R. Azadbakht, et al.
InorganicaChimicaActa514(2021)120021
128.32, 132.30, 132.99, 135.66, 141.83, 160.69 and162.51. The mass
spectrum shows peak at m/z = 450.2 corresponding to the H2L (Figs.
S1–S4).
NO2
NO2
O2N
(1)
Cl
H2N
NH2
K2CO3
+
2
NH
HN
3. Results and discussion
OH
HO
Zn/NH4Cl
H2N
3.1. Synthesis
H2L was readily synthesized in 74% yield by condensation of N,N’-
bis(2-aminophenyl)-1,2-ethanediamine and salicylaldehyde in ethanol
(scheme 1). Its structure was investigated by mass, 1HNMR, 13C NMR
2
OH
O
N
N
NH2
NH
HN
NH
HN
(2)
The main band appearing in the FTIR spectrum was related to
stretching vibration of C]N bands and no bands attributable to C]O
were observed. The stretch vibration of secondary amines (NeH) ap-
pear at ca 3396 cm−1. In 1H NMR spectrum, a singlet signal at
3.52 ppm and a broad signal at 4.59 ppm were appeared related to
methylen protons and amine protons, respectively. A single 1H imine
resonance at 8.51 ppm was appeared demonstrating the equivalence of
the two imine environments. The signal at 12.82 ppm can be attributed
to the hydroxyl protons (the protons related to the intramolecular hy-
drogen bonds were appeared in very low-field proton resonance). Four
signals have been observed in the aromatic region (6.74–7.37 ppm). In
13C NMR spectrum, one signal at 43.08 ppm was observed attributed to
methylene carbons. There is one type for the imine carbon atoms
(162.51 ppm) demonstrating the equivalence of the two imine en-
vironments. Eleven peaks have been observed in the aromatic region
(110.79–160.69 ppm).
H2L
Scheme 1. The synthetic route of H2L.
further purification. A Bruker A V300 MHz spectrometer was used to
obtain NMR spectra. A BIO-RAD FTS-40A spectrophotometer was used
to record infrared spectra in KBr pellets (4000–400 cm−1). A Kratos-
MS-50 spectrometer was used to record positive ion FAB mass spectra
with 3-nitrobenzyl alcohol as the matrix solvent. A Varian Cary Eclipse
300 spectrophotometer was used to obtain UV–Vis absorption spectra.
The fluorescence spectra were recorded on a Varian spectrofluorometer.
Both emission and excitation bands were set at 5 nm.
2.2. N,N’-bis(2-nitrophenyl)-1,2-ethanediamine (1)
Potassium carbonate (2.76, 20 mmol), 1-chloro-2-nitrobenzene
(3.14 g, 20 mmol) and 1,2-diaminoethane (0.64 g, 10 mmol) were
completely mixed in a round-bottomed flask. The reaction was heated
at 175 ˚C in an oil bath for 3 h. After cooling, the yellow solid was
collected and washed by 3:1 H2O/EtOH (×3). Yield (82%), Scheme 1.
Anal. Calc. for C14H14N4O4: C, 55.63; H, 4.67; N, 18.53. Found: C,
55.82; H, 4.70; N, 18.49%. IR (KBr, cm−1) 1350, 1570 m (NO2),
3360(NH); 1HNMR δH (CDCl3, ppm) 3.40 (t, 4H, CH2–CH2), 6.70 (m,
4H, Ar), 7.35(t, 2H, Ar), 7.90 (d, 2H, Ar), 7.35 (t, 2H, NH).
From reaction if H2L with MgCl2, the complex of [MgL] was syn-
thesized. The IR spectra of H2L and [MgL] were prepared and com-
pared. As can be seen from Fig. S3, two differences have been observed:
(i) The absorption band at 3397 cm−1 corresponding to the NeH
stretching vibration shifted to 3381 cm−1 (ii) the stretch vibration of
imine group (C]N) at 1609 cm−1 shifted to 1624 cm−1. These ob-
servations suggest that the imine groups and the amine groups may
participate in the coordination interaction to Mg2+ ions.
3.2. Spectral properties of fluorescent H2L
2.3. N,N’-bis(2-aminophenyl)-1,2-ethanediamine (2)
H2L (10 μM) exhibits a weak fluorescence intensity around 490 nm
when excited at 423 nm. The fluorescence emission measurements of
H2L were made at room temperature in different solvents: water,
ethanol, methanol, chloroform, acetonitrile and dimethylformamide
(DMF). Investigation of the solvent-dependent fluorescence emission -
displayed that the fluorescence is strongly quenched in protic solvents.
The magnitude of the quenching depends on the H bond- donating
ability of the solvent (Fig. 1).
A
mixture of ammonium chloride (4 g), 2-nitro-N-(2-(2-ni-
trophenylamino)propyl)benzenamine (3.16 g, 10 mmol), and H2O
(2 ml) in 100 ml of ethanol was heated to boiling and then 3 g of zinc
dust were gradually added over a period of 0.5 h. When the color of the
solution changed from brown to pale yellow, it was filtered and wa-
shed. Distilled water (1000 ml) was added to the filtrated solution and
the pH was adjusted to 12 with potassium hydroxide. The product as
brown powder participates were appeared in the solution. Yield (1.3 g,
62%). Anal. Calc. for C14H18N4: C, 69.39; H, 7.46; N, 23.12. Found: C,
69.20; H, 7.34; N, 23.32%. IR (KBr, cm−1) 3452 and 3464 m (NH2);
3344 m (NH); 1H NMR δH (CDCl3, ppm) 3.33 (br, 10H, CH2–CH2 and
NH), 6.64 (m, 8H, Ar); 13C NMR δC (CDCl3, ppm) 40.0, 135.9, 134.7,
120.1, 118.0, 113.4, 109.1
The salicylimine- derivatives are known to be good ligands for
fluorescence studies and used to develop chemosensors. The excitation
and emission wavelengths of the H2L were found at higher wavelength,
in compared to naphthalene groups. This red-shift is related to the
delocalization the imine π-electrons on the aromatic amines results in a
red-shift of the excitation and emission wavelengths of the related
aromatic rings. The emission spectra of H2L on excitation at 423 nm
shows a broad band at 490 nm. The selective binding behavior of H2L
towards different metal nitrates (Na+, K+, Cs+, Mg2+, Ba2+, Ca2+
Al3+, Pb2+, Mn2+, Fe2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+
and Ag+) was studied by fluorescence spectroscopies. All of the titra-
tion experiments were carried out in EtOH/H2O (9/1, v/v) upon adding
the respective metal ions. Fig. 2 exhibits the changes in the fluorescence
2.4. Synthesis of H2L
To a solution of 2-hydroxybenzaldehyde (0.24 g, 2 mmol) in abso-
lute ethanol, N,N’-bis(2-aminophenyl)-1,2-ethanediamine (0.23 g,
1 mmol) was added and the reaction was gently refluxed approximately
for 3 h. The product precipitating was filtered off and washed with
ethanol, and dried in air at room temperature. Yield (70%). Anal. Calc.
for C36H30N4O2: C, 74.65; H, 5.82; N, 12.44. Found: C, 74.88; H, 5.70;
N, 12.61%. IR (KBr, cm−1) 3412 (OH), 1621 (C]N);1H NMR δH
(DMSO‑d6, ppm) 3.52 (s, 4H, CH2), 4.59 (s, 2H, NH) 6.74–7.37 (4
signals, 16H, Ar), 8.51 (s, CH = N, 2H), 12.82 (s, OH, 2H); 13C NMR δC
(DMSO‑d6, ppm) 43.08, 110.79, 117.10, 117.36, 118.31, 119.18,
The complexation reaction occurs with formation of neutral com-
plex [MgL] coupling with r+
elease of H+ ions:
It should be noted that H2L molecules are functioning as charged
2