168
C. Çelik et al. / Journal of Molecular Structure 985 (2011) 167–172
8300 FT-IR spectrophotometer. The electronic spectra in the
200–500 nm range were obtained on a Perkin Elmer Lambda 45
spectrophotometer. Molar conductance measurement of the Schiff
base ligand (L) was determined in methanol (ꢁ10ꢀ3 M) at room
temperature using a Jenway Model 4070 conductivity meter. Mass
spectrum of the ligand was recorded on an LC/MS APCI AGILENT
1100 MSD spectrophotometer. 1H and 13C NMR spectra were re-
corded on a Varian XL-200 instrument. TMS was used as internal
standard and d6-DMSO solvent.
positions [0.93–0.98 (CH) and 0.97 Å (CH2)] and treated as riding,
with Uiso(H) = 1.2Ueq(C) or 1.5Ueq(C7 and C14). The final cycle of
the refinement included 342 variable parameters R1 = 0.0595,
x
R2 = 0.1013 where x
= 1/[r2 (F2o) + (0.044 P)2 + 1.1428 P] where
P = (F2o + 2F2c )/3 were obtained. A summary of the key crystallo-
graphic information is given in Table 1.
3. Results and discussion
Cyclic voltammograms were recorded on a Iviumstat Electro-
chemical workstation equipped with a low current module (BAS
PA-1) recorder. The electrochemical cell was equipped with a
BAS glassy carbon working electrode (area 4.6 mm2), a platinum
coil auxiliary electrode and a Ag+/AgCl reference electrode filled
with NBu4BF4 (0.1 M) in DMF solvent and adjusted to 0.00 V vs
SCE. Cyclic voltammetric measurements were made at room tem-
perature in an undivided cell (BAS model C-3 cell stand) with a
platinum counter electrode and an Ag+/AgCl reference electrode
(BAS). All potentials are reported with respect to Ag+/AgCl. The
solutions were deoxygenated by passing dry nitrogen through
the solution for 30 min prior to the experiments, and during the
experiments the flow was maintained over the solution. Digital
simulations were performed using DigiSim 3.0 for windows (BAS,
Inc.). Experimental cyclic voltammograms used for the fitting pro-
cess had the background subtracted and were corrected electroni-
cally for ohmic drop.
The reaction of triethylenetetramine and 3,4-dichlorobenzalde-
hyde in 1:3 M ratio in methanol affords the
l-bis(tetradentate)
ligand (L) through the formation of an imidazolidine ring in place
of the ethylenediamine part of the parent tetradentate precursor.
This semi-rigid 3,4-dichlorophenyl-substituted five-membered
imidazolidine ring inside the ligand backbone acts as a spacer-
cum-bridging-cum-heterocyclic backbone unit. Synthesis of the
compound (L) had been achieved in a two step reaction which
was initiated by an inter-molecular nucleophilic attack on the
incoming 3,4-dichlorobenzaldehyde carbon atom by imine nitro-
gen of the parent tetradentate ligand as shown in Scheme 1. In
the second step of the reaction, the intra-molecular rearrangement
(via SN2 attack) takes place which finally introduces the imidazoli-
dine ring through an alkylating cyclization process centred on the
two secondary amine functions of the intermediate species. A plau-
sible mechanism for this reaction leading to the final ligand (L) is
given in Scheme 1. The analytical, spectroscopic and physical data
of the Schiff base ligand (L) are given in the experimental section.
The analytical data confirm that the 3,4-dichlorobenzaldehyde to
triethylenetetraamine ratio is 3:1. The ligand (L) is soluble in com-
mon polar organic solvents such as EtOH, MeOH, CHCl3, and
CH2Cl2. The ligand (L) is a very stable solid at room temperature
without decomposition. The ligand (L) was obtained as light yellow
crystals with 80% yield. This yield was a normal value for the Schiff
base ligand. The low molar conductance value (experimental
section) of 1 ꢂ 10ꢀ3 M solution in methanol showed to be non-
electrolytes [22]. From the methanol solution, we obtained suitable
single crystals for X-ray diffraction analysis.
2.2. Preparation of the ligand (L)
A solution of triethylenetetramine (0.146 g, 1.00 mmol) in
methanol (15 ml) was added drop wise to an ice cold methanolic
solution (30 ml) of 3,4-dichlorobenzaldehyde (0.525 g, 3.00 mmol)
with stirring the yellow solution was stirred for 1 h and the solvent
was evaporated in air. The yellow solid was separated by filtration
through G4 sintered bed and washed thoroughly with hexane and
water. Finally, the isolated compound was dried in vacuo over
P4O10. Single crystals of the ligand (L) were obtained by recrystal-
lization from CH3OH solution.
The 1H- and 13C NMR spectra of the ligand (L) were recorded
using DMSO-d6 as a solvent, and the spectral data are given in
L: Yield: 80%, color: light yellow, m.p. 81–83 °C. Analysis Calc.
for C27H24Cl6N4: C, 52.54; H, 3.92; N, 9.08%. Found: C, 52.56; H,
3.95; N, 9.10%. Mass spectrum (LC/MS APCI): m/z 617 (M+@L+).
Infrared spectrum (cmꢀ1, KBr disc): 2960, 2845
m
(CH2), 1625
m
max, Mꢀ1 cmꢀ1), CH3OH as solvent):
Table 1
(CH@N). UV–Vis: (kmax, nm;
e
Crystal data and structure refinement for the title compound.
342 (1805), 315 (1900), 286 (1.6 ꢂ 10ꢀ3), 250 (7.2 ꢂ 10ꢀ3). 1H
NMR: (DMSO-d6 as solvent, d in ppm): 2.4 (4H, m, H8 and H13),
2.7 (4H, m, H9 and H12), 3.44 (4H, m, H10 and H11), 3.75 (H, m,
H21), 7.23–7.29 (4H, m, H1, H2, H19 and H20), 7.34–7.36 (2H, m,
H5 and H16), 7.66–7.67 (3H, m, H23, H26 and H27), 8.25 (2H, s,
H7 and H14). 13C NMR (DMSO-d6 as solvent, d in ppm): 51.80
(C8 and C13), 53.35 (C9 and C12), 60.61 (C10 and C11), 89.60
(C21), 96.14 (C6 and C15), 104.15 (C22), 110.70 (C5 and C16),
11.20 (C1 and C20), 117.40 (C2 and C19), 119.40 (C23), 126.35
(C26 and C27), 143.10–144.81 (C3, C4, C17, C18, C24 and C25),
Empirical formula
Formula weight
Temperature
C27H24Cl6N4
617.20
296(2) K
Wavelength
0.71073 Å
Crystal system, space group
Cell dimensions
Monoclinic, P 21/c
a = 6.056(10) Å
b = 20.546(3) Å
c = 22.270(4) Å
b = 91.179(3)o
2771(5) Å3
Cell volume
Z
4
(1 ꢂ 10ꢀ3 M): 1.5
X .
ꢀ1 cm2 molꢀ1
Density (calculated)
Absorption coefficient
F000
1.480 mg/m3
0.646 mmꢀ1
163.50 (C7 and C14).
K
1264
2.3. X-ray structure solution and refinement for the Schiff
base ligand (L)
Crystal size
h(°) range for data collection
Index ranges
0.34 ꢂ 0.25 ꢂ 0.16 mm
1.35–28.37
ꢀ8 6 h 6 8
ꢀ27 6 k 6 27
ꢀ29 6 l 6 29
27657/6897 [R(int) = 0.0458]
Full-matrix least-squares on F2
6897/0/342
A
block colorless crystal with dimensions 0.34 ꢂ 0.25 ꢂ
0.16 mm was chosen for the structure determination. Diffraction
experiment was carried out at 150(2) K on a Bruker APEX-II CCD
diffractometer. The structure was solved by SHELXS-97 [20] and
refined by SHELXL-97 [21] software package. The H atom on C7
and C14 were located in difference maps and their coordinates
and Uiso values were refined freely. In the final stage of refinement,
Reflections collected/unique
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
1.025
Final R indices [I > 2
Largest diff. peak and hole
CCDC deposition number
r
(I)]
R1 = 0.0413, wR2 = 0.0935
0.318 and ꢀ0.263 eÅꢀ3
740397
the other
H atoms were located in geometrically idealized