Structural Diversity of Coordination Polymers Based on a Heterotopic Ligand: Cu(II)-Carboxylate vs Cu(I)-Thiolate

Article abstract of DOI:10.1021/acs.inorgchem.7b03090

Two copper(II)-carboxylate disulfide coordination polymers [Cu₂((O₂CPhS)₂)₂(H₂O)₂]_n (1, 2) and one copper(I)-thiolate coordination polymer [Cu(p-SPhCO₂H)]_n

Full text of DOI:10.1021/acs.inorgchem.7b03090

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Structural Diversity of Coordination Polymers Based on a
Heterotopic Ligand: Cu(II)-Carboxylate vs Cu(I)-Thiolate
Oleksandra Veselska,† Liwen Cai,†,‡ Darjan Podbevsek,§ Gilles Ledoux,§ Nathalie Guillou,∥
̌
Guillaume Pilet,‡ Alexandra Fateeva,*,‡ and Aude Demessence*,†
†Univ Lyon, Universite
́
Claude Bernard Lyon 1, Institut de Recherches sur la Catalyse et l’Environnement de Lyon (IRCELYON),
UMR 5256 CNRS, Villeurbanne, France
‡Univ Lyon, Universite
Villeurbanne, France
́
́
Claude Bernard Lyon 1, Laboratoire des Multimateriaux et Interfaces (LMI), UMR CNRS 5615,
§Univ Lyon, Universite
́
̀ ̀
Claude Bernard Lyon 1, Institut Lumiere Matiere (ILM), UMR CNRS 5306, Villeurbanne, France
∥Universite
́
de Versailles Saint-Quentin-en Yvelines, Universite
́
Paris-Saclay, Institut Lavoisier de Versailles (ILV), UMR CNRS 8180,
Versailles, France
S
* Supporting Information
ABSTRACT: Two copper(II)-carboxylate disulfide coordination polymers [Cu2((O2CPhS)2)2(H2O)2]n (1, 2) and one
copper(I)-thiolate coordination polymer [Cu(p-SPhCO2H)]n (3) have been synthesized using either the 4-mercaptobenzoic acid
(HSPhCO2H) or the 4,4′-dithiodibenzoic acid ((SPhCO2H)2) as ligand. These three compounds were characterized by X-ray
diffraction, IR, and thermogravimetric analyses. Compounds 1 and 2 are polymorphs with the presence, for both, of dinuclear
paddle-wheel copper(II)-carboxylates. In 1, the adjacent dimeric Cu2 units are linked by two (O2CPhS)2 ligands generating a
cyclic loop chain, and in 2, each pair of Cu (II) atoms is linked by four ligands to create 2D networks, that are 2-fold
interpenetrated. Compound 3 presents a lamellar structure, with an exceptional thermal and chemical stability, and exhibits
intrinsic multiple emission between 485 and 660 nm. The different intensities of these bands generate a cyclic luminescence
thermochromism from yellow to green to yellow.
the carboxylate and the metallic ion and their diverse
coordination modes. HKUST-1 (copper benzene-1,3,5-tricar-
boxylate) is an archetype MOF with a highly porous network
based on Cu(II)-carboxylate paddle wheel units.3 Nevertheless,
one of the drawbacks of most Cu(II)-carboxylate MOFs is their
lack of stability in water or air due to the relatively weak
interaction between the metal and the carboxylate.4 Among the
diverse coordinating functions, thiolates are largely used in
nanotechnology to synthesize, functionalize, and protect
metallic nanoparticles, as they display strong affinity toward
coinage metals through soft−soft interactions. In copper
coordination chemistry, a limited number of nine structures
of neutral Cu(I)-thiolate coordination polymers, [Cu(SR)]n,
INTRODUCTION
■
The design and synthesis of coordination polymers have
achieved considerable progress over the past decade, in order to
control the molecular organization in the solid state and
generate hybrid materials with novel topological structures and
promising properties.1 One approach to reach (multi)-
functional materials is to use heterotopic ligands to induce
heterometallic or mixed valency materials that will exhibit their
own properties and potential applications in the fields of gas
storage, magnetism, optical properties, or catalysis.2 Thus, the
organic ligands play a crucial role for the construction of
coordination networks, and their most important parameters
are the coordinating function, number and mode, the
flexibility/rigidity, and the geometry. Among various coordinat-
ing groups, carboxylic acids have been extensively used, mainly
due to their ability to generate iono-covalent bonding between
Received: December 12, 2017
© XXXX American Chemical Society
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have been reported so far.5 Copper thiolates with SR = SMe,6
p-SPhX (X = H, Me, OMe, NO2),7 and S(di)adamantane8 form
chain-like coordination polymers, while when X = OH9 and
CO2Me10 the compounds display layered structures. Some of
these emerging [Cu(SR)]n coordination polymers exhibit
electrical conductivity through 1D structures,8 or 2D sheets,11
and some are photoluminescent with unusual intrinsic triple
emission, being of a great potential as ratiometric temperature
sensing.10 These limited but promising studies on copper
thiolates highlight their high potential as multifunctional
materials.
RESULTS AND DISCUSSION
Synthesis. In this study, we used systematically both ligands
■
under the same reaction conditions to evaluate their reactivity:
methods a and b are respectively assigned for the synthesis
starting from the thiol-based ligand HSPhCO2H or the
disulfide-based ligand (SPhCO2H)2 (see syntheses in the
Supporting Information). When either of these two ligands is
reacted with Cu(II) in DMF at 90 °C in a closed vessel, the
same compound 1 is obtained by methods a and b, as
evidenced from PXRD data (Scheme 1 and Figure 1). When
In addition, due to the rich redox chemistry of thiols,
oxidative formation or reductive cleavage of the disulfide bonds
can be induced depending on the reaction medium. Numerous
coordination polymers have been prepared with bidentate
disulfide-based ligands in different basic or acidic media at room
temperature or under solvothermal conditions.12 The diversity
of the structures is due to the flexibility/rotation of the S−S
bond. In situ cleavage of the S−S bond has already been
observed under solvothermal conditions, implying the for-
mation of coordination polymers with either coordinated
thiolate, sulfinate, or sulfonate functionalities.12a,f,13 Synthesis of
coordination polymers with in situ S−S formation from a thiol
ligand has also been reported.14 Finally, a same coordination
polymer could also be obtained by either a direct assembly
synthetic route with a disulfide or with an in situ S−S bond
formation from the thiol parent.14c Interestingly, a simultaneous
Cu(II) to Cu(I) reduction and S−S reductive cleavage of 4,4′-
dipyridyl disulfide was reported to happen under solvothermal
conditions.13g
In this work, we aimed to rationalize and understand the
coordination of the thiolate to Cu(I) and of the carboxylate
moiety to Cu(II) for closely related organic ligands. The
heterotopic 4-mercaptobenzoic acid (HSPhCO2H) and its
oxidized dimeric form, the 4,4′-dithiodibenzoic acid
((SPhCO2H)2), are studied to evaluate the impact of the
reaction conditions on the redox chemistry of thiol/disulfide
functions, meaning formation/breaking of S−S bonds and the
coordination of thiolate and carboxylates with copper. Two
polymorphic copper(II)-carboxylate disulfide coordination
polymers [Cu2((O2CPhS)2)2(H2O)2]n, 1 and 2, and one
lamellar copper(I)-thiolate compound [Cu(p-SPhCO2H)]n, 3,
have been successfully synthesized starting with either the
oxidant or the reductive forms of the ligand (Scheme 1). In-
depth structural characterizations, chemical and thermal
stability studies, and photoluminescence properties for 3 are
discussed.
Figure 1. Powder X-ray diagrams of compounds 1−3 and 1′−3′
obtained by method a and b, respectively.
the reaction conditions are slightly changed by adding a 0.1 M
solution of a strong acid and lowering the temperature to 80
°C, a second compound 2 is isolated either by method a or b
(Scheme 1 and Figure 1). Compounds 1 and 2 are polymorphs,
with the formula, [Cu2((O2CPhS)2)2(H2O)2]n, based on the
same Cu(II)-carboxylate paddle wheel motif. This observation
points out that the addition of an acid plays here a crucial role
on the structure but not on the connectivity; this will be further
discussed in the structural description part. Nevertheless, the
synthesis of pure 1 and 2 is highly dependent on the type of
metallic salt and the acid, as reported in the Supporting
Information, and changing the conditions will afford a mixture
of compounds, including other polymorphs impossible to
isolate as a pure phase. Finally, when harsher conditions are
employed, 120 °C with the addition of 1 M acid solution, S−S
bond cleavage and Cu(II) to Cu(I) reduction are observed for
both methods a and b (Scheme 1 and Figure 1). The formation
of the Cu(I)-thiolate, [Cu(p-SPhCO2H)]n (3), is less sensitive
to the type of precursors and can be obtained with either
copper nitrate or copper chloride, with 0.1 or 1 M nitric or
hydrochloric acid and even at 80 °C (Scheme 1 and the
Supporting Information). High yield and the best crystallinity
were obtained at 120 °C with 1 M acid. In 3, the coordination
proceeds through the thiolates to Cu(I) and the carboxylic
acids remain protonated. The formation of a coordination
polymer involving in situ reduction of Cu(II) to Cu(I) coupled
with the reductive cleavage of the S−S bond has also been
observed with the 4,4′-dithiodipyridine under solvothermal
conditions.13g
Scheme 1. Synthetic Routes of Compounds 1−3
Thus, under mild conditions of temperature (80−90 °C) and
with or without a small amount of acid, an oxidative medium is
favored and leads to the formation or conservation of S−S
bonds and coordination of the carboxylates with Cu(II). The
formation of compounds 1 and 2 from method a is explained
B
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by the redox chemistry of Cu(II) and mercaptans that is known
as the “Perco” process to sweeten gasoline and to convert the
foul smelling thiols into less offensive disulfides (Scheme 2a).15
[(O2CPhS)2]2− ligands adopt a V-shaped conformation
illustrated by a C−S−S disulfide bond angle of 105.92 (2)°
and a C−S−S−C torsion angle of 73.64(2)°. Each ligand
bridges two dimeric {Cu2} units, giving rise to a 1D cyclic loop
chain (Figure 2a and b) running along the [001] direction of
the unit-cell. A view along the c-axis of the unit-cell (Figure 2c)
clearly shows that there is no connection between the metal−
organic chains. The distance between the chains is 3.682(3) Å
along the b axis (distance between disulfide bonds of two
chains).
Scheme 2. Reaction Mechanisms Involved in the Formation
a
(a) of 1 and 2 and (b) of 3
Compound 2 crystallizes in the monoclinic centrosymetrical
C2/c space group and displays a 2D framework. The
asymmetric unit here is made up of one Cu(II) atom and
one [(O2CPhS)2]2− ligand (Figure 3 and Table S1). Each
Cu(II) atom, located in a ML5 {O5} square-base pyramidal
environment, is coordinated in the same way as for 1, by four
oxygen atoms from four carboxylate ligands in the equatorial
plane and one oxygen atom from a water molecule which
occupies the axial position. The Cu−O bond lengths range
from 1.951(4) to 1.983(4) Å in the equatorial plane and are
shorter than the one (2.150(4) Å) located in the axial position
(Table S2). Comparably to what was observed for 1, Cu(II)
atoms are arranged in dimeric paddle wheel units by bidentate
bridging carboxylate functions with a Cu···Cu distance of
2.609(1) Å (Figure 3a and Table S2). The [(O2CPhS)2]2−
adopts a V-shaped conformation with a C−S−S angle identical
to the precedent one but with a different C−S−S−C torsion
angle (91.10(3)°). Each ligand bridges two dimeric Cu paddle
wheel units, and each dimer is connected to four ligands; this
gives rise to a 2D polymer (Figure 3b and c), and two identical
2D networks are interpenetrated with each other to result in a
2-fold interpenetrated framework (Figure S1).
In these two compounds, the inorganic paddle wheel units
display the same coordination environments but the overall
framework arrangements greatly differ between 1 and 2.
Compound 1 crystallizes in the C2/m space group with the
mirror plane (0,1,0) passing through the two Cu(II) atoms of
the paddle wheel. This particular situation imposes the
metallocyclic motif for the ligand arrangement, generating the
1D looplike chain. In this structure, all of the Cu(II) dimers are
aligned in (a,c) planes. In the case of compound 2, the Cu(II)
dimers are no longer aligned, and if considering two dimers
bridged by one ligand molecule, a torsion angle of 59.87(3)°
appears between the directions of each Cu···Cu dimer. This
a
HSR and RSSR are for thiol and disulfide ligands.
In that case, the Cu(II) is not consumed in the process because
the dioxygen from the air reoxidizes Cu(I) back to Cu(II).
When more extreme conditions of temperature (120 °C) and
acidity (1 M) are employed, the formation of copper(I)-thiolate
is favored. The effect of Cu(II) Lewis acidity on S−S
polarization may be involved in the S−S breaking,16 and
then, the redox reaction between Cu(II) and the thiols results
in the formation of 3. This study shows that the coordination of
carboxylates or thiolates is controlled by the synthesis medium
rather than by the redox state of the sulfur atoms.
Structural Description. 1 crystallizes in the monoclinic
centrosymetrical C2/m space group and displays a 1D
framework with the asymmetric unit consisting of one Cu(II)
atom lying in the mirror plane and one-half of a ligand unit
(O2CPhS)− (Figure 2 and Table S1). The metal center
environment can be described as a distorted square-pyramidal
geometry within each Cu(II) being coordinated in the
equatorial plane to four oxygen atoms, each of these later
belonging to four different carboxylate ligands. The coordina-
tion sphere around the 3d metal is completed by one oxygen
atom from a water molecule in the axial position. Cu−O bond
lengths are equal to 1.958(4) and 1.972(6) Å for the
carboxylate oxygen atoms and are shorter than the one
(2.139(6) Å) involving the coordinated water molecule
(Table S2). Two adjacent Cu(II) atoms are bridged by four
carboxylate units from four ligand molecules giving rise to a
paddle-wheel-shaped geometry exhibiting a short Cu···Cu
distance (2.647(2) Å, Figure 2a and Table S2).
Figure 2. (a) Local coordination environment of the Cu(II) ion in compound 1. (b) View of the 1D coordination polymeric ribbon in compound 1
along the c axis. (c) Projection of the 1D coordination polymer 1 on the c axis. Blue, Cu(II); yellow, S; red, O; gray, C. Hydrogen atoms and water
molecules are omitted for clarity.
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Figure 3. (a) Local coordination environment of the Cu(II) ion in compound 2. (b) View of 2D coordination polymer in compound 2 and (c)
central projection of 2 along the b axis. Blue, Cu(II); yellow, S; red, O; gray, C. Hydrogen atoms and water molecules are omitted for clarity.
way, the polymeric network expands in two directions,
generating a 2D network. The disulfide S−S bond in the
[(O2CPhS)2]2− ligand can rotate freely, hence bringing
flexibility to the possible conformations. In compounds 1 and
2, the C−S−S−C torsion angles are quite different: 73.64(2)°
for 1 that allows a metallocyclic motif to be generated and
91.10(3)° for 2 where the ligand has a more corrugated nature
that favors the formation of the 2D interpenetrating structure
(Figure 4). These results show that the flexibility of the
interpenetrating 2D structure in compound 2. However, the
particular factors ruling the particular structure formation with
the flexible S−S spacer of [(O2CPhS)2]2− ligand have not been
well explored so far and more work is needed to elucidate them.
Compound 3 crystallizes in the orthorhombic centrosy-
metrical Pbca space group (Figure 5 and Table S1). Its formula
is [Cu(p-SPhCO2H)]n, and its refined structural model displays
a layered structure, related to the only two other 2D Cu(I)
9
thiolate polymers reported to date, [Cu(p-SPhOH)]n and
[Cu(p-SPhCO2Me)]n.10 The Cu(I) atoms are in trigonal
geometry and are linked to three sulfur atoms from three (p-
SPhCO2H)− ligands. Each sulfur bridges three Cu(I) atoms,
generating {Cu3S3} distorted hexagons that lie in layers
propagating in the (ab) plane (Figure 5a and b). The Cu−S
distances are 2.243(3), 2.290(2), and 2.302(3) Å, and the S−
Cu−S angles are 104.12(7), 125.96(11), and 129.82(10)°
(Table S2). The shortest Cu···Cu distance is 3.030(2) Å which
is slightly shorter to those which were reported before in similar
structures but still greater than the sum of van der Waals radii
(2.80 Å). Therefore, no cuprophilic interactions are expected in
compound 3. In between the Cu−S layers lies the organic part,
and the presence of carboxylic acids generates interactions
between the layers through dimeric hydrogen bonds (Figure 5c
and d). The presence of these weak interactions possibly favors
the formation of the distorted {Cu3S3} hexagons compared to
Figure 4. Coordination modes of the [(O2CPhS)2]2− ligand in 1 (a)
and 2 (b) with a projection along the −S−S− axis. Blue, Cu(II);
yellow, S; red, O; gray, C. Hydrogen atoms are omitted for clarity.
disulfide ligand [(O2CPhS)2]2− can lead to a structural diversity
when keeping the inorganic unit unchanged. Here, linear
metallocyclic motifs are obtained in compound 1 and
Figure 5. Structure of 3: (a) representation of the Cu3S3 network on the (ab) plane, (b) view of a Cu3S3 cycle, (c and d) projections of the lamellar
structure on the (bc) and (ac) planes, respectively. Orange, Cu(I); yellow, S; gray, C. Red dotted lines show the hydrogen bonds. Hydrogen atoms
are omitted for clarity.
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the half-chair observed for the analogue with the ester functions
[Cu(p-SPhCO2Me)]n.10
MeOH (Figure S10). The TGA curve shows the presence of
5% MeOH that is removed at 100 °C (Figure S12). In addition,
2 is still stable under the reducing conditions of NaBH4 for 3 h
at room temperature; no S−S bond breaking is observed, and
the PXRD pattern remains unchanged (Figure S10). FT-IR of
the solids heated at 150 °C and after MeOH Soxhlet extraction
shows the disappearance of the CO vibration of the DMF at
1680 cm−1, meaning the total removal of the solvent molecules
(Figure S13). Nevertheless, the N2 adsorption at 77 K on 2
after activation does not show any permanent porosity.
Characterizations. The phase purity of 1−3 was confirmed
by powder X-ray diffraction (PXRD), scanning electron
microscopy (SEM), Fourier transform Infrared spectroscopy
(FTIR), and thermogravimetric analysis (TGA) carried out
under air. The experimental PXRD patterns of 1−3 are
consistent with the calculated diagrams (Figure S2), and the
Rietveld refinement of 3 provides excellent factors of merit
(Figure S3), demonstrating an effective method to obtain these
compounds with extremely high purity and crystallinity. SEM
images reveal that the crystallites of each phase display their
own particular shape; 1 has a cuboid form, 2 has an elongated
stick shape, and 3 is constituted of plates characteristic of
lamellar compounds (Figure S4). More importantly, only one
type of crystal morphology is observed for each solid,
confirming the purity. Both Cu(II)-based compounds, 1 and
2, show the same FTIR spectra (Figure S5). Compared to the
noncoordinated ligands, the disappearance of the large band at
2500−3100 cm−1, which is attributed to −OH stretching of
carboxylic acid, is in good accordance with the coordination of
the carboxylate to Cu(II). In addition, the asymmetric and
symmetric vibrations of the carboxylates at 1590 and 1400 cm−1
are typical of a bridging coordination mode (Figure S6). The
band at 1680 cm−1 is attributed to the vibration of the CO of
the DMF that was used as a solvent. The FTIR spectrum of 3
exhibits the same large and intense band at 2500−3100 cm−1 as
the starting ligands, showing that the carboxylic acids interact
together through hydrogen bonds (Figure S5). The presence of
the uncoordinated carboxylic acids is also confirmed by the
antisymmetric vibration of COO at 1680 cm−1 (Figure S6).
The TGA profiles of 1 and 2 under air are quasi similar, and
solvent molecules are removed up to 200 °C with a total weight
loss of 12.7%, pointing out that the free and coordinated water
and DMF molecules are removed (Figure S7). The compounds
1 and 2 start to decompose at 320 °C and 3 at 290 °C under air
flow. The remaining CuO at 800 °C for 1 and 2 of 22.9% (calc.
21.6%) and for 3 of 37.1% (calc. 36.7%) are close to the
expected values. The slight difference between calculated and
experimental values can be explained by the formation of
Cu2O(SO4) along with CuO. Indeed, the three compounds
exhibit a first plateau at 400 °C which corresponds to a majority
of Cu3(OH)4(SO4) with a small amount of Cu(SO4)(H2O)5
and a second one at 700 °C which is mainly CuO with a minor
quantity of Cu2O(SO4) (Figure S8). Thus, when the TGA is
carried out under nitrogen flow, 2 exhibits the same
temperature of decomposition, while 3 remains more stable
and starts to decompose at 350 °C (Figure S7). The final
product obtained at 800 °C under nitrogen has been analyzed
by PXRD and proves the presence of chalcocite (Cu2S), which
is more crystalline in 3 than in 2, plus an amorphous phase in
both compounds (Figure S9).
The solid 3 exhibits an exceptional thermal and chemical
stability. Indeed, after heating at 250 °C under air for 1 h, the
PXRD reveals no changes (Figure S14). When dispersed in
boiling water for 24 h, the solid remains crystallographically
intact (Figure S14). Even better, under acidic conditions, the
powder is still highly crystalline after 24 h stirring in a 1 M HCl
solution, as shown by the PXRD (Figure S15). In basic media,
no structural change is observed from the PXRD data when the
solid is dispersed for 24 h in 0.1 M NaOH solution (Figure
S15). However, in a more basic solution of 1 M NaOH, the
reflections of 3 disappear for a new lamellar phase with a shift
of the first peak from 5.20 to 4.89° (2θ). This observation
points out a structural change to a different lamellar compound
with a longer interlamellar distance of 1.80 nm (instead of 1.70
nm) that most probably corresponds to the insertion of sodium
cation to form [Cu(p-SPhCO2Na)]n. The saponification of the
carboxylic acids is also confirmed by FT-IR that shows the
disappearance of the large band at 2500−3100 cm−1 coming
from the hydrogen bonds and the shift of the νas(COO) at
1680 cm−1 (Figure S16). Nevertheless, the formation of aligned
wires of a couple of hundred nanometers of thickness on the
SEM images of [Cu(p-SPhCO2Na)]n, points out that the
topology of Cu−S may be different from 3, and that a
dissolution-recrystallization mechanism may had happened
(Figure S17). Finally, the solid 3 is still stable when it is
stirred for 24 h in an oxidant media with 1% H2O2 but starts to
decompose in strong oxidizing solution of 10% H2O2 and the
formation of crystalline disulfide ligand, (SPhCO2H)2, is
observed (Figure S18). Consequently, the copper(I)-thiolate
coordination polymer is stable up to 250 °C in air and under
acidic and basic conditions as well as in mild oxidant medium.
The thermal and chemical stability observations agree with the
stronger nature of the Cu(I)-thiolate coordination bonds when
compared to the Cu(II)-carboxylate one.
Photophysical properties of 3. Cu(I)-thiolates have been
attracting considerable attention owing to their interesting
photochemical properties.17 With respect to the luminescence
mechanism, the coordination of Cu(I) with thiolate ligands
usually leads to ligand-to-metal charge transfer (LMCT) and/
or ligand-to-metal−metal charge transfer (LMMCT), which
can generate radiative relaxation via a metal-centered triplet
state.10,13g,18 The UV−vis absorption spectrum of 3 shows an
intense band with a maximum centered at 364 nm and a smaller
one at 278 nm (Figure S19). The deduced optical bandgap of
2.79 eV is close to the one reported for the 1D and 2D
[Cu(SR)]n analogues (2.2−2.9 eV).5,10
As depicted in Figure S20, 3 exhibits some luminescence
thermochromism when irradiated under UV light in the solid
state. It is light yellow from room temperature to 243 K,
becomes green between 213 and 153 K, and is back to intense
yellow from 123 to 93 K. Thus, the photoluminescence studies
have been carried out in the solid state in the range from 93 to
293 K. Excitation vs emission is plotted at different temper-
Thermal and Chemical Stability. Due to the potential
porosity of compound 2 and the luminescent properties of 3,
their thermal and chemical stability were studied (see the
Supporting Information for experimental conditions). First,
when the solid 2 is heated under air at 150 °C for 12 h, the
PXRD shows a phase change with the appearance of new peaks;
nevertheless, no decomposition is observed (Figure S10). SEM
images show that crystals of 2 are sliced upon the heat
treatment (Figure S11). Second, when the solid 2 is introduced
in a Soxhlet with several cycles of MeOH for 12 h, its structure
remains unchanged, pointing out its chemical stability in hot
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Figure 6. 2D maps of the emission and excitation spectra of 3, [Cu(p-SPhCO2H)]n, carried out in the solid state at 273, 183, and 93 K. The white
squares correspond to the coordinates (λex, λem) in nm of the peaks.
atures on the 2D maps, and the coordinates (λex, λem) in nm are
used to describe the peak positions (Figures 6 and S21). From
the 2D map at 273 K, 3 exhibits two peaks with the more
intense one at (370, 530) and the second one at (370, 570).
When the temperature decreases, a third peak appears at (350,
485) and is predominant from 213 to 123 K. Then, at 123 K,
two other peaks appear at (400, 500) and (360, 660). Finally,
those two peaks still increase when the temperature decreases
and the one at (400, 500) becomes dominant. The presence of
these four maxima of excitation from 350 to 400 nm and the
five maxima of emission at 485, 500, 530, 570, and 660 nm can
also be clearly seen on the 1D graphs of excitation and emission
plotted at variable temperatures (Figures 7 and S22−S25). The
Figure 8. CIE chromaticity diagram showing the temperature-
dependent luminescence color change of 3 in the 93−293 K
temperature range (λex = 352 nm).
K the emission lifetime has four contributions between 1 and
764 μs and at 93 K this lifetime increases with the contributions
between 44 μs and 9.2 ms (Figure S26, Table S3). These long
radiative lifetimes, in the microsecond and even millisecond
ranges, are characteristic of triplet states and phosphorescent
processes. From these different observations, the vibronic
structure of the emission between 485 and 570 nm can be
attributed to the aromatic thiolate as intraligand or ligand-to-
3
ligand charge transfer IL/LLCT involving π → π* transitions.
Indeed, when compared to the photoemission of the
noncoordinated p-mercaptobenzoic acid, which exhibits a
Figure 7. Emission spectra (λex = 352 nm) of 3 in the solid state with
single emission band centered around 530 nm in the same
the temperature.
range of temperature,20 the apparition of the vibronic structure
can be due to the rigidity of the ligand when coordinated to the
temperature dependent CIE (Commision Internationale de
l’Eclairage) chromaticity diagram (Figure 8) confirms the back
and forth color change from yellow to green to yellow from 293
to 93 K, which is consistent with the changing intensities ratio
of the multiple bands. To get more insight into the
photophysical processes involved in 3 with the temperature,
single crystal XRD analysis has been carried out at 120 K.
When lowering the temperature, the space group of 3 is
identical and the reduction of the cell volume of 0.55% from
293 to 120 K can be considered as negligible (Tables S1 and
S2). Hence, the luminescence thermochromism of 3 is not
directly correlated to some structural changes, as has been
observed in some Cu(I) analogues.19 The lifetime decay
measurements carried out with λex = 379 nm show that at 273
metal or to the perturbation of a charge transfer due to the
metal. The emission band at low energy, 660 nm, originates
most probably from the triplet states of ligand-to-metal
(3LMCT) and/or metal-to-ligand charge-transfer transitions
(3MLCT), mixed with metal-centered (ds/dp) states. Hence,
the luminescence thermochromism of 3 is a subtle equilibrium
between ligand-centered (at high energy) and metal-centered
(at low energy) charge transfers and the diminution of the
nonradiative decays when the temperature decreases.21 More
detailed spectroscopic and theoretical studies need to be
pursued to fully explain the origin of the bands. Two
comparisons of the photoluminescence properties of Cu(I)-
thiolates can be made with 3: (i) the analogue [Cu(p-
10
SPhCO2Me)]n exhibits intense luminescence thermochrom-
F
DOI: 10.1021/acs.inorgchem.7b03090
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
ism with three well-separated emission bands at 460, 560, and
740 nm and emission up to 500 K, associated with a similar
Cu3S3 lamellar structure, and (ii) [Cu(I)(pyridine-4-thiolate)]3,
made of interconnected clusters, is a green phosphor, with a
single emission band centered at 560 nm.13g These
comparisons point out that the origin of the multiple emission,
the ratio and position of the bands, are a subtle combination of
rigidity of the network induced by the hydrogen bonds, the π-
stacking, the bond distances, and the function of the ligand. In
fact, the photoluminescence of compound 3 presents more
similarities with the lamellar compound, [Au(p-SPhCO2H)]n,20
meaning the importance of the ligand in the photophysical
properties. Thus, the MOCs are coordination polymers with a
rich potential in terms of tuning the structures and the
properties.5
*E-mail: aude.demessence@ircelyon.univ-lyon1.fr.
ORCID
Gilles Ledoux: 0000-0002-0867-1285
Aude Demessence: 0000-0002-8690-5489
Author Contributions
All authors have given approval to the final version of the
manuscript.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors acknowledge the Synchrotron Soleil for providing
access to the crystal beamline (proposal 20150723) and are
grateful to Dr. Erik ELKAIM for his assistance with running the
experiments. They also thank the CTμ (Centre Technologique
des Microstructures of Lyon Univ.) for providing SEM. O.V.
CONCLUSIONS
■
̂
thanks the Rhone-Alpes region (ARC 6) for her Ph.D. grant.
A.D. thanks the Agence Nationale pour la Recherche for the
financial support (FULOR project ANR-13-JS08-0005-01).
In summary, we demonstrate the successful syntheses of three
new coordination polymers, two copper(II)-carboxylate disul-
fide compounds 1 and 2, [Cu2((O2CPhS)2)2(H2O)2]n, and one
copper(I)-thiolate solid 3, [Cu(p-SPhCO2H)n]. This study
shows that the reactivity of either the reduced HSPhCO2H or
the oxidized dimeric (SPhCO2H)2 form of the ligand is ruled
by the mild or harsh synthetic conditions in play. Under lower
temperature and acidity conditions, the coordination of the
carboxylates to Cu(II) and the S−S bond formation/
preservation are observed when an in situ reduction of Cu(II),
cleavage of the S−S bond, and coordination of the thiolates
with Cu(I) are happening under harsher conditions of
temperature and acidity. Compounds 1 and 2 are polymorphs
built up with {Cu2(COO)4} paddle wheel inorganic units with
different dimensionalities: 1 is a 1D structure, and 2 is a 2D
network. 3 is a copper-thiolate compound with a lamellar
structure of Cu3S3 inorganic layers linked through hydrogen
bonds between the carboxylic acids. Among those three
compounds, the Cu(I)-thiolate solid shows considerably higher
chemical and thermal stabilities than the Cu(II)-carboxylates.
In addition, 3 exhibits luminescence thermochromism
associated with a multiple emission that can be a good
potential for temperature sensing.
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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.7b03090.
Experiments and methods, chemicals, syntheses, thermal
and chemical stability tests, crystallographic data, PXRD,
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CCDC 1581240−1581241 and 1822344−1822345 contain the
supplementary crystallographic data for this paper. These data
can be obtained free of charge via www.ccdc.cam.ac.uk/
data_request/cif, or by emailing data_request@ccdc.cam.ac.
uk, or by contacting The Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44
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AUTHOR INFORMATION
Corresponding Authors
*E-mail: alexandra.fateeva@univ-lyon1.fr.
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