Synthesis, structure, terahertz spectroscopy and luminescent properties of copper(I) complexes with mercaptan ligands and triphenylphosphine

Article abstract of DOI:10.1016/j.molstruc.2013.12.076

The reactions of copper(I) halides with triphenylphosphine (PPh ₃) and mercaptan ligand [2-mercapto-6-nitrobenzothiazole (HMNBT), 2-amino-5-mercapto-1,3,4-thiadiazole (HAMTD) and 2-mercapto-5-methyl- benzimidazole (MMBD)] yielded seven complexe

Full text of DOI:10.1016/j.molstruc.2013.12.076

Journal of Molecular Structure 1062 (2014) 125–132
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, structure, terahertz spectroscopy and luminescent properties
of copper(I) complexes with mercaptan ligands and triphenylphosphine
a
c
Qi-Ming Qiu a, Min Liu b, Zhong-Feng Li a, Qiong-Hua Jin a, , Xu Huang , Zhen-Wei Zhang ,
⇑
Cun-Lin Zhang c, Qing-Xuan Meng a,d
a Department of Chemistry, Capital Normal University, Beijing 100048, China
b The College of Materials Science and Engineering, Beijing University of Technology, Beijing 100022, China
c Beijing Key Laboratory for Terahertz Spectroscopy and Imaging, Key Laboratory of Terahertz Optoelectronics, Ministry of Education, Department of Physics, Capital Normal
University, Beijing 100048, China
d Daxing High School Attached to CNU, Beijing 102600, China
h i g h l i g h t s
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Seven new complexes were synthesized and characterized.
Complexes 1–5 represent first examples of HMNBT and HAMTD with copper(I) halides.
The complexes 1, 5, 6 and 7 exhibit interesting fluorescence in the solid state.
THz-TDS of starting materials and complexes were investigated.
Our results show several factors can affect the THz spectra of the complexes.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 24 July 2013
Received in revised form 28 December 2013
Accepted 28 December 2013
Available online 8 January 2014
The reactions of copper(I) halides with triphenylphosphine (PPh3) and mercaptan ligand [2-mercapto-6-
nitrobenzothiazole (HMNBT), 2-amino-5-mercapto-1,3,4-thiadiazole (HAMTD) and 2-mercapto-5-methyl-
benzimidazole (MMBD)] yielded seven complexes, [CuCl(HMNBT)(PPh3)2] (1), [CuX(HMNBT)(PPh3)]2
(X = Cl, Br) (2–3), [Cu(MNBT)(HMNBT)(PPh3)2] (4), [CuBr(HAMTD)(PPh3)2]ÁCH3OH (5) and [CuX(MMBD)
(PPh3)2]Á2CH3OH (X = Br, I) (6–7). These complexes were characterized by elemental analysis, X-ray dif-
fraction, 1H NMR and 31P NMR spectroscopy. In these complexes the mercaptan ligands act as monoden-
tate or bridged ligand with S as the coordination atom. In complexes 1 and 4, hydrogen bonds CAHÁ Á ÁX
Keywords:
Copper(I) halides
Triphenylphosphine
Mercaptan ligands
Luminescence
and weak interactions CAHÁ Á Á
p lead to the formation of chains and 2D network respectively, while com-
plexes 2 and 3 are dinuclear. In 5–7, intramolecular hydrogen bonds link the [CuX(thione)(PPh3)2]
molecules and the solvated methanol molecules into centrosymmetric dimers. Complexes 1–5 represent
first copper(I) halide complexes of HMNBT and HAMTD. The complexes 1, 5, 6 and 7 exhibit interesting
fluorescence in the solid state at room temperature and their terahertz (THz) time-domain spectroscopy
was also studied.
Terahertz spectroscopy
Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction
In previous literature, the mercaptan ligands have been known
as co-ligands in forming mono or dinuclear Cu(I)-PPh3 complexes.
Copper(I) is an important metal ion, which has a strong ten-
dency to form covalent bonds with ligands containing sulphur or
phosphorus donor atoms. Copper(I) complexes containing triphen-
lyphosphine (PPh3) and heterocyclic mercaptan ligands have re-
ceived much attention in the past, mainly because of their
interesting coordination chemistry [1] and potential applications
in biochemistry [2], photography [3] and enzymatic reactions [4].
There are mainly two types of structures for this kind of com-
plexes: the first kind is like [CuX(thione)(PPh3)2] (X = Cl, Br, I) [5]
and [Cu(
act as a monodentate ligand with the S atom as a coordination
atom; the second kind is like [CuX( -S)(thione)(PPh3)]2 [7], where
l-X)(thione)(PPh3)]2 [6], where the mercaptan ligands
l
the mercaptan ligands act as a bridged thiol. Apart from these
mono or dinuclear Cu(I)-PPh3 complexes, Safin and Klein have also
synthesized a series of Cu(I) clusters containing PPh3 and mercap-
tan ligands [8,9]. The luminescence properties of the Cu(I) halide
aggregates have been also investigated in recent years [10]. Che
and his co-workers have prepared several d10 metal complexes
⇑
Corresponding author. Tel.: +86 10 68903033; fax: +86 10 68902320.
E-mail address: jinqh@mail.cnu.edu.cn (Q.-H. Jin).
0022-2860/$ - see front matter Ó 2014 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2013.12.076

126
Q.-M. Qiu et al. / Journal of Molecular Structure 1062 (2014) 125–132
which exhibit emissive
p–p
IL (intraligand) charge-transfer ex-
bond interactions can affect the THz spectra of the Cu(I)
complexes.
⁄
cited states by utilizing the ‘‘donor–acceptor’’ type ligand [3a].
Gdaniec and his co-workers also investigate the luminescence
properties of Cu(I) compounds. The [CuX(L)(PPh3)2] compounds
show intense luminescence in both the solid state and in solution,
which originates probably from mixed LMCT/LLCT transitions [11].
Terahertz time-domain spectroscopy (THz-TDS) is a vibrational
spectroscopic technique that is used to probe the infrared active
vibrational modes in the far-infrared and sub-millimeter region
of the electromagnetic spectrum by measuring the ultrashort
pulses of coherent terahertz radiation (0.1–4 THz) (3–133 cmÀ1).
Compared with conventional spectroscopic techniques, THz-TDS
has a high signal-to-noise ratio. This spectroscopic technique also
enables the characterization of solid-state materials through the
excitation of soft intramolecular vibrational modes, intermolecular
modes, and hydrogen-bonding modes. In regard to border security,
the inspection and identification of contraband drugs using tera-
hertz TDS could be an additional tool of great significance [12].
Although THz-TDS has been utilized in a wide range of research
fields in the past ten years, including chemical and biological
detections and identifications [13], this technique is seldom used
for organic/inorganic compounds and inorganic–organic hybrid.
So, in this work, some complexes were characterized by THz-TDS.
We focus our attention on Cu(I) complexes with different het-
erocyclic mercaptan ligands containing PPh3, aiming to gain insight
into the interplay between the ligand’s characteristics and the
structural diversity observed. We also want to investigate the ef-
fect of halide ions, PPh3, heterocyclic mercaptan ligands as well
as hydrogen bonds on luminescence properties. The three mercap-
tan ligands 2-mercapto-6-nitrobenzothiazole (HMNBT), 2-amino-
5-mercapto-1,3,4-thiadiazole (HAMTD) and 2-mercapto-5-
methyl-benzimidazole (MMBD) are capable to coordinate with
metal atoms (Scheme 1) because they all contain a ASH group
and potential coordination N atoms, and their amino or imino
group may form intramolecular and intermolecular hydrogen
bonds with other acceptors [14–16]. These free ligands can exhibit
fluorescence signal and the emission band may shift after their
coordinating to the Cu(I) atom in complexes. The strong electron-
withdrawing substituent (ANO2) on the phenyl in HMNBT ligand
and the electron-donating substituent (ACH3) on the phenyl in
MMBD ligand may also affect the structure and luminescence
property of the complexes. Furthermore, to our best knowledge,
only one literature have reported the Cu(I) complex with HMNBT,
HAMTD and MMBD [17].
2. Experimental
2.1. Materials and measurements
All chemical reagents are commercially available and used
without further purification. Elemental analyses (C, H, N) were
determined on a Vario EL elemental analyzer. Infrared spectra were
recorded on a Nicolet Avatar 360 FT-IR spectrometer using the KBr
pellet in the range of 400–4000 cmÀ1. Excitation and emission
spectra of the solid samples were recorded on an F-4500 fluores-
cence spectrophotometer at room temperature. 1H NMR was re-
corded at room temperature with a Varian VNMRS 600 MHz
spectrometer and 31P NMR was recorded at room temperature
with a Bruker DPX 400 MHz spectrometer. The THz absorption
spectra were recorded on the THz time domain device of Capital
Normal University of China, based on photoconductive switches
for generation and electro-optical crystal detection of the far-infra-
red light. The experimental apparatus for terahertz transmission
measurements has been discussed in detail elsewhere [19]. The
preparation of the samples is by pressing the pure crystals into pel-
let. The detection of THz absorption spectra is carried out at N2
atmosphere to avoid the influence of water vapor. The thick of
the samples 1, 5, 6, 7 and ligands are about 1 mm. The THz absorp-
tion spectra of the samples are obtained by the THz time-domain
device and the effective spectrum range is 0.2–1.6 THz.
2.2. Synthesis of complexes 1–7
Compound 1: A mixture of CuCl (0.0198 g, 0.2 mmol) and
HMNBT (0.0424 g, 0.2 mmol, HMNBT = 2-mercapto-6-nitrobenzo-
thiazole) in MeOH and CH2Cl2 (10 mL, v/v = 1:1) was stirred for
2 h and PPh3 (0.1049 g, 0.4 mmol) was added to the mixture which
was stirred for further 4 h. The insoluble residues were removed by
filtration, and the filtrate was evaporated slowly at room tempera-
ture for a week to yield orange crystalline products. Compounds 2–
3 was prepared in a manner similar to that described for 1, using
CuCl (0.0198 g, 0.2 mmol) or CuBr (0.0287 g, 0.2 mmol), HMNBT
(0.0424 g, 0.2 mmol) and PPh3 (0.0525 g, 0.2 mmol) as starting
materials. After three days, orange crystals were formed. Com-
pound 4: using CuSCN (0.0243 g, 0.2 mmol), HMNBT (0.0424 g,
0.2 mmol), PPh3 (0.0525 g, 0.2 mmol) as starting materials. After
three days, orange crystals were formed. Compound 5: using CuBr
(0.0287 g, 0.2 mmol), HAMTD (0.0266 g, 0.2 mmol, HAMTD = 2-
amino-5-mercapto-1,3,4-thiadiazole), PPh3 (0.1049 g, 0.4 mmol)
as starting materials. After a week, colorless crystals were formed.
Compounds 6–7: using CuBr (0.0287 g, 0.2 mmol) or CuI (0.0381 g,
0.2 mmol), MMBD (0.0328 g, 0.2 mmol, MMBD = 2-mercapto-5-
methyl-benzimidazole), PPh3 (0.1049 g, 0.4 mmol) as starting
materials. After a week, colorless crystals were formed (see
Scheme 2).
In light of these facts, we thought it was worthwhile to study
Cu(I) complexes of PPh3 with HMNBT, HMNBT and MMBD, espe-
cially their luminescence properties. The Cu(I) complexes are often
prepared in acetonitrile and dichloromethane [18], but these seven
Cu(I) complexes were synthesized in the mixture of methanol and
dichloromethane. In this paper, terahertz time-domain spectra of
four copper(I) complexes (1, 5–7) and their starting materials
(including PPh3, mercaptan ligands and copper salts) were mea-
sured, and found that their effective signals are in the range from
0.2 to 1.6 THz. The above results are supplement of spectroscopy,
our results show the anions, ligands, coordination and hydrogen
Scheme 1. The molecular structures of three mercaptan ligands, I–III for 2-mercapto-6-nitrobenzothiazole (HMNBT), 2-amino-5-mercapto-1,3,4-thiadiazole (HAMTD) and 2-
mercapto-5-methyl-benzimidazole (MMBD).

Q.-M. Qiu et al. / Journal of Molecular Structure 1062 (2014) 125–132
127
Scheme 2. The routine of synthesis for complexes 1–7.
2.3. Crystal structure determination and refinement
[CuCl(HMNBT)(PPh3)2] (1), Mr: 835.77. Z = 2. Yield: 88%. Mp:
250–252 °C. Anal. Calc. for C43H34ClCuN2O2P2S2: C, 61.74; H,
4.07; N, 3.35. Found: C, 61.51; H, 3.97; N, 3.39%. IR (KBr disc,
cmÀ1): 3435m, 3052m, 2498m, 1602m, 1584m, 1530s, 1484vs,
1433s, 1397m, 1363w, 1334vs, 1301m, 1265s, 1183m, 1158w,
1134m, 1093s, 1054s, 1026s, 997m, 890w, 873w, 836m, 743s,
693vs, 657m, 517s, 498s, 462m, 425w. 1H NMR (600 MHz, CDCl3,
298 K): d = 7.2–7.4 (m, overlapping with the solvent signal,
Ph + HMNBT-Ph), 8.2 (d, 1H, HMNBT-Ph), 8.3 (s, 1H, HMNBT-Ph)
ppm. 31P NMR (400 MHz, CDCl3, 298 K): d = À2.4 (s, PPh3) ppm.
[CuCl(HMNBT)(PPh3)]2 (2), Mr: 1147.00. Z = 1. Yield: 23%. Mp:
241–244 °C. Anal. Calc. for C50H38Cl2Cu2N4O4P2S4: C, 52.31; H,
3.31; N, 4.88. Found: C, 51.99; H, 3.27; N, 4.74%. IR (KBr disc,
cmÀ1): 3437w, 3053m, 2758w, 2499m, 1678vw, 1602m, 1584m,
1530s, 1484vs, 1433s, 1397m, 1363w, 1334vs, 1302s, 1265s,
1183m, 1158w, 1134m, 1094s, 1054s, 1026s, 997m, 890w, 873w,
837m, 744s, 693vs, 657m, 618w, 542vw, 517s, 499s, 462m,
425w. 1H NMR (600 MHz, CDCl3, 298 K): d = 7.2–7.4 (m, overlap-
ping with the solvent signal, Ph + HMNBT-Ph), 8.2 (d, 1H,
HMNBT-Ph), 8.3 (s, 1H, HMNBT-Ph) ppm. 31P NMR (400 MHz,
CDCl3, 298 K): d = –2.0 (s, PPh3) ppm.
The X-ray single crystal data collections for the seven com-
plexes were performed on a Bruker SMART CCD diffractometer
with graphite monochromatized Mo K
a radiation (k = 0.71073 Å).
Semi-empirical absorption corrections were applied. The struc-
tures were solved by direct methods and refined by the full-matrix
least-squares method on F2 using the SHELXS 97 and SHELXL-97
programs [20,21]. All non-hydrogen atoms in the complexes were
refined anisotropically. The hydrogen atoms were generated geo-
metrically and treated by a mixture of independent and con-
strained refinements.
3. Results and discussion
3.1. General aspects
Seven Cu(I) complexes were characterized by elemental analy-
sis, X-ray diffraction, IR, 1H NMR and 31P NMR spectroscopy, the
data are listed below. A summary of the crystallographic data
and details of the structural refinements are listed in Table 1. Se-
lected bond distances and bond angles are listed in Tables S1–S4.
[CuBr(HMNBT)(PPh3)]2 (3), Mr: 1235.92. Z = 1. Yield: 25%. Mp:
253–254 °C. Anal. Calc. for C50H38Br2Cu2N4O4P2S4: C, 48.55; H,
Table 1
Crystallographic data for complexes 1–7.
Complex
Formula
1
2
3
4
5
6
7
C
43H34ClCuN2O2P2S2 C50H38Cl2Cu2N4O4P2S4 C50H38Br2Cu2N4O4P2S4 C50H37CuN4O4P2S4 C39H36BrCuN3OP2S2 C46H46BrCuN2O2P2S C46H46CuIN2O2P2S
Crystal system Triclinic
Triclinic
P1
Triclinic
P1
Monoclinic
P21/c
Monoclinic
P21/c
Monoclinic
P21/c
Monoclinic
P21/c
ꢀ
ꢀ
ꢀ
Space group
P1
a (Å)
b (Å)
c (Å)
9.6892(8)
13.5820(13)
15.9842(15)
89.987(2)
72.8710(10)
80.0090(10)
1976.8(3)
2
9.2301(9)
10.6540(10)
13.4181(12)
86.300(2)
70.1020(10)
87.997(2)
1238.0(2)
1
9.2716(8)
10.6403(9)
13.4775(13)
86.985(2)
70.1970(10)
87.848(2)
1248.94(19)
1
12.3106(11)
36.653(3)
11.1401(10)
90.00
111.8630(10)
90.00
13.0137(5)
16.3117(7)
18.3089(10)
90.00
100.5590(10)
90.00
12.7732(13)
18.4028(18)
18.7296(19)
90.00
92.4710(10)
90.00
12.8018(11)
18.6030(19)
18.7696(16)
90.00
93.0850(10)
90.00
a
(°)
b (°)
c
(°)
V (Å3)
4665.1(7)
4
3820.7(3)
4
4398.5(8)
4
4463.5(7)
4
Z
F(000)
860
584
620
2080
1700
1848
1920
Reflections
collected
Independent
reflections
Goodness-of-
fit on F2
Rint
9960
6215
6269
23,579
13,996
21,833
22,101
6868
1.027
4289
1.013
4312
1.013
8227
1.034
6736
1.028
7752
1.019
7752
1.072
0.0331
0.0471
0.1047
0.0889
0.1322
0.0235
0.0367
0.0848
0.0570
0.0993
0.0271
0.0385
0.0832
0.0677
0.0968
0.0861
0.0534
0.0854
0.1072
0.0959
0.0366
0.0598
0.1347
0.0963
0.1582
0.0436
0.0377
0.0820
0.0693
0.0960
0.0501
0.0410
0.0868
0.0801
0.1144
R1[I > 2r(I)]
wR2[I > 2
r
(I)]
R1 (all data)
wR2(all data)

128
Q.-M. Qiu et al. / Journal of Molecular Structure 1062 (2014) 125–132
3.07; N, 4.53. Found: C, 48.91; H,3.10; N, 4.49%. IR (KBr, cmÀ1):
3437m, 3052m, 2968m, 2888m, 2820m, 2714m, 1604m, 1582w,
1521s, 1475vs, 1433s, 1393s, 1334vs, 1302s, 1250s, 1179ww,
1132w, 1095w, 1051m, 1023s, 997w, 900w, 838m, 821m, 746s,
694s, 674m, 654w, 552w, 520s, 507m, 491m, 458m. 1H NMR
(600 MHz, CDCl3, 298 K): d = 7.2–7.6 (m, overlapping with the sol-
thiocyanate anion is substituted by the deprotonated mercaptan
ligand.
To obtain the full series of this type of complexes, we studied
the reactions of CuX (X = Cl, Br, I, SCN) with three mercaptan ligand
and PPh3 in the molar ratio 1:1:1 or 1:1:2 in the mixed solvent of
CH2Cl2 and CH3OH. Except the reactions which produce the seven
title compounds and [CuI(MMBD)(PPh3)2]ÁCH3OH [17], the other
reactions were failed and many of them only produced the adducts
CuX:PPh3. The possible reason is that anions induce PPh3 substi-
tutes mercaptan ligand in the Cu(I) complexes.
vent signal, Ph + HMNBT-Ph), 8.3–8.4 (m, 2H, HMNBT-Ph) ppm. 31
P
NMR (400 MHz, CDCl3, 298 K): d = À2.4 (s, PPh3) ppm.
[Cu(MNBT)(HMNBT)(PPh3)2] (4), Mr: 1011.56. Z = 4. Yield: 15%.
Mp: 222–223 °C. Anal. Calc. for C50H37CuN4O4P2S4: C, 59.31; H,
3.66; N, 5.54. Found: C, 60.00; H, 3.61; N, 5.62%. IR (KBr disc,
cmÀ1): 3435m, 3051m, 2095vw, 1606w, 1586w, 1569w, 1529w,
1529m, 1480m, 1433s, 1396m, 1366m, 1331vs, 1312vs, 1272s,
1122m, 1092m, 1048m, 1028m, 1003s, 880w, 836m, 822m, 740s,
691s, 647m, 512s, 488m, 465m, 425w. 1H NMR (600 MHz, CDCl3,
298 K): d = 7.2–7.6 (m, overlapping with the solvent signal,
Ph + HMNBT), 8.3–8.4 (m, 4H, HMNBT), 10.8 (s, 1H, HMNBT-NH)
ppm. 31P NMR (400 MHz, CDCl3, 298 K): d = À2.4 (s, PPh3) ppm.
[CuBr(HAMTD)(PPh3)2]ÁCH3OH (5), Mr: 832.22. Z = 4. Yield: 69%.
Mp: 233–235 °C. Anal. Calc. for C39H36BrCuN3OP2S2: C, 56.24; H,
4.32; N, 5.05. Found: C, 56.30; H, 4.27; N, 5.00%. IR (KBr disc,
cmÀ1): 3398m, 3238m, 3137m, 3053m, 2905m, 1606s, 1552vs,
1480s, 1433vs, 1350m, 1312m, 1183w, 1094s, 1051s, 1027s,
998m, 856vw, 743vs, 695vs, 618w, 582w, 544w, 516s, 491m,
432w. 1H NMR (600 MHz, CDCl3, 298 K): d = 4.8 (s, 2H, HAMTD-
NH2), 7.2–7.5 (m, overlapping with the solvent signal, PPh3-Ph)
ppm. 31P NMR (400 MHz, CDCl3, 298 K): d = À4.3 (s, PPh3) ppm.
[CuBr(MMBD)(PPh3)2]Á2CH3OH (6), Mr: 896.30. Z = 4. Yield:
As regards to the IR spectra, the absorptions in the 3437–
3393 cmÀ1 region are attributed to
v(NH) stretching frequencies
for complexes 1–4 and 6–7. In complex 5, the stretching at
3398 cmÀ1 and 3238 cmÀ1 is attributed to ligand’s ANH2 group.
The absorptions around 3053 cmÀ1 are caused by the CAH stretch-
ing vibration of the phenyl ring in all the complexes. The v(C@S)
bands are located at 856–801 cmÀ1, showing that the ligands bind
the metal via the sulfur atoms [22,23]. The typical absorptions
around 512 cmÀ1 in all the complexes are due to the CuAP bonds
[24].
The 1H NMR and 31P NMR spectra of complexes 1–7 have been
measured at room temperature in CDCl3 solution. The 1H NMR
spectra of complexes 4, 6 and 7 exhibit the signal of NH group at
10.8 ppm, 10.9 ppm and 10.6 ppm, respectively. The lack of the sig-
nal of the NH group in the 1H NMR spectra of complexes 1–3 shows
that the ligand is deprotonated in the solution. For complexes 1–7,
the resonance signals in the range of 7.0–8.4 ppm are assigned to
the protons of PPh3 and the mercaptan ligand. The broad multiplet
signals of aromatic protons of PPh3 for 1–7 are in the range of 7.2–
7.4 ppm, 7.2–7.4 ppm, 7.2–7.6 ppm, 7.2–7.5 ppm, 7.2–7.5 ppm,
7.2–7.4 ppm and 7.2–7.4 ppm, respectively. For 1–4, the multiple
signals at range 8.20–8.45 ppm are assigned to 2-mercapto-6-
nitrobenzothiazole protons. For 5, the signal of NH2 in 2-amino-
5-mercapto-1,3,4-thiadiazole ligand is at 4.78 ppm. In 1H NMR
spectra of complex 6–7, there is a multiplet in the range 7.0–
7.1 ppm, which is assigned to benzimidazole protons. There is a
singlet at 2.4 ppm in 6–7, which is attributed to methyl protons
of benzimidazole. In 31P NMR spectra of 1–7, all phosphorus atoms
in each molecule are chemically equivalent because only a single
resonance signal is found (À2.4 ppm for 1, À2.0 ppm for 2,
À2.4 ppm for 3, À2.5 ppm for 4, À4.3 ppm for 5, À4.2 ppm for 6,
À5.3 ppm for 7). The similarity of resonance signals in solution of
1–7 show that the chemistry environment for the phosphorus
atom from PPh3 in 1–7 is similar.
74%. Mp: 287–288 °C. Anal. Calc. for
C46H46BrCuN2O2P2S: C,
61.59; H, 5.13; N, 3.12. Found: C, 61.77; H, 5.04; N, 3.04%. IR
(KBr disc, cmÀ1): 3393m, 3050s, 1671m, 1615m, 1585w, 1514s,
1479vs, 1434vs, 1382m, 1322m, 1224w, 1182m, 1094s, 1027m,
997w, 857w, 801m, 743s, 694vs, 629w, 594vw, 545w, 515s,
493m, 425w. 1H NMR (600 MHz, CDCl3, 298 K): d = 2.4 (s, 3H,
MMBD-CH3), 7.0–7.1 (m, 3H, MMBD-Ph), 7.2–7.4 (m, overlapping
with the solvent signal, PPh3-Ph), 10.9 (d, 2H, MMBD-NH) ppm.
31P NMR (400 MHz, CDCl3, 298 K): d = À4.2 (s, PPh3) ppm.
[CuI(MMBD)(PPh3)2]Á2CH3OH (7), Mr: 943.29. Z = 4. Yield: 89%.
Mp: 293–295 °C. Anal. Calc. for C46H46ICuN2O2P2S: C, 58.52; H,
4.88; N, 2.97. Found: C, 58.44; H, 4.90; N, 2.99%. IR (KBr disc,
cmÀ1): 3400 m, 3176s, 3053s, 1963w, 1891w, 1816w, 1668w,
1615 m, 1585 m, 1571w, 1510 m, 1476vs, 1433vs, 1383 m, 1319s,
1222 m, 1183 m, 1092s, 1025 m, 998 m, 921vw, 852w, 804 m,
741s, 692vs, 626 m, 594 m, 543 m, 507s, 425w. 1H NMR
(600 MHz, CDCl3, 298 K): d = 2.4 (s, 3H, MMBD-CH3), 7.0–7.1 (m,
3H, MMBD-Ph), 7.2–7.4 (m, overlapping with the solvent signal,
PPh3-Ph), 10.6 (d, 2H, MMBD-NH) ppm. 31P NMR (400 MHz, CDCl3,
298 K): d = À5.3 (s, PPh3) ppm.
3.2. Crystal structures of the complexes
3.2.1. [CuCl(HMNBT)(PPh3)2] (1)
Generally, the Cu(I) complexes of halides with triphenylphos-
phine (PPh3) are prepared in acetonitrile and dichloromethane
[18]. In our work, these Cu(I) complexes were synthesized at room
temperature in the mixture of methanol and dichloromethane
mainly because the crystal of good quality could be obtained.
The coordination properties of the mercaptan ligand and PPh3 to-
wards the Cu(I) precursors CuX (X = Cl, Br, I) were investigated.
The Cu(I) metal centre is coordinated by the soft P donor atoms
and the soft S donor atoms, which help to stabilize the lower oxi-
dation state of Cu atom.
It’s should be mentioned that molar ratio and solvent are
important to the formation of the title compounds. The direct reac-
tion of copper(I) halides with mercaptan ligand and PPh3 in
1:1:2 M ratio yield the complexes 1, 5–7, and the dinuclear com-
plexes 2 and 3 are formed by the reaction of CuX (X = Cl, Br) with
HMNBT and PPh3 in 1:1:1 M ratio. It is interesting that in complex
4, the HMNBT ligand is connected to the nitrogen atom of the
deprotonated HMNBT molecule by hydrogen bond, and the
The perspective view of 1 is shown in Fig. 1. The Cu(I) atom is
coordinated by two phosphorus atoms from two PPh3 ligands,
one chloride atom and one sulfur atom from HMNBT. The CuAS
bond distance [2.414(1) Å] and CuAP bond distances [2.266(1)–
2.270(1) Å] are similar to those reported in other copper(I) com-
plexes [25–27]. The bond angles around Cu atom ranging from
98.5(1)° to 131.2(1)° are similar to those of the previously reported
similar complex [25]. The tetrahedral distortion may be attributed
to steric interactions between the bulky phosphine ligands, which
is common among a large series of monomeric Cu(I) halide
complexes containing one heterocyclic thione and two monoden-
tate PPh3 ligands [25,27–29]. The SACuACl angle is almost the
same as those in other similar complexes, this is due to the
existence of the strong intramolecular NAHÁ Á ÁCl [174(1)°]
hydrogen bond of chlorine atom with the imino hydrogen in its
vicinity [N1Á Á ÁCl1, 3.001 Å]. The chain is generated via weak
C28AH28Á Á ÁCl1 bond [C28Á Á ÁCl1, 3.605(6) Å] formed by the
chloride atom and the CAH group of PPh3 ligand (Fig. S1 in the

Q.-M. Qiu et al. / Journal of Molecular Structure 1062 (2014) 125–132
129
the benzothiazole ring and benzene ring is 3.784(2) Å with the
dihedral angle of 5.5°, which suggests the existence of inter-
pÁ Á Áp
actions between them [complex 3: 3.766(2) Å, 6.3°]. Furthermore,
intramolecular hydrogen bonds NAHÁ Á ÁCl and NAHÁ Á ÁBr are also
observed [N1ÁÁÁCl1 = 3.096(3) Å, N1AH1ÁÁÁCl1 = 157(1)°; N1ÁÁÁBr1 =
3.247(4) Å, N1AH1ÁÁÁBr1 = 153(1)°].
3.2.3. Cu(MNBT)(HMNBT)(PPh3)2 (4)
In complex 4, two phosphorus atoms from two triphenylphos-
phines, two sulfur atoms from the neutral ligand HMNBT and the
deprotonated ligand MNBT are coordinated to the Cu(I) cation
(Fig. 3). The NAH group of the HMNBT ligand is connected to the
nitrogen atom of the MNBT ligand by the hydrogen bond NAHÁ Á ÁN
[N1Á Á ÁN3 = 2.817(4) Å, N1AH1Á Á ÁN3 = 168(1)°]. This mode of intra-
molecular association between MNBT and HMNBT leads to the for-
mation of an eight-membered ring. It is interesting that the
thiocyanate anion in complex 4 is successfully substituted by the
mercaptan ligand. The structure of complex 4 is the first authenti-
cated example with the coordinated neutral HMNBT ligand. Fur-
thermore, intramolecular NAHÁ Á ÁS hydrogen bond is also
observed [N1Á Á ÁS4 = 3.540(4) Å, N1AH1Á Á ÁN3 = 125(1)°]. It is
noticeable that O4 atom is connected to another HMNBT ligand
via C4AH4Á Á ÁO4 hydrogen bond to form the chain (Fig. S2). In com-
plex 4, the centroid to centroid distance between parallel adjacent
benzene rings of HMNBT ligand is 3.654(2) Å, which suggests the
Fig. 1. The molecular entities of complex 1. Thermal ellipsoids drawn at the 50%
probability level. The intramolecular hydrogen bonds NAHÁ Á ÁCl are shown with
dashed lines. Omit all of the other H-atoms not involved in H-bonding.
Supporting information), and weak CAHÁ Á Á
(C29AH29Á Á ÁPh, 2.86 Å) involving phenyl groups of two different
phosphines. There is also a weak interaction between the O1
p
interactions
p
atom and the C2AC7 ring (by using PLATON software), which ex-
plain the difference in the shape of O1 and O2 (the ellipsoid for
O2 is elongated whereas O1 is regular).
existence of
with each other via
tions (C13AH13Á Á ÁPh, 2.84 Å) involving phenyl groups of two dif-
p
Á Á Á
p
interactions between them. The chains interact
interac-
pÁ Á Á
p
interactions and weak CAHÁ Á Á
p
ferent phosphines to form the network structure (Fig. S3).
3.2.2. [CuX(HMNBT)(PPh3)]2 (X = Cl, Br) (2–3)
The perspective view of 2 and 3 are shown in Fig. 2. The basic
structural units of 2 and 3 are dimer in which the two copper
atoms are doubly bridged by two S atoms of the thione ligand to
form a strict planar four-membered Cu2S2 core. The CuÁ Á ÁCu dis-
tances are 2.832(1) and 2.805(1) Å in 2 and 3, respectively. These
values are slightly longer than the sum of van der Waals radii of
two copper atoms (2.80 Å) [30]. The CuAP bond distances in 2
[2.239(1) Å] and 3 [2.244(1) Å] are slightly shorter than the corre-
sponding distances in complex 1. The two non-equivalent CuAS
bond distances are 2.349(1) and 2.494(1) Å in 2, and 2.340(1)
and 2.506(1) Å in 3, which are within the range expected for dinu-
clear Cu(I) complexes with double bridging sulfur atoms [28,31].
The angles of S(2)#1-Cu(1)AS(2) [108.5(1)°] and Cu(1)#1-
S(2)ACu(1) [71.5(1)°] are not equal, the sum of the internal angles
of the four-membered ring [ACuASACuASA] in the Cu2S2 core are
approximately 360°, which indicates that the ring is a parallelo-
gram. In complex 2, the centroid to centroid distance between
3.2.4. [CuBr(HAMTD)(PPh3)2]ÁCH3OH (5),
[CuX(MMBD)(PPh3)2]Á2CH3OH (X = Br, I) (6–7)
The molecular structures of 5–7 are similar, and complexes 6
and 7 are isostructural. HAMTD and MMBD act as neutral, mono-
dentate ligand with the S atom as a coordination atom. Other sites
of the coordination tetrahedron are occupied by two P atoms from
two PPh3 ligands and one halide anion (Figs. S4 and S5). As in sim-
ilar Cu(I)-PPh3 complexes, the environment around copper(I) is
distorted tetrahedral, the PACuAP angle between the triphenyl-
phosphine ligands in 5–7 varies between 121.5(1)° and 122.0(1)°
[25]. The arrangement of the mercaptan ligand within the complex
is dictated by the intramolecular NAHÁ Á ÁX hydrogen bond. In 5–7,
Fig. 2. The molecular entities of complexes 2–3. Thermal ellipsoids drawn at the
50% probability level. The intramolecular hydrogen bonds NAHÁ Á ÁX are shown with
dashed lines. Omit all of the other H-atoms not involved in H-bonding.
Fig. 3. The molecular entities of complex 4. Thermal ellipsoids drawn at the 50%
probability level. The intramolecular hydrogen bonds NAHÁ Á ÁN and NAHÁ Á ÁS are
shown with dashed lines. Omit all of the other H-atoms not involved in H-bonding.

130
Q.-M. Qiu et al. / Journal of Molecular Structure 1062 (2014) 125–132
a dimer is formed by hydrogen bonds NAHÁ Á ÁX, OAHÁ Á ÁX and
OAHÁ Á ÁO between the unit [CuX(thione)(PPh3)2] and the solvent
methanol molecules. In complex 6, the centroid to centroid dis-
tance between the benzothiazole ring and benzene ring is
3.553(2) Å with the dihedral angle of 0.4°, which suggests the exis-
same excitation wavelength of 439 nm, and found that the emis-
sion maximum are exhibited at 467, 552 (HMNBT); 468, 539
(HAMTD); and 469, 546 nm (MMBD), respectively. In the fluores-
cence emission spectra of 1, 5, 6 and 7, the emission peaks are
found at 405, 468, 568 nm (kex = 340 nm for 1), 395, 475 nm
(kex = 244 nm for 5), 396, 507 nm (kex = 344 nm for 6), 394,
478 nm (kex = 339 nm for 7), respectively. Emission peaks of the
above complexes around 400 nm are similar to that of PPh3, which
indicates that the origin of these emissions involves emissive state
tence of
0.8°].
pÁ Á Áp interactions between them [complex 7: 3.511(3) Å,
3.3. Discussion of the crystal structures
derived from ligand-centered [
ima at around 300 nm and emissions around 450–510 nm are typ-
ical of CuAP containing chromophores with either ILCT ( -a );
MLCT (d- ) excited states [32].
p–
p⁄] transition. Absorption max-
In the seven title Cu(I) complexes, the CuI ion as a metal center
adopts tetrahedral coordination geometry when the coordination
number is four. In complexes 1–2, the ligand HMNBT plays differ-
ent roles: the HMNBT in complex 1 acts as a monodentate ligand
with the S atom as a coordination atom, while the mercaptan li-
gand in complex 2 acts as a bridged thiol. The different roles of
HMNBT are possibly due to the different molar ratio of the reac-
tants. Complex 1 and 2 are formed by the reaction of CuCl with
HMNBT and PPh3 in molar ratios 1:1:2 and 1:1:1 respectively. It
is interesting that in the reaction of 4 the thiocyanate anion is suc-
cessfully substituted by the mercaptan ligand. The structure of
complex 4 is the first authenticated example containing coordi-
nated neutral HMNBT ligand. The results show that SCNÀ may be
substituted easier than ClÀ/BrÀ anion. It is noticeable that CAHÁ Á ÁO
r
p
r
⁄
It is interesting that the solid sample of 1 exhibits an intense
low-energy emission with kem at 568 nm, which is slightly red-
shifted with respect to the free mercaptan ligand HMNBT. But for
5–7, no emission peak appears in the range of 520–600 nm. Among
these four complexes, 1 is un-solvated while 5–7 are methanol-sol-
vated. In 5–7, the OAH group of solvated methanol molecules
forms hydrogen bonds OAHÁ Á ÁX and OAHÁ Á ÁO with other atoms,
which may cause the quenching of the low-energy emission peak.
Although the slight red shift in 1 and 6–7 are considered as evi-
dence for participation of Cu ? S charge transfer in the emissive
excited state since the CuI ion express strong tendency for charge
transfer of this type, the emissions cannot be considered as one
of pure thione centred intraligand origin [11,33,34]. The halogen
could affect the emission spectra, in the form of a ligand-to-metal
charge-transfer (XMCT) or an interligand charge-transfer (XLCT,
X ? thione) [35]. There is a small dependence of the emission
maxima on the kind of the halide present, the kmax values of com-
plexes 6 and 7 are in the order 7 < 6, which is consistent with the
order of ligand field strength of the halide ions in the complexes
(IÀ < BrÀ) [36,37]. From the above results, we can conclude that
PPh3 and mercaptan ligands are sensitizers for luminescence of 1
and 5–7. And the complexes 1, 5, 6 and 7 act as green, cyan and
blue emitter component, respectively.
hydrogen bonds, CAHÁ Á Á
p
interactions and
p p interactions lead
Á Á Á
to the formation of 2D networks in complex 4, which may be due
to the existence of conjugated system and strong electron-with-
drawing group (ÀNO2) in HMNBT ligand and the inexistence of ha-
lides ions in 4. However, the solvent methanol molecules in
complexes 5–7 lead to the formation of a dimer. In complexes 6–
7, due to the existence of a phenyl group in the ligand MMBD, there
are intermolecular
p p interactions between benzothiazole ring
Á Á Á
and benzene rings which help to stabilize the dimer. Furthermore,
the isostructure of 2 and 3, 6 and 7 shows that the anions ClÀ, BrÀ
and IÀ do not affect the final structures.
In summary, the determination of the emissive excited states in
the Cu(I) complexes is still a difficult topic. The emissive states are
most likely of mixed MLCT/XLCT/IL character. Since the lumines-
cence properties of the Cu(I) halide aggregates have been widely
investigated, the complexes might have potential applications in
fluorescent sensors, electroluminescent devices and nonlinear op-
tics [18,38,39].
3.4. Luminescence
The excitation and emission spectra of free ligands HMNBT,
HAMTD and MMBD, and the complexes 1, 5, 6 and 7 are measured
in the solid state at room temperature (Fig. 4). The ligand PPh3
exhibits fluorescence signal centered at 402 nm with an excitation
maximum at 370 nm. Free mercaptan ligands were excited at the
3.5. THz properties of complexes
The room temperature terahertz (THz) absorption spectra of
CuCl, CuBr, CuI, triphenylphosphine (PPh3) 2-mercapto-6-nitro-
benzothiazole (HMNBT), 2-amino-5-mercapto-1,3,4-thiadiazole
(HAMTD), 2-mercapto-5-methyl-benzimidazole (MMBD), com-
plexes 1 and 5–7 were measured in the range of 0.2–1.6 THz. All
the above compounds except PPh3 ligand have characteristic reso-
nance peaks. The found peaks for each compound are as following:
HMNBT (0.87, 1.25, 1.36 and 1.49 THz), HAMTD (0.65, 1.09, 1.18
and 1.24 THz), MMBD (0.84 and 1.08THz), complex 1 (0.69, 0.78
and 0.87 THz), complex 5 (0.89 and 1.46THz), complex 6 (1.10,
1.33 and 1.48 THz), complex 7 (1.14, 1.25 and 1.40 THz) (Fig. 5a–
c). Although the agreement between crystal structure and ob-
served spectra does not allow a definitive characterization of the
spectra, it is possible to make tentative assignments of many ob-
served features in the terahertz region for the samples. By compar-
ing the THz absorption spectra of the products with those of the
reactants, we can see that after reaction, most peaks of the mercap-
tan ligands and CuX disappeared or moved, and new peaks in the
range of 1.25–1.48 THz appear in the obtained complexes. For
example, one peak at 1.46 THz appears in the spectrum of complex
Fig. 4. The luminescent excitation and emission spectra of 1, 5–7 in the solid state
at room temperature.

Q.-M. Qiu et al. / Journal of Molecular Structure 1062 (2014) 125–132
131
both of them exhibit a similar pattern of absorption features in
the range 1.2–1.5 THz. In complex 7, this pattern comprises two
absorption peaks at 1.25 THz and 1.40 THz, which appear blue-
shifted in complex 6 at 1.33 THz and 1.48THz. This shows that
the THz spetra can distinguish BrÀ from IÀ, this is to say the differ-
ence of anion can affect the THz spectra of compounds. The above
results show that the ligands, metal salts, the coordination and
hydrogen bonding interactions can affect the THz spectrum. So
THz spectroscopy may be a sensitive method to determine some
of the inorganic–organic hybride complexes, especially those iso-
structural complexes which are difficult to identify by other
spectroscopy.
4. Conclusion
Seven new Cu(I)-PPh3 complexes of 2-mercapto-6-nitrobenzo-
thiazole (HMNBT), 2-amino-5-mercapto-1,3,4-thiadiazole (HAM-
TD) and 2-mercapto-5-methyl-benzimidazole (MMBD) have been
synthesized and characterized for the first time. Copper(I) atom
has a strong tendency to form covalent bonds with S/P ligands
and the molar ratio and solvent has played an important role in
the synthesis of this series of complexes. Among these complexes,
1–5 represent first copper (I) examples of HMNBT and HAMTD. In
complex 4, a unique coordination mode of HMNBT was found.
Complexes 1 and 5–7 exhibit interesting emission in the solid
state. The hydrogen bond interactions may cause the quenching
of the low-energy emission peak in 5–7. Terahertz time-domain
spectra of four Cu(I) complexes and the starting materials were
measured. Our results indicate that the ligands, anions, and the
metal–ligand coordination and hydrogen bonding interactions
can affect the THz spectra of Cu(I) complexes. The above results
may be useful in characterizing the isostructural complexes which
are difficult to identify by other spectroscopy. Currently, there is
not enough THz information for inorganic–organic hybrid com-
plexes and their starting materials. Further studies on the synthe-
ses, structures and THz properties of Cu(I) complexes with
different heterocyclic ligands containing sulphur or phosphorus
donor atoms are in progress.
Acknowledgements
This work has been supported by the National Natural Science
Foundation of China (Grant No. 21171119), the National High
Technology Research and Development Program 863 of China
(Grant No. 2012AA063201), the Committee of Education of the
Beijing Foundation of China (Grant No. KM201210028020),
Program for Excellent Talents of Beijing City (Grant No.
2010D005016000002), the Beijing Municipal Natural Science
Foundation (Grant No. 7122015).
Appendix A. Supplementary data
CCDC 890632, 892818, 890635, 893648, 890630, 890636 and
893864 contain the supplementary crystallographic data for 1–7.
These data can be obtained free of charge via http://www.ccdc.ca-
m.ac.uk/conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: (+44) 1223 336033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.molstruc.2013.12.
076.
Fig. 5. (a) THz absorption spectra of CuCl, HMNBT and complex 1. (b) THz
absorption spectra of CuBr, HAMTD and complex 5. (c) THz absorption spectra of
CuBr, CuI, MMBD, and complexes 6 and 7.
5; two new peaks at 1.33 and 1.48 THz appears in the spectrum of
complex 6; two new peaks at 1.25 and 1.40 THz appear in the spec-
trum of complex 7. These changes in the THz spectra may be re-
lated to the coordination of the ligands to the Cu(I) metal atoms,
and also related to the inter- or intra-molecular hydrogen bonds.
It is interesting that though complexes 6 and 7 are isostructural,
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