Synthesis, Crystal Structure and Photophysical Properties of Two Reduced Schiff Bases Derived from 5-Aminoisophthalic Acid

Article abstract of DOI:10.1007/s10870-018-0761-z

Two reduced Schiff bases, namely 5-[(2-hydroxybenzyl)amino]isophthalic acid (1) and 5-[(pyridin-4-ylmethyl)amino]isophthalic acid (2), were synthesized in two-step method using 5-aminoisophthalic acid as the starting material, and were characterized by si

Full text of DOI:10.1007/s10870-018-0761-z

Journal of Chemical Crystallography
https://doi.org/10.1007/s10870-018-0761-z
ORIGINAL PAPER
Synthesis, Crystal Structure and Photophysical Properties of Two
Reduced Schiff Bases Derived from 5-Aminoisophthalic Acid
1
1
1
1
1
1
1
1
Lai‑Jun Zhang · Li Qi · Xiu‑Ying Chen · Feng Liu · Li‑Juan Liu · Wen‑Li Ding · De‑Lin Li · Guo‑Cai Yuan ·
1
1
1
1
Ji‑Zao Tong · Fa‑Yun Chen · Hai‑Jin Huang · Yong‑Hua Wang
Received: 30 August 2018 / Accepted: 11 December 2018
©
Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract
Two reduced Schiff bases, namely 5-[(2-hydroxybenzyl)amino]isophthalic acid (1) and 5-[(pyridin-4-ylmethyl)amino]
isophthalic acid (2), were synthesized in two-step method using 5-aminoisophthalic acid as the starting material, and were
1
characterized by single-crystal X-ray diffraction, elemental analysis, infrared, H NMR, mass, absorption and fluorescence
spectra. Both 1 and 2 crystallize in monoclinic system with space groups P2 /c for 1 and P2 /n for 2. Photophysical prop-
1
1
erties of both 1 and 2 are significantly different from those of raw material 5-aminoisophthalic acid due to stronger p→π
conjugation when one amino hydrogen atom in 5-aminoisophthalic acid is substituted with electron-donor group. 1 displays
a very strong narrow-band blue fluorescence with the maximum peak at 439 nm, a high quantum efficiency up to 64%, and
a narrow full width at half maximum of 35 nm, while 2 has a broader and weaker fluorescence with the peak at 418 nm and
FHWM of about 50 nm.
Graphical Abstract
Two reduced Schiff bases with blue fluorescence were synthesized from 5-aminoisophthalic acid in two-step method includ-
ing formation of the corresponding Schiff bases and further reduction by NaBH .
4
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10870-018-0761-z) contains
supplementary material, which is available to authorized users.
Extended author information available on the last page of the article
Vol.:(0
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Journal of Chemical Crystallography
Keywords Reduced Schiff base · 5-[(2-Hydroxybenzyl)amino]isophthalic acid · 5-[(Pyridin-4-ylmethyl)amino]isophthalic
acid · 5-Aminoisophthalic acid · Crystal structure · Photophysical property
Introduction
In this paper, two reduced Schiff bases, 5-[(2-hydroxy-
benzyl)amino]isophthalic acid (1) and 5-[(pyridin-4-yl-
methyl)amino]isophthalic acid (2), were synthesized by
using AIP as raw materials, and their single crystals were
obtained by recrystallization in N,N-dimethylformamide/
water mixed solvents. The corresponding synthetic routes
for 1 and 2 were displayed in Scheme 1. The crystal struc-
tures and photophysical properties of 1 and 2 were further
characterized by single-crystal X-ray diffraction, infrared
Schiff bases usually have bright colors, strong fluorescence
as well as important physiological functions and have been
widely applied as pH sensors, drugs, organic dyes, organic
ligands for synthesizing metal complexes [1–5]. Innumer-
able Schiff bases have been already synthesized in the past
several decades [5–7]. Compared with Schiff bases featured
with rigid C=N double bond, the structure flexibility of the
corresponding reduced Schiff bases obtained through the
reduction of rigid C=N double bond to C–N single bond
increases significantly accompanying with the change of
electronic effect, which will further result in diverse struc-
tures and various properties for the formed metal complexes
1
spectrum, nuclear magnetic resonance spectrum ( H NMR),
electrospray ion trap mass spectrum, absorption spectrum,
fluorescence spectrum and elemental analysis.
[
8–11]. Therefore, the reduced Schiff base has received
Experimental
much attention recently.
5
-Aminoisophthalic acid (AIP) was an important and
Materials and Methods
widely used organic compound with several functional
groups including two carboxyl (–COOH) groups and one
AIP, salicylaldehyde, 4-pyridinecarboxaldehyde, sodium
amino (–NH ) group, which has been used as organic drug
borohydride (NaBH ), sodium hydroxide (NaOH) and
2
4
intermediates and organic ligands of metal complexes
hydrochloric acid (HCl, 37 wt%) were purchased from
Sinopharm Chemical Reagent Co., Ltd. Ethanol and N,N-
dimethylformamide (DMF) were purchased from Shantou
Xilong Chemical Plant. All the commercially available
chemicals were of analytical grade and were utilized with-
out further purification.
[
12–14]. Due to the present of –NH group, AIP can react
2
with various aldehydes to produce diverse Schiff bases by
taking off water molecules, which may further be reduced
to the corresponding reduced Schiff bases by some common
reducing agents such as NaBH .
4
Scheme 1 Synthetic routes for
reduced Schiff bases 1 and 2
(
(
a) NaOH
b) NaBH4
HO
HO
H
O
OH
HN
N
(c) HCl
NH2
HO
O
HO
O
O
OH
O
OH
HO
O
1
O
OH
N
N
AIP
(a) NaOH
N
(b) NaBH4
c) HCl
(
N
HN
H
O
HO
O
HO
O
O
OH
O
OH
2
1
3

Journal of Chemical Crystallography
Crystal structure determinations were performed on an
Agilent Xcalibur Eos diffractometer for 1 and a Bruker
SMART APEX II CCD diffractometer for 2, respec-
tively. Infrared (IR) spectra were recorded in the range of
S1, ESI). Anal. Calcd. for C H NO (287.27): C, 62.72; H,
15 13 5
4.56; N, 4.88. Found: C, 62.81; H, 4.63; N, 4.82.
Synthesis of 5‑[(Pyridin‑4‑ylmethyl)amino]
isophthalic Acid (2)
−1
4
000–400 cm on a Nicolet 6700 FT-IR infrared spectrom-
1
eter using KBr pellets technique. H NMR spectra were per-
formed on a Bruker AVANCE III 400 MHz nuclear magnetic
Similar to 1, reduced Schiff base 2 was also synthesized
including the following two steps: (1) at room tempera-
ture, AIP (150 mmol, 27.16 g) was first dissolved in DMF
(80 mL) under magnetic stirring, followed by the addition of
ethanol (20 mL) and 4-pyridine formaldehyde (13 mL). The
resulting mixture was stirred for 20 h to generate pale yellow
precipitation which was further collected by centrifugation
at a rate of 4000 rpm, washed with ethanol and dried under
vacuum at 50 °C for 12 h to obtain 35.33 g (87%) pale yel-
low Schiff base 5-[(pyridin-4-ylmethyl)amino]isophthalic
acid powder. (2) Under continuous and vigorous stirring,
NaOH (150 mmol, 6.0 g), the above 5-[(pyridin-4-ylme-
thyl)amino]isophthalic acid powder (75 mmol, 20.32 g)
resonance spectrometer (DMSO-d , TMS internal standard).
6
Mass spectra were obtained using a Bruker Esquire HCT
ultra ion trap mass spectrometer, equipped with an Agilent
electrospray ion source. UV–Vis absorption spectra and
fluorescence spectra were conducted at room temperature
on a Shanghai Mapada 3300 UV–Vis spectrophotometer and
a Hitachi F-7000 fluorescence spectrometer, respectively.
Elemental analyses for C, H and N were performed on a
Perkin–Elmer 240C element analyzer.
Synthesis of 5‑[(2‑Hydroxybenzyl)amino]isophthalic
Acid (1)
and NaBH (112.5 mmol, 4.25 g)-contain DMF solution
4
(
20 mL) were added into ethanol (300 mL) at time interval
Reduced Schiff base 1 was synthesized from AIP
of 5 min, followed by the successive addition of 150 mL
through two steps including the formation of Schiff base
of H O at 2 h later for dissolving completely, the freshly
2
5
-[(2-hydroxybenzylene)amino]isophthalic acid and its fur-
prepared 1 M HCl solution (200 mL) for adjusting pH to 6,
ther reduction by NaBH , and the detailed synthesis was as
and H O (825 mL) promoting precipitation during 1 h. The
4
2
follows: (1) AIP (20 mmol, 3.58 g) was first dissolved in
DMF (20 mL) under magnetic stirring at room tempera-
ture, followed by successive addition of ethanol (60 mL) and
salicylaldehyde (20 mmol, 2.442 g). Then a large amount
of orange–red precipitation was generated after a continu-
ous stirring of 24 h, further collected by centrifugation at
precipitate was filtered, washed with H O and dried at 50 °C
2
for 1 day to obtain 14.3 g (70.0%) colorless reduced Schiff
base 2 powder. Colorless plate single crystals of 2 were
obtained by recrystallisation from DMF/H O mixed solvent
2
−
1
with a volume ratio of 2:1. FT-IR (KBr pellet, ν/cm ): 3318
1
(s), 1695 (s), 767 (s). H NMR (DMSO-d , 400 MHz) δ
6
4
000 rpm, washed with ethanol and dried under vacuum
for 12 h at 50 °C to yield 3.3 g (58%) dried Schiff base
-[(2-hydroxybenzylene)amino]isophthalic acid powder.
2) Under continuous magnetic stirring, NaOH (10 mmol,
12.96 (s, 2H), 8.51 (d, J= 4.0 Hz, 2H), 7.70 (s, 1H), 7.36
(d, J = 4.0 Hz, 2H), 7.33 (s, 2H), 6.96 (t, J= 8.0 Hz, 1H).
+
5
4.42 (d, J=8.0 Hz, 2H). MS (DMF): m/z [M+H] 273.09,
−
(
[M–H] 271.08 (Fig. S2, ESI). Anal. Calcd. for C H N O
1
4
12
2
4
0
.4 g) and the above Schiff base powder (5 mmol, 1.42 g)
(2, 272.26): C, 61.76; H, 4.44; N, 10.29. Found: C, 61.71;
were added into ethanol (60 mL) at time interval of 5 min,
H, 4.48; N, 10.33.
followed by the addition of NaBH (5 mmol, 0.18 g)-con-
4
taining DMF solution (60 mL). Then the resulting mixture
Crystal Structure Determination
was allowed to react for 1 h before adding H O (10 mL) to
2
dissolve completely. Finally, HCl solution (20 mL, 1 M) and
Crystal data of 1 and 2 were collected at 293 K on an
Agilent Xcalibur Eos diffractometer with SuperNova (Mo)
X-ray source mirror monochromator (λ = 0.71073 Å) and
a Bruker SMART APEX II CCD diffractometer equipped
with graphite-monochromatised Mo Κα radiation
(λ = 0.71073 Å), respectively. Using Olex2, both crystal
structures were solved with the ShelXS-2014 structure
solution program using direct methods and refined with
the ShelXL-2014 refinement package using a full-matrix
H O (40 mL) were successively added to produce a large
2
amount of white precipitate. The precipitate was then fil-
tered, washed with water and ethanol, and dried at 50 °C
for 1 day, providing a dried powder of reduced Schiff base
1
with a yield of 1.32 g (92%). Colorless block single crys-
tals of 1 were obtained by recrystallisation from DMF/H O
2
mixed solvent with a volume ratio of 1:2. FT-IR (KBr pellet,
−
1
1
ν/cm ): 3415 (s), 1687 (s), 756 (s). H NMR (DMSO-d ,
6
2
4
00 MHz) δ 12.93 (s, 2H), 9.60 (s, 1H), 7.95 (s, 1H), 7.67
least-squares method on F . Absorption corrections were
(
t, J=4.0 Hz, 1H), 7.36 (s, 2H), 7.15 (d, J=12.0 Hz, 1H),
applied by using CrysAlis PRO for 1 and SADABS for
2 based on multi-scan techniques. Anisotropic thermal
parameters were employed to refine all non-hydrogen
7
1
.08 (m, 1H). 6.83 (d, J=8.0 Hz, 1H), 6.69(m, 1H), 4.26 (s,
+
−
H). MS (DMF): m/z [M+H] 287.82, [M–H] 285.67 (Fig.
1
3

Journal of Chemical Crystallography
atoms. Hydrogen atoms were treated by a mixture of
independent and constrained refinement. The crystallo-
graphic data and structure refinement details are listed in
Table S1. Crystallographic data files of 1 and 2 have been
deposited in the Cambridge Crystallographic Data Center
with CCDC reference numbers 1815474 and 994623,
respectively.
Results and Discussion
Crystal Structures of 1 and 2
The single crystal structure analysis reveals that both
reduced Schiff bases 1 and 2 belong to monoclinic system
with space groups P2 /c for 1 and P2 /n for 2 (Table S1).
1
1
Both crystal structures of 1 and 2 were herein reported
for the first time although powdery 2 has been reported
previously but without providing the corresponding crystal
structure information and photophysical properties [10, 11,
1
5]. Recently, the salt form of 2 has been also obtained
[
11], but it can be found that the cell parameter and space
group of both 2 and its salt form are obviously different
from each other. From their crystal structures shown in
Fig. 1, it can be found that both 1 and 2 contain isophtha-
late and phenol(1)/pyridine(2) units which are connected
by a NH–CH segment. All bond lengths and angles are
2
in reasonable range (Tables S2, and S3, ESI). For 1, the
benzene rings from the isophthalate and phenol units are
in different planes with a dihedral angle of 75.67° and
the C(8)–N(1)–C(7)–C(2) torsional angle of − 86.4(2)°,
while the pyridine and isophthalate units of 2 are also in
different planes with a dihedral angle of 88.33° and the
C(7)–N(2)–C(6)–C(3) torsional angle of 88.7(4)°. The
results coincide with the formation of flexible reduced
Schiff bases 1 and 2 through reducing the corresponding
rigid Schiff bases.
Additionally, the infinite two-dimensional network
of 1 can be formed along the (101) plane through the
intermolecular O–H⋯O hydrogen-bonding interac-
tions between phenolic hydroxyl group and carboxy-
late group (O(1)–H(1)⋯O(4) hydrogen bond), and
between carboxylic hydroxyl group and carboxyl group
(
O(3)–H(10)⋯O(4) and O(5)–H(12)⋯O(2) hydrogen
bond) (Table 1; Fig. 2). For 2, very rich intermolecu-
lar hydrogen-bonding interactions including O–H⋯N,
N–H⋯O, C–H⋯O besides O–H⋯O hydrogen bonds were
Fig. 1 ORTEP plots of a 1 and b 2, with the atom-numbering
scheme. Displacement ellipsoids are drawn at the 30% probability
level. H atoms are presented as small green spheres
Table 1 Hydrogen-bond geometry of 1 and 2
Compound
D–H⋯A
D⋯H (Å)
H⋯A (Å)
D⋯A (Å)
<D–H⋯A (°)
Symmetry codes
1
O(1)–H(1)⋯O(4)
O(3)–H(10)⋯O(4)
O(5)–H(12)⋯O(2)
N(2)–H(7)⋯O(1)
O(2)–H(9)⋯N(1)
O(3)–H(11)⋯O(2)
C(6)–H(3)⋯O(3)
C(5)–H(5)⋯O(4)
C(10)–H(10)⋯O(3)
0.82
0.82
0.82
0.89(3)
0.82
0.93(4)
0.97
0.93
1.94
1.87
1.80
1.98(3)
1.75
1.68(4)
2.60
2.57
2.743(2)
2.687(2)
2.615(2)
2.850(3)
2.561(3)
2.606(3)
3.465(4)
3.325(4)
3.233(4)
167
178
175
164(3)
172
175(3)
149
139
1−x, −1/2+y, 3/2−z
−x, −1/2+y, 1/2−z
−x, 1/2+y, 1/2−z
−1/2+x, 3/2−y, −1/2+z
5/2−x, 1/2+y, 3/2−z
1−x, 2−y, 1−z
1/2+x, 3/2−y, −1/2+z
3/2+x, 3/2−y, 1/2+z
1−x, 2−y, 1−z
2
0.93
2.45
142
1
3

Journal of Chemical Crystallography
also observed, and further assemblied 2 into an infinite
three-dimensional supramolecular network (Table 1;
Fig. 3).
IR Spectra
Figure 4 shows the IR spectra of raw material AIP, reduced
Schiff bases 1 and 2. For AIP, strong carboxylic C=O
−
1
asymmetric stretch peak appears at 1698 cm , which red-
−
1
−1
shifts slightly to 1687 cm and 1695 cm for the obtained
reduced Schiff bases 1 and 2, respectively. Meanwhile,
the C–H vibration peak of meta-disubstituted benzene
−
1
−1
ring blue-shifts from 750 cm for AIP to 756 cm for 1
−
1
and to 767 cm for 2. The sharp, strong and single peak
−
1
−1
at 3318 cm for 1 or at 3415 cm for 2 is attributed to
the N–H vibration peak from their imino group other than
amino group. The very small shifts of both C=O asymmetric
stretch peak and C–H vibration peak of meta-disubstituted
benzene ring as well as significant shift of the N–H vibration
peak are consistent with the facts that both 1 and 2 not only
retain the isophthalic acid moiety but also contain the imino
group derived from the amino group in AIP.
Absorption and Fluorescence Spectra
Fig. 2 Infinite two dimensional network of compound 1 viewed along
the a [100] and b [001] direction
Different substitute groups usually result in different pho-
tophysical properties due to their electronic effect and/or
steric effect [16]. The normalized absorption spectra of AIP,
reduced Schiff bases 1 and 2 dissolved in DMF were shown
in Fig. 5a. In the spectral range from 250 to 450 nm, two
sharp characteristic absorption peaks at 293 and 356 nm
for 1 or at 291 and 351 nm for 2, respectively, were sig-
nificantly red-shift as compared with those of AIP at 270
and 344 nm. The red shift of two characteristic absorption
2
1
AIP
4000
3500
3000
2500
2000
1500
1000
500
-
1
Wavenumber (cm )
Fig. 3 Three dimensional packing of 2 viewed along the a [100] and
b [101] direction
Fig. 4 IR spectra of AIP, 1 and 2
1
3

Journal of Chemical Crystallography
(
a)
1
3
51
Conclusion
AIP
1
.2
.8
.4
.0
AIP
2
1
Reduced Schiff bases 1 and 2 have been synthesized by the
first reaction of AIP acid with two different aldehydes (salic-
ylaldehyde and 4-pyridinecarboxaldehyde) to form Schiff
2
70 291 293
2
3
56
0
0
0
344
bases and their further reduction by NaBH . The crystal
4
structures and some photophysical properties both 1 and
2
were also provided. Relatively strong narrow-band fluo-
rescence and rich functional groups make them applicable
in the fields such as fluorescent probes/labels and flexible
organic ligands for synthesizing various metal complexes.
250
300
350
400
450
Acknowledgements This work was supported by the National Natural
Science Foundation of China (21561028), Science and Technology
Program of Department of Education of Jiangxi Province (GJJ151064),
and the National Natural Science Foundation of Jiangxi Province
(2016BAB203071).
Wavelength (nm)
(b)
AIP 2
1
AIP
4
39
1
2
4
10 418
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8
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conjugation when electron-donor–NH group was substi-
Publisher’s Note Springer Nature remains neutral with regard to
2
jurisdictional claims in published maps and institutional affiliations.
tuted with electron-donor–NHR group [16], consistent with
the observation shown in absorption spectra (Fig. 5a).
1
3

Journal of Chemical Crystallography
Affiliations
1
1
1
1
1
1
1
1
Lai‑Jun Zhang · Li Qi · Xiu‑Ying Chen · Feng Liu · Li‑Juan Liu · Wen‑Li Ding · De‑Lin Li · Guo‑Cai Yuan ·
1
1
1
1
Ji‑Zao Tong · Fa‑Yun Chen · Hai‑Jin Huang · Yong‑Hua Wang
1
*
Lai-Jun Zhang
School of Chemistry and Environmental Science, Shangrao
Normal University, Shangrao 334001, China
ljzhang2015@126.com
1
3