Syntheses, crystal structures and photophysical properties of d10 transition-metal (Ag+, Cu+, Cd2+ and Zn2+) coordination complexes based on a thiophene-containing heterocyclic thioamide

Article abstract of DOI:10.1080/00958972.2017.1364374

Four d¹⁰ transition-metal coordination complexes 1–4 (1: [Ag₂(TPT)₂(TPTH)₂]; 2: [Cu₆(TPT)₆]·2DMF; 3: [Cd(TPT)₂(TPTH)]·CH₃CH₂OH, 4: [Zn(TPT)₂]_n) have been constructed from a newly designed heterocyclic thioamide ligand, TPTH (TPTH?=?4-(thiophen-2-yl)-pyrimidine-2-thiol). All complexes have been structurally elucidated by single crystal X-ray diffraction analyses. Except for 4, which shows a one-dimensional (1-D) chain structure, 1–3 are all discrete coordination complexes featuring dinuclear, hexanuclear and mononuclear entities, respectively. Their photophysical properties have been evaluated in the solid state at room temperature by UV–vis diffuse reflectance and luminescence spectra. Among them, 2 exhibits a strong red luminescence (λ_em?=?699?nm) with a remarkable red-shift of the maximum emission compared to that of the TPTH ligand (λ_em?=?536?nm). The red emission observed with 2 is ascribed to a LMCT (ligand-to-metal charge transfer) transition which agrees with the DFT calculations.

Full text of DOI:10.1080/00958972.2017.1364374

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Syntheses, crystal structures and photophysical
properties of d10 transition-metal (Ag+, Cu+, Cd2+
and Zn2+) coordination complexes based on a
thiophene-containing heterocyclic thioamide
Yu-Zhen Wei, Zheng Cheng, Wei Li & Hai-Bin Zhu
To cite this article: Yu-Zhen Wei, Zheng Cheng, Wei Li & Hai-Bin Zhu (2017): Syntheses,
crystal structures and photophysical properties of d10 transition-metal (Ag+, Cu+, Cd2+ and Zn2+)
coordination complexes based on a thiophene-containing heterocyclic thioamide, Journal of
Coordination Chemistry, DOI: 10.1080/00958972.2017.1364374
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Date: 17 August 2017, At: 12:09

Journal of Coordination Chemistry, 2017
https://doi.org/10.1080/00958972.2017.1364374
Syntheses, crystal structures and photophysical properties
of d10 transition-metal (Ag+, Cu+, Cd2+ and Zn2+) coordination
complexes based on a thiophene-containing heterocyclic
thioamide
Yu-Zhen Weia, Zheng Chengb, Wei Lib and Hai-Bin Zhua
b
aschool of Chemistry and Chemical engineering, southeast university, nanjing, China; school of Chemistry
and Chemical engineering, nanjing university, nanjing, China
ABSTRACT
ARTICLE HISTORY
received 20 february 2017
accepted 10 July 2017
Four d10 transition-metal coordination complexes 1–4 (1: [Ag2(TPT)2
(TPTH)2]; 2: [Cu6(TPT)6]·2DMF; 3: [Cd(TPT)2(TPTH)]·CH3CH2OH, 4:
[Zn(TPT)2]n) have been constructed from a newly designed heterocyclic
thioamide ligand, TPTH (TPTH = 4-(thiophen-2-yl)-pyrimidine-2-thiol).
All complexes have been structurally elucidated by single crystal X-ray
diffraction analyses. Except for 4, which shows a one-dimensional (1-D)
chain structure, 1–3 are all discrete coordination complexes featuring
dinuclear, hexanuclear and mononuclear entities, respectively. Their
photophysical properties have been evaluated in the solid state at room
temperature by UV–vis diffuse reflectance and luminescence spectra.
Among them, 2 exhibits a strong red luminescence (λem = 699 nm) with
a remarkable red-shift of the maximum emission compared to that of
the TPTH ligand (λem = 536 nm). The red emission observed with 2 is
ascribed to a LMCT (ligand-to-metal charge transfer) transition which
agrees with the DFT calculations.
KEYWORDS
d10 transition-metal;
heterocyclic thioamide;
crystal structures;
photophysical properties
CONTACT hai-Bin Zhu
zhuhaibin@seu.edu.cn
supplemental data for this article can be accessed at https://doi.org/10.1080/00958972.2017.1364374.
© 2017 informa uK limited, trading as taylor & francis Group

2
Y.-Z. WEI ET AL.
1. Introduction
Owing to their rich coordination chemistry, there is a long-standing interest in heterocyclic
thioamide (HTA) ligands [1–13]. All sorts of coordination modes with heterocyclic thioamides
have been well summarized in two earlier excellent reviews [12, 13]. They can behave either
as unidentate or multidentate ligand, binding metal centers via exocyclic sulfur and/or het-
erocyclic nitrogen atoms [14–20]. Besides, the –N(H)–C(=S)–↔–N=C(–SH)– tautomerization
with heterocyclic thioamides provides an interesting structural variant that would add more
uncertainties into the final metal-coordination structures [6, 21, 22].
As the simplest member of the HTA family, pyrimidine-2-thiol (pymtH) as well as its sub-
stituted derivatives have been extensively studied [10, 16, 19, 20, 23–28]. As demonstrated
by these preceding works, the introduction of different substituents onto pymtH might
prevent the rapid formation of polymeric precipitates as the result of an increase in steric
hindrance. In our previous research, we have reported one class of substituted pymtH ligands
(n-PPT, n = 2, 3, 4) that couples one coordinative pyridine group at its C-4 site [10, 29, 30]. In
continuation of our previous work, herein we have designed a new 4-substituted pymtH
ligand, TPTH (TPTH=4-(thiophen-2-yl)-pyrimidine-2-thiol), that incorporates a thiophene
unit (Scheme 1). The introduction of a thiophene substituent may favor the formation of
discrete oligonuclear complexes with the TPTH ligand, owing to its hindering effect. More
importantly, the conjugation of the electron-rich thiophene to the electron-deficient pyrim-
idine ring may induce a push–pull effect which is expected to have great influence on the
photophysical properties of the resultant coordination complexes with the TPTH ligand.
Coordination complexes based on transition metal ions with a d10 closed-shell electronic
configuration have attracted attention largely not only because of their catalytic and bio-
logical properties, but also because of their intriguing photophysical properties [31–41],
which have found wide applications such as emissive materials, imaging probes, and pho-
tocatalysts. In this context, d10 transition-metal complexes with heterocyclic thioamides have
been reported to display interesting photoluminescence properties [7, 16, 42, 43], possibly
because the thiolate-S bridged metal centers may establish super-exchange interactions
between them through spin density delocalization toward the bridging S atom in the case
that the selected metal orbital energies are better matched for the sulfur atom.
For the aforementioned reasons, we have prepared four d10 metal-ion-based (Ag+, Cu+,
Cd2+, Zn2+) coordination complexes (1–4) with TPTH ligand in this work and studied the
correlation between their crystal structures and photophysical properties.
2. Experimental
2.1. Materials and measurements
All chemicals were of analytical grade and used as received. The reagents for synthesis of
the TPTH ligand including 2-acetylthiophene, N,N′-dimethylformamide dimethylacetal, and
thiourea were obtained from J&K China Chemical Ltd. Metal salts for preparation of coordi-
nation complexes 1–4 including AgNO3, Cu(NO3)2·3H2O, Cd(ClO4)2·6H2O, and Zn(ClO4)2·6H2O
were all purchased from Sinopharm Chemical Reagent Co., Ltd. (China). IR spectra were
recorded with a Thermo Scientific Nicolet 5700 FT-IR spectrophotometer as KBr pellets from
400 to 4000 cm−1. 1H NMR spectra were recorded with a Bruker AVANCE-500 spectrometer.
Powder X-ray diffraction (PXRD) data were collected on an XRD diffractometer (D8 Discover,

JOURNAL OF COORDINATION CHEMISTRY
3
Scheme 1. schematic representation of n-heterocyclic thioamide ligands of Pymth and n-PPt (n = 2,
3, and 4).
Bruker-AXS) with Cu-Kα radiation (λ = 1.54056 Å). The UV–vis diffuse-reflectance spectra of
samples of 1–4 were recorded on a Shimadzu UV–2450 spectrophotometer equipped with
an integrating sphere and using BaSO4 as the reference. The luminescence spectra were
measured via fluorescent spectra (Horiba Fluoromax4 spectrometer) using a Xe lamp as the
excitation source at room temperature.
2.2. Computational details
The cluster structure of 2 was obtained from its crystal structure, and the lowest excitation
state of 2 was obtained by time-dependent density functional theory (TDDFT) calculations
with the Austin–Frisch–Petersson function with dispersion (APFD) and the 6-31G(d) basis
set [44]. All the TDDFT calculations were carried out using the Gaussian 09 package [45].
2.3. Synthesis of 4-(thiophen-2-yl)-pyrimidine-2-thiol (TPTH)
2-Acetylthiophene (3.80 g, 30.0 mmol) and N,N-dimethylformamide dimethylacetal (3.95 g,
33.1 mmol) were added to 50 mL of DMF (DMF=N,N-dimethylformamide). The mixture was
stirred under reflux for 7 h. Upon cooling to room temperature, the solution was concentrated
by rotatory evaporation to give a semisolid which was further washed with ether and dried
under vacuum to afford intermediate P1 ((Z)-3-(dimethylamino)-1-(thiophen-2-yl)prop-2-
en-1-one) as a yellow solid powder and the yield was 87% (Calcd, 5.46 g).
0.6 g (26.0 mmol) of sodium was added into 50 mL of absolute ethanol at room temper-
ature. After the sodium was completely consumed, 2.50 g (13.8 mmol) of P1 and 1.30 g
(17.1 mmol) of thiourea were added into the above solution, and the reaction mixture was
then refluxed for 6 h. Upon cooling to room temperature, the reaction mixture was adjusted
to pH = 6–7 with 2 M HCl which resulted in TPTH (4-(thiophen-2-yl)-pyrimidine-2-thiol) as a
yellow precipitate, which was washed with water and dried under vacuum. Yield: 76% (Calcd,

4
Y.-Z. WEI ET AL.
2.68 g). IR (KBr, cm−1): 1605 (s), 1560 (s), 1523 (w), 1468 (s), 1417 (w), 1398 (w), 1253 (s), 1226
1
(w), 1204 (w), 1170 (s), 971 (w), 799(w), 713 (w). H NMR (d6-DMSO/TMS, 500 MHz, ppm):
δ 13.50 (s, 1H), 8.02 (s, 1H), 8.00 (s, 2H), 7.35 (d, 2H). ESI-MS: m/z = 195.00 [M + H+]+ (100%).
Anal. Calcd for C8H6N2S2 (%): C, 49.45; H, 3.11; N, 14.42. Found: C, 49.32; H, 3.01; N, 14.31.
2.4. Synthesis of complexes 1–4
2.4.1. Synthesis of [Ag2(TPT)2(TPTH)2]{bis(4-(thiophen-2-yl)pyrimidine-2-thiolate)
bis(4-(thiophen-2-yl)pyrimidine-2(1H)-thione)disilver(I)} (1)
A methanol solution (3 mL) of AgNO3 (4.25 mg, 0.025 mmol) was carefully layered above a
DMF solution (1 mL) of TPTH (9.71 mg, 0.05 mmol). Bulk orange block crystals were obtained
after 1–2 weeks. The orange crystals of 1 were collected and dried under vacuum. Single
crystals suitable for X-ray diffraction analysis were selected from the crystals (yield: 4.43 mg,
35% based on TPTH). IR (KBr, cm−1): 1610 (w), 1559 (s), 1519 (w), 1404 (s), 1355 (w), 1312 (w),
1266 (s), 1228 (w), 1189 (s), 1095 (w), 806 (w), 716 (w). Anal. Calcd for C32H22Ag2N8S8 (%): C,
38.79; H, 2.23; N, 11.31. Found: C, 38.65; H, 2.12; N, 11.19.
2.4.2. Synthesis of [Cu6(TPT)6]·2DMF {hexa(4-(thiophen-2-yl)pyrimidine-2-thiolate)
hexacopper(I) dimethylformamide disolvate} (2)
A methanol solution (5 mL) of Cu(NO3)2·3H2O (24.1 mg, 0.1 mmol) was carefully layered above
a DMF solution (1 mL) of TPTH (9.71 mg, 0.05 mmol). Bulk red block crystals of 2 were
obtained after 2–3 weeks by slow evaporation at room temperature (yield: 5.81 mg, 27%
based on TPTH). IR (KBr, cm−1): 1665 (w), 1565 (s), 1535 (w), 1518 (w), 1426 (w), 1400 (w), 1356
(w), 1322 (s), 1165 (w), 1092 (w), 821 (w), 793 (w), 715 (w). Anal. Calcd for C54H44Cu6O2N14S12
(%): C, 38.44; H, 2.63; N, 11.63. Found: C, 38.31; H, 2.50; N, 11.52.
2.4.3. Synthesis of [Cd(TPT)2(TPTH)]·CH3CH2OH {bis(4-(thiophen-2-yl)pyrimidine-2-
thiolate)(4-(thiophen-2-yl)pyrimidine-2(1H)-thione)cadmium(II) ethanol solvate} (3)
An ethanol solution (3 mL) of Cd(ClO4)2·6H2O (10.48 mg, 0.025 mmol) was carefully layered
above a DMF solution (1 mL) of TPTH (9.71 mg, 0.05 mmol). Bulk yellow block crystals of 3
were obtained after 3–4 weeks (yield: 3.39 mg, 27% based on TPTH). IR (KBr, cm−1): 1672 (w),
1617 (w), 1561 (s), 1427 (w), 1403 (w), 1362 (s), 1334 (w), 1168 (w), 1111 (w), 814 (w), 785 (w),
720 (w). Anal. Calcd for C26H22CdON6S6 (%): C, 42.24; H, 3.00; N, 11.37. Found: C, 42.12; H, 2.89;
N, 11.23.
2.4.4. Synthesis of [Zn(TPT)2]n {poly-[bis(4-(thiophen-2-yl)-pyrimidine-2-thiolate)
zinc(II)} (4)
Zn(ClO4)2·6H2O (9.31 mg, 0.025 mmol) and TPTH (9.71 mg, 0.05 mmol) in the H2O-DMF mix-
ture solution (v:v = 3:1, 4 mL) was added to a Teflon-lined autoclave (23 mL) and heated at
120° for 72 h affording as a single phase, yellow block-shaped crystals of 4, which were fil-
tered, washed with DMF and dried under vacuum (yield: 2.65 mg, 23% based on TPTH). IR
(KBr, cm−1): 1610 (w), 1559 (s), 1519 (w), 1419 (w), 1404 (s), 1312 (w), 1266 (s), 1228 (w), 1189
(s), 1167 (w), 806 (w), 732 (w), 716 (w). Anal. Calcd for C16H10ZnN4S4 (%): C, 42.52; H, 2.23; N,
12.40. Found: C, 42.41; H, 2.12; N, 12.31.

JOURNAL OF COORDINATION CHEMISTRY
5
2.5. X-ray crystallography
Diffraction intensity data for 1–4 were collected at 298(2) K with a Bruker SMART CCD-4 K
diffractometer by employing graphite-monochromated MoKα radiation (λ = 0.71073 Å). The
data were collected using SMART and reduced using SAINT [46]. A semi-empirical absorption
correction was applied using SADABS [47]. All the structures were solved by direct methods
and refined by full-matrix least squares methods on F2 using the SHELXTL-97 crystallo-
obs
graphic software package [48]. All non-hydrogen atoms were refined anisotropically. All
hydrogens were calculated by geometrical methods and refined as a riding model. The
crystallographic data of 1–4 are presented in Table 1. The selected bond lengths and angles
of 1, 3 and 4 are summarized in Table 2. The selected bond lengths and angles of 2 are
summarized separately in Table S1. The bond lengths and angles of the hydrogen bonds in
1–4 are listed in Table S2.
3. Results and discussion
3.1. Synthetic procedure for TPTH
The synthetic procedure forTPTH was developed on the basis of our previous work [49–51]. As
outlined in Scheme 2, the title organic molecule, TPTH, was prepared in two steps. In the first
step, the aldol condensation of 2-acetylthiophene with N,N-dimethylformamide dimethylacetal
almost quantitatively produced the P1 intermediate. In the second step, the installation of the
pyrimidinylthiol moiety of the TPTH ligand was accomplished by reaction of P1 with thiourea
under basic conditions.The molecular structure ofTPTH was confirmed by 1H NMR, ESI-MS and
elemental analysis.The 1H NMR spectrum ofTPTH in d6-DMSO shows a singlet for the pyrimidine
protons at δ = 8.00 ppm, two resonances at δ = 7.31 and 8.20 ppm corresponding to thiophene
protons, and one signal at δ = 13.50 ppm from the -SH proton (Figure S1). The ESI-MS spectra
of TPTH exhibits a signal at m/z = 195.00, which agrees well with the formula weight of TPTH.
Table 1. Crystallographic data for 1–4.
Complex
1
2
3
4
formula
formula weight
Crystal system
space group
a (Å)
b (Å)
c (Å)
C
32h22ag2n8s8
990.80
monoclinic
C2/c
17.504(4)
11.645(2)
18.063(4)
90.00
106.53(3)
90.00
3529.9(12)
4
C54h44Cu6o2n14s12
1686.99
monoclinic
C2/c
29.515(4)
11.3462(15)
20.503(3)
90.00
C26h22Cdon6s6
739.26
C16h10Znn4s4
451.91
monoclinic
C2/c
26.307(17)
7.007(5)
19.582(13)
90.00
99.626(8)
90.00
triclinic
Pī
9.759(3)
10.248(3)
17.137(4)
100.102(4)
90.353(4)
109.747(4)
1584.1(7)
2
α (°)
β (°)
106.398(2)
90.00
6586.8(16)
4
1.701
3392
γ (°)
V (Å3)
3559(4)
8
1.687
Z
Dcalc (g cm−3
F(000)
)
1.865
1968
1.550
744
1824
reflections collected
unique reflections
Rint
20,384
5862
0.031
22,943
5809
0.043
8778
5539
0.020
11,598
3077
0.052
R1, wR2[I> 2σ(I)]
R1wR2 (all data)
Goodness-of-fit
0.0388/0.1093
0.0452/0.1154
1.05
0.0403/0.1092
0.0546/0.1158
1.08
0.0404/0.1163
0.0518/0.1229
1.03
0.0463/0.1411
0.0518/0.1491
1.04
R1 = Σ||Fo| − |Fc||/Σ|Fo|. wR2 = |Σw(|Fo|2 − |Fc|2)|/Σ|w(Fo)2|1/2, where w = 1/[σ2(Fo2) + (aP)2 + bP]. P = (Fo2 + 2Fc2)/3.

6
Y.-Z. WEI ET AL.
Table 2. selected bond lengths (Å) and angles (°) for 1, 3, and 4.
1
3
4
Bond lengths
ag1-s3
ag1-s1
ag1-s3a
ag1-ag1a
s1-C1
2.4426(8)
2.4802(9)
2.9117(9)
3.0872(7)
1.705(2)
Cd1-s2
Cd1-s4
Cd1-s6
Cd1-n2
Cd1-n4
Cd1-n6
s2-C8
2.595(1)
2.515(1)
2.483(1)
2.458(3)
2.780(3)
2.769(4)
1.738(4)
1.722(4)
1.723(4)
Zn1-n1a
Zn1-n3B
Zn1-s3
Zn1-s2
s2-C8
2.053(4)
2.102(4)
2.3356(16)
2.4048(15)
1.733(4)
s3-C9
1.744(2)
s3-C16
1.752(4)
s6-C24
s4-C16
Bond angles
s3-ag1-s3a
n4-C9-s3
n1-C1-s1
110.21(2)
117.85(16)
118.77(18)
n2-Cd1-s2
n4-Cd1-s4
n6-Cd1-s6
n2-Cd1-n
n2-C8-s2
n4-C16-s4
n6-C24-s6
62.29(9)
60.13(7)
60.37(7)
676.6(1)
115.6(3)
120.1(3)
118.2(3)
n1a-Zn1-n3B
n1a-Zn1-s3
n3B-Zn1-s3
n1a-Zn1-s2
n1-C8-s2
97.51(14)
144.62(11)
100.67(10)
102.46(10)
115.3(3)
n3-C16-s3
116.1(3)
Scheme 2. synthesis of tPth.
Apart from 4, afforded by a solvothermal reaction, the complexes were all obtained by a
slow diffusion method using dilute solutions in order to control the reaction rate. Crystal
structures of 1–4 have been further ascertained by single-crystal X-ray diffraction analysis
(vide infra). The phase purity of the as-synthesized samples of 1–4 was confirmed by the
consistency between the experimental PXRD pattern and the simulated PXRD pattern
(Figure S2).
3.2. Crystal structure of [Ag2(TPT)2(TPTH)2] (1)
Single crystal X-ray crystallography reveals that 1 crystallizes in the monoclinic space group
C2/c with the asymmetric unit comprising one Ag atom and two independent TPTH ligands
(Figure S3). As shown in Figure 1, 1 shows a discrete binuclear structure composed of two
Ag atoms and four TPTH ligands that are related by a symmetry center. The Ag (I) center is
three-coordinate by three S atoms from three ligands, and the Ag-S bond distances (Ag1-S1:
2.4802(9) Å, Ag1-S3A: 2.9117(9) Å, Ag1-S3: 2.4426(8) Å) are comparable to those reported
for silver complexes with pyridine-2-thiolate and pyrimidine-2-thiolate derivatives [19,
52–55]. Interestingly, there exist two forms of TPTH ligands in a 1:1 ratio, viz. thiolate anion
and neutral thione (Figure S4), which differ in their C-S bond lengths (C-S bond of thiolate:
1.744(2) Å; C-S bond of neutral thione: 1.705(2) Å). The former is connected to two Ag atoms
through a single thiolate-S atom, and the latter is terminally bonded to one Ag atom through
the thione-S atom. Two Ag atoms and two thiolate-S atoms build a Ag2S2 parallelogram

JOURNAL OF COORDINATION CHEMISTRY
7
Figure 1. orteP view of 1 drawn at the 50% probability level (hydrogens omitted for clarity; symmetry
code: (a) −x + 1/2, −y + 1/2, −z + 1).
(Ag1-S3A: 2.9117(9) Å, Ag1A-S3A: 2.4426(8) Å, S3-Ag1-S3A: 110.21(2)°, Ag1-S3A-Ag1A:
69.79(1)°). With reference to the Ag2S2 parallelogram, fourTPTH ligands are alternate arranged
in cis- and trans-conformations. The Ag⋯Ag distance of 3.0872(7) Å is much shorter than
the sum of the van der Waals radii (3.44 Å), which falls into the range of 2.89–3.15 Å found
in the reported Ag clusters with strong Ag⋯Ag interactions [56, 57]. The binuclear Ag entities
of 1 are adhered to each other through N–H⋯N hydrogen bonds (N–H⋯N: 2.768(3) Å)
between two forms of TPTH ligands and form a 1-D supramolecular chain (Figure S5a). More
interestingly, the adjacent 1-D chains form a 2-D honeycomb supramolecular network via
π–π stacking between the pyrimidine ring and the thiophene ring (Figure S5b).
3.3. Crystal structure of [Cu6(TPT)6]·2DMF (2)
Single crystal X-ray crystallography indicates that 2 crystallizes in the monoclinic space group
C2/c with the asymmetric unit comprising three copper(I) atoms, three TPTH ligands and
one DMF guest molecule (Figure S6). As depicted in Figure 2, 2 shows a discrete centrosym-
metric hexanuclear structure comprising six TPTH ligands and six Cu(I) atoms; the O atom
of the guest DMF solvent is 5.379(4) Å away from Cu3. The Cu(I) atom resulted from in situ
reduction of Cu(II) ion during the assembly reaction [16, 40, 58–60]. Each Cu(I) atom is trigo-
nally coordinated to one nitrogen and two sulfur atoms from three different TPTH ligands
with bond distances (Cu-S: 2.230(1) Å and 2.266(1) Å, Cu-N: 2.019(3) Å and 2.050(2) Å) being
close to those copper(I) complexes with derivatives of heterocylic-2-thiolates and hetero-
cylic-4-thiolates [58, 59, 61–66]. Different from 1, the TPTH ligand in 2 only exist as thiolate
anion, each linking three copper atoms in μ3-Nexo, ҡ1: S, ҡ2 coordination fashion. The overall
shape of 2 looks like a molecular paddlewheel in which six Cu(I) atoms form a distorted
octahedron with Cu⋯Cu separations in the range of 2.7377(7)–4.1995(8) Å (Figure S7), and
each ligand linking three Cu(I) atoms defines one of the faces of this octahedron. It resembles

8
Y.-Z. WEI ET AL.
Figure 2. orteP view of 2 drawn at the 50% probability level (hydrogens omitted for clarity; symmetry
code: (a) −x + 1/2, −y + 1/2, −z).
in structure the reported hexanuclear Cu(I) clusters with derivatives of pyridine-2-thiolate
and pyrimidine-2-thiolate [67–74]. In the packing structure, complex 2 hexamers are further
associated to each other through C-H⋯O (3.526(7) Å) and C–H⋯N (3.523(5) Å) hydrogen
bonds (Figure S8).
3.4. Crystal structure of [Cd(TPT)2(TPTH)]·CH3CH2OH (3)
Single-crystal X-ray crystallography shows that 3 crystallizes in the triclinic crystal system
and Pī space group and is composed of a discrete mononuclear Cd(II) coordination entity
and one ethanol guest molecule. The six-coordinate Cd(II) atom in 3 is bound by three groups
of N,S-chelating sets from three individualTPTH ligands, and the O atom of the guest ethanol
solvent molecule is 7.84(1) Å from the Cd1 atom (Figure 3). Similar to 1, 3 also possesses two
forms of TPTH ligands, viz. thiolate anion (C-S bond: 1.737(4) Å) and neutral thione (C-S bond:
1.723(4) Å), but the thiolate anion/neutral thione ratio is 2:1 instead of 1:1. More interestingly,
twoTPTH thiolate anions are also distinct from each other regarding the coordinated N atom,
wherein one is based on the endo-pyrimidine-N atom and the other on the exo-pyrimidine-N
atom. In this aspect, the Cd(II) atom in 3 is actually bound by three types of TPTH ligands
which is quite uncommon as far as we know. The Cd-S distances range from 2.483(1) Å to
2.595(1) Å, and the Cd-N distances are between 2.458(3) and 2.780(3) Å. The N–Cd–S angles
lie within a very compact span of 60.13(7)–62.29(9)°. Finally, the mononuclear entities of 3

JOURNAL OF COORDINATION CHEMISTRY
9
Figure 3. orteP view of 3 drawn at the 50% probability level.
are linked to each other through intermolecular N–H⋯N (2.825(5) Å) hydrogen bonds, lead-
ing to formation of a 1-D chain structure (Figure S9).
3.5. Crystal structure of [Zn(TPT)2]n (4)
X-ray crystallography reveals that 4 crystallizes in the monoclinic crystal system and C2/c
space group. The asymmetric unit of 4 consists of one Zn atom and two TPTH ligands (Figure
S10). The Zn(II) atom in 4 adopts a distorted tetrahedral coordination geometry defined by
two nitrogen atoms and two sulfur atoms belonging to four individual TPTH ligands
(Figure 4(a)). All TPTH ligands in 4 are thiolate anions, each linking two Zn(II) atoms in a
μ2-Nexo, ҡ1: S, ҡ1 bridging mode (Zn1-S2: 2.405(2) Å; Zn-S3: 2.336(2) Å; Zn-N1A: 2.053(4) Å;
Zn-N3B: 2.102(3) Å). Unlike the discrete structures of 1–3, 4 shows a 1-D polymeric chain
structure along the b axis that is built from adjacent Zn atoms doubly bridged by two TPTH
ligands (the Zn⋯Zn distance is 3.982(3) Å) (Figure 4(b)). Moreover, adjacent 1-D chains are
connected by π⋯π stacking interactions between thiophene rings to give a 2-D layered
structure (Figure S11).
3.6. Coordination modes of TPTH ligand in 1–4
As demonstrated by 1–3, the TPTH ligand favors the formation of discrete rather than pol-
ymeric coordination structures under ambient conditions, which can be attributed to the
presence of non-coordinative thiophene groups that increase the steric hindrance for metal

10
Y.-Z. WEI ET AL.
Figure 4. (a) orteP showing coordination environment of Zn atom of 4 drawn at the 50% probability
(hydrogens omitted for clarity; symmetry codes: (a) −x + 1/2, −y + 3/2, −z; (B) −x + 1/2, y + 5/2, −z); (b)
1-d chain structure of 4.
coordination. By contrast, the generation of 1-D Zn(II)-based polymeric coordination chains
of 4 under solvothermal conditions might be the thermodynamic-driven product. Despite
the non-coordinative nature of the thiophene substituent, TPTH exhibits versatile coordi-
nation modes (A-G) (Scheme 3). It may singly use an S atom as coordination donor either in
the form of thiolate (A) or thione (B), or adopt mixed S, N-coordination (C, D, E, F, and G). In
summary, coordination modes A and B in 1, single coordination mode C in 2; coordination
modes D, E and F in 3, and coordination mode G in 4 have been found.
3.7. Photophysical properties of 1–4
As shown in Figure 5(a), the absorption edge (λ = 537 nm) of TPTH is obviously extended
toward long wavelength compared to the pymtH (λ = 504 nm), which can be accounted for
by two factors pertinent to the thiophene substituent. On the one hand, the electron-rich
nature of the thiophene substituent can raise the HOMO energy level with concomitant
reduction of the HOMO–LUMO band gap. On the other hand, the introduction of the con-
jugated thiophene substituent facilitates the electron delocalization which also contributes

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11
Scheme 3. the coordination modes of tPth observed in 1–4.
Figure 5. (a) solid uV–vis absorption spectra of (a) tPth and Pymth, (b) 1–4.
to the lower energy absorption. As depicted in Figure 5(b), the solid-state UV–vis absorption
spectra of 1–4 resemble in shape that of the TPTH ligand, all being characterized by a narrow
absorption band in the 204–300 nm region and a broad band in the 300–500 nm region,
respectively. Accordingly, the UV–vis absorption properties of 1–4 can be attributed to the
intraligand transitions of the TPTH ligand, wherein the absorption between 204–300 nm
could be assigned to a π→π* transition, and that in the 300–500 nm range to an n→π* tran-
sition. Compared to the TPTH ligand, an obvious red-shift in the π→π* absorption maximum
is observed for 1 and 2 (λ = 248 nm for ligand, λ = 266 nm for 1, λ = 295 nm for 2) and slightly
blue-shift for 3 and 4 (λ = 258 nm for 3 and λ = 254 nm for 4). Compared to TPTH, the n→π*
absorption band is slightly broadened in 1 and 2, but apparently narrowed for 3 and 4.
Finally, a further extension of the absorption edge (1: 587 nm, 2: 591 nm) toward longer

12
Y.-Z. WEI ET AL.
wavelength is observed for 1 and 2 (Figure S12) compared to that of TPTH ligand, indicating
that coordination to Ag+/Cu+ further narrows the optical band gap of TPTH. By contrast, the
absorption edges of 3 and 4 are shifted remarkably toward shorter wavelength, inferring
that the optical band gap is broadened upon coordination of TPTH to Zn2+/Cd2+ ion.
Figure 6(a) shows the emission spectra of 1–4 and the free TPTH ligand, which exhibits
emission peaks at 569 nm, 699 nm, 465 nm, 464 nm, and 536 nm (1, 3, 4 and ligand:
λex = 375 nm, 2: λex = 466 nm), respectively. It is known that the emission in Ag(I) complexes
is predominantly originated from cluster-centered (MC) or ligand-centered (IL) excited states
[32]. In the case of 1, the maximum emission wavelength (λem = 569 nm) is a little red-shifted
compared to the free ligand and is assigned to a ligand-centered (IL) state that is slightly
perturbed by the coordination interaction of silver ions [75]. For Zn/Cd complexes, obvious
blue-shift and significant enhancement in emission intensity are observed. Because the
Zn(II) and Cd(II) ions are difficult to be oxidized or reduced, and there are no d–d transitions
with a d10 closed shell electronic configuration, the emissions of 3 and 4 possibly originate
from ligand-centered (LC) and/or ligand-to-ligand charge transfer (LLCT) [76–80]. By sharp
contrast, a striking red-shift of the emission is found for 2 that displays an intense low-energy
red emission. Time-resolved emission measurements disclosed that the red emission follows
a double-exponential decay with a decay lifetime of 1.37 μs (λex = 466 nm) (Figure 6(b)),
which can be assigned as a weak phosphorescence [5, 43, 81, 82]. In general, possible assign-
ments for the excited states which are responsible for emission phenomena of Cu(I)-
complexes includes ligand-centered π–π* transitions (LC), metal-cluster-centered transitions
(CC), ligand-to-ligand (LLCT), ligand-to-metal (LMCT), metal-to-ligand (MLCT) charge transfer
transitions or metal centered d10→d9s1(MC) transitions [43, 83, 84]. In the case of 2, the emis-
sion may be tentatively ascribed to a LMCT band by comparison to the luminescence prop-
erties of reported polynuclear Cu(I)-thiolated clusters [40, 69, 85–90].
The photoluminescence properties of 1, 3, and 4 are quite common. By contrast, such a
low energy emission observed with 2 is rare among the reported metal coordination com-
plexes with heterocyclic thioamides. To our knowledge, there is only one example precedent
to our report from Hong’s group who reported a red luminescent polymeric cuprous coor-
dination polymer with the pymtH ligand [42]. To better understand the origin of the red
emission with 2, density function theory (DFT) calculations with the ground-state geometries
adapted from the X-ray data were performed for 2. As shown in Figure 7, the LUMO (the
Figure 6. (a) emission spectra oftPth and 1–4 in the solid state at room temperature; (b) emission decay
time of 2 (powder).

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13
Figure 7. electron-density distributions of homo and lumo frontier orbitals of 2.
lowest unoccupied molecular orbital) mainly comprises p-orbitals of C, N and S in TPTH,
while the HOMO (the highest occupied molecular orbital) mainly consists of p-orbitals of
ligand TPTH as well as d-orbitals of Cu(I) atom. Upon excitation, the electron density has
moved from Cu d-orbitals together withTPTH p-orbitals to p-orbitals of C, N, and S. Moreover,
the excitation energy is 1.93 eV (or 644.0 nm), which is close to the experimental emission
value (1.77 eV or 699 nm). Taken together, it can be concluded that the red emission at
699 nm of 2 originates from a ligand to metal charge transfer.
4. Conclusion
In this article, we describe the synthesis, structural characterization, and photophysical prop-
erties of four d10 transition-metal complexes with the TPTH (4-(thiophen-2-yl)-pyrimi-
dine-2-thiol) ligand. Under ambient conditions, slow diffusion reactions between TPTH and
d10 metal ions (Ag+, Cu+ and Cd2+) favor the formation of discrete coordination complexes
possibly caused by the steric hindrance of the thiophene substituent. However, a solvother-
mal reaction between Zn2+ and TPTH can thermodynamically lead to a 1-D polymeric chain
structure. Seven coordination modes (A–G) of TPTH have been observed in 1–4. Complex 2
based on Cu(I) atom exhibits a strong red photoluminescence, and the DFT calculations
suggest that the red emission of 2 is possibly caused by LMCT transition.
Supplementary material
CCDC 1526027–1526030 contains the supplementary crystallographic data for 1–4. These data can be
obtained free of charge via https://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Center, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: (+44) 1223 336 033; or
E-mail: deposit@ccdc.cam.ac.uk. Supplementary data associated with this article can be found in the
online version.
Disclosure statement
No potential conflict of interest was reported by the authors.

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Y.-Z. WEI ET AL.
Funding
This work was supported by the National Natural Science Foundation of China [grant number
21171036]; Fundamental Research Funds for the Central Universities [grant number 3207047406].
ORCID
Wei Li
http://orcid.org/0000-0001-7801-3643
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