ARTICLE IN PRESS
JID: MOLSTR
[m5G;October 17, 2020;3:19]
C. Garcias-Morales, J. Espinosa Maldonado, A. Ariza Castolo et al.
Journal of Molecular Structure xxx (xxxx) xxx
coordinated with Pb2+, they are highly fluorescent due to a photo-
induced electronic transfer, which indicates the Pb2+ presence.
Some compounds derived from rhodamine B [27], have been
used as colorimetric and fluorescent chemo-sensors for Pb2+ de-
tection; these compounds showed high selectivity and detection at
2.1. Synthesis
2.1.1. General procedure
The corresponding amine was placed in a porcelain mortar, and
the aldehyde was subsequently added. The reaction was ground
for 30 min at room temperature. The reaction was monitored by
thin-layer chromatography and was terminated when no change
in products and reagents was observed. In all cases, a paste was
obtained. After the reaction, ethyl acetate was added. The mixture
was cooled to 3°C to purify by recrystallization. The solid was re-
covered by filtration and dried at room temperature using a stream
of nitrogen.
low concentrations (1 mM) using perchlorate salts of Ag+, Ca2+
Cd2+, Co2+, Cs+, Cu2+, Hg2+, K+, Li+, Mg2+, Mn2+, Na+, Ni2+, Pb2+
,
,
Rb+ and Zn2+ in acetonitrile [28]. Chalcones have also been re-
ported as selective colorimetric chemo-sensors for Cu2+, Ni2+, and
Cd2+ in a mixture of CH3CN/H2O (95/5, v/v) [29]. The structure of
the L+M coordination complex in these compounds was studied
by IR and NMR spectroscopy. It was determined that metal coor-
dination with the molecule is through the lone pair electrons of
nitrogen (nN) and oxygen (nO).
2.1.2. 2-(((2,4-dimethoxyphenyl)imino)methyl)phenol (3a)
In a porcelain mortar 0.30 g (2.0 mmol) of 2,4-dimethoxyaniline
and 0.24g (2 mmol) of salicylaldehyde were placed, and then
the general procedure was followed. A brown viscous liquid was
obtained; yield: 88%, IR (ATR, cm−1): 3371 (OH), 1640 (C=N),
1455 (C=C). 1H NMR (CDCl3, 500 MHz, δ): 8.7 (s, 1H, H9), 7.3
(m, 2H, H12 and H14), 7.2 (d, 1H, H6), 7.0 (d, 1H, H15), 6.9 (t,
1H, H13), 6.5 (m, 2H, H5 and H3), 3.9 (s, 3H, H8), 3.8 (s, 3H,
H7). 13C NMR (CDCl3, 125 MHz, δ): 161.4 (C11), 159.9 (C4), 159.5
(C=N), 154.3 (C2), 132.4 (C13), 131.6 (C15), 130.1 (C10), 119.7 (C6),
119.7 (C1), 118.6 (C4), 117.2 (C12), 99.4 (C3), 55.8 (C7), 55.5 (C8).
[M+H]+ C15H15NO3 calculated: 258.112469, [M+H]+ C15H15NO3
found: 258.1127467.
The Schiff bases have attracted attention due to its easy prepa-
ration and purification, considering its since its synthesis is in-
herent to the 12 principles of green chemistry [30]. Have a high
atomic economy since the reaction proceeds only with water as
a byproduct; its structures are easily adjustable and efficiently de-
graded after use; therefore, they are promising molecules as chem-
ical sensors [31–34]. Rodriguez et al. reported π-conjugated imines
derived from N,N’-dimethyl cinnamaldehyde. These molecules are
colorimetric sensors of Cu2+ and Ni2+, with detection limits of
The Cu2+ detection in water for human consumption is es-
sential because a high concentration of this metal is related to
Alzheimer’s and Parkinson’s disease [37,38] (since copper regularly
coordinates proteins by changing its folding and aggregation prop-
erties). Consequently, developing a highly selective chemo-sensor
to this metal is of great importance, enabling easy detection in
real-time.
2.1.3. 2-(((4-nitrophenyl)imino)methyl)phenol (3b)
In a porcelain mortar 0.276 g (2.0 mmol) of 4-nitroaniline and
0.24g (2 mmol) of salicylaldehyde were placed, and then the gen-
eral procedure was followed. An orange solid was obtained; yield:
86%, mp: 121.7 °C, IR (ATR, cm−1): 3479 (N-H), 3356 (OH), 1655
(C=N), 1588 (N-H), 1480 (C=C). 1H NMR (500 MHz, DMSO-d6)
δ 12.33 (s, 1H, O-H), 8.97 (s, 1H, H7), 8.32 – 8.24 (m, 2H, H3,
H5), 7.72 (dd, J = 8.1, 1.7 Hz, 1H, H13), 7.62 – 7.53 (m, 2H, H6
and H2), 7.46 (td, J = 7.7, 1.8 Hz, 1H, H11), 7.00 (m, 2H, H10 and
H12). 13C NMR (125 MHz, DMSO-d6) δ 166.05 (C=N), 160.75 (C9),
154.97 (C1), 145.86 (C4), 134.79 (C11), 132.95 (C13), 125.49 (C2 and
C6), 122.90 (C3 and C5), 119.91 (C10), 119.81 (C8), 117.23 (C12).
[M+H]+ C13H10N2O3 calculated: 242.06914, [M+H]+ C13H10N2O3
found: 242.06916.
In this work, the synthesis of six Schiff bases derivatives (3a-
3f), which functions as a colorimetric chemical-sensor for metal
detections, is described. The chemical-sensors 3e can detect Cu2+
at concentrations of 4.9 × 10−6 M, in aqueous solution. The ad-
dition of the aqueous metal ion (M) to the sensor 3e (L) solu-
tion in CH3CN causes an optical change since the initially color-
less solution changes to yellow when forming the L+M complex.
UV-Visanalysis showed the formation of two absorption bands at
406 and 420 nm, both attributed to the ICT of the L+M complex.
The relationship between the structure, the HOMO-LUMO energy
levels, and the selectivity to metal ions was also studied.
2.1.4. ((1H-1,2,4-triazole-3,5-
2. Experimental section
diyl)bis(azanylylidene))bis(methanylylidene))diphenol
(3c)
All reagents and chemicals were used without further pu-
rification unless stated otherwise. The salts used to prepare the
solutions were: Zn(ClO4)2·6H2O, Ni(ClO4)2·6H2O, CoCl2·6H2O,
In a porcelain mortar 0.30 g (3.0 mmol) of 3,5-diamino-1,2,4-
triazole and 0.74 g (6 mmol) of salicylaldehyde were placed, and
then the general procedure was followed. A yellow powder was
obtained; yield: 76%; mp: 227 °C, IR (ATR, cm−1): 3389 (N-H) 3200
(O-H), 2298 (C-H), 1570 (N-H), 1471 (C=C). 1H NMR (500 MHz,
DMSO-d6) δ 12.78 (s, 1H, NH), 12.14 (s, 2H, OH), 9.13 (s, 2H, H2),
7.67 – 7.62 (m, 2H, H8), 7.44 – 7.33 (m, 2H, H6), 6.92 (m, 4H, H7
and H5). 13C NMR (126 MHz, DMSO-d6) δ 163.71 (C=N), 160.77
(C4), 157.28 (C1), 134.04 (C8), 133.03 (C6), 119.88 (C3), 119.64 (C7),
117.15 (C5). [M+H]+ C16 H13N5O2 calculated: 307.10692, [M+H]+
C16 H13N3O2 found: 282.279689 (loss of N2).
Mg(ClO4)2,
Pb(ClO4)2·3H2O,
FeCl2·4H2O,
Cu(ClO4)2·6H2O,
Ba(ClO4)2, Cd(ClO4)2, and Hg(ClO4)2. The salts of metals, or-
ganic solvents, 2-hydroxymethyl aniline, 2-formyl pyrrole, 2-
thiophenecarboxaldehyde, salicylaldehyde, 2,6-diaminopyridine,
3,5-diamino-1,2,4-triazole, 4-nitroaniline, 2,4-dimethoxyaniline,
were purchased from Aldrich.
The infrared spectra were obtained using a Perkin-Elmer 16F PC
FT-IR spectrometer, using the ATR technique in a range of 4000-
500 cm−1. Nuclear magnetic resonance spectra of 1H and 13C were
obtained in a Jeol/ECA at 500 MHz for 1H and 125 MHz for 13C.
The chemical shift is expressed in ppm using Si(CH3)4 as internal
reference (δ = 0 ppm) and CDCl3 as a solvent. The high-resolution
MS spectra were obtained by direct insertion in an Agilent G1969
LC/MSD-TOF. The UV-Vis absorption spectra were obtained in a
Jenway model 7315 spectrophotometer, using a 1cm cell and a
stock solution of 10 μM in acetonitrile analytical grade. Simultane-
ously, the salts were prepared in a concentration of 10 μM, using
distilled and deionized water.
ꢀ
ꢀ
2.1.5. 2,2 -((1E,1 E)-(pyridine-2,6-
diylbis(azanylylidene))bis(methanylylidene))diphenol
(3d)
In a porcelain mortar 0.30 g (2.7 mmol) of 2,6-Diaminopyridine
and 0.64 g (5.4 mmol) of salicylaldehyde were placed, and then
the general procedure was followed. An orange powder was ob-
tained, yield: 85%; mp: 167 °C, IR (ATR, cm−1): 1H NMR (500 MHz,
CDCl3) δ 13.42 (s, OH), 9.47 (s, 2H, H7), 7.82 (t, J = 7.7 Hz, 1H,
H10), 7.58 – 7.51 (m, 2H, H6), 7.45 – 7.36 (m, 2H, H4), 7.27 – 7.19
2