/v, 1/1) and dried at room temperature; yield: 12.76 g
(75%) as a yellow solid; mp 230 °C. Calc. for C40H44N2O8 (680.31):
C, 70.57; H, 6.51; N, 4.11. Found: C, 70.53; H, 6.53; N, 4.13%.
x
matrices were obtained from four sets of frames. Unit cell dimen-
sions were determined from the setting angles of 6903 reflections
in the range 2.17° < h < 25.79°. Integration and scaling of intensity
data was accomplished using the SAINT program [20]. The structure
was solved by direct methods using SHELXS97 [21] and refinement
was carried out by full-matrix least-squares techniques using SHEL-
XL97 [21]. Anisotropic displacement parameters were included for
all non-hydrogen atoms. The side chain atoms were disordered
and refined with site-occupation factors of 0.563(7) and 0.437(7).
The geometries of the disordered atoms were refined with distance
restraints. The displacement parameters of the disordered atoms
were restrained with SIMU and DELU commands.
2.4.2. Synthesis of the MnII complex
Yield: 0.50 g (68%) as a brown coloured solid; mp 200 °C
(decomposes). Calc. for C40H42MnN2O8 (733.71): C, 65.48; H,
5.77; N, 3.82; Mn, 7.49. Found: C, 65.50; H, 5.74; N, 3.80; Mn,
7.52%.
2.4.3. CoII complex
Yield: 0.52 g (70%) as an olive green solid; mp 210 °C (decom-
poses). Calc. for C40H42CoN2O8 (737.70): C, 65.12; H, 5.74; N,
3.80; Co, 7.99. Found: C, 65.15; H, 5.72; N, 3.81; Co, 8.01%.
2.4. Synthesis and analyses
2.4.4. NiII complex
N,N0-Di-4-(40-pentyloxybenzoate)salicylidene diaminoethane, 3
(Scheme 1), was synthesized from the precursor materials 1 and 2,
as reported earlier [15,16]. The [ML5] (M = Mn, Co, Ni, Cu and Zn)
complexes were prepared by refluxing solutions of the Schiff-base
H2L5 and the corresponding metal acetate in a 1:1 molar ratio in
dichloromethane/ethanol medium for ꢁ2 h at 80 °C. The reaction
mixture was left overnight in the flask, closed with a guard tube.
The solid complex that separated out in each case was filtered un-
der suction and washed repeatedly with cold ethanol and dried
over fused CaCl2 in a desiccator.
Yield: 0.58 g (79%) as a dark orange solid; mp 255 °C. Calc. for
C40H42N2O8Ni (737.46): C, 65.15; H, 5.74; N, 3.80; Ni, 7.96. Found:
C, 65.27; H, 5.80; N, 3.85; Ni, 8.01%.
2.4.5. CuII complex
Yield 0.52 g (70%) as a violet solid; mp 260 °C. Calc. for
C40H42N2O8Cu (742.32): C, 64.72; H, 5.70; N, 3.77; Cu, 8.56. Found:
C, 64.77; H, 5.72; N, 3.80; Cu, 8.53%.
2.4.6. ZnII complex
Yield 0.48 g (65%) as a white solid; mp 140 °C. Calc. for
C40H42N2O8Zn (744.16): C, 64.56; H, 5.69; N, 3.76; Zn, 8.79. Found:
C, 64.57; H, 5.71; N, 3.77; Zn, 8.78%.
2.4.1. Synthesis of N,N0-di-4-(40-pentyloxybenzoate)salicylidene
diaminoethane, H2L5
N,N0-Di-4-(40-pentyloxybenzoate)salicylidene diaminoethane,
H2L5, was prepared by mixing together absolute ethanolic solu-
tions of 4-pentyloxy-(40-formyl-30-hydroxy)benzoate (16.42 g,
50 mmol, in 100 mL) and 1,2-diaminoethane (1.9 mL, 25 mmol in
10 mL) and magnetically stirring for ꢁ1 h in the presence of a
few drops of acetic acid and leaving the resultant solution over-
night in the reaction flask at room temperature. The micro-crystal-
3. Results and discussion
3.1. Physical properties and spectral investigation
The Schiff-base ligand H2L5 as well as the metal complexes are
soluble in chloroform, dichloromethane, DMF and DMSO, but are
Ethanol, KOH, Reflux, 14h
dry atmosphere; 6 N HCl / H3O+
H2O
C5H11Br
KBr
C5H11O
COOH
HO
COOH
1
DCC, DMAP
C5H11O
COOH
HO
CHO
Dry CHCl3, Stirring ~12 h at RT
OH
O
O
C5H11O
CHO
H2O
2
OH
O
O
C5H11O
2
EtOH, AcOH
NH2
H2N
CHO
Reflux ~4h, dry atmosphere
1"'
3"'
5"'
OH
O
4'
2"'
4"'
O
O
OH
5'
6'
3'
2'
H
6
3
1''
N
5
N
1
1'
2''
4
H
2
HO
O
O
3
O
Scheme 1. Synthetic steps involved in the synthesis of 1 (p-pentyloxybenzoic acid), 2 (4-pentyloxy-(40-formyl-30-hydroxy)benzoate) and 3 (N,N0-di-4-(40-pentyloxy
benzoate)salicylidene diaminoethane, H2L5.

3712
A.K. Singh et al. / Polyhedron 27 (2008) 3710–3716
Table 2
insoluble in water, methanol, ethanol and acetonitrile. The struc-
ture and purity of the parent ligand and the complexes were
checked and confirmed by elemental analyses, IR, 1H and 13C
NMR and FAB mass spectra. The mass spectral features of H2L5
were characterized by the base peak (m/e = 191 corresponding to
the fragment C5H11O–Ph–CO+), and the molecular ion peak (m/
e = 681) with ꢁ72% intensity, and those of ML5 (M = MnII, CoII, NiII
and CuII) by the base peak (m/e = 121 corresponding to the frag-
ment, HO–Ph–CO+) and the molecular ion peak (m/e = 734, 737,
737 and 742, respectively) with ꢁ92–98% intensity. Further, addi-
tional peaks (corresponding to the formation of dimeric units)
were observed in the FAB mass spectra of the MnII, CoII and NiII
complexes; based on the decomposition behaviour of the former
two complexes, they may be presumed to be polymeric, which
upon bond rupture under the experimental conditions might give
rise to dimeric units. A comparison of the 1H and 13C{1H} NMR
spectral data of the ligand with those of the diamagnetic NiII and
ZnII complexes shows the absence of the phenolic-OH signal
Crystal structure data and structure refinement parameters
Details
Ligand, H2L5 [jpl5] [NiL5]2 [jpni1] [CuL5] [ac27]
Formula
FW
Crystal system
Space group
a (Å)
C40H44N2O8
680.77
Orthorhombic
Pna21
C40H42N2O9Ni C40H43N2O9Cu
737.47
759.30
Monoclinic
P21/c
Monoclinic
P21/c
20.573(4)
5.868(1)
29.867(7)
90
3605.8(13)
4
17.8641(19)
18.6864(19)
11.4267(12)
104.004(2)
3701.0(7)
4
17.7902(12)
18.7711(13)
11.4585(8)
104.355(1)
3707.0(4)
4
b (Å)
c (Å)
b (°)
V (Å3)
Z
qcalc (g/cm3)
1.254
1.324
1.361
l(Mo K
a
(I)]
) (mmꢀ1
)
0.087
0.579
0.647
R [I > 2
r
0.0637
0.1468
1.027
0.0588
0.0924
1.053
0.0449
0.0547
1.061
Rw
Goodness-of-fit
F(000)
2h Range (°)
Range of h, k, l
1448
1552
1592
1.98–25.00
ꢀ24, 23
ꢀ6, 6
1.17–25.00
ꢀ21, 21
ꢀ21, 22
ꢀ13, 13
26479
1.18–25.00
ꢀ21, 21
ꢀ22, 22
ꢀ13, 13
35252
(13.537 ppm) and
a significant shift (8.358 to 7.195 and
ꢀ35, 35
8.458 ppm, respectively) in the peak position for –N@CH in the
spectra of the metal complexes, which implies bonding through
the phenolate anion and azomethine nitrogen atom [22] of the li-
gand. Similar shifts observed in the 13C{1H} NMR spectra were of
considerable magnitude in the case of the carbon atoms directly at-
tached to the bonding atoms. Thus, the NMR spectral data imply a
tetra-dentate bonding of (L5)2ꢀ through the two ˜C@N groups and
two phenolate oxygen atoms. In the IR spectrum of H2L5 the broad
Total number of reflections 24264
Unique reflections
Number of parameters
wR2_all
3228
6517
6537
461
524
524
0.1680
0.1296
0.296, ꢀ0.248
0.1673
0.1472
0.1419
0.1299
wR2_obs
D
qmax
,
D
qmin (e Åꢀ3
)
0.604, ꢀ0.485 0.723, ꢀ0.466
absorptions centred at 3443 cmꢀ1 may be assigned to the
H)phenolic vibration, and further the strong bands occurring at
1740 and 1255 cmꢀ1 may be assigned [23] to
(˜C@O) and (C–
O) modes of the aromatic ester; the band occurring at 1628 cmꢀ1
may be due to the (C@N) absorption of the azomethine moiety.
m(O–
m
(M–N) [25,26]. Coordination through the phenolate oxygen to
the metal ion is implied by the shifts of the (C–O) band in the
complexes [27] and by the appearance of new bands, assignable
to
(M–O), in the 440–448 cmꢀ1 region in the spectra of the
complexes.
The room temperature magnetic moments and electronic spec-
m
m
m
m
m
These bands are shifted to lower frequencies in the complexes,
indicating that the nitrogen atom of the azomethine group is coor-
dinated to the metal ion [24]. Coordination through one of the
nitrogen atoms of the ligand is also implied by the appearance of
a new band (468–472 cmꢀ1) in the complexes, assignable to
tral data of the present complexes are included in Table 1 while the
spectra of the complexes of CoII, NiII and CuII are shown in Fig. 1.
The overall geometry assigned to the metal ion is based not only
on the
l
eff values and the nature of the electronic spectra, but also
Table 1
Magnetic and electronic spectral dataa of the complexes of H2L5
Complex
Colour
leff (B.M)
d–d transitions (nm)
Transition
Assignment
Ground state(s)
Excited state(s)
[MnL5]n
[CoL5]n
[NiL5]2
[CuL5]
Brown
5.85
3.52
Diamag
2.74
317, 260
974, 895, 860
530, 406
562
6A1g
2Eg
4A2g(F); 4Eg(D)
2A1
Octahedral with M–M bonding
Olive green
Dark orange
Violet
Octahedral with M–M bonding (l.s.)
Square-pyramidal (M–M bondingb of 3.337 Å)
Sq. planar (M–M distanceb of 3.457 Å)
1A1
1E; 1A2
x2–y2
xz, yz
a
Spectra recorded in chloroform solutions.
Vide single crystal structure data.
b
Fig. 1. Absorption spectra of: (a) [CoL5], (b) [NiL5]2 and (c) [CuL5].

A.K. Singh et al. / Polyhedron 27 (2008) 3710–3716
3713
on the denticity of the ligand (vide IR and NMR) and the number of
such ligands coordinated to the metal ion (vide elemental analy-
ses). Although the leff values imply ferromagnetic type interac-
tions in the MnII, CoII and CuII complexes, no concrete conclusion
to this effect could be drawn in the absence of variable tempera-
ture magnetic moment data. The [MnL5]n complex gives rise to ex-
tremely weak bands in the electronic spectrum, presumably with
an octahedral environment (square-planar units polymerically
Fig. 2. The asymmetric unit of H2L5, with the atom numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. H atoms are shown as small spheres of
arbitrary radii. Hydrogen bonds are shown as dashed lines.
Fig. 3. The asymmetric unit of the isomorphous complexes [ML5] [M = Ni or Cu] with the atom numbering scheme. Displacement ellipsoids are drawn at the 30% probability
level. The disordered atoms of the minor component (C161 and C361/C371/C381/C391/C401) have been omitted for clarity.
Fig. 4. A view of H2L5 molecules in the crystal lattice showing [C–HꢂꢂꢂO] intermolecular interactions along the b axis.

3714
A.K. Singh et al. / Polyhedron 27 (2008) 3710–3716
connected with M–M bonding) for the metal ion. The spectrum of
the [CoL5]n complex shows bands at 860, 895 and 974 nm which
may be assigned to the transition(s) from the 2Eg ground state to
the 2A1 excited state in an octahedral (low-spin) environment
around the metal ion [28]. The electronic spectrum of the [NiL5]2
complex shows two absorptions at 406 and 530 nm which may
be assigned to the 1E and 1A2 excited states from the 1A1 ground
state in a low-spin square-pyramidal environment of the diamag-
netic metal ion [28]. The spectrum of [CuL5] shows a single band
at 562 nm, assignable to the transition from the xz, yz ground state
to the x2–y2 excited state in a square-planar environment [28].
The Schiff-base crystallizes in the non-centrosymmetric space
group Pna21 with Z = 4. The conformation of the ligand (Fig. 2) pre-
sents several interesting features: the molecule prefers to be as an
extended linear conformation with all trans central linkages; the
angle between the two six-membered rings adjacent to the central
linkage is 0.39° (nearly planar); however, the angle between the
adjacent rings in each flank is 52.50° (avg.); the extended arms
of the aliphatic chains show large thermal vibrations compared
to the central atoms, typical of any such molecule. Table 3 provides
the details of the short intramolecular contacts while Fig. 4 repre-
sents a section of the intermolecular space, highlighting the C–
HꢂꢂꢂO–H bond regions.
3.2. Crystal structure and molecular association
Both the isomorphic nickel and copper complexes [NiL5]2 and
[CuL5] crystallize in the centrosymmetric space group P21/c with
The crystal data and structure refinement details for H2L,5
[NiL5]2 and [CuL5] are given in Table 2. The molecular structure
and atomic labelling scheme of the ligand and its nickel and copper
complexes are as shown in Figs. 2 and 3, respectively, while their
packing diagrams are shown in Figs. 5, 6 and 8.
Fig. 7. A view of the [NiL5]2 molecule in the crystal lattice showing [C–HꢂꢂꢂO] inter
Fig. 5. Packing diagram of H2L5 showing intra molecular interactions along the c
axis.
molecular interactions.
Fig. 6. Packing of molecules in the unit cell of [NiL5]2.
Fig. 8. Packing of molecules in the unit cell of [CuL5] along the b axis.

A.K. Singh et al. / Polyhedron 27 (2008) 3710–3716
3715
Table 3
Table 5
Intramolecular hydrogen bonding data of H2L5
Transition temperatures and enthalpy changes of H2L5 and of the [NiL5]2 and [CuL5]
complexes
D–HꢂꢂꢂA
O1–H1O...N1
O5–H5O...N2
D–H (Å)
HꢂꢂꢂA (Å)
DꢂꢂꢂA (Å)
D–HꢂꢂꢂA (°)
147(7)
137(9)
Symmetry
Compound
H2L5
Transitiona
Tb (°C)
dHb (kJ molꢀ1
)
0.87(7)
0.86(9)
1.81(7)
1.88(10)
2.582(10)
2.576(10)
x,y,z
x,y,z
Cr–N
N–I
I–N
Cr–Cr
Cr–N
N–Ic (dec.)
Cr–Cr
Cr–N
N–Ic
174.81
229.30
216.04
144.72
245.09
255.00
136.21
224.94
260.50
199.84
35.06
10.81
1.69
8.79
19.52
[NiL5]2
[CuL5]
Table 4
Selected bond lengths (Å) and bond angles (°) of the isomorphous [NiL5]2 and [CuL5]a
10.07
20.25
complexes
M1–O1
M1–O2
O1–M1–O2
O1–M1–N1
O2–M1–N1
1.850(3) [1.8988(18)]
1.848(3) [1.8956(17)]
84.9(1) [88.95(8)]
94.6(2) [93.23(8)]
177.2(2) [175.19(9)]
M1–N1
M1–N2
O1–M1–N2
O2–M1–N2
N2–M1–N1
1.860(3) [1.933(2)]
1.846(4) [1.939(2)]
178.0(2) [175.17(9)]
94.7(1) [ 93.73(8)]
85.9(2) [84.40(9)]
N–Cr
5.39
a
Cr: Crystal, N: Nematic, I: Isotropic liquid.
Data as obtained from the first DSC cycle.
b
a
The data for [CuL5] are given in square brackets.
six-membered rings in one flank is 88.04° while in the other it is
56.82°. The angle between the planes containing the C24, O2, Ni1
and N2 atoms and C5, O1, Ni1 and N1 atoms is 2.74°. The Ni atom
is penta-coordinated with a Ni–Ni metal bond of 3.336 Å; the distor-
tion of the square base from planarity is quite negligible since the
angles between the diagonal atoms of the square base are close to
180° (N2NiO1: 177.83 and N1NiO2: 177.17) in both the planes of
the dimeric unit. Fig. 7 shows the packing features of [NiL5]2 along
with the intermolecular interactions.
Z = 4 and the ORTEP diagram is shown in Fig. 3. It appears that the
ligand takes up an entirely different conformation, effectively gen-
erating a ‘‘V” shaped molecular unit. The coordination around NiII
is believed to be a distorted square-pyramidal environment, gener-
ating a tricyclic moiety, while that around CuII is considered to be
square-planar with a cis-conformation, which may be invoked on
the basis of the four adjacent bond angles around the metal ion
which are close to 90° (84.40(9), 88.95(8), 93.23(8), 93.73(8)) and
the angles between the diagonal atoms of the square plane are
close to 180° (175.19(9), 175.17(9)).
Table 4 describes the conformational features of the isomor-
phous NiII and CuII complexes. The angle between the two six-mem-
bered rings nearest to Ni is 2.92° while such an angle on the outside
flanks is 73.81°. As expected, the thermal ellipsoids are once again
large on the terminal chain atoms on either side. It is noteworthy
that the conformations of the two flanks are different from each
other, with one of the flanks displaying an intramolecular C–HꢂꢂꢂO
interaction (C10–H10ꢂꢂꢂO3). Also, the angle between the adjacent
The mesogenic nature of the ligand (H2L5) as well as the [NiL5]2 and
[CuL5] complexes has been studied by two methods, using polarized
optical microscopy and differential scanning calorimetry (DSC); the
introduction of the metal ion into the metal-coordination sphere, as
expected, resulted in the elevation of the transition temperature,
melting and clearing points. The assignment of the mesophase (nema-
tic) in each case is on the basis of the optical textures (Fig. 9a–c) and the
DSC thermograms (Fig. 10a–c). The details of the transition tempera-
tures, enthalpy changes and the mesophases of H2L5, [NiL5] and [CuL5]
are given in Table 5. However, no such mesogenic property was ob-
served with the complexes of MnII, CoII and ZnII.
Fig. 9. Optical textures of: (a) H2L5 at 210 °C (b) [NiL5]2 at 252 °C and (c) [CuL5] at 245 °C.
Fig. 10. DSC thermograms of: (a) H2L5 (b) [NiL5]2 and (c) [CuL5].

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A.K. Singh et al. / Polyhedron 27 (2008) 3710–3716
[5] P. Kirsch, M. Bremer, Angew. Chem., Int. Ed. Engl. 39 (2000) 4216.
4. Conclusion
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The mesogenic (nematic) Schiff-base N,N0-di-(40-pentyloxybenzo-
ate)salicylidene diaminoethane (H2L5) coordinates to MnII, CoII, NiII,
CuII and ZnII to yield the isomorphous mesogenic (nematic) NiII, CuII
complexes and the non-mesogenic MnII, CoII, ZnII complexes. The
Schiff-base crystallizes in the non-centrosymmetric space group
Pna21 with Z = 4 and the nickel and copper complexes, [NiL5]2 and
[CuL5], inthe centrosymmetric space group P21/c, with Z = 4. The coor-
dination geometry around NiII is low-spin distorted square-pyramidal
(cis-NiN2O2) while that of the CuII complex is square-planar with a cis-
CuN2O2 configuration.
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We wish to acknowledge the recording of FAB mass spectra and
elemental analyses at the Central Drug Research Institute, Luc-
know, India. One of the authors, T.R. Rao, gratefully acknowledges
the financial grant received from the Council of Scientific & Indus-
trial Research, New Delhi [vide Grant No. 01(1834)/03/EMR-II], the
University Grants Commission, New Delhi [vide grant No. F.12-26/
2003 (SR)] and the Department of Science and Technology, New
Delhi [vide Grant No. SR/S1/IC-26/2004].
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crystallographic data for this paper. These data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
ing.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.2008.09.013.
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