I.M. Khan, A. Ahmad / Journal of Molecular Structure 1050 (2013) 122–127
123
the above mentioned potentials of
L
-tartaric acid, many H-bonded
1.2
(C)
CT complexes of it and other acceptors with organic bases were re-
ported [29–42] and some of them were deposited in the CCDC [43].
Here-in, we report for the first time, to the best of our knowl-
edge, new 1:1 H-bonded complex [(OPD)+(TART)ꢁ] of o-phenylene-
diamine with tartaric acid. The 1:1 H-bonded complex was
synthesized and characterized by absorption spectra, elemental
analysis, FTIR, 1H NMR, and single-crystal X-ray studies. The aim
of the work is to determine the reaction stoichiometry, formation
(C) Donor
(B) CT Complex
(A) Acceptor
1.0
0.8
0.6
0.4
0.2
0.0
(B)
constant (KCT), molar extinction coefficient (
eCT), free energy
(A)
(D
G°), and also transition energy (ECT) of the H-bonded complex
by using Benesi–Hildebrand equation. H-bonded complex was
investigated in both solution and solid state and the nature of these
interactions was interpreted using above mentioned spectral
techniques.
250
300
350
400
450
Wavelength, nm
Fig. 1. Electronic absorption spectra of (A)
L
-tartaric acid, Acceptor (1 ꢃ 10ꢁ4 M);
(B) Donor–Acceptor CT complex and (C) o-phenylenediamine, Donor (1 ꢃ 10ꢁ4 M),
2. Experimental
in methanol at room temperature.
2.1. Materials
0.00024
0.00022
0.00020
0.00018
0.00016
0.00014
0.00012
0.00010
0.00008
0.00006
0.00004
0.00002
Analytical grade o-phenylenediamine and L-tartaric acid were
employed for the synthesis of H-bonded complexes. Methanol, ace-
tonitrile and DMSO were taken as HPLC grade.
2.2. Synthesis of H-bonded complex
The solid [(OPD)+(TART)ꢁ] was prepared by mixing the satu-
rated solution of OPD (0.108 g, 1 mmol) in acetonitrile (25 ml) with
saturated solution of TART (0.636 g, 1 mmol) also in acetonitrile. A
pink color solution was formed upon the mixing and continuous
stirring of these two reactants produced pink precipitate. The pre-
cipitate was filtered off and washed several times with small
amounts (5 ml) of acetonitrile and dried under vacuum over CaCl2.
The melting point and transition energy of H-bonded complex
were found to be >300 °C and 4.6061 eV, respectively. The result
of the elemental analysis of the H-bonded complex is given as:
(theoretical values are shown in brackets): [(OPD)+(TART)ꢁ],
(C10H14N2O6) H-bonded complex (M/w: 258.23 g): C, 46.51%
(47.00%); H, 5.42% (5.40%); N, 32.57% (32.77%).
0
1
2
3
4
5
6
7
8
1/[D] x 103
Fig. 2. Benesi–Hildebrand plots of charge transfer complex of o-phenylenediamine
with -tartaric acid, [D]o/A vs. 1/[A]o in methanol at room temperature.
L
2.3. Single crystal growth
Table 1
The electronic absorption spectral data for [(OPD)+(TART)ꢁ] CT complex of OPD with
TART in methanol at room temperature.
A saturated solution of the synthesized title complex [(OPD)+
(TART)ꢁ] was prepared in methanol, stirred well for about 1 h
and heated slightly to dissolve well. Then the solution was filtered
through a Whatmann: 41 grade filter paper to remove the sus-
pended impurities. The clear filtrate was collected in 50 ml conical
flask and kept unperturbed in a dust free chamber for the growth
of single crystal of the [(OPD)+(TART)ꢁ]. Well defined, bright col-
ored, transparent and needle shaped crystals were harvested at
the end of the fifth day.
Concentration
of donor
Concentration
of acceptor
(M)
Absorbance
at kCT
238 nm
Formation
constant
Molar
extinction
coefficient
(ꢃ10ꢁ4 M)
(KCT
)
l molꢁ1
(
eCT)
l cmꢁ1 molꢁ1
1.50
2.00
2.77
10.00
15.00
1 ꢃ 10ꢁ4
0.481
0.588
0.769
1.609
2.023
1.337 ꢃ 103 2.842 ꢃ 105
2.4. Spectrophotometric analyses
When 3 ml solution each of the acceptor and the donor were
mixed, a charge transfer complex was formed. The wavelength of
maximum absorption of the resulting solution was determined.
The H-bonded complex of the 1:1 reaction mixture was kept over
night at room temperature to form stable complexes, were ana-
lyzed as shown in Fig. 3. The maximum wavelength of the charge
transfer complex was determined by spectrophotometer to be
270 nm. The concentration of acceptor (TART) in the reaction mix-
ture was maintained at 1.0 ꢃ 10ꢁ4 M, whereas the concentration of
the donor (OPD) changed over a wide range of concentrations
(1.5 ꢃ 10ꢁ4–15 ꢃ 10ꢁ4 M) to maintain the conditions [D] ꢄ [A]o
or [D] ꢅ [A]o for applying Benesi–Hildebrand, which is valid under
this condition, to calculate the formation constant, KCT, and the
absorptivity, eCT, values for H-bonded complex in methanol. The
stoichiometry of the H-bonded complex was also obtained from
the Benesi–Hildebrand plots.
2.5. Spectral and crystal structure Analyses
The electronic absorption spectra of the donor (O-phenylenedi-
amine), acceptor (L-tartaric acid) and the resulting H-bonded
Khan, Ishaat M.
