Four new CuI/AgI-based coordination compounds containing 2-mercapto-5-methyl-1,3,4-thiadiazole: Synthesis, crystal structures and fluorescence properties

Article abstract of DOI:10.1016/j.ica.2021.120596

Effectively constructing Cu^I/Ag^I-based coordination polymers containing Hmthd ligands is a challenging work, here, four new coordination compounds [Cu(Hmthd)₂Cl]_n (1), [Cu₃(mthd)₂Br]_n (2), [Ag(mthd)]_n (3) and [Ag₂(mthd)I]_n (4) have been obtained by reactions of the corresponding metal salts and 2-mercapto-5-methyl-1,3,4-thiadiazole (Hmthd) ligand under solvothermal conditions. All the compounds were fully characterized by single-crystal X-ray diffraction, elemental analysis, IR spectrum, thermalgravimetric analysis and powder X-ray diffraction. Compound 1 is a mononuclear coordination compound, in which two neutral Hmthd molecules and CuCl unit are coplanar. In compound 2, the anionic [CuBr(mthd)]₂^2– units and one-dimensional coplanar cationic {[Cu₂(mthd)]⁺}_n chains are connected to each other to form a two-dimensional layered structure. In compound 3, two different one-dimensional puckered [Ag(mthd)]_n chains are connected to each other to form a two-dimensional irregular layered structure, in which a (AgS)_n chain constructed by staggered Ag₃S₃ rings is observed. Compound 4 is a two-dimensional double layer coordination framework containing a two-dimensional inorganic (Ag₂IS)_n double layer. Compound 4 shows the apparent yellow emission with the maximum at 551 nm while exciting at 333 nm, and displays sensitive luminescence quenching response to nitrobenzene with quenching constant (K_sv) of 5.07 × 10³ M^?1 and detection limit of 5.33 × 10^?6 M. This research provides a new strategy to construct the Cu^I/Ag^I-based coordination compounds containing Hmthd ligands with extended structures through the synergistic effect of (mthd)^- and halide ions.

Full text of DOI:10.1016/j.ica.2021.120596

Inorganica Chimica Acta 528 (2021) 120596
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Research paper
I
I
Four new Cu /Ag -based coordination compounds containing 2-mercap-
to-5-methyl-1,3,4-thiadiazole: Synthesis, crystal structures and
fluorescence properties
a
a
a
a,
*
b,*
Ying Geng , Wen Zhang , Jiang-Feng Song , Rui-Sha Zhou , Wei-Zhou Jiao
a
Department of Chemistry, North University of China, Taiyuan, Shanxi 030051, PR China
b
Shanxi Province Key Laboratory of Higee-Oriented Chemical Engineering, North University of China, PR China
A R T I C L E I N F O
A B S T R A C T
I
I
Keywords:
Effectively constructing Cu /Ag -based coordination polymers containing Hmthd ligands is a challenging work,
here, four new coordination compounds [Cu(Hmthd) Cl] (1), [Cu (mthd) Br] (2), [Ag(mthd)] (3) and
Ag (mthd)I] (4) have been obtained by reactions of the corresponding metal salts and 2-mercapto-5-methyl-
,3,4-thiadiazole (Hmthd) ligand under solvothermal conditions. All the compounds were fully characterized
Coordination polymers
Crystal structure
Fluorescence
Organic sulfur
Sensing
2
n
3
2
n
n
[
2
n
1
by single-crystal X-ray diffraction, elemental analysis, IR spectrum, thermalgravimetric analysis and powder X-
ray diffraction. Compound 1 is a mononuclear coordination compound, in which two neutral Hmthd molecules
2
–
and CuCl unit are coplanar. In compound 2, the anionic [CuBr(mthd)]
2
units and one-dimensional coplanar
+
cationic {[Cu
2
(mthd)] }
n
chains are connected to each other to form a two-dimensional layered structure. In
chains are connected to each other to form a
chain constructed by staggered Ag rings is
observed. Compound 4 is a two-dimensional double layer coordination framework containing a two-dimensional
inorganic (Ag IS) double layer. Compound 4 shows the apparent yellow emission with the maximum at 551 nm
compound 3, two different one-dimensional puckered [Ag(mthd)]
two-dimensional irregular layered structure, in which a (AgS)
n
n
3 3
S
2
n
while exciting at 333 nm, and displays sensitive luminescence quenching response to nitrobenzene with
3
ꢀ 1
ꢀ 6
quenching constant (Ksv) of 5.07 × 10
M
and detection limit of 5.33 × 10 M. This research provides a new
I
I
strategy to construct the Cu /Ag -based coordination compounds containing Hmthd ligands with extended
-
structures through the synergistic effect of (mthd) and halide ions.
1
. Introduction
Luminescent coordination compounds are a rapidly burgeoning class
example, organic amine, organo-phosphine and organic-sulfur ligands
are frequently used to construct the targeted compounds with novel
structures and excellent properties[21–41]. Compared with organic
amines and organophosphines, the sulfur atoms on organosulfur ligands
display richer coordination modes and stronger bonding ability to match
metal orbitals together with various in situ ligand/metal redox reactions
[27,42–44]. Therefore, the controlled syntheses of organosulfur-based
coordination compounds arouse widespread interests due to their
structural diversity and potential applications such as sensing, hetero-
geneous catalysis and biological anti-bacterials [30,36].
of crystalline materials which show great potential of a broad range of
applications such as light emission, sensitive sensor, photo-catalysis, and
I
I
so on[1–11]. Thus far, especially precious metal species such as Re , Au ,
II
II
III
Os , Pt , Ir [12–14], lanthanide ions with narrow and characteristic 4f-
f transitions together with transition metals with d1 electronic con-
0
4
figurations are often utilized to construct the target luminescent coor-
I
I
dination compounds[15–20]. Of particular interests are Cu /Ag -based
coordination compounds with d10 electronic configurations, which are a
developing class of luminescent materials based on an inexpensive and
abundant metal sources as well as their remarkable luminescent per-
mercapto-5-methyl-1,3,4-thiadiazole (Hmthd) is a typical multi-
dentate five-membered heterocyclic compound which contains two
heterocyclic nitrogen, one heterocyclic sulfur and one sulfhydryl
group. Hmthd ligand has obvious advantages in the construction of
I
I
formances. A typical strategy to synthesize Cu /Ag -based compounds
usually requires the satisfactory choice of coordinating ligands, for
*
Corresponding authors.
E-mail addresses: rszhou0713@nuc.edu.cn (R.-S. Zhou), zbdxjwz@nuc.edu.cn (W.-Z. Jiao).
https://doi.org/10.1016/j.ica.2021.120596
Received 17 July 2021; Received in revised form 16 August 2021; Accepted 26 August 2021
Available online 8 September 2021
0
020-1693/© 2021 Elsevier B.V. All rights reserved.

Y. Geng et al.
Inorganica Chimica Acta 528 (2021) 120596
◦
the coordination compounds: (1) the two nitrogen and one sulfur of
and heated at 80 C for 72 h under autogenous pressure. After slowly
cooling to room temperature, yellow rod-shaped crystals of 1 were
collected by filtration and washed with distilled water and ethanol
several times. Yield: 35% (based on the Hmthd). Elemental anal. calcd
thiadiazole ring together with the introduced sulfhydryl group can
be used as chelating ligands or bridging ligands to coordinate with
metal ions; (2) the large-size sulfur can interact with metal ions
through various coordination modes ranging from
μ
1
to
μ
4
, and its 3p
6 8 4 4
C H ClCuN S (363.39): C, 19.81; H, 2.20; N, 15.41. Found: C, 19.85; H,
ꢀ 1
orbitals show strong coordination ability to match metal orbitals, as
result in the formation of multi-nucleus clusters or high-dimensional
2.16; N, 15.44. IR data (KBr, cm ): 2904(w) 1479(w), 1419(w), 1335
(s), 1188(m), 1079(m), 1025(m), 965(w), 768(m), 671(w), 622(w), 535
(w).
–
structures [43]; (3) Hmthd ligand shows a thione-thiol (–N
–
C–SH
–
–NH–C
–
↔
S) tautomeric transformation, resulting in the diversity
of coordination modes. As far as we know, most of the reported
3 2 n
3.2. Synthesis of [Cu (mthd) Br] (2)
-
compounds based on Hmthd or (mthd) were zero-dimensional (0 D)
mononuclear compounds through the assembly of Hmthd and tran-
The procedure was the same as that for compound 2 except that CuCl
was replaced by CuBr (2.87 mg, 0.02 mmol). After slowly cooling to
room temperature, yellow rhomboid crystals of 2 were collected by
filtration and washed with distilled water and ethanol several times.
2
+
2+
2+
2+
2+
sition metal ions such as Ni , Cu , Zn , Cd , Hg [45] or main
metal ions Pb2 [46], Sn [47], and only Me
+
4+
3
3 3 2
Sn[S(C H N S)] dis-
played one-dimensional (1 D) polymeric chain [47]. Notably, the
I
I
Cu /Ag -based compounds containing Hmthd ligands are less re-
Yield: 47% (based on the Hmthd). Elemental anal. calcd C
6 6 3 4 4
H BrCu N S
I
I
ported, therefore, effectively constructing Cu /Ag -based coordina-
tion compounds containing Hmthd ligands with extended structures
is a challenging work.
(532.92): C, 13.51; H, 1.13; N, 10.51. Found: C, 13.55; H, 1.09; N, 10.55.
ꢀ 1
IR data (KBr, cm ): 2909(w), 1566(w), 1452(m), 1349(s), 1108(s),
1039(w), 994(w), 884(w), 780(w), 617(vs).
I
I
According to hard-soft-acid-base theory, Cu /Ag belonging to soft
acids should easily coordinate with soft bases such as S atom in organic
sulfur ligands and obtain the targeted coordination compounds. In
3.3. Synthesis of [Ag(mthd)] (3)
n
A mixture of AgNO3 (3.40 mg, 0.02 mmol), KBr (2.38 mg, 0.02
mmol) and Hmthd (2.64 mg, 0.02 mmol) was dissolved in a CH CH OH :
I
I
addition, considering that Cu /Ag ions have good binding ability with
halogen ions, the introduction of halogen ions can effectively adjust the
diversity of the target structures. Herein, we successfully synthesize four
3
2
CH CN solution (v : v = 3 : 2, 5 mL). The pH value of above mixture was
3
adjusted through addition of 0.05 mL ethylenediamine (0.1 mol/L), then
new coordination compounds through the synergistic interactions of
was sealed in a 20 mL Teflon-lined stainless-steel reactor and heated at
-
◦
(
mthd) and halide ions, [Cu(Hmthd)
2
Cl]
(4), (Hmthd = 2-mercapto-5-methyl-
,3,4-thiadiazole). All the compounds were fully characterized by
n
(1), [Cu
3
(mthd)
2
Br]
n
(2), [Ag
80 C for 72 h under autogenous pressure. After slowly cooling to room
(
mthd)]
n
(3) and [Ag
2
(mthd)I]
n
temperature, white needle crystals of 3 were collected by filtration and
washed with distilled water and ethanol several times. Yield: 43%
(based on the Hmthd). Elemental anal. calcd C H AgN S (239.06): C,
1
single-crystal X-ray diffraction, elemental analysis, IR spectrum, ther-
3
3
2 2
malgravimetric analysis and powder X-ray diffraction. Compound 1 is a
15.06; H, 1.25; N, 11.71. Found: C, 15.02; H, 1.19; N, 11.76. IR data
ꢀ
1
0
D
mononuclear compound while compounds 2–4 show two-
(KBr, cm ): 2920(w), 1572(w), 1430(w), 1354(s), 1190(m), 1097(w),
1043(m), 977(w), 879(w), 769(m), 617(vs).
dimensional (2 D) layered structures, the results show introduction of
halogen ions finely modulate the structural features of the target com-
pounds. The fluorescence properties of compound 4 in the solid state
and in various solvent molecules have also been investigated, displaying
highly luminescence quenching response to nitrobenzene (NB).
3.4. Synthesis of [Ag (mthd)I] (4)
2
n
The procedure was the same as that for compound 3 except that KBr
was replaced by KI (3.32 mg, 0.02 mmol). After slowly cooling to room
temperature, white rhomboid crystals of 4 were collected by filtration
and washed with distilled water and ethanol several times. Yield: 58%
2
. Experimental
2
.1. Materials and physical measurements
(based on the Hmthd). Elemental anal. calcd C
3 3 2 2 2
H Ag IN S (473.83): C,
7
.60; H, 0.63; N, 5.91. Found: C, 7.58; H, 0.64; N, 5.93. IR data (KBr,
ꢀ 1
All reagents and solvents were commercially available and used as
cm ): 2920(w), 1474(w), 1414(w), 1363(vs), 1196(m), 1119(w), 1086
(w), 1032(m), 972(w), 764(w), 737(w), 666(w), 617(w).
received without further purification. Elemental analysis (C, H and N)
was performed on a Perkin-Elmer 240C elemental analyzer. Infrared (IR)
spectra were obtained with KBr pellets on a Perkin Elmer Spectrum One
3.5. Single crystal structure determination
ꢀ 1
FTIR spectrometer in the range of 4000–400 cm . Powder X-ray
diffraction (PXRD) patterns of the samples were recorded by a RIGAKU-
DMAX2500 X-ray diffractometer using Cu-Kɑ radiation (λ = 1.542 Å)
The crystal structures were determined by single-crystal X-ray
diffraction. Reflection data were collected on a Bruker SMARTCCD area-
◦
ꢀ 1
◦
with a scanning rate of 10 min and a step size of 0.02 . Thermal-
gravimetric analysis (TGA) was performed on a Perkin-Elmer TGA-7000
detector diffractometer (Mo-K
α
radiation, graphite monochromator) at
room temperature with -scan mode. Empirical adsorption correction
ω
◦
ꢀ 1
thermogravimetric analyzer with a heating rate of 10 C min . The
solvent emulsion and solid fluorescent spectra of compound 4 were
obtained on a HITACHI F-2700 fluorescence Spectrophotometer at room
temperature.
was applied to all data using SADABS. The structure was solved by direct
methods and refined by full-matrix least squares on F2 using SHELXTL
2014 software[48]. Non-hydrogen atoms were refined anisotropically.
All C-bound H atoms were refined using a riding model with Uiso(H) =
1
.2. The crystallographic data and pertinent information are given in
3
. Synthesis of compounds 1–4
Table 1; the selected bond lengths and angles in Table S1.
3
.1. Synthesis of [Cu(Hmthd) Cl] (1)
2
n
4. Results and discussion
A solution of Hmthd (3.97 mg, 0.03 mmol) in ethanol (3 mL) was add
to a solution of CuCl (1.98 mg, 0.02 mmol) in CH CN (3 mL), and the
4.1. Synthesis of compounds 1–4
3
mixed solution was stirred for about 20 min. The pH value of the above
mixture was adjusted through addition of 0.15 mL HCl (0.1 mol/L), then
the mixture was sealed in a 20 mL Teflon-lined stainless-steel reactor
During the synthesis process, we found that ethanol is helpful to the
I
I
-
-
-
dissolution of Hmthd ligand while MX (M = Ag or Cu , X = Cl , Br or I )
can be soluble in acetonitrile, which provide a facility for solvothermal
2

Y. Geng et al.
Inorganica Chimica Acta 528 (2021) 120596
Table 1
Crystal and structure refinement data for compounds 1–4.
Compound
1
2
3
4
Empirical formula
Formula weight
Crystal system
Space group
a/Å
C
6
H
8
ClCuN
4
S
4
C
6
H
6
BrCu
3
N
4
S
4
C
3
H
3
AgN
2
S
2
C
3
H
3
Ag
473.83
orthorhombic
Pca2
2 2 2
IN S
363.39
532.92
monoclinic
P2 /n
239.06
triclinic
P-1
monoclinic
C2/c
1
1
15.922 (3)
5.9559 (8)
13.740 (2)
90
8.650 (4)
10.046 (4)
15.793 (6)
90
4.1986 (2)
10.056 (4)
11.206 (5)
7.964 (3)
90
b/Å
12.5171 (7)
12.6172 (7)
64.4150 (10)
85.277 (2)
86.921 (2)
595.92 (6)
4
c/Å
◦
◦
◦
α
/
β/
102.454 (9)
90
91.786 (15)
90
90
γ/
90
3
Volume/(Å )
Z
1272.3 (3)
4
1371.7 (10)
4
897.5 (7)
4
ꢀ
3
ρ
calc/Mg/m
1.897
2.581
2.665
3.507
Absorption coef.
2.559
8.112
3.960
8.196
Reflections collected
15,528
8293
11,951
8398
Unique (Rint
)
1446 (0.0213)
99.4 %
3083 (0.0711)
97.9 %
2073 (0.0288)
96.9 %
1909 (0.0516)
94.0 %
1.119
Completeness
GooF
1.102
1.038
1.210
[
a]
R , wR
1
2
[I > 2
σ
(I)]
R
1
= 0.0184, wR
2
2
= 0.0467
= 0.0482
R
1
= 0.0683,
wR
= 0.1690
= 0.1389, wR
R
1
= 0.0300, wR
2
2
= 0.0822
= 0.0850
R
1
= 0.0308, wR
2
2
= 0.0717
= 0.0741
2
[
a]
R , wR
1
2
(all data)
R
1
= 0.0201, wR
R
1
2
= 0.2039
R
1
= 0.0359, wR
R
1
= 0.0347, wR
[
a]
2
2
c
2 2 1/2
R
1
= Σ||F
o
| – |F
c
||/Σ|F
o
|; wR = [Σw(F
o
– F
)
2
/Σw(F
o
) ]
.
reaction. As is well known, self-assembly processes under solvothermal
conditions are often influenced by solvent composition, reaction tem-
perature, solution pH, etc. The experiments show lower pH values
(
acidic conditions) are beneficial to the formation and growth of crys-
talline 1 and 2, however, when alkaline substances such as ethylenedi-
amine or NaOH as a regulator were added to the reaction system, some
unrecognizable flocculent or powdery substances are often obtained. If
CuCl and CuBr were replaced by CuI in acidic conditions, some unrec-
ognizable fine solid powders were often obtained; When ethylenedi-
amine adjusts the pH of the reaction system to alkaline conditions,
(
H
2
en)SO
4
is easily obtained, and the possible reason is that Hmthd
2
-
ligand is desulfurized and oxidized to SO
4
. For compounds 3–4, in
acidic conditions, the crystals were too small to be characterized by
single crystal X-ray diffraction, while weakly alkaline conditions are
beneficial to the formation and growth of the targeted crystals suitable
for characterization. Notably, it is difficult to get the target crystals of 3
3
through the reaction between AgNO and Hmthd ligand. We have also
tried to synthesize AgCl-based coordination complex, unfortunately,
some small needle-like crystals were obtained but could not be charac-
terized by single crystal X-ray diffraction. The successful synthesis of
compounds 1–4 demonstrates that the composition of the solvent and
the pH value of the solution played an important role in the preparation
I
I
Fig. 1. (a) Coordination environment of the Cu(I) ion, (b) the 3D supramo-
lecular network in compound 1. The hydrogen atoms are omitted.
of Cu /Ag -based compounds containing Hmthd ligands.
. Crystal structures of 1–4
.1. Crystal structure of [Cu(Hmthd)
Single-crystal X-ray diffraction shows that compound 1 crystallizes
5
C
–
S bond distances observed in Hmthd ligand are longer than that of
–
C
S double bond of 1.62 Å, while shorter than that of C–S single bond
–
5
2 n
Cl] (1)
–
–
of 1.81 Å[24], indicating that partial C
S double bond characters in
Hmthd ligand are observed. Therefore, the above results indicate there
–
–
exist in a thione-thiol (–N
–
C–SH ↔ –NH–C
1-қS2 coordination mode
–
S) transformation equi-
in the monoclinic system with space group C2/c. The asymmetric unit of
librium in Hmthd ligand.
compound 1 is composed of half a Cu(I) ion, half a chloride anion, one
-
Two neutral Hmthd molecules in a
μ
electrically neutral Hmthd ligand. Both Cu(I) and Cl are located on a 2
1
interact with one CuCl unit to form a mononuclear coordination com-
pound, in which two neutral Hmthd molecules and CuCl unit are
coplanar and the largest deviation is 0.1565 Å. The intra-molecular
symmetry axis with occupancy of 0.5. The Cu(I) center shows a planar
triangular geometry and coordinates with two sulfur atoms from two
different neutral Hmthd ligand and one chloride ion (Fig. 1a). The Cu-S
and Cu-Cl bond distances are 2.2211(5) and 2.2358(7) Å, respectively;
-
hydrogen bonds between protonated N1 and Cl anion play an impor-
tant role in the formation of coplanar molecule. The coplanar mono-
and the S/Cl-Cu-S/Cl bond angles range from 118.737(13) to 122.52
◦
nuclear molecules are assembled into
a
three-dimensional (3D)
(
3) . Notably, the C3-S2 bond length (1.69 Å) in neutral Hmthd ligand is
supramolecular network through C
–
H⋅⋅⋅S and C H⋅⋅⋅Cl hydrogen
–
apparently shorter than that of C
diazole ring (dC2-S1 = 1.74 Å and dC3-S1 = 1.73 Å), indication C3-S2
–
S bonds within aromatic 1,3,4-thia-
bonds (Fig. 1b).
–
bond has the characteristics of C S double bond. Notably, all the
–
3

Y. Geng et al.
Inorganica Chimica Acta 528 (2021) 120596
5
.2. Crystal structure of [Cu
3
(mthd)
2
Br]
n
(2)
and Ag-N bond distances are in the range of 2.4593(19)-2.712(2) Å
and 2.253(6)-2.630(6) Å, respectively, and the S/N-Ag-S/N bond angles
◦
Single-crystal X-ray diffraction shows that compound 2 crystallizes
in the monoclinic system with space group P2 /c. The asymmetric unit
range from 84.57(14) to 155.34(16) . The C
–
S bond distances (dC1-S1
=
1
1.72 Å and dC3-S4 = 1.71 Å) outside the thiadiazole rings in compound 3
is slightly shorter than that inside thiadiazole ring (average C S bond
length is 1.74 Å), but slightly longer than C S bond distance in com-
pound 1. The (mthd) anion displays two kinds of coordination modes:
-1қN1, 2қS1, 3қS1, 4қS1 and
ꢀ 1қN3, 2қN4, 3қS3, 4қS3 (Fig. 3b).
The (mthd)- anions containing S3 atoms interact with Ag1 ions
through Ag-S and Ag-N bonds into a 1D puckered [Ag(mthd)] chain
of compound 2 is composed of three Cu(I) ions, two completely depro-
–
-
tonated (mthd) anions and one bromide anion. The Cu1 and Cu3 centers
–
-
both display a distorted tetrahedral geometry, and Cu1 is bound to one
-
sulfur atom and two nitrogen atoms from three different (mthd) anions
μ
4
μ
4
and one bromide anion, while Cu3 is coordinated with two sulfur atoms,
-
one nitrogen atom from three different (mthd) anions and one bromide
n
anion. The Cu2 center exhibits a planar triangular geometry and is
structure (marked as chain 1) in which two parallel zigzag (AgS) chains
with the shortest Ag⋅⋅⋅Ag distance is 3.08 Å are observed (Fig. 3c), which
is shorter than the sum of Vander Waals radius (3.44 Å) of Ag atoms, but
slightly longer than that of the Ag-Ag separation in bulk metallic silver
(2.89 Å)[49–50], indicating that obvious Ag-Ag interactions. Interest-
bound to two sulfur atoms and one nitrogen atom from three different
-
(
mthd) anions (Fig. 2a). The Cu–N, Cu-S and Cu-Br bond distances are in
the range of 2.009(8)-2.040(9) Å, 2.258(3)-2.429(3) Å and 2.426(2)-
2
.460(3) Å, respectively, and the S/N/Br-Cu-S/N/Br bond angles
◦
range from 99.0(3) to 132.62(11) . The C
–
S bond distances (dC4-S1
=
n
ingly, similar 1D puckered [Ag(mthd)] chain (marked as chain 2) is
-
1
.73 Å and dC1-S3 = 1.74 Å) outside the thiadiazole ring in compound 2 is
equivalent to that inside the ring (average C S bond length is 1.73 Å),
but apparently longer than C S bond distance (1.69 Å) in compound 1.
The (mthd) anion displays two kinds of coordination modes: -1қN1,
қN2, 3қS3, 4қS3 and
ꢀ 1қN3, 2қN4, 3қS1, 4қS1, 5қS1 (Fig. 2b).
Two (mthd) anions containing S4 atom and two CuBr molecules
coordinate with each other through Cu–N bonds to form an anionic
formed through the interaction of (mthd) anions containing S1 atoms
and Ag2 ions, and the corresponding shortest Ag⋅⋅⋅Ag distance is 3.11 Å
(Fig. S1). Notably, two nitrogen atoms of thiadiazole ring in chain 1 are
involved in the coordination with Ag ions, however, only one nitrogen
atom of thiadiazole ring in chain 2 coordinates with Ag ions. The chains
1 and chains 2 are further connected to each other to form a 2D irregular
layered structure through Ag-S and Ag-N bonds (Fig. 3d), in which a
–
–
-
μ
4
2
μ
5
-
2
–
[
CuBr(mthd)]
2
unit with Cu⋅⋅⋅Cu distance of 3.44 Å (Fig. 2c), however,
n 3 3
(AgS) chain constructed by staggered Ag S rings is formed (Fig. 3e).
-
the (mthd) anion containing S2 atom links Cu2 and Cu3 ions into a 1D
+
coplanar cationic {[Cu
2
(mthd)] }
n
chain with the shortest Cu⋅⋅⋅Cu dis-
5
2 n
.4. Crystal structure of [Ag (mthd)I] (4)
tance of 3.33 Å through Cu-S and Cu–N bonds (Fig. 2d). The anionic
2
–
+
n
[
CuBr(mthd)]
2
units and 1D coplanar cationic {[Cu (mthd)] } chains
2
Single-crystal X-ray diffraction shows that compound 4 crystallizes
are connected to each other to form a 2D layered structure through Cu-S,
in the orthorhombic system with space group Pca2
1
, its asymmetric unit
Cu–N and Cu-Br bonds (Fig. 2e).
+
-
is composed of two Ag ions, one completely deprotonated (mthd)
-
anion and one I anion. The Ag1 and Ag2 centers both display distorted
5
.3. Crystal structure of [Ag(mthd)]
n
(3)
tetrahedral geometries, and Ag1 is bound to two sulfur atoms and one
-
-
nitrogen atom from three different (mthd) anions and one I anion,
while Ag2 is coordinated with one sulfur atom and one nitrogen atom
Single-crystal X-ray diffraction shows that compound 3 crystallizes
in the triclinic system with space group P-1, its asymmetric unit contains
-
-
from two different (mthd) anions and two I anions (Fig. 4a). The Ag-S
and Ag-N bond distances are in the range of 2.528(3)-2.893(3) Å and
+
-
two Ag ions and two completely deprotonated (mthd) anions. The Ag1
and Ag2 centers both display a distorted tetrahedral geometry, and Ag1
2.290(8)-2.421(10) Å, respectively, and the S/N-Ag-S/N bond angles
◦
is bound to three sulfur atoms and one nitrogen atom from four different
range from 93.33(5) to 116.4(2) . The C
–
S bond distances (dC3-S2
=
-
(
mthd) anions, while Ag2 is coordinated with two sulfur atoms and two
1.73 Å) outside the thiadiazole rings in compound 4 is equivalent to that
-
nitrogen atoms from four different (mthd) anions (Fig. 3a). The Ag-S
–
inside the ring (average C S bond length is 1.73 Å), similar to the
-
22–
Fig. 2. (a) Coordination environments of the Cu(I) ions, (b) coordination modes of (mthd) anion, (c) [CuBr(mthd)]
unit, (d) 1D coplanar cationic
+
{
[Cu
2
(mthd)] }
n
chain, (e) the 2D layer in compound 2. The hydrogen atoms are omitted.
4

Y. Geng et al.
Inorganica Chimica Acta 528 (2021) 120596
-
n
Fig. 3. (a) Coordination environments of the Ag(I) ions, (b) coordination modes of (mthd) anion, (c) 1D puckered [Ag(mthd)] chain (Chain 1), (d) 2D irregular
layered structure, (e) the (AgS)
n
chain constructed by staggered Ag
3
S
3
rings in compound 3. The hydrogen atoms are omitted.
-
Fig. 4. (a) Coordination environments of the Ag(I) ions, (b) coordination mode of (mthd) anion, (c) 1D inorganic (AgI)
n
chain, (d) 1D zigzag inorganic (AgS)
n
chain,
(
e) 2D organic–inorganic layer, (f) 2D double-layer structure along ac plane, (g) 2D double layer structure along bc plane, (h) 2D inorganic (Ag
2
n
IS) double layer in
compound 4. The hydrogen atoms are omitted.
5

Y. Geng et al.
Inorganica Chimica Acta 528 (2021) 120596
-
-
(
mthd) anion in compound 2. Each (mthd) anion coordinates with five
Ag(I) ions through
μ
5
-1қN1, 2қN2, 3қS2, 4қS2, 5қS2 coordination mode
-
(
Fig. 4b), and each I anion joins three Ag(I) ions in a
μ
3
coordination
mode. Interestingly, the three silver ions connected to the sulfur atom of
-
the (mthd) anion in compound 4 are evenly arranged in a semicircle and
◦
◦
the corresponding Ag-S-Ag bond angles range from 79.46 to 163.48 ,
however, the three silver ions bound to the sulfur atom of the (mthd)-
anion containing S2 atom in compound 3 are evenly arranged in a circle
◦
◦
and the corresponding Ag-S-Ag bond range from 99.47 to 120.46 .
-
The I anions link Ag2 ions to form an 1D inorganic (AgI)
n
chain with
the shortest Ag⋅⋅⋅Ag distance of 4.16 Å (Fig. 4c), and the S2 atoms of
-
(
mthd) anions and Ag1 ions are connected to each other to assemble a
1
D zigzag inorganic (AgS)
n
chain with the shortest Ag⋅⋅⋅Ag distance of
5
.42 Å (Fig. 4d). Then the (AgI)
n
and (AgS)
n
chains are further assem-
bled into a 2D inorganic (Ag
2
IS)
n
layer through Ag-I bonds with the
shortest Ag⋅⋅⋅Ag distance of 3.15 Å, in which a 10-membered ring con-
-
+
structed by two S ions, three I anions and five Ag ions is observed.
-
Notably, thiadiazole rings of (mthd) anions located in the 10-membered
n n
rings link (AgI) and (AgS) chains through Ag-N and C S bonds to form
–
a 2D organic–inorganic layer (Fig. 4e). The 2D organic–inorganic layers
are further joined into a 2D double layer through Ag-S bonds (Fig. 4f and
Fig. 5. Solid-state emission spectrum of compound 4. Insets are the photo
images of compound 4 under daylight (left) and UV illumination (right) at 365
nm, respectively.
Fig. 4g), interestingly, a 2D inorganic (Ag
Fig. 4h), where the interactions between the organic ligands and the
inorganic layers are conducive to the stability of the 2D layer.
2 n
IS) double layer is formed
In order to investigate the potential application of 4 for small
molecule sensing, 4-solvent emulsions were prepared by immersing 1.0
mg ground crystals of 4 into 2.00 mL of acetonitrile, dichloromethane
(
(
CH
2
Cl
2
), dimethylacetamide (DMA), N,N-dimethyl-formamide (DMF),
O, methanol, formaldehyde, and NB, and
5
.5. Characterization
ethanol, ethylene glycol, H
2
then the corresponding PL spectra were measured after 4-solvent
emulsions are dispersed by ultrasound for about 5 min. Fig. 6a shows the
peak shapes and peak positions of emission spectra of 4-solvent emul-
sions (λex = 333 nm) are similar to that of solid-state fluorescence
spectrum of compound 4, while the fluorescent intensities vary with the
solvent molecules. The maximum luminescence intensity of 4-solvent
The PXRD patterns of compounds 1–4 are consistent with the
simulated patterns generated by single crystal X-ray diffraction data
(
Fig. S2), indicating the high purity of the obtained crystalline products
of compounds 1–4, and the different intensities between the simulated
and experimental patterns may be attributed to the preferred orientation
of the powder samples.
emulsions gradually decreased in the following order: ethanol > H
2
O >
Fig. S3 shows the FT-IR spectra of compounds 1–4 and Hmthd.
ꢀ 1
CH Cl > acetonitrile > methanol > formaldehyde > ethylene glycol >
Notably, the wide absorption peaks located at 3050 cm and 2867
2
2
ꢀ
1
DMA > DMF > NB. Obviously, 4-ethanol emulsion shows the strongest
fluorescence, however, the fluorescence of 4-NB emulsion can’t be
detected, indicating that NB is an effective quencher and results in a
nearly 100% fluorescence quenching for compound 4. All 4-solvent
emulsions under UV light except NB showed obvious yellow light
emission (Fig. 6b), such solvent- dependent luminescence quenching
might become an effective luminescent sensing probe for NB molecules.
Fluorescence-quenching titration tests were performed with an in-
cremental addition of NB (0.01 mol/L) to 4-ethanol emulsion as a
standard emulsion. Fig. 6c shows that the fluorescence intensity of the 4-
ethanol emulsion gradually decreased with increasing NB concentra-
tion, when the concentration of NB increased to 0.225 mM, 93% fluo-
rescence intensity was quenched. The fluorescence quenching efficiency
cm can be ascribed to the stretching vibration of the N H and S H
– –
bonds in the IR spectrum of Hmthd ligand[46], respectively, however,
the adsorption peaks in this region for compounds 1–4 disappeared,
possibly due to the deprotonation of N H and S H bonds or thione-
– –
–
–
thiol (–N
–
C–SH ↔ –NH–C
–
S) tautomeric transformation. The char-
ꢀ
1
ꢀ 1
acteristic peaks at 1456 cm and 1384 cm correspond to the sym-
–
–
metric and asymmetric stretching vibrations of the C
–
N and C
N bonds
–
C
bonds [37], respectively. Notably, the absorption peaks of N
–
-
–
–
of (mthd) might appear to overlap significantly with that of C
N and
–
ꢀ 1
ꢀ 1
C
–
C bonds. The multiple peaks ranging from 1260 cm to 1039 cm
in the IR spectrum of Hmthd ligand are related to the C
–
S bond, while
ꢀ 1
the disappearance of the peak at 1260 cm in compounds 1–4 may be
due to the coordination of S with metal ions [51–52].
was further analyzed using the Stern- Volmer (SV) equation: I
0
/I = 1 +
To investigate thermal stability of compounds 1–4, their thermal-
gravimetric analyses (TGA) were measured under nitrogen atmosphere
K
sv [M] (where I is the initial fluorescence intensity of the 4-ethanol
0
◦
◦
emulsion without NB molecules, I is the fluorescence intensity of 4-
from 30 C to 800 C, and the corresponding TGA curves shown in
ethanol emulsion with NB molecules, KSV is the quenching constant
Fig. S4 have similar thermal behaviors with a one-step loss weight. The
ꢀ 1
frameworks of compounds 1–4 were thermally stable up to 272 ◦C,
(M ), [M] is the molar concentration of NB). The SV plot for NB was
nearly linear at low concentrations and subsequently deviated from
linearity, bending upwards at higher concentrations (Fig. 6d). The KSV
further heating, due to the decomposition of the organic linkers, the
skeletons began to collapse rapidly.
3
ꢀ 1
value of compound 4 for NB is 5.07 × 10 M , higher than that of the
reported fluorescent MOF sensors for the detection of NB in the organic
phase (Table 2), indicating a higher quenching efficiency. According to
5
.6. Luminescence property
3
δ/K equation (where δ is the standard deviation and K is the slope of
The fluorescence of compounds 1–3 and Hmthd ligand are too weak
the fitting curve of the luminescence intensity of 4 at different analyte
to be observed under ultraviolet light and difficult to be detected on a
fluorescence spectrometer, however, compound 4 gives off apparent
yellow light under the ultraviolet lamp, perhaps due to the combined
ꢀ 6
concentration), the detection limit of NB is 5.33 × 10 M. The above-
mentioned result revealed that compound 4 could be a promising
luminescent probe for sensing NB molecules. Additionally, the recy-
clable performance of 4 for NB sensing were also investigated and found
that compound 4 can be easily regenerated by washing with distilled
ethanol after five runs tests (Fig. S5).
effect of short Ag… Ag interactions, Ag
3
I cluster, molecular packing, and
so on[14,53]. The solid-state fluorescence spectrum of compound 4 at
room temperature exhibits yellow light emission with the maximum at
5
51 nm when excited at 333 nm (Fig. 5).
6

Y. Geng et al.
Inorganica Chimica Acta 528 (2021) 120596
Fig. 6. (a) Emission spectra of compound 4 in different solvents when excited at 333 nm, (b) luminescence photographs of compound 4 in different solvent emulsions
under UV light, (c) the fluorescence titration of 4-ethanol emulsion with the addition of different concentrations of NB, (d) the Stern-Volmer plot for the luminescence
intensity of 4 upon addition of NB solution in ethanol. The insert is Stern-Volmer plot at low analytes concentrations.
6
. Conclusion
Table 2
Comparison among various MOF-based sensors for detection of NB.
In summary, four new coordination compounds based on Hmthd
ꢀ
1
MOFs
dispersion solvent
KSV[M
]
Refs.
ligand have been synthesized and characterized in detail. Compounds
2
2
2
[
[
[
Zn
Zn(L)(dipb)]⋅(H
Zn (L) (dpyb)]
[Tb (L) (H O)
[Cd
(L)(DMA)]⋅[H
[Zn(L)](DMF)
Zn (NDC)
(BTC)
(TATMA)
(mthd)I]
3
(TTPA)
2
(DHTP)
3
]⋅2DMF
ethanol
DMA
1.86 × 10
2.31 × 10
3.09 × 10
[54]
1–4 display rich structural chemistry ranging from 0 D (1) to 2 D (2–4)
I
I
2
O)
2
[55]
structures, providing a new strategy to construct the Cu /Ag -based co-
ordination compounds containing Hmthd ligands with extended struc-
2
2
DMA
[55]
3
{
{
{
2
3
2
4
]⋅10H
O}
2 n
DMF
1.8 × 10
[56]
-
3
tures through the synergistic effect of (mthd) and halide ions. Notably,
2
2
N(Me)
2
]}
n
n
DMA
2.7 × 10
[57]
3
3
3
3
}
n
methanol
ethanol
methanol
DMF
2.87 × 10
3.05 × 10
3.95 × 10
[58]
compound 4 shows efficiently fluorescent quenching response to NB
molecules. The further research for the construction of new fluorescent
coordination compounds based on organic sulfur ligands is underway in
our laboratory.
[
2
2
(bpy)]⋅G
x
[59]
Zn
3
2
: 4% Eu(III)
[60]
3
[
[
(Pr
Ag
2
2
)⋅4DMF⋅4H
2
O]
4.1 × 10
[61]
3
2
n
ethanol
5.07 × 10
This work
CRediT authorship contribution statement
To analyze the mechanism of luminescent quenching by NB, the IR
spectrum and PXRD pattern of 4 after immersion in NB were measured.
The IR spectrum and PXRD pattern of compound 4 after immersion in
NB matched well with that obtained from the untreated crystals of
compound 4 (Fig. S3 and Fig. S6), indicating that the framework of 4 can
be kept intact in NB. Therefore, the fluorescence quenching behavior
was not caused by the framework collapse. In order to further investi-
gate the quenching mechanism, the UV–Vis spectra of NB and other
solvents were measured (Fig. S7). The results reveal that only NB have a
strong absorption ranging from 300 to 440 nm, while other solvents
have no significant absorption in this range. Notably, the excitation
wavelength of the compound 4 is 333 nm, which is completely over-
lapped by the absorbing band of NB. So, the efficient quenching of NB in
this system might be ascribed to a competition for the excitation energy
between the emission band of the fluorophore and the absorption band
of the analyte [25,27,62]. Moreover, the luminescence quenching
behavior may be due to the electron transfer from the electron-donating
materials to the electron-deficient NB molecules [55,63–64].
Ying Geng: Methodology, Software, Writing - original draft. Wen
Zhang: Validation, Investigation, Writing - original draft. Jiang-Feng
Song: Conceptualization, Formal analysis, Resources, Supervision,
Writing - review & editing, Project administration. Rui-Sha Zhou:
Writing - review & editing. Wei-Zhou Jiao: Project administration.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Acknowledgements
This work was supported by the National Natural Science Foundation
of China (No.: 21961027), the Natural Science Foundation of Shanxi
Province (No.: 201801D121068), the Foundation of Shanxi Province
Key Laboratory of Higee Oriented Chemical Engineering (No. CZL2020-
0
5), Foundation of State Key Laboratory of High-efficiency Utilization of
7

Y. Geng et al.
Inorganica Chimica Acta 528 (2021) 120596
Coal and Green Chemical Engineering (Grant No. 2019-KF-25),
respectively.
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