Non-phase-transition luminescence mechanochromism of a copper(I) coordination polymer

Article abstract of DOI:10.1021/acs.inorgchem.6b02571

A copper(I) coordination polymer, [Cu₂I₂L₂]_n (CP 1), shows luminescence mechanochromism with a color change from greenish-blue to yellow upon the application of pressure. Powder X-ray diffraction and Raman studies reveal that the changes in the bond lengths in crystalline CP 1 are the main cause of luminescence mechanochromism. The luminescence mechanochromic process of CP 1 preserves its crystallinity with a small lattice distortion, despite very high pressure, and it is a non-phase-transition process. After the addition of several drops of acetonitrile to the ground and compressed samples, the original greenish-blue emissive and crystalline states are restored. Therefore, the luminescence color conversion processes are fully reversible.

Full text of DOI:10.1021/acs.inorgchem.6b02571

Article
pubs.acs.org/IC
Non-Phase-Transition Luminescence Mechanochromism of a
Copper(I) Coordination Polymer
Eunjin Kwon, Jineun Kim, Kang Yeol Lee,* and Tae Ho Kim*
Department of Chemistry (BK21 plus) and Research Institute of Natural Science, Gyeongsang National University, Jinju 52828,
Korea
*
S Supporting Information
ABSTRACT: A copper(I) coordination polymer, [Cu I L ]
2 2 n
2
(
CP 1), shows luminescence mechanochromism with a color
change from greenish-blue to yellow upon the application of
pressure. Powder X-ray diffraction and Raman studies reveal
that the changes in the bond lengths in crystalline CP 1 are the
main cause of luminescence mechanochromism. The lumines-
cence mechanochromic process of CP 1 preserves its
crystallinity with a small lattice distortion, despite very high
pressure, and it is a non-phase-transition process. After the
addition of several drops of acetonitrile to the ground and
compressed samples, the original greenish-blue emissive and
crystalline states are restored. Therefore, the luminescence
color conversion processes are fully reversible.
INTRODUCTION
mechanochromism. However, CPs with luminescence mecha-
nochromic properties are still rarely studied, although
mechanochemical processes have a long history.
■
(
Recently, research on novel functional coordination polymers
CPs) as stimuli-responsive intelligent materials with tunable
In this work, our aim was to examine the reversibility of the
luminescence mechanochromism of a new copper(I) CP under
the application of a mechanical stress. To this end, we designed
and synthesized an organic functional ligand 3-(2-(benzylthio)-
ethoxy)pyridine (L) for the formation of a coordination
polymer (CP 1) with CuI. Herein, we show that the
luminescence mechanochromism of CP 1 is caused by
modification of the bond strengths accompanied by changes
of the d-spacing distances of the specific lattice planes, which
are also proved by the bathochromic shifts of Raman
frequencies. Interestingly, the luminescence mechanochromism
of CP 1 is a non-phase-transition process, despite the
application of very high pressures (>0.1 GPa).
photoluminescence (PL) has gained substantial momentum,
1
2
because of their potential applications as sensors, PL switches,
3
and optical recording devices. An external stimuli-induced
4
reversible color change is called chromism. Several different
5
types of chromisms, such as photochromism, electrochrom-
6
7
8
ism, thermochromism, mechanochromism, solvatochrom-
9
ism, etc., have been defined and commonly reported. Among
these, mechanochromism represents a color change initiated by
mechanical stresses, such as grinding, compressing, shearing,
and other external mechanical forces.
The phenomenon of luminescence mechanochromism,
which is also known as mechanoluminescence, was first
10
discovered by Francis Bacon. Interestingly, mechanochrom-
ism is mostly accompanied by a phase transition such as a
11
RESULTS AND DISCUSSION
crystal-to-amorphous transition and/or an aggregation state
■
1
2
change. Furthermore, design strategies for luminescence
mechanochromism are few and an understanding of the
underlying mechanism is still lacking. Although several
structural factors, such as molecular arrangement, conforma-
tional flexibility, and intermolecular interactions, have been
proposed to result in luminescence mechanochromism, its exact
origin has remained unclear. The main reason behind the
difficulty in identifying the origin of luminescence mechano-
chromism is the loss of crystallinity when emissive samples are
mechanically compressed. A majority of the reports on this
An N/S donor ligand, L, was synthesized from 3-hydroxypyr-
idine and benzyl 2-chloroethylsulfide via a previously reported
20
method (see Scheme S1 in the Supporting Information (SI))
since Cu I complexes with aromatic N and S donor ligands
2 2
show photoluminescence. In addition, a benzyl group was
introduced for possible intermolecular π−π interactions. The
luminescent CP 1, [Cu I L ] , was prepared by the reaction
2 2 2 n
between CuI and L, taken in a 1:1 molar ratio in acetonitrile.
Figure 1 shows the single-crystal X-ray structure of CP 1. The
pale yellow crystalline CP 1 crystallizes with a monoclinic
13
phenomenon are based on organic systems. So far, complexes
1
4
15
16
17
18
containing several metal ions (Cu(I), Zn(II), Pt, Ag,
Received: October 25, 2016
1
9
and Au ) have been reported to show excellent luminescence
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.6b02571
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Article
Figure 1. (a) Synthetic scheme of CP 1 and (b) its coordination
environment. Hydrogen atoms are omitted for the sake of clarity.
crystal system, space group C2/c (Figure S1 in the SI). CP 1
shows a one-dimensional (1D) loop chain structure (Figure 1a,
right).
Crystallographic data and bond lengths/angles for CP 1 are
summarized in Table 1 and Table S2 in the SI. Figure 1b shows
Table 1. Crystallographic Data of CP 1
parameter
value
formula
C H CuINOS
1
4
15
formula weight
435.77
temperature
173(2) K
crystal system
monoclinic
C2/C
space group
a
14.9694(8) Å
17.0368(8) Å
11.7309(6) Å
92.621(2)°
b
c
β
3
V
2988.6(3) Å
Z
8
1.937 g cm−
3
Dcalc
F(000)
1696
q range
1.812−27.607
reflections collected
independent reflections
R (int)
13679
3441
0.0281
goodness of fit, F2
1.037
2
R, wR (I > 2σ(I))
R = 0.0273, wR = 0.0708
1
2
a
R and wR indices (all data)
R = 0.0313, wR = 0.0738
1 2
1
2
a
R = ∑∥F | − |F ∥/∑|F |. ωR = ∑[w(F − F ) ]/∑[w(F ) ]1/2.
2
2
2
2 2
1
0
c
o
2
0
c
o
the coordination environment of CP 1. The asymmetric unit of
CP 1 consists of a Cu(I) ion, an μ -iodide, and a L. Cu(I)
2
bonding with two iodides, a S atom, and a pyridyl N atom
exhibits a distorted tetrahedral coordination geometry. A Cu2I2
rhomboid dimer is generated by an inversion symmetry
operation of the asymmetric unit. The packing diagrams and
intermolecular interactions of CP 1 are shown in Figure 2.
Each compartment of the loop chain contains one rhomboid
dimer Cu I cluster and two L. The Cu−Cu (2.9456(8) Å),
Figure 2. Packing diagrams of CP 1 along (a) the a-axis, (b) the b-axis,
(c) the c-axis, and (d) the [101] direction.
intermolecular C−H···π (C3−H3···Cg = 2.63 Å, where Cg is
2
2
the centroid of the C9−C14 ring) and π−π interactions (Cg1···
Cg1 = 3.6546(17) Å, where Cg1 is the centroid of the ring
formed by N1 and C1−C5 atoms) (see Figure 1b for labeling).
The loop chains are lined up along the [101] direction. The
chains are linked by weak intermolecular C−H···π interactions
(2.63 Å), resulting in a three-dimensional architecture.
2
2
Cu−S (2.3246(9) Å), Cu−I (2.6380(4)−2.6762(4) Å), and
Cu−N (2.066(2) Å) distances are similar to those in Cu(I)
complexes. In the crystal, C−H···O hydrogen bonds (C7···O1,
3
.532(4) Å; H7B···O1, 2.56 Å) link adjacent molecules (see
Figure 2). In addition, crystal packing is stabilized by weak
B
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Thermogravimetric analysis (TGA), shown in Figure 3, was
conducted to investigate the thermal stability of CP 1. The
Figure 3. TGA (black) and DTA (blue) traces of CP 1.
weight loss of CP 1 occurred in two distinct regions: the 147−
4
3
1
87 °C range and the 487−780 °C range (black trace in Figure
). The first weight loss (∼56%) in the temperature range of
47−487 °C was induced by the decomposition of the ligand
molecules in CP 1 crystals. This is in good agreement with the
calculated value of 56.3%. The second weight loss originated
from the decomposition of the residual compound left behind
from the first step, leaving ∼5% residue.
The differential thermal analysis (DTA) data (black trace in
Figure 3) was also acquired during the TGA measurements;
these results indicated a remarkable endothermic reaction at
Figure 4. (a) Variation of PL spectra of the solid-state CP 1
coordination polymers with pressure. (b) Variation of emission
maximum with pressure, showing a plateau after ∼0.4 GPa. (c)
Photographic images of compressed CP 1 pellets under UV
irradiation; the dark spots in the compressed sample disks are due
to small defects.
1
75 °C, which was assigned to the decomposition of the
organic ligands in CP 1 (blue trace in Figure 3). We believe
that the endothermicity of the peak in the DTA trace is caused
by breaking of the covalent coordination bonds, and the
corresponding weight loss is due to the low thermal stability of
from 472 nm to 500 nm. The PL maximum plateaus after 0.4
GPa (Figure 4b). The spectral shift was also accompanied by a
distinct color change from greenish-blue to yellow (Figure 4c).
The above-mentioned bathochromic shift of the PL peak
induced by mechanical pressure, which is the so-called
“luminescence mechanochromism”, can be reasonably ex-
plained in terms of the release of internal energy by the
crystalline CP 1. Generally, when work is done on a crystal via
coercive compression, the internal energy in an adiabatic
process increases. In the case of CP 1, positions of the
molecular orbitals will probably rearrange for compensating the
increased internal energy caused by the applied high pressure.
In particular, the energy gap between the highest occupied
molecular orbital (HOMO) and lowest unoccupied molecular
orbital (LUMO) of CP 1 must be reduced in order to explain
the bathochromic shift.
Therefore, the emission energy by the metal-to-ligand charge
transfer (MLCT) and halide-to-metal charge transfer (XMCT)
will decrease with increasing pressure. In our case, however, the
PL maximum reaches a plateau after 0.4 GPa. This implies that
consumption of the increase in internal energy with increasing
applied pressure is limited.
The lattice parameters or the d-spacing distances of specific
lattice planes are also expected to change in the compressed CP
1 crystals. Variation of the lattice parameters of CP 1 with
pressure were further confirmed by systematically investigating
the PXRD patterns before and after compression (Figure 5), in
comparison with the single-crystal X-ray diffraction (SCXRD)
data at atmospheric pressure (Figure S2 in the SI). It can be
seen that no new diffraction peak(s) appeared after the
compression process, implying that no new crystalline phase
21
the bond between Cu and S atoms.
Cu I cluster compounds have been studied by many
x x
research groups in regard to their photophysical properties
such as luminescence thermochromism, luminescence
vapochromism, and luminescence mechanochromism. PL
in Cu(I) CPs with N/S or N/P donor ligands and various Cu I
geometries such as rhomboid-like, stair step-like,
like, etc. is a phenomenon observed in many cases. CP 1
radiates a greenish-blue light upon ultraviolet (UV) irradiation
2
2
2
3
24
x x
cubane-
25
26,27
2
7
(
356 nm).
The PL color of CP 1 changed from greenish-blue to yellow
after grinding in a mortar (Figure S2a in the SI). Overall, the
crystallinity of CP 1 was preserved, despite the strenuous
grinding (Figure S2b). Interestingly, the powder X-ray
diffraction (PXRD) patterns (Figure S2a) of CP 1 before and
after grinding indicate that CP 1 did not undergo any phase
transition, such as crystal-to-amorphous conversion, even
though the PL color changed from greenish-blue to yellow.
Based on the above observations, the crystal structure of CP 1
is expected to sustain even high pressures. Therefore, a high
pressure (0.1−0.9 GPa) was gradually applied on CP 1 crystals
in order to observe any change in its crystallinity and PL
spectra.
Figure 4a shows the spectral shift of the PL band of
polycrystalline CP 1 after compression. It can be easily noticed
from the figure that increasing the pressure from 0 to 0.9 GPa
leads to a gradual bathochromic shift of the PL band of CP 1
C
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Article
appearance of vibrational frequencies at lower values in the
Raman spectra of the compressed samples.
To validate the change of the coordination environment
around the [Cu I ] core (i.e., an increase in bond distances by
2
2
applied pressure), Raman spectroscopy was performed and the
spectra are shown in Figure 6. Raman spectra of solid CP 1 and
compressed samples of CP 1 (0.1 and 0.6 GPa) were obtained
with an excitation wavelength of 785 nm (Figure 6a). The black
Figure 5. (a) PXRD patterns of CP 1 crystals before compression
(
black trace) and after compression (0.1 GPa, red trace; 0.1 GPa blue
trace; 0.2 GPa green trace; 0.6 GPa pink trace). (b) Magnified PXRD
patterns of the region depicted by dashed lines in panel (a).
was formed. Each PXRD pattern exhibits several diffraction
peaks in the range of 4° < 2θ < 60°, which indicates that the
crystallinity was preserved, despite the formation of the many
defects induced by the high pressure. For further detailed
PXRD analyses, the dashed region of the PXRD patterns in the
range of 9.8° < 2θ < 14° in Figure 5a were magnified in Figure
5
b. When pressure is increased, a (111) major peak is shifted to
smaller 2θ values (Figure 5b).
d = 2 λ
sin θ
(1)
The d-spacing value of the (111) lattice plane in CP 1 crystal
28
can be determined by eq 1. The d-spacing of the (111) plane
was 7.96, 7.99, and 8.09 Å at 0, 0.05, and 0.4 GPa, respectively.
Interestingly, the d-spacing value of the (111) plane of the
sample compressed with 0.4 GPa is ∼0.13 Å and longer than
that of CP 1 at 1 atm (see Figure S3 in the Supporting
Information). As mentioned earlier, when work is done on a
crystal by coercive compression, the internal energy in an
adiabatic process will increase. Generally, under this condition,
the d-spacing of the crystal plane under high pressure should be
shorter than that of the crystal plane at normal pressure.
However, in this study, the d-spacing of the crystal plane of CP
1
increased with applied high pressure, because the internal
energy accumulated during compression was released by the
change of the packing state of the lattice. Presumably, if the
pressure acts on the samples in the side or vertical direction of
the single crystal structure, as shown in Figure S3, the d-spacing
value will increase and the chains of CP 1 will be elongated,
resulting in longer bond distances. This can be validated by
Figure 6. (a) Raman spectra of uncompressed CP 1 (black trace) and
compressed CP 1 (0.1 GPa, red trace; 0.6 GPa, blue trace) obtained
using excitation wavelength of 785 nm. (b) Magnified Raman spectra
of the underlined region 1 shown in panel (a). (c) Magnified Raman
spectra of the underlined region 2 shown in panel (a). (d) Magnified
Raman spectra of the underlined region 3 shown in panel (a).
D
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trace in Figure 6 shows the Raman spectrum obtained with CP
1
. The Raman spectra exhibited ∼10 major vibrational peaks.
The observed peaks at 128.2, 208.0, 253.4, 291.2, 478.8, (621.0,
−1
638.1, 688.6), 1002.8, and (1023.6 and 1056.6) cm can be
29
30
assigned to the Cu−I stretching, N−Cu stretching, I−I
3
1
30
30
32
stretching, Cu−Cu stretching, S−Cu, N−Cu stretching,
−1
33
S−C stretching (∼620−689 cm ), ring breathing (pyr-
3
4
34
idine), and C−H in plane bending (1023.6 and 1056.6
−1
cm ), respectively. Under high pressure, neither any Raman
peaks disappeared nor any new Raman peaks were observed,
indicating that the luminescence mechanochromic process in
CP 1 is not accompanied by a phase change, as inferred from
the PXRD patterns.
Figure 7. Photoluminescence spectra of CP 1 before (red curve) and
after (black curve) the addition of acetonitrile on the compressed
sample (0.6 GPa).
Generally, it is known that stretching and bending vibration
modes adequately reflect bond lengths and bond angles.
Modification of the coordination bond strengths (i.e., the peak
shifts for each vibration mode), because of the applied pressure,
can also influence the bathochromic shift of the MLCT or
XLCT. In Figure 6a, the red and blue traces display the
spectral data of CP 1 compressed by a pressure of 0.1 and 0.6
GPa, respectively.
3
5
CONCLUSION
■
We designed and synthesized a bidentate ligand, 3-(2-
(benzylthio)ethoxy)pyridine (L). A Cu(I) coordination poly-
mer (CP 1) was successfully synthesized by a self-assembly
reaction between CuI and L and characterized by thermogravi-
metric analysis (TGA), photoluminescence (PL), and powder
X-ray diffraction (PXRD). CP 1 was determined to have a one-
dimensional loop-chain structure comprising of rhomboid Cu−
The original backbone structure is retained in the com-
pressed CP 1 samples (Figure 6a), since their Raman spectra
show the same peaks as the uncompressed CP 1. However, the
Raman peaks for the compressed CP 1 occur at lower
−1
frequencies (0.5−2 cm ). Except for the ring breathing and in-
plane bending modes, the peaks corresponding to Cu−I, N−
Cu, I−I, and Cu−Cu vibrations shift from 128.2, 174.3, 208.0,
I −Cu units interconnected by L. The luminescence
2
and 253.4 cm−1 to 123.8, 169.8, 206.5, and 252.3 cm−1,
mechanochromism of CP 1 involving a color change from
greenish-blue to yellow was induced by applying pressure (0.1−
respectively. This is in good agreement with elongation of the
bonds around the coordination sphere, which is consistent with
longer d-spacing distances induced by pressure. This elongation
of the coordination covalent bonds raises the energy levels of
the bonding orbitals between Cu(I) and ligands and lowers
0
.9 GPa), while the crystallinity was preserved in the
compressed CP 1 samples. The luminescent mechanochrom-
ism of CP 1 was a non-phase-transition process, despite very
high applied pressures, as evidenced by PXRD patterns of the
compressed samples. After the addition of several drops of
acetonitrile to the ground samples (shown in Figure S4 in the
SI) and compressed samples (see Figure 7), the emission color
was reverted to the original greenish-blue and also the samples
themselves were restored to the original state of CP 1.
1
3
those of the antibonding orbitals ( (M+X)LCT or (M
+
X)LCT levels).
Therefore, the energy difference between the antibonding
orbitals and HOMO becomes smaller, resulting in a bath-
ochromic shift. Systematic correlation of the pressure-induced
data obtained thus far can be summarized as follows. The solid-
state emission, PXRD, and Raman studies show that the
internal energy consumption and bond length (between the
metal cation and organic ligand) variation by applied high
pressure in the crystalline state are the main causes of the
luminescence mechanochromism of CP 1.
Interestingly, CP 1 also exhibits solvatochromic behavior
with the color changing from yellow to greenish-blue by adding
a few drops of acetonitrile solvent on the ground and
compressed CP 1 samples, as shown in Figure 7 and Figure
S4 in the SI, respectively.
We also showed that the coordination environment around
the Cu cation can be easily perturbed by physical pressure
(
0.1−0.9 GPa) to change the PL property. Both the d-spacing
distance calculation and Raman frequency shifts strongly
supported that external mechanical force can have a significant
influence on the bond distances in the solid state. CP 1
exhibited luminescence mechanochromic behavior with a color
contrast between greenish-blue and yellow. The solid-state
emission, PXRD and Raman studies reveal that the internal
energy consumption and bond length variations between metal
cation and L induced by the applied high pressures in the
crystalline state are the main cause of the luminescence
mechanochromism of CP 1.
Thus, the PL property of CP 1 was reversibly controlled by
36
applying pressure and adding an organic solvent. The change
of PL by addition of acetonitrile may be understood in terms of
the restoration of any defects or squeezed internal spaces and of
This high-pressure-induced phenomenon not only suggests a
novel field for luminescence mechanochromic materials, but
also motivates and accelerates further development of CP-based
pressure sensors. In addition to providing a fundamental
understanding of their properties, this study demonstrates their
potential for applications in sensing and detection devices.
Finding recoverable mechanochromic materials with a fast
response remains a challenge for their potential applications.
The development of stimuli responsive materials based on
these copper(I) clusters is currently under investigation.
the coordination environment of Cu I cores in the compressed
2
2
crystals to their original states within 1 min of adding a few
drops of acetonitrile. We found that this process could be
repeated for several cycles without any decomposition. To the
best of our knowledge, this is the first report of luminescence
mechanochromism exhibited by Cu(I) complexes comprising
of a rhomboid Cu−I −Cu unit.
2
E
DOI: 10.1021/acs.inorgchem.6b02571
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Inorganic Chemistry
Article
Solid-State Luminescence Spectra Measurement. Solid-state
luminescence spectra were recorded with powder and pellet samples
on a Shimadzu Model JP/SSP-10A system at room temperature. The
pellet samples were prepared by applying pressures of 0.1−0.9 GPa at
a constant time of 10 s after putting the powder into the KBr pellet
making device (hand press).
EXPERIMENTAL SECTION
■
Chemicals. 2-Bromoethanol (C H BrO, ≥95.0%, 124.97 g/mol)
2
5
was purchased from TCI. Thionyl chloride (SOCl , ≥99%, 118.97 g/
2
mol), benzyl mercaptan (C H S, 99%, 124.2 g/mol) and 3-
7
8
hydroxypyridine (C H NO, 98%, 95.10 g/mol) were purchased
5
5
from Sigma−Aldrich. Potassium hydroxide (KOH, 56.11 g/mol) was
purchased from Daejung Chemicals. All reagents were used as received
without further purification.
Synthesis of 3-(2-(Benzylthio)ethoxy)pyridine (L). Benzyl
mercaptan (6.8 g, 55 mmol) was added to 2-bromoethanol (6.8 g,
ASSOCIATED CONTENT
Supporting Information
■
*
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.6b02571.
5
5 mmol) in the presence of potassium hydroxide (3.1 g, 55 mmol) in
tetrahydrofuran (THF). The mixture was refluxed for 3 h and cooled
to room temperature, at which point it was back-extracted with THF.
The combined organic layers, dried with anhydrous sodium sulfate,
were evaporated. Thionyl chloride (4.0 mL, 55 mmol) in chloroform
then was added to the resulting solution. The solution was refluxed
and stirred for 1 h. After being sufficiently cooled, it was then placed
into a small amount of methanol, followed by stirring for 1 h to
decompose the excess of thionyl chloride. The mixture was added to 3-
hydroxypyridine (5.2 g, 55 mmol) in the presence of potassium
hydroxide (3.1 g, 55 mmol) in THF. The mixture was refluxed for 24 h
and cooled to room temperature. An organic layer was collected and a
water layer was extracted with dichloromethane. The combined
organic layers dried with anhydrous sodium sulfate were evaporated.
Experimental details for the synthesis of ligand L; PXRD
patterns and photoluminescence spectra of a ground
sample; copies of the data CCDC 1505970 can be
obtained free of charge from the Cambridge Crystallo-
graphic Data Centre via http://www.ccdc.cam.ac.uk/
data_request/cif(PDF)
(CIF)
AUTHOR INFORMATION
Corresponding Authors
*E-mail: k9876047266@gmail.com.
*E-mail: thkim@gnu.ac.kr.
■
Column chromatography (silica gel, ethyl acetate/n-hexane = 40/60
1
(
v/v), R = 0.33) gave a pure product (8.3 g, 62%). H NMR (300
f
MHz, CDCl ): δ = 8.16 (d, 2H, Py), 7.22 (t, 2H, Py), 7.19 (m, 5H,
3
Ph), 3.94 (t, 2H, OCH ), 3.69 (s, 2H, SCH Ph), 2.68 (t, 2H, CH S).
2
2
2
ORCID
1
3
C NMR (75.4 MHz, CDCl ): δ = 156.66, 142.31, 138.096, 137.98,
3
Kang Yeol Lee: 0000-0001-8055-1635
Tae Ho Kim: 0000-0003-0415-7374
Notes
1
7
2
28.94, 128.86, 128.62, 127.23, 123.88, 121.11, (solvent: 77.72, 77.30,
6.87), 67.93, 36.79, 29.99. IR (KBr, ν, cm ): 3060 s, 3029 s, 2923 s,
502 m, 1702 m, 1576 s, 1476 s, 1460 s, 1426 s, 1264 s, 1231 s, 1204
−
1
m, 1130 m, 1049 s, 1009 s, 801 s, 768 s, 702 s, 621 m, 565 m, 474 m,
The authors declare no competing financial interest.
+
4
15 m. Mass spectrum m/z 245 (M ).
Synthesis of [Cu I L ] (1). L (0.012 g, 0.05 mmol) and CuI
0.010 g, 0.05 mmol) was allowed to mix in an acetonitrile (1 mL)
2
2 2 n
ACKNOWLEDGMENTS
(
■
solvent. Pale yellow precipitates were filtered and washed with diethyl
This research was supported by the Basic Science Research
Program through the National Research Foundation of Korea
NRF) funded by the Ministry of Education, Science and
T e c h n o l o g y ( N o s . 2 0 1 4 R 1 A 1 A 4 A 0 1 0 0 9 1 0 5 ,
015R1D1A4A01020317, and 2016R1D1A3B03934096).
−1
ether/acetonitrile (2/1) solution (0.033 g, 66%). IR (KBr, ν, cm ):
060 w, 3029 w, 2913 w, 1574 s, 1475 s, 1460 m, 1426 s, 1266 s, 1227
s, 1202 m, 1140 m, 1055 m, 995 s, 802 m, 779 m, 700 s, 637 w, 567 w,
3
(
4
3
80 w, 418 w. [CuIL] Anal. Calcd for C H CuINOS: C 38.59, H
n 14 15
2
.47, N 3.21, S 7.36. Found: C 38.42, H 3.37, N 3.60, S 7.23%.
Characterization. The powder X-ray diffraction (PXRD) patterns
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