The hydroxylic position mediated the luminescent properties based on 4-amino-4H-1,2,4-triazole: Syntheses, crystal structures and Hirshfeld analyses

Article abstract of DOI:10.1016/j.jssc.2021.122300

A set of compounds based on 4-amino-4H-1,2,4-triazole group, namely, x,x'-(4-amino-4H-1,2,4-triazole-3,5-diyl) diphenol [x ?= ?2 (1), x ?= ?3 (2), x ?= ?4 (3)], were obtained through reacting a set of cyano-phenol and hydrazine under the solvothermal cond

Full text of DOI:10.1016/j.jssc.2021.122300

Journal Pre-proof
The hydroxylic position mediated the luminescent properties based on 4-
amino-4H-1,2,4-triazole: syntheses, crystal structures and Hirshfeld analyses
Yu-Rong Xi, Xu-Kai Chen, Yu-Song Wu, Yun-Kai Xue, Wen-Chao Sun, Xiao-Min
Chen, Xing-Rui Liu, Yong-Tao Wang, Gui-Mei Tang
PII:
S0022-4596(21)00345-5
DOI:
https://doi.org/10.1016/j.jssc.2021.122300
YJSSC 122300
Reference:
To appear in: Journal of Solid State Chemistry
Received Date: 12 April 2021
Revised Date: 11 May 2021
Accepted Date: 25 May 2021
Please cite this article as: Y.-R. Xi, X.-K. Chen, Y.-S. Wu, Y.-K. Xue, W.-C. Sun, X.-M. Chen, X.-R.
Liu, Y.-T. Wang, G.-M. Tang, The hydroxylic position mediated the luminescent properties based on 4-
amino-4H-1,2,4-triazole: syntheses, crystal structures and Hirshfeld analyses, Journal of Solid State
Chemistry, https://doi.org/10.1016/j.jssc.2021.122300.
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The hydroxylic position mediated the luminescent properties based on
4-amino-4H-1,2,4-triazole: syntheses, crystal structures and Hirshfeld analyses
Yu-Rong Xia, Xu-Kai Chena, Yu-Song Wua, Yun-Kai Xuea, Wen-Chao Suna, Xiao-Min Chena,
Xing-Rui Liua, Yong-Tao Wanga,*, Gui-Mei Tangb
aSchool of Chemistry and Chemical Engineering, Qilu University of Technology (Shandong
Academy of Sciences), Jinan, 250353, China
aSchool of Pharmaceutical Sciences, Qilu University of Technology (Shandong Academy of
Sciences), Jinan, 250353, China
*Corresponding authors. Fax: int code +86 0531 8963 1207. Tel: +86 0531 8963 1207.
E-mail: ceswyt@qlu.edu.cn (Y. T. Wang)
Abstract
A
set
of
compounds
based
on
4-amino-4H-1,2,4-triazole
group,
namely,
x,x'-(4-amino-4H-1,2,4-triazole-3,5-diyl) diphenol [x=2 (1), x=3 (2), x=4 (3)], were obtained through
reacting a set of cyano-phenol and hydrazine under the solvothermal conditions, respectively. The
title compounds 1-3 have been characterized by IR, element analysis (EA), single crystal X-ray
diffraction, and powder X-ray diffraction (PXRD). A lot of hydrogen bonds (C/N/O–H∙∙∙O/N) and
C-H∙∙∙π can be clearly observed in these compounds. It surprisedly occurs the presence of trans- and
cis-conformation for compounds 3. The increasing order of the dihedral angles between the phenyl
and triazole-yl rings is 1<2<3. The solid-state luminescent spectra of 1-3 show that the emission
maxima are observed at 461, 414 and 402 nm, respectively, which shows the declining order of
1>2>3. The luminescent maximal peaks decrease with the diminution of hydroxylic steric effects.

The Hirshfeld surface analyses reveal that the contribution order of the O∙∙∙H/H∙∙∙O contacts in
compounds 1-3 is listed: 1<2<3, which is in a good agreement with that of the dihedral angles, and
an inverse proportional to the fluorescent maxima of compounds 1-3.
Keywords: 4-Amino-4H-1,2,4-triazole; Crystal structures; Supramolecular interactions; Hirshfeld
surface analysis; Dihedral angles
1. Introduction
The triazole-based derivatives are one of the most significant N-heterocyclic compounds and have
extensively applied in the fields of materials and medicine [1-15] [16-19] [20-21], which can be
assigned to their strong coordination abilities and important biologically activities. Among these
triazole-containing compounds, the derivatives based on amino-1,2,4-triazole nuclei show interesting
properties such as optics, gas absorption and magnetism [22-27]. Recently, the composite consisting
of nickel flakes on 4-amino-4H-1,2,4-triazole/graphene has been designed for sustainable hydrogen
evolution in acid and alkaline media [28]. 3,5-Diaryl-4-amino-1,2,4-triazole derivatives have been
used as effective corrosion inhibitors for steel in acid solution [29]. Nickel clusters with
amino-1,2,4-triazole scaffold have been proved to have good catalysis for ethene [30]. Additionally,
4-amino-1,2,4-triazole have been proved to play pivotal roles in anti-cancer cells and various types
of anti-disease in the human body [31]. However, it still remains unexplored for the luminescent
materials with 4-amino-1,2,4-triazole moieties though some derivatives containing
amino-1,2,4-triazole have been synthesized [32-33]. Very importantly, it is urgent to design and
investigate the derivatives based on 4-amino-1,2,4-triazole skeleton with the controllable
photoluminescent behaviours through the position of substituted functional groups.

Based on these elegant works mentioned above, in this contribution, we would like to report a
set of 4-amino-1,2,4-triazole functional groups, namely, x,x'-(4-amino-4H-1,2,4-triazole-3,5-diyl)
diphenol [x=2 (1), x=3 (2) and x=4 (3)], were obtained through reacting a set of cyano-phenol and
hydrazine under the solvothermal conditions, respectively. The single crystal structures of 1-3 have
been discussed, their photoluminescent properties and thermal behaviors were investigated in details.
As we expected, the hydroxylic position can obviously control the luminescent properties of these
amino-triazole derivatives, which can be further confirmed by the Hirshfeld surface analyses. To our
best knowledge, there is not the record of the tunable luminescent behaviors of compounds
containing amino-4H-1,2,4-triazole through the position of the substituted functional groups.
2. Experimental
2.1 Materials and measurements
The reagents and solvents employed were used as received without further purification.
Elemental analyses were performed on an Elementar vario EL III microanalyser. The FT-IR spectra
were recorded from KBr pellets in the range 400-4000 cm−1 on a Bruker spectrometer. The
absorption spectra were recorded with an absorption spectrophotometer model TU-1900/1901.
Thermogravimetric analysis (TGA) data were collected with a TA SDT Q600 analyzer in N2 at a
heating rate of 10 °C min−1 in the range of 20-600 °C. The solid–state fluorescence spectra were
recorded on a HITACHI–4500 spectrometer at room temperature.
2.1. The synthesis of compound 1.
To a mixture solution of ethylene glycol (10 mL) and 85% hydrazine hydrate (3.8 mL, 60
mmoL), 2-hydroxybenzonitrile (1.180 g, 10 mmoL) were heated at 130 °C for 3 days in a 15 ml
Teflon-lined vessel container. Then an ice water (30 ml) was added to the cooled reaction mixture.

The production was filtered and dried. The sample (0.134 g, 0.5 mmol) was dissolved in methanol (5
ml). The solution was stood for one week. Brown block crystals suitable for X-ray diffraction were
collected by vacuum filtration. Yield: 0.100 g, 75%. M.p. 258-260 °C. Elemental analysis calcd (%)
for C14H12N4O2 (268.28): C, 62.68; H, 4.51; N, 20.88; Found: C, 62.53; H, 4.52; N, 20.79. IR (KBr,
cm–1): 3333(s), 3287(w), 3224(w), 3076(w), 2914(w), 2677(w), 2554(w), 1962(w), 1933(w), 1634(s),
1608(s), 1525(w), 1483(s), 1457(m), 1422(w), 1381(s), 1292(m), 1278(w), 1268(w), 1249(s),
1227(m), 1171(w), 1162(w), 1153(w), 1134(w), 1109(w), 1095(w), 1008(m), 971(w), 950(w),
948(w), 829(w), 754(vs), 702(m), 692(m), 650(w), 607(m), 559(w), 533(w), 490(w), 471(w), 458(m),
430(vw).
2.2. The synthesis of 2.
The synthesis procedure of compound 2 was similar to that of compound 1 when the
3-hydroxybenzonitrile took place of 2-hydroxybenzonitrile. The orange block crystals were collected.
Yield: 0.221 g, 70%. M.p. 289-291°C. Elemental analysis calcd (%) for C31H36N8O7 (632.68): C,
58.85; H, 5.74; N, 17.71; Found: C, 58.71; H, 5.73; N, 17.74. IR (KBr, cm–1): 3354(w), 3327(w),
3189(w), 1589(s), 1528(m), 1487(m), 1458(s), 1435(w), 1333(w), 1313(m), 1286(m), 1241(w),
1223(w), 1203(w), 1146(w),1170(w), 1158(w),1137(w), 1090(w), 1075(w), 1037(w), 995(s), 978(w),
944(s), 888(s), 788(s), 724(s), 690(s), 633(w), 538(w), 472(w), 447(w), 412(w).
2.3. The synthesis of compound 3
The synthesis procedure of compound 3 was similar to that of compound 1 when the
4-hydroxybenzonitrile took place of 2-hydroxybenzonitrile. The colorless needle crystals were
collected. Yield: 0.107 g, 80%. M.p. 298-300 °C. Elemental analysis calcd (%) for C14H12N4O2
(268.28): C, 62.68; H, 4.51; N, 20.88; Found: C, 62.79; H, 4.50; N, 20.82. IR (KBr, cm–1): 3476(b),

3416(s), 3223(m), 2809(w), 2678(w), 2509(w), 2362(w), 1915(w), 1772(w), 1613(s), 1481(s),
1363(m), 1236(s), 1173(s), 1108(m), 979(m), 902(m), 842(s), 744(m), 671(w), 598(m), 534(s),
453(w).
2.4. Single-crystal structure determination
Single-crystal structures of compounds 1-3 were measured by a Bruker Smart CCD equipped
with graphite–monochromator Mo Kα radiation (λ = 0.71073 Å). The lattice parameters were
obtained by a least-squares refinement of the diffraction data. All the measured independent
reflections were used in the structural analysis, and semi-empirical absorption corrections were
applied using the SADBASE program [34]. The program SAINT was used for integration of the
diffraction profiles [35]. The structure was solved by direct methods using the SHELXS and OLEX2
program of the SHELXTL package and refined with SHELXL [36-38]. All non-hydrogen atoms
were located in successive difference Fourier syntheses. The final refinement was performed by
full-matrix least-squares methods with anisotropic thermal parameters for all the non-hydrogen
atoms based on F2. The hydrogen atoms were placed in the calculated sites and included in the final
refinement in the riding model approximation with displacement parameters derived from the parent
atoms to which they were bonded. Special computations for the crystal structure discussions were
carried out with PLATON for Windows. A summary of the crystallographic data and structure
refinements are listed in Table 1. Selected bond lengths and bond angles are summarized in Table 2.
Corresponding hydrogen bond and packing interactions data for compounds 1-3 are listed in Tables 3
and 4, respectively. Other parameters of compounds 1-3 are presented in Table 5.
2.5. Hirshfeld surface analyses
The Hirshfeld surface were calculated by the program of CrystalExploer [39-40]. The

contribution of the bond contacts was listed in Table 6.
3. Results and discussion
3.1. Description of the crystal structures
3.1.1. Structure of 2,2’-(4-amino-4H-1,2,4-triazole-3,5-diyl)diphenol (1).
Single X-ray crystallographic analysis results reveal that compound 1 belongs to the P212121
space group with the orthorhombic crystal system. In the unsymmetric unit, there is only one
2,2’-(4-amino-4H-1,2,4-triazole-3,5-diyl) diphenol (2OH) molecule (Fig. 1a). The bond lengths and
the bond angles containing the amino-triazole group is analogous to those observed in other
triazole-based moieties. The dihedral angle between the phenyl rings and the triazole one can be
found to be 13.0(1)° and 50.2(1)°, where the former is significantly smaller than the latter. The
observed results can be assigned to the presence of intramolecular hydrogen bonds. The present
value is obviously lower/higher than those in the literature.
The supramolecular structures mainly rely on intermolecular hydrogen bonds and the C-H⋯π
packing interactions. As shown in Fig. 1, the responding interactions are described as the following:
a
(a) The O-H⋯N (O1–H1···N1a, 2.703(2) Å, -x,1/2+y,-1/2-z) intermolecular hydrogen interconnects
occur between the oxygen atoms from the hydroxylic groups and the triazole-yl nitrogen atoms. (b)
b
There exist the weak C4–H4···Cg1b (3.563(2) Å, -x,-1/2+y,-1/2-z) packing interactions, where the
Cg1 represents the center of the triazole-yl ring. The adjacent 2OH molecules alternatively arrange
into a supramolecular one-dimensional (1D) chain along the crystallographic b axis through the O1–
H1···N1a intermolecular hydrogen bonds and the C4–H4⋯Cg1b packing interactions (Fig. 1b). (c) The
a
C3–H3⋯Cg3a (3.374(2) Å, 1/2+x,-3/2-y,-z; Cg3=C9–C10–C11–C12–C13–C14) and the C12–H12⋯
c
Cg2c (3.480(2) Å, -1/2-x,-1-y,1/2+z; Cg2=C1–C2–C3–C4–C5–C6) can be discovered, which

connects the adjacent 1-D chains. As a result, a two-dimensional (2-D) supramolecular layer is built
along the crystallographic bc plane (Fig. 1c). (d) The N–H⋯O (N4–H4A···O2b, 3.135(2) Å, b1+x,y,z)
intermolecular hydrogen bonds derive from the amino-nitrogen atoms and the another hydroxylic
oxygen atoms. Based on the hydrogen bonds, the adjacent 2D sheets can extend into a
three-dimensional (3-D) supramolecular architecture along the crystallographic a direction (Fig. 1d).
Notably, there does not exist the stacking interactions among the aromatic rings, where the shortest
distance can be observed to be 4.1313(12) Å.
3.1.2Structure description of 3,3’-(4-amino-4H-1,2,4-triazole-3,5-diyl)diphenol (2)
When 3-hydroxy-benzonitril replaced 2-hydroxy-benzonitril, compound 2 cam be generated
under the similar reaction conditions. Single X-ray crystallographic analysis reveals that compound 1
crystallizes in the orthorhombic crystal system with the P212121 space group. The unsymmetric unit
contains two 3,3’-(4-amino-4H-1,2,4-triazole-3,5-diyl)diphenol (3OH) molecules and three
methanol molecules (Fig. 2a and Table 1). Notably, it happens two different isomers for 3OH
molecules. One is trans-isomer; another is cis-isomer. In trans-3OH structure, the dihedral angles
with 28.5(1)° and 36.5(1)° can be found between the triazole ring and phenyl groups. In cis-3OH
structure, there exist the dihedral angles with 28.4(1)° and 36.7(1)° among the aromatic rings, which
are comparable to those found in the trans-3OH. The observed values are larger than that (13.0(1)°)
found in 2OH structure and are smaller than that (50.2(1)°) observed in 2OH molecule. The bond
lengths and the bond angles around the triazole-core is normal, which are similar to those observed
in other triazole-based compounds.
Generally, it often happens the hydrogen bonds and the packing interactions in the supramolecular
structures. In compound 2, there exist many kinds of hydrogen bonds as the following: (a) The

a
b
O-H···N (O2-H···N1a 2.763(3) Å, 1/2+x,3/2-y,1-z; O3-H3···N6b 2.662(3) Å, -1/2+x,1/2-y,1-z)
intermolecular hydrogen bonds can be found. The former originates from the oxygen atoms and the
nitrogen atoms of the triazole-yl group in the trans-3OH molecules; while the latter does from the
oxygen atoms and the nitrogen atoms of in the cis-3OH molecules. (b) The N-H···N (N4-He···N2a
a
3.380(3) Å, 1/2+x,3/2-y,1-z) intermolecular hydrogen interactions derive from the triazole-yl and
amino nitrogen atoms in trans-3OH molecules. (c) The C-H···N (C20-H20···N5b 3.432(4) Å,
b-1/2+x,1/2-y,1-z) intermolecular hydrogen bonds occur between the phenyl carbon atoms and the
triazole-yl nitrogen atoms of cis-3OH molecules. The C4-Hl···N4 and C20-H20···N8 (3.015(5) and
3.096(5) Å, respectively) intramolecular hydrogen interactions become from the phenyl carbon
atoms and the amino-nitrogen atoms in trans-3OH molecules. (d) The C-H···O (C18-H18···O1d
d
3.273(4) Å, 1+x,y,z) intermolecular hydrogen connections produce between the phenyl carbon
atoms of cis-3OH skeleton and the oxygen atoms of trans-3OH molecules. The C30-Hs···O2e
e
3.392(5) Å, 1/2-x,1-y,1/2+z) intermolecular hydrogen bonds stem from the carbon atoms of the
guest methanol and the oxygen atoms of the cis-3OH molecules. (e) The O-H···O (O1-Ha···O5
2.658(4) Å, O6-Hb···O3 2.733(3) Å, O4-H4···O7 2.640(4) Å) hydrogen bonds originate from the
oxygen atoms of the 3OH hosts and the methanol molecules. The O-H···O (O5-Hc···O6b 2.789(3) Å,
c
b-1/2+x,1/2-y,1-z; O7-Hd···O6c 2.798(3) Å, 1/2-x,1-y,-1/2+z) intermolecular interactions emerge
from the oxygen atoms of different methanol molecules. (f) The N4-Hf···O4 hydrogen bonds with
the distance of 3.042(4) Å can be found, which happen between the amino-nitrogen atom from the
cis-3OH and the hydroxylic oxygen atoms from the trans-3OH moieties. Apart from hydrogen
bonds mentioned above, the packing interactions also made a significant contribution in crystal
structure. The packing interactions can be observed in structure 2: (i) it occurs the π⋯π packing

interactions such as Cg1···Cg6d (d-1/2+x,3/2-y,1-z), Cg2···Cg4b (b-1/2+x,1/2-y,1-z), Cg4···Cg2e
(e1/2+x,1/2-y,1-z) as well as Cg6···Cg1a (a1/2+x,3/2-y,1-z), where the bond distances are 3.506(2),
3.594(2), 3.594(2) and 3.506(2) Å, respectively. The Cg1, Cg2, Cg4 and Cg6 indicate the centers of
the triazole-yl and phenyl rings, respectively. (ii) The C-H⋯π interactions occur too, for examples,
C31-Ho⋯Cg5c (c1/2-x,1-y,-1/2+z) and C29-Hw⋯Cg2f) (f-x,-1/2+y,3/2-z) with the distance of 3.739(4)
and 3.355(4) Å, respectively.
It is obvious that it happens the π⋯π and C-H⋯π packing interactions (Cg1···Cg6d, Cg2···Cg4b,
C31-Ho ⋯ Cg5c and C29-Hw ⋯ Cg2f) accompanying with hydrogen interactions (intramolecular
C4-Hl···N4, intermolecular O5-Hc···O6b and C20-H20···N8 hydrogen interactions), which connects
3OH molecules and the guest methanol molecules. As a result, a supramolecular1-D chain is built
along the crystallographic b axis (Fig. 2b), where the guest methanol molecules decorate the
supramolecular chain. Further, the O1-Ha···O5, O6-Hb···O3, O4-H4···O7 and C30-Hs···O2e
intermolecular hydrogen bonds make every two neighboring supramolecular 1-D chains expand into
a supramolecular 2-D waveform layer along the crystallographic bc plane (Fig. 2c). The host 3OH
molecules align in the formation of herringbone. Finally, the supramolecular 2-D sheets extend into a
supramolecular 3-D framework along the crystallographic a direction through the O2-H···N1a,
O3-H3···N6b, O7-Hd···O6c, N4-He···N2a, N4-Hf···O4, C18-H18···O1d and C20-H20···N5b
intermolecular hydrogen interconnections (Fig. 2d).
To further investigate the interactions between the host and the guest, the related figures can be
drawn. As shown in Figs. 2b-2d, there exist the strong hydrogen bonds (O1-Ha···O5 and
O4-H4···O7) between the methanol molecules and the host skeleton, where two methanol molecules
act as the acceptor of hydrogen bonds and 3OH molecules do as the donor of the hydrogen bonds.

Another methanol molecule plays a role in the donor of the hydrogen bonds (O6-Hb···O3), where
the acceptor of the hydrogen bonds is one trans-3OH molecule. Meanwhile, this methanol molecue
(O6) acts as the acceptor of the hydrogen bonds (O7-Hd···O6c and O5-Hc···O6b), where other two
methanol molecules (O5 and O7) serve as the donors of the hydrogen bonds. In order to consolidate
the interactions between the host and the guest, we can find that the weak hydrogen bonds of
C30-Hs···O2e and the packing interactions of C31-Ho⋯Cg5c and C29-Hw⋯Cg2f can be observed.
3.1.3 Structure description of 4,4’-(4-amino-4H-1,2,4-triazole-3,5-diyl)diphenol) (3)
When 4-hydroxy-benzonitril took place of 2-hydroxy-benzonitril, compound 3 can be generated
under the similar reaction conditions. The single X-ray crystallographic diffraction results indicate
that the compound 3 crystallizes in the orthorhombic P21/n group. The asymmetric unit consists of
one 4,4´-(4-amino-4H-1,2,4-triazole-3,5-diyl)diphenol molecule (4OH) (Fig. 3a and Table 1).
Noteworthy, the dihedral angle between the triazole-yl and the phenyl rings can be observed to be
38.3(1)° and 41.3(1)°, which are higher than those found in compound 2.
Generally, there exist the supramolecular interactions (hydrogen bonds, π⋯π and C-H⋯π packing)
in the supramolecular architectures. In compound 3, two kinds of interactions can be observed to be
intermolecular hydrogen bonds and C-H⋯π packing interactions (Fig. 3, Tables 3-4). As shown in Fig.
3, it occurs the O-H···N (O1-H1···N2a (a-1+x,y,z), O2-H2···N1b (b1/2+x,3/2-y,1/2+z) and
O2-H2···N2b) intermolecular hydrogen contacts, which become from the hydroxylic oxygen atoms
and the triazole-yl nitrogen atoms from the 4OH molecules. The bond distances are 2.794(3),
2.833(3) and 3.302(3) Å, respectively. The hydrogen bonds of N4-H4A···O2c (c2-x,1-y,1-z) and
N4-H4B···O1d (d1/2-x,1/2+y,1/2-z) can also be found, which happen between the amino N atoms
and the hydroxylic O atoms from the 4OH skeleton. The bond lengths are 3.267(3) and 3.245(3) Å,

respectively. Obviously, each 4OH molecule makes use of the hydrogen bonds of O2-H2···N1b and
O2-H2···N2b hydrogen bonds to form the head-hail mode, which results into building a 1-D
supramolecular chain (Fig. 3b). Then, through these hydrogen bonds the neighboring supramolecular
1-D chains can extend into a supramolecular 2-D laminated structure along the crystallographic ac
plane (Fig. 3c). Except from the intermolecular hydrogen bonds, the C-H⋯π packing interactions also
play a key role in strengthening the stabilities of the supramolecular structures. The C-H⋯π packing
interactions are summarized as the following: C3-H3⋯Cg2a (a1/2-x,1/2+y,1/2-z) and C5-H5⋯Cg3b
(b3/2-x,-1/2+y,1/2-z), where the bond separation is 3.573(3) and 3.302(3) Å, respectively. Both the
Cg2 and Cg3 rings represent the centers of the phenyl rings. Based on the intermolecular hydrogen
interactions of N4-H4A···O2c and N4-H4B···O1d and C-H⋯π packing interactions of C3-H3⋯Cg2a
and C5-H5⋯Cg3b, a 3-D supramolecular framework can be generated along the crystallographic a
direction (Fig. 3d). Interestingly, the smallest stacking distance with the distance of 3.8222(18) Å can
be found between two phenyl rings (Table 5).
3.3. IR spectra
The IR spectra of compounds 1-3 containing amino-triazole moiety are shown in Fig. 4. As
shown in Fig. 4, the characteristic bands of the amino/hydroxylic groups are observed at 3333, 3413
and 3416 cm-1 for compounds 1-3, respectively. It happens the bands located at 1608 and 1483 cm-1,
1589 and 1487 cm-1, 1613 and 1481 cm-1 for 1-3, respectively, which indicates the stretching
vibration of aromatic C=C and C=N. There exist the peaks observed at range of 971-754, 978-724,
and 979-744 cm−1 for compound 1-3, respectively, suggesting the existence of the in-plane and
out-plane bending vibration of γ(CH) and δ(CH) modes of phenyl rings.
3.4. Thermogravimetric analysis

To study the thermal stabilities of the title compounds, thermogravimetric analyses (TGA)
were carried out [41]. The experiments were performed on samples containing numerous single
crystals under a N2 atmosphere with a heating rate of 10 °C min−1 (Fig. 5). The TGA curves of
compounds 1 and 3 reveal that it happens a platform found at about 290 °C, showing that there exists
high thermal stability for compounds 1 and 3. The present results indicate that there exist strong
hydrogen bonds among compounds 1 and 3. Then, it occurs to start the weight loss up to 295 and
320 °C for compounds 1 and 3, respectively, which can be assigned to the decomposition of the
organics. For compound 2, the TGA curve shows that it happens a weight loss at range of 75-150 oC,
suggesting the departure of the crystallized methanol molecules (cald. 15.1%, obsd. 9.0%). The
observed results reveal that it occurs the strong hydrogen bonds between the host and the guest
molecules. Then, a plateau can be found at the range of 150-325 oC. After that, the weight loss can be
observed, indicating the decomposition of organic skeleton.
In order to investigate the relationship between the thermal stabilities and the molecular
structures, we carefully check the supramolecular interactions of these compounds. In compounds 1
and 3, the whole molecule shows the trans-isomer and cis-isomer features, respectively, which leads
o
to the low decomposition temperature (295 and 320 C, respectively). However, in compound 2, we
can observe the existence of cis-isomer and trans-3OH structures, which accounts for the high
thermal stabilities (decomposition temperature of 325 oC).
3.5. Luminescent properties
To investigate the luminescent properties of the title compounds, the solid-state
photoluminescent spectra of 1-3 were performed at room temperature [42-43]. As shown in Fig. 6,
the emission peaks can be found at 461, 414 and 402 nm for compounds 1-3, respectively, when the

excitation wavelengths are 350, 320 and 300 nm for compounds 1-3, respectively. The observed
results may be attentively ascribed to the π* → π or π* → n transitions [44-50]. Notably, there exist
an order of the maximal peaks for these compounds: 1>2>3. Interestingly, we can find that
compounds 1-3 have different position for the -OH group connected to the phenyl rings, and their
position changes from orth-, meta- to para-location. It happens an order of the steric effects for the
hydroxylic groups: 1>2>3. As discussed above, we can find that in compound 1, there exists the big
conjugation system originated from the phenyl and triazole-yl rings with the dihedral angle of 63.3°
(Table 5). In compounds 2 and 3, the dihedral angles are 65.0° and 79.6°, respectively, suggesting
the conjugation degree decreases, which results into a blue phenomenon. Obviously, the order of the
dihedral angles is listed: 1<2<3, which is an inverse-proportional to that of the maximal peaks.
Thus, we can conclude that the luminescent maximal bands decline down the steric effects for the
hydroxylic groups. Thus, the photoluminescent behaviors can be controlled by the hydroxylic
position.
3.6.Hirshfeld surface analysis
To further quantitatively evaluate the relationship between the intermolecular interactions and
the properties for these compounds, the Hirshfeld surface analyses were performed [51-53]. The
Hirshfeld surface and the corresponding finger print plots were used to visualize the intermolecular
interactions of the compounds 1-3. The Hirshfeld surface mapped over the dnorm (normalized connect
distance, which equal to the Van der Walls radii), di (the distance from the distance from the nucleus
to the nearest nucleus which is inside the surface) and de (the distance from the nucleus to the nearest
nucleus which is outside the surface). The strong, the weak and no intermolecular interactions are
represented in the red, blue and white region, respectively (Figs. 7-9a). The shape index reveals the

hollows and the humps of the crystal, which are represented by the red regions and the blue regions,
respectively (Figs. 7-9b). The green area and the blue line were shown in the curvedness (Figs. 7-9c).
Herein, we discuss the varieties of the intermolecular interactions in compounds 1-3 based on
different position of the hydroxyl groups bonded to the aromatic rings (Table 6).
In compound 1, the strong hydrogen bonds are C-H∙∙∙O hydrogen as deep red spot (Fig. 7).
Intermolecular contacts are exhibited by finger print plots shown in Fig. 11a. The interactions of
O∙∙∙H/H∙∙∙O with the contribution of 8.8% can be found. A spur in lower left region represents the
contact of H∙∙∙H (38.4%) interactions. Strong interactions in crystal 1 are C∙∙∙H/H∙∙∙C and N∙∙∙H/H∙∙∙N
with the contribution of 31.4% and 14.5%, respectively. The interactions of C∙∙∙C can be found to be
2.4%. Specially, the two blunt spikes display the C∙∙∙H/H∙∙∙C interconnections, and the two sharp
nails reveal the N∙∙∙H/H∙∙∙N interactions (Fig. 10a).
When the hydroxyl groups are located in the 3-position of aromatic rings, the strong interactions
shown as bright red dots are C-H∙∙∙O and C-N∙∙∙H hydrogen bonds (Fig. 8a). The contacts of
O∙∙∙H/H∙∙∙O can be found to be 11.8%, which is larger than that observed in compound 1. Compared
with crystals 1, compound 2 has higher the H∙∙∙H contacts with the contribution of 44.9%. The
contribution of 19.6% can be observed for the C∙∙∙H/H∙∙∙C contacts. The rest of the contacts
interactions are listed as the following: N∙∙∙H/H∙∙∙N (11.9%) and C∙∙∙C (3.8%) (Fig. 10b).
When the hydroxyl groups can be bonded to the para-position of the phenyl rings, the red spots
reveal the strong N-H∙∙∙O and O-H∙∙∙N intermolecular hydrogen bonds (Fig. 9a). As shown in Fig.
10c, among all interactions the H∙∙∙H interactions give the maximal contribution of 33.2%. The
contacts of O∙∙∙H/H∙∙∙O can be found to be 14.4%, which is higher than those observed in compounds
1 and 2. The other intermolecular contacts to the surface are shown as the followings: H∙∙∙C/C∙∙∙H

(29.1%), H∙∙∙N/N∙∙∙H (16.0%) and C∙∙∙C (2.3%). The overall contributions of intermolecular
interactions to the crystal are illustrated in Fig. 10c.
Notably, the O∙∙∙H/H∙∙∙O close contacts exhibit the increasing order from compound 1 to 3:
1<2<3, where the same order can be observed for the total dihedral angles between the phenyl and
triazole-yl rings (Table 5). As mentioned above, there exist an order of the luminescent maximal
peaks for compounds 1-3 (1>2>3). Obviously, the maximal peaks decrease with the growth of the
O∙∙∙H/H∙∙∙O close contacts and the dihedral angles, and with the reduction of the hydroxylic steric
effects. The observed results can be quantitatively responsible for the luminescent behaviors.
4. Conclusion
In summary, we have successfully prepared a set of 4H-amino-1,2,4-triazole derivatives with
different hydroxylic positions under the solvothermal reaction conditions. The title compounds are
characterized by EA, IR, and powder/single-crystal X-ray diffraction. Notably, it happens the
interesting feature with both trans- and cis-conformation for compound 3. The photoluminescent
properties can be tuned through the position of the substituent groups, but also the luminescent peaks
decline down the diminution of the hydroxyl steric effects. The observed results can be further
confirmed by the Hirshfeld surface analyses and the dihedral angles between the phenyl and
triazole-yl rings. The present strategies based on the design and development of the molecular
engineering open an avenue to explore the promising photoluminescent materials. Furthermore, the
investigation of compounds based on 4-amino-4H-1,2,4-triazole group with the controlled
fluorescent behaviors are under the way in our laboratory.
Acknowledgement
This work was financially supported by Shandong Distinguished Middle-aged Young Scientist

Encouragement and Reward Foundation (BS2011CL034) and Shandong Provincial Natural Science
Foundation (ZR2017MB041), and College Student Innovation and Entrepreneurship Training
Program (S201910431065, S202010431073 and S202010431001).
Appendix A. Supplementary data
CCDC 2067931-2067933 contains the supplementary crystallographic data for compounds 1-3.
These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
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A set of x,x'-(4-amino-4H-1,2,4-triazole-3,5-diyl) diphenol [x=2 (1), x=3 (2), x=4 (3)],
were prepared, which have been characterized by IR, element analysis (EA), single
crystal X-ray diffraction, and powder X-ray diffraction (PXRD). Hydrogen bonds
(C/N/O–H∙∙∙O/N) and C-H∙∙∙π can be clearly observed in these compounds. It
surprisedly occurs the presence of trans- and cis-conformation for compounds 3. The
increasing order of the dihedral angles between the phenyl and triazole-yl rings is
1<2<3. The solid-state luminescent spectra of 1-3 show that the emission maxima are
observed at 461, 414 and 402 nm, respectively, which shows the declining order of
1>2>3. The luminescent maximal peaks decrease with the diminution of hydroxylic
steric effects. The Hirsfeld surface analyses reveal that the contribution order of the
O∙∙∙H/H∙∙∙O contacts is 1<2<3, which is in good agreement with that of the dihedral
angles, and an inverse proportional to the fluorescent maxima of compounds 1-3.

Table 1. Crystal data and structure refinement parameters for compounds 1-3.
Compound reference
Chemical formula
Formula Mass
Crystal system
a/Å
1
2
3
C14H12N4O2
268.28
C31H36N8O7
632.68
C14H12N4O2
268.28
Monoclinic
9.436(2)
7.5468(19)
18.151(5)
90
Orthorhombic Orthorhombic
8.2534(3)
9.3891(3)
15.4850(5)
90
11.4472(4)
11.5244(4)
22.5678(10)
90
b/Å
c/Å
α/°
β/°
90
90
101.976(8)
90
γ/°
90
90
Unit cell volume/Å3
Temperature/K
Space group
No. of formula units per
unit cell, Z
1199.96(6)
100.01(10)
P212121
4
2977.2(2)
99.98(11)
P212121
4
1264.5(6)
100(2)
P21/n
4
Radiation type
Absorption coefficient,
μ/mm-1
Mo Kα
Mo Kα
Mo Kα
0.104
0.103
0.099
No. of reflections measured7106
20206
7044
10203
2881
No. of independent
reflections
2652

Rint
0.0305
0.0485
0.0506
0.1137
0.0787
0.0685
0.1824
Final R1 values (I > 2σ(I)) 0.0358
Final wR(F2) values (I > 0.0797
2σ(I))
Final R1 values (all data) 0.0394
0.0799
0.1276
0.0989
0.1991
Final wR(F2) values (all
data)
0.0817
Goodness of fit on F2
Flack parameters
CCDC number
1.052
1.075
1.069
0.2(7)
-0.6(7)
2067932
2067931
2067933
2
2 2
aR1= Fo-Fc/Fo. bwR2=[[w(Fo -Fc2)2] /[w(Fo ) ]]1/2.

Table 2. Selected bond lengths (Å) and angles (°) for complexes 1-3.
Bond lengths/bond angles Bond lengths (Å)/BondBond lengths/bond angles Bond lengths (Å)/Bond
angles (°)
angles (°)
1
O1-C1
N1-N2
N2-C8
N3-C7
C1-C2
C2-C3
C3-C4
C5-C6
C9-C10
C10-C11
C12-C13
1.369(2)
1.386(2)
1.325(3)
1.364(3)
1.403(3)
1.397(3)
1.388(3)
1.392(3)
1.401(3)
1.381(3)
1.381(3)
O2-C14
N1-C7
N3-N4
N3-C8
C1-C6
1.362(3)
1.318(3)
1.416(2)
1.364(3)
1.387(3)
1.473(3)
1.390(3)
1.471(3)
1.414(4)
1.392(4)
1.392(3)
C2-C7
C4-C5
C8-C9
C9-C14
C11-C12
C13-C14
N2-N1-C7
N4-N3-C7
C7-N3-C8
O1-C1-C6
C1-C2-C3
107.14(16)
126.15(17)
106.66(17)
121.88(18)
119.14(18)
N1-N2-C8
N4-N3-C8
O1-C1-C2
C2-C1-C6
C1-C2-C7
108.17(17)
126.68(17)
117.86(19)
120.25(18)
120.84(17)

C3-C2-C7
C3-C4-C5
C1-C6-C5
N1-C7-C2
N2-C8-N3
N3-C8-C9
C8-C9-C14
C9-C10-C11
C11-C12-C13
O2-C14-C9
C9-C14-C13
2
119.64(17)
119.33(18)
119.7(2)
C2-C3-C4
120.77(18)
120.8(2)
C4-C5-C6
N1-C7-N3
109.49(19)
125.09(19)
122.8(2)
125.34(18)
108.48(18)
128.31(19)
118.83(19)
121.1(2)
N3-C7-C2
N2-C8-C9
C8-C9-C10
C10-C9-C14
C10-C11-C12
C12-C13-C14
O2-C14-C13
122.7(2)
118.23(19)
120.1(2)
119.8(2)
120.8(2)
123.40(18)
119.91(19)
116.7(2)
O1-C1
1.354(4)
1.386(4)
1.317(4)
1.359(4)
1.394(5)
1.391(5)
1.397(5)
1.469(5)
1.395(4)
1.375(5)
O2-C11
N1-C7
N3-N4
N3-C8
C1-C6
C3-C4
C5-C6
C8-C9
C9-C14
C11-C12
1.360(4)
1.321(4)
1.418(3)
1.378(4)
1.389(5)
1.378(5)
1.390(5)
1.473(5)
1.394(5)
1.395(5)
N1-N2
N2-C8
N3-C7
C1-C2
C2-C3
C4-C5
C5-C7
C9-C10
C10-C11