Synthesis and Characterization of "atlas-Sphere" Copper Nanoclusters: New Insights into the Reaction of Cu2+ with Thiols

Article abstract of DOI:10.1021/acs.inorgchem.9b01140

Thiolates are a widely used ligand class for the stabilization of M(0)-containing gold and silver nanoclusters. Curiously, though, very few thiolate-stabilized Cu nanoclusters are known. Herein, we report an examination of the reactivity of RSH (R = CH₂CH₂Ph, n-Bu, n-C₁₂H₂₅) with Cu²⁺ under anhydrous conditions. These reactions result in the formation of fluorescent "Atlas-sphere"-type copper thiolate nanoclusters, including [Cu₁₂(SR′)₆Cl₁₂][(Cu(R′SH))₆] (2, R′ = ⁿBu) and [H(THF)₂]₂[Cu₁₇(SR′′)₆Cl₁₃(THF)₂(R′′SH)₃] (3, R′′ = CH₂CH₂Ph), which were characterized by X-ray crystallography, electrospray ionization mass spectrometry, NMR spectroscopy, as well as X-ray absorption near-edge structure and extended X-ray absorption fine structure (EXAFS) spectroscopies. Consistent with our X-ray crystallographic results, the edge energies of 2 and 3 suggest they are constructed exclusively with Cu(I) ions. Similarly, EXAFS of 2 and 3 reveals long Cu-Cu pathlengths, which is also consistent with their X-ray crystal structures. Given these results, as well as past work on Cu²⁺/thiol reactivity, we suggest that Cu(0) is unlikely to be formed by the reaction of Cu²⁺ with a thiol and that previous reports of Cu(0)-containing nanoclusters synthesized by reaction of Cu²⁺ with thiols are likely erroneous.

Full text of DOI:10.1021/acs.inorgchem.9b01140

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Synthesis and Characterization of “Atlas-Sphere” Copper
Nanoclusters: New Insights into the Reaction of Cu2+ with Thiols
Andrew W. Cook,† Zachary R. Jones,§ Guang Wu,† Simon J. Teat,‡ Susannah L. Scott,*,§
and Trevor W. Hayton*,†
§
†Department of Chemistry and Biochemistry and Department of Chemical Engineering, University of California, Santa Barbara,
California 93106, United States
‡Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
S
* Supporting Information
ABSTRACT: Thiolates are a widely used ligand class for the
stabilization of M(0)-containing gold and silver nanoclusters.
Curiously, though, very few thiolate-stabilized Cu nanoclusters
are known. Herein, we report an examination of the reactivity of
RSH (R = CH2CH2Ph, n-Bu, n-C12H25) with Cu2+ under
anhydrous conditions. These reactions result in the formation of
fluorescent “Atlas-sphere”-type copper thiolate nanoclusters,
n
including [Cu12(SR′)6Cl12][(Cu(R′SH))6] (2, R′ = Bu) and
[H(THF)2]2[Cu17(SR′′)6Cl13(THF)2(R′′SH)3] (3, R′′ =
CH2CH2Ph), which were characterized by X-ray crystallography,
electrospray ionization mass spectrometry, NMR spectroscopy,
as well as X-ray absorption near-edge structure and extended X-
ray absorption fine structure (EXAFS) spectroscopies. Consistent with our X-ray crystallographic results, the edge energies of 2
and 3 suggest they are constructed exclusively with Cu(I) ions. Similarly, EXAFS of 2 and 3 reveals long Cu−Cu pathlengths,
which is also consistent with their X-ray crystal structures. Given these results, as well as past work on Cu2+/thiol reactivity, we
suggest that Cu(0) is unlikely to be formed by the reaction of Cu2+ with a thiol and that previous reports of Cu(0)-containing
nanoclusters synthesized by reaction of Cu2+ with thiols are likely erroneous.
Given this context, it is surprising that Cu(0)-containing,
thiolate-stabilized Cu APNCs are essentially unknown, and of
the few Cu APNCs that have been reported, most have only
been partially characterized.12−14 For example, Mukherjee and
co-workers synthesized a glutathione-stabilized Cu APNC with
the formula [Cu15(GSH)4].15 This material was characterized
by transmission electron microscopy (TEM), matrix-assisted
laser desorption ionization-time of flight (MALDI-TOF) mass
spectrometry, and UV−vis spectroscopy, but a single-crystal X-
ray structure was not forthcoming. Similarly, Chang and co-
workers reported the synthesis of a mixture of mercaptoben-
zoic acid-stabilized Cu nanoclusters, but these materials were
not structurally characterized.16 In contrast, structurally
characterized mercaptobenzoic acid-stabilized APNCs of
both Ag and Au are well-known.1 Cu APNCs of aryl thiolates
have also been reported, such as [Cu9(SC6H4-p-F)7] and
[Cu9(SC6H4-p-Br)6], but again structural characterization by
X-ray crystallography has remained elusive.17 Finally, it is
worth noting that a 2011 report of a thiolate-stabilized Cu8
nanocluster, [Cu8(MPP)4] (HMPP = 2-mercapto-5-n-propyl-
pyrimidine), was recently found to be erroneous.18,19
INTRODUCTION
■
The past decade has seen a dramatic increase in the number of
reported atomically precise nanoclusters (APNCs) of gold and
silver.1 Many of these APNCs have been characterized by X-
ray crystallography, giving researchers a level of structural
detail that is not available for traditional nanoparticles. For Ag
and Au, the most common capping ligands are thiolates (RS−)
(R = alkyl, aryl). For example, one of the first structurally
characterized Au APNCs, [Au25(SCH2CH2Ph)18]−, features
phenylethylthiolate capping ligands.2,3 Other notable thiolate-
stabilized Au APNCs include [Au38(SCH2CH2Ph)24],
[Au144(SCH2CH2Ph)60], [Au246(SC6H4-p-Me)80], and
Au279(SC6H4-p-tBu)84.4−7 Similarly, many of the first structur-
ally characterized Ag APNCs also featured thiolate ligands,
including [Ag44(p-MBA)30]4− (p-MBAH = para-mercaptoben-
zoic acid) and [Ag25(SCH2CH2Ph)18]−.8−10 As seen in these
aforementioned examples, both alkyl and aryl thiolates are
effective at stabilizing Ag and Au APNCs. The ubiquitous use
of thiolates for this purpose is likely related to the strength of
the M−S bond,11 which protects the APNCs against
agglomeration and unwanted reactivity. As a result, these
materials have been proposed for a variety of applications for
which high stability is desired, including in vivo chemical
sensing and drug delivery.1
Received: April 18, 2019
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.9b01140
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
In 2015, Zhang and co-workers reported the synthesis of a
mixed-valent Cu-thiolate APNC Cu14(SR)10 (R = C12H25),
which was formed by the reaction of CuCl2 with excess RSH in
dibenzyl ether.20 Under these conditions, the thiol acts as both
the capping ligand and the reductant. Cu14(SR)10 was
characterized by UV−vis and fluorescence spectroscopies,
thermogravimetric analysis (TGA), and TEM, among other
techniques. While its exact structure could not be verified by
single-crystal X-ray diffraction, the authors use mass spectrom-
etry and density functional theory (DFT) analysis to support
their proposed formulation. Significantly, this Cu APNC was
reported to have attractive photophysical properties,21−23
prompting speculation that it could be incorporated into
light-emitting diodes and displays.17
Cu14(SR)10 is especially intriguing to us, given our long-
standing interest in Cu nanocluster chemistry19,24−27 and
because it represents a rare example of a Cu nanocluster with
partial Cu(0) character. Only a handful of low-valent, Cu(0)-
containing nanoclusters have been reported, including
[Cu25H22(PPh3)12]Cl, [Cu29Cl4H22(Ph2phen)12]Cl,
[Cu13{S2CNnBu2}6(CCR)4][PF6] (R = C(O)OMe, C6H4F),
[Cu2 0 (CCPh)1 2 (OAc)6 ], [Cp*1 2 Cu4 3 Al1 2 ], and
[Cu53(CF3CO2)10(CCtBu)20Cl2H18]+.24,26−30 Cu14(SR)10
would also be an exceptionally rare example of a copper
superatom with N* = 4, which is not a magic number.20 While
nonmagic number copper superatoms are known, such as
[Cp*12Cu43Al12], their anticipated lower stability makes them
unusual.1,19,29
Consequently, we attempted to remake Cu14(SR)10 in an
effort to further investigate its structure. Surprisingly, we found
that the reaction of CuCl2 with RSH (R = C12H25) does not
result in a Cu APNC with Cu(0) character. Instead, the
product is most likely a Cu(I)-containing “Atlas-sphere”-type
thiolate nanocluster. Our conclusion is supported by a
comparative synthetic and spectroscopic study, which includes
analysis by X-ray absorption near-edge spectroscopy (XANES)
and extended X-ray absorption fine structure (EXAFS). During
the course of this work, we also synthesized and structurally
characterized two other Cu(I) thiolate-containing clusters,
[Cu12(SR′)6Cl12][(Cu(R′SH))6] (R′ = nBu) and [H(THF)2]2-
[Cu17(SR′′)6Cl13(THF)2(R′′SH)3] (R′′ = CH2CH2Ph) using
similar conditions to those reported for the Cu14(SR)10
synthesis.20
experimental description it appears to be insoluble in both
CHCl3 and acetone.
Zhang and co-workers characterized their material using a
variety of methods, including UV−vis and emission spectros-
copies, as well as mass spectrometry. The Cu14(SR)10
formulation was proposed primarily on the basis of the MS
data; however, neither an exact mass match nor an analysis of
the isotope pattern was provided.20,21
We attempted to repeat the synthesis of Cu14(SR)10, using
the originally reported procedure with a few minor
modifications. In particular, we used anhydrous CuCl2 in
place of CuCl2·2H2O,31 we did not sonicate our CuCl2
suspension, and we performed the reaction at room temper-
ature. We believe that these minor changes should not affect
the product speciation; however, they could affect the rate of
reaction by modifying the solubility and grain size of the CuCl2
starting material. The reaction generally proceeded as
originally described (Scheme 1). Thus, addition of CuCl2 (1
equiv) to dibenzyl ether (2 mL) at room temperature resulted
in formation of a pale brown slurry. Addition of 1-
dodecanethiol (4 equiv) to this suspension resulted in
dissolution of the brown solid over the course of 20 min,
concomitant with the deposition of a very pale gray solid,
which is similar in appearance to the material reported by
Zhang and co-workers.20 The solid was then collected on a
fritted glass filter and rinsed with hexanes to give 1 as an off-
white solid (Figure S29). We also performed the reaction in
THF. In this solvent, addition of 1-dodecanethiol to the slurry
of CuCl2 in THF initially resulted in dissolution of all the solid
over the course of 2 min, concomitant with formation of a
clear, pale-yellow solution. However, upon further stirring, a
very pale-yellow powder began to precipitate from the solution
(Figure S30). After 20 min of stirring, this solid was collected
on a fritted glass filter and rinsed with several portions of
hexanes to give 1 as a very pale-yellow powder. Whether
prepared from dibenzyl ether or THF, complex 1 is insoluble
in alkanes, diethyl ether, benzene, toluene, THF, CH2Cl2,
chloroform, MeCN, DMSO, DMF, MeOH, EtOH, and water.
While complex 1 is also insoluble in pyridine, it does appear to
very slowly react with this solvent.
To better ascertain the reaction stoichiometry, we collected
the colorless filtrate from the THF reaction mixture and
1
removed the volatiles in vacuo to yield a colorless oil. A H
NMR spectrum of this colorless oil, recorded in CD2Cl2
(Figure S8), reveals the presence of unreacted 1-dodecane-
thiol, as well as di(1-dodecane)disulfide.32 These observations
are consistent with the proposed reaction stoichiometry of
Zhang and co-workers, who also noted the reduction of the
Cu(II) ions via thiol oxidation.
A diffuse reflectance spectrum of solid 1 features the onset of
an absorption band at ca. 425 nm (Figure 1, black trace). A
fluorescence spectrum of the same material excited at 365 nm
reveals a very broad emission centered at 510 nm (Figure 1,
red trace). These data are broadly consistent with the spectra
reported by Zhang and co-workers. For example, Cu14(SR)10
was reported to have an absorption band centered at 368 nm,20
along with emission peaks centered at 490 or 550 nm
(depending on the method of sample preparation). Overall,
the similarity of our spectroscopic results with those previously
reported by Zhang, along with the similar physical descriptions
of the two materials, leads us to believe that we are making the
same material. The TGA trace recorded for 1 is also a close
RESULTS AND DISCUSSION
■
Attempted Synthesis of Cu14(SR)10 (R = C12H25).
Cu14(SR)10 was reportedly formed by the reaction of CuCl2·
2H2O (1 equiv) with 1-dodecanethiol (22 equiv) in dibenzyl
ether (6 mL) (Scheme 1). A yield was not reported, and the
color of the material was not described, but photographs
provided in their Supporting Information show that the solid is
a pale-yellow powder.20,21 The solubility of this material was
also not explicitly discussed, but on the basis of the
Scheme 1. Synthetic Procedure Used to Prepare Cu14(SR10)
B
DOI: 10.1021/acs.inorgchem.9b01140
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Scheme 2. Synthesis of 2
Figure 1. Solid-state absorbance (black) and emission (red, λex = 365
nm) spectra for complex 1, synthesized from THF.
mixture after 20 min resulted in the isolation of pale-yellow
crystals of the Cu(I) nanocluster, [Cu12(SR′)6Cl12][(Cu-
match with that reported previously for Cu14(SR)10 (Figure
S31).20
n
(R′SH))6] (2, R′ = Bu), in 90% yield.
Finally, we recorded an X-ray photoelectron spectrum
(XPS) of cluster 1 to confirm the Cu oxidation state and
determine its elemental composition. Specifically, the spectrum
features two prominent peaks at 932.70 and 952.70 eV, which
are attributable to the Cu 2p3/2 and Cu 2p1/2 binding energies,
respectively. These values are similar to the binding energies
reported for other Cu(I)-containing materials.24,33 Unfortu-
nately, the similarity of Cu(I) and Cu(0) binding energies34
generally makes it difficult to discriminate between these two
states, and so we cannot rule out the presence or absence of
Cu(0) in this sample. Nonetheless, the absence of satellite
peaks in this region of the spectrum is consistent with absence
of Cu(II). Moreover, the Cu LMM transitions for 1 appear at
918.3, 915.5, and 911.6 eV. These values are also consistent
with the presence of Cu(I), in multiple chemical environments.
As with the Cu 2p binding energies, it is difficult to use the Cu
LMM data to discriminate between the Cu(0) and Cu(I)
states. That said, our Cu LMM data closely match that
originally reported for Cu14(SR)10, which exhibits transitions at
ca. 918 and 915 eV.20 Curiously, our XPS spectrum also reveals
the presence of Cl, as revealed by the Cl 2s and Cl 2p3/2 peaks
at 269.7 and 199.2 eV (Figures S21 and S25).34 According to
XPS data, the Cu/S/Cl ratio is approximately 2:2:1.
Significantly, these data are not consistent with the original
Cu14(SR)10 formulation, which should not contain Cl−, but are
in line with our findings from a comparative synthetic study
using different thiols (see below). To be fair, though, Zhang
and co-workers may not have tested their material for the
presence of Cl−. Nonetheless, on the basis of these results, we
believe that complex 1 is not a partially metallic, mixed-valent
Cu nanocluster. Instead, we believe that this material is likely
an “Atlas-sphere” [Cu12(SR)6]6+-type cluster. That is, it does
not have any Cu(0) character but instead contains exclusively
Cu(I). Our evidence to support this conclusion is outlined in
the next sections.
Complex 2 crystallizes in the triclinic space group P1
̅
(Figure 2). It features a [Cu12(SR′)6]6+ “Atlas-sphere” core
(Figure 2a), which has been observed for several other Cu(I)
thiolate clusters.12,36−39 Within the Cu12S6 core, each Cu
occupies the vertex of a regular cuboctahedron, while each
thiolate ligand is bound in a μ4 fashion and occupies one of the
six square faces of the cuboctahedron. The Cu−Cu distances
range from 2.6524(7) to 3.7110(8) Å, while the Cu−SR′
distances range from 2.225(2) to 2.276(1) Å. Both of these
ranges are comparable to those seen in other [Cu12(SR)6]6+-
containing clusters.12,36−39 Each of the 12 Cu atoms in the
“Atlas-sphere” core is also coordinated to a Cl− ligand. Six
additional Cu+ ions are bound to the outer surface of the
cluster, via bridging interactions with the Cl− ions. Two of
these outer Cu+ ions are each coordinated to a single thiol
ligand, while the remaining four Cu+ ions are each coordinated
to two thiol ligands, four of which originate from an adjacent
cluster. These bridging interactions give rise to a ladder-type
coordination polymer bridging through two μ2-HSR linkages
(Figure 2c).38 The average Cu−Sthiol distance is 2.30 Å (range:
2.257(1)−2.346(2) Å), which is slightly longer than the Cu-
thiolate distance, as expected.
The 1H NMR spectrum of 2 in THF-d8 (Figure S2) features
resonances at 3.26 and 2.53 ppm, assigned to the α-CH2
resonances of the six μ4-SnBu ligands and the six nBuSH
ligands, respectively. These resonances are present in a 1:1
ratio, consistent with the solid-state structure. Also present in
this spectrum is a broad singlet at 1.85 ppm, assigned to the
SH proton of the six nBuSH ligands. The ESI-MS of 2,
recorded in THF in negative ion mode, features a major peak
at m/z = 2039.9023, which corresponds to the fragment
[Cu17(SR′)6Cl12]− (calcd m/z = 2039.6666) (Figure 3).
Several other peaks are also present in this spectrum. Each
of these peaks is related to the parent ion by loss/gain of CuCl
(m/z = 99). These data suggest that the [Cu12(SR′)6Cl12]6−
core is relatively stable but that the six outer Cu+ ions, outer
Cl− ions, and coordinated thiol ligands are quite labile.
Interestingly, an ESI-MS signal for 2 was only observed upon
addition of [NEt4][Cl] to the ESI-MS sample. It was observed
previously that addition of salts to a nanocluster sample can
facilitate transfer of material into the gas phase during the MS
analysis.40 Finally, a UV−vis spectrum of 2 in THF (Figure
S16) reveals the presence of an absorption band at 370 nm.
The spectrum is qualitatively similar to the spectrum recorded
for Cu14(SR)10,20 providing further support for the structural
n
Synthesis of [Cu12(SR′)6Cl12][(Cu(R′SH))6] (R′ = Bu).
The insolubility of 1 greatly limited our ability to confirm its
formulation. Therefore, we attempted to generate a more
tractable material by substituting the 1-dodecanethiol ligand
for an aliphatic thiol that was more amenable to crystallization,
yet similar in structure and reducing ability (Scheme 2).35
Thus, reaction of a slurry of CuCl2 (1 equiv) in THF (2 mL)
with n-butylthiol (5 equiv) at room temperature immediately
results in dissolution of the CuCl2, concomitant with the
generation of a bright yellow solution. Workup of the reaction
C
DOI: 10.1021/acs.inorgchem.9b01140
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 2. Ball-and-stick diagram showing (a) the [Cu12(SR′)6Cl12]6− core, (b) the structure of the monomeric unit, and (c) the polymeric structure
of 2 (hydrogen atoms omitted for clarity). Color legend: orange, Cu; yellow, S; green, Cl; gray, C.
To better understand the stoichiometry of the trans-
n
formation, the reaction of CuCl2 with BuSH (5 equiv) was
monitored by 1H NMR spectroscopy (Figure S4). Addition of
thiol to a THF-d8 slurry of CuCl2 results in the rapid
dissolution of all solids and the formation of a bright yellow
solution. After 20 min, the 1H NMR spectrum of this solution
revealed a resonance at 3.24 ppm, assigned to the α-CH2
resonance of the six μ4-SnBu ligands in 2, a resonance at 2.68
ppm, assigned to the α-CH2 resonance of di-n-butyl disulfide,
and a broad resonance at 8.56 ppm, assigned to HCl.
Integration of the methylene resonances against an internal
standard (hexamethyldisiloxane) indicates that 2 was formed
in 99% yield, while only 0.5 equiv of di-n-butyl disulfide was
generated per CuCl2. Similarly, integration of the HCl
resonance indicates that 1.3 equiv of HCl is formed relative
to the initial amount of CuCl2. Importantly, these amounts of
disulfide and HCl are consistent only with reduction of Cu(II)
to Cu(I) and formation of 2. If Cu14(SR)10 were to be formed
in this transformation, we would expect 0.64 equiv of di-n-
butyl disulfide and 2.0 equiv of HCl to be formed instead.
We also briefly examined the chemical properties of complex
2. Complex 2 is insoluble in alkanes, Et2O, benzene, toluene,
CH2Cl2, and MeCN. It is soluble in THF, although it partially
decomposes if left in solution at room temperature, as
evidenced by the gradual bleaching of the pale-yellow color
in conjunction with the deposition of a copious amount of
Figure 3. Partial ESI-MS of complex 2 in negative ion mode.
white powder, presumably CuCl. This process occurs over the
Assignments: m/z = 2039.9023 [Cu17(SR′)6Cl12]− (calcd m/z =
course of 24 h. Finally, complex 2 reacts immediately upon
2039.6666), m/z = 2139.7942 [Cu18(SR′)6Cl13]− (calcd m/z =
dissolution in pyridine, to form [CuCl(pyridine)3] (4) as the
2139.5649), m/z = 1940.9977 [Cu16(SR′)6Cl11]− (calcd m/z =
1940.7682), m/z = 1842.0930 [Cu15(SR′)6Cl10]− (calcd m/z =
only isolable product. This complex can be isolated in 68%
yield (based on Cl−) after workup.41 The isolation of 4 from
the reaction mixture demonstrates that, under the appropriate
conditions, the “Atlas-sphere” core is susceptible to dis-
assembly.
1841.8719), m/z = 1744.1725 [Cu14(SR′)6Cl9]− (calcd m/z =
1743.9734).
similarity of that material and 2. The fluorescence spectrum of
solid 2 (λex = 365 nm) reveals a broad emission peak at 585
nm (Figure S19).
Synthesis of [H(THF)2]2[Cu17(SR′′)6Cl13(THF)2(R′′SH)3]
(R′′ = CH2CH2Ph). To further understand the reactivity of
D
DOI: 10.1021/acs.inorgchem.9b01140
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Cu(II) with thiols, we explored the reaction of CuCl2 with 2-
phenylethanethiol. This specific thiol was chosen because it is
widely used in the synthesis of Ag and Au APNCs,1 and yet an
isolable 2-phenylethylthiolate-containing Cu APNC has so far
remained elusive. Thus, reaction of a slurry of CuCl2 (1 equiv)
in THF with 2-phenylethanethiol (4 equiv) at room temper-
ature immediately generates a bright yellow solution
concomitant with dissolution of the CuCl2 (Scheme 3).
the “core” Cu atoms (Cu10) is also bound by a THF ligand.
Additionally, complex 3 features a [Cu(HSR′′)2] fragment
appended to its outer surface via dative interactions with two
Cl− ligands (Cl12 and Cl13). It is likely that this peripheral
fragment, along with the peripheral THF and R′′SH ligands, is
extremely labile. Not surprisingly, the 1H NMR spectrum (vide
infra) in THF-d8 reveals a highly symmetric cluster, with only
one magnetically unique thiolate ligand. Finally, the overall
cluster charge is balanced by the presence of two [H(THF)2]+
cations. While the H-bonded protons in these cations were not
located in the difference Fourier map, their presence is
supported by the close approach of two sets of THF molecules.
Specifically, the distances between O3 and O4 (2.47(2) Å) and
O8 and O8* (2.36(1) Å) are similar to the O−O distances in
other [H(THF)2]+ and [H(Et2O)2]+ cations.42−49
Scheme 3. Synthesis of 3
1
The H NMR spectrum of 3 in THF-d8 reveals resonances
at 3.47 and 3.37 ppm, assigned to the CH2 resonances of the
six μ4-SCH2CH2Ph ligands. Likewise, resonances at 2.88 and
2.77 ppm are assigned to the CH2 resonances of the thiol
ligands. The thiol SH proton resonance at 1.95 ppm is also
present. A very broad resonance at 8.82 ppm is assigned to the
O−H−O proton of the [H(THF)2]+ counterion.45,48,49 For
comparison, the O−H−O proton of the [H(THF)2]+
counterion in [H(THF)2][Al{OC(CF3)3}4] is reported to
appear at ca. 8 ppm.45 The presence of thiolate and thiol
environments in a 6:4 ratio, instead of the expected 6:3 ratio,
suggests that a small amount of excess of thiol is present in the
final product, which we have been unable to remove.
ESI-MS data were collected in negative ion mode for a THF
solution of 3. The major feature of the spectrum at m/z =
2129.8726 corresponds to the fragment [Cu15(SR′′)6Cl10]−
(calcd m/z = 2129.8718) (Figure 5). Several other peaks are
also observed. They are related to the parent ion by loss/gain
of CuCl (m/z = 99). These data suggest that the
[Cu12(SR′′)6]6+ core of 3 is relatively stable, but that the
outer Cl− anions, Cu+ cations, and thiol ligands are more labile.
Once again, we observed a signal only after addition of
[NEt4][Cl] to the ESI-MS sample. A UV−vis spectrum of 3 in
THF features a broad absorption band at 355 nm (Figure
S17), in good agreement with the spectrum observed for 2.
Workup of the reaction mixture after 20 min resulted in the
formation of pale-yellow crystals of the Cu(I) nanocluster
[H(THF)2]2[Cu17(SR′′)6Cl13(THF)2(R′′SH)3] (R′′ =
CH2CH2Ph, 3), which can be isolated in 93% yield.
Complex 3 crystallizes in the triclinic space group P1 as a
̅
THF solvate, 3·1.5THF (Figure 4). Like 2, complex 3 features
a [Cu12(SR′′)6]6+ “Atlas-sphere” core (Figure 4a). Within the
core, the Cu−Cu distances range from 2.685(3) to 3.678(4) Å,
while the average Cu−SR distance is 2.28 Å. These values are
similar to those observed for 2. Each of the 12 Cu atoms in the
[Cu12(SR′′)6]6+ core is coordinated to one Cl− ligand. These
Cl− ions are grouped into four groups of three. Each group of
Cl− ions forms a trigonal planar bonding pocket, which is filled
with a Cu+ ion. A 13th Cl− ligand (Cl13) is also bound to the
[Cu12(SR′′)6]6+ core, in an μ2 interaction with Cu6 and Cu7.
One of the outer Cu+ ions (Cu11) is bound by an R′′SH
ligand, while another (Cu5) is bound by a THF ligand. One of
Figure 4. Ball-and-stick diagram showing (a) the [Cu16(SR)6Cl12]2− core, (b) the full structure of 3·1.5THF, including one [H(THF)2]+ cation
(hydrogen atoms, THF ligands, and THF solvate molecules omitted for clarity). Color legend: orange, Cu; yellow, S; green, Cl; red, O; gray, C.
E
DOI: 10.1021/acs.inorgchem.9b01140
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
8979.6 eV for [Cu25H22(PPh3)12][Cl] or 8979.0 eV for Cu foil,
for example).24,26,27
The EXAFS spectra for nanoclusters 1, 2, and 3 show similar
features (Table 1 and Figure 6). Specifically, there are two
Table 1. Comparison of Average FEFF-Predicted Paths for
the “Atlas-Sphere” Core [Cu12(SR)6Cl12]6−, with EXAFS
Curve Fit Parameters for Nanoclusters 1, 2, and 3
cluster
[Cu12(SR)6Cl12]6−
path
N
R (Å)
2.278
103 σ2 (Å2)
Cu−L1
1.5
n.a.
Cu−Cu1
Cu−Cu2
Cu−Cu3
Cu−L
Cu−Cu1
Cu−Cu2
Cu−Cu3
Cu−L
Cu−Cu1
Cu−Cu2
Cu−L
Cu−Cu1
Cu−Cu2
1.33
0.67
2.87
2.718
2.944
4.03
a
1
1.8(3)
1.6(3)
0.4(2)
2.4(4)
1.2(2)
1.5(4)
0.4(2)
1.5(3)
1.6(5)
0.7(3)
2.249(6)
2.796(9)
2.983(9)
4.047(2)
2.240(2)
2.77(4)
2.982(1)
2.298(6)
2.71(1)
2.92(2)
3.9(3)
4.6(2)
4.6(2)
b
b
8.9(5)
3.0(9)
c
2
d
11(4)
11(4)
d
e
3
4.1(3)
f
12(4)
12(4)
f
a
Nidp = 23, ΔR = 1.0−4.5 Å, Δk = 3.0−13.5 Å−1, ΔE0 = 5.7(5).
b
c
Constrained to the same value. Nidp = 15, ΔR = 1.0−3.0 Å, Δk =
d
e
3.0−14.5 Å−1, ΔE0 = 5.7(2). Constrained to the same value. Nidp
=
f
13, ΔR = 1.0−3.0 Å, Δk = 3.0−13.3 Å−1, ΔE0 = 4.7(5). Constrained
Figure 5. Partial ESI-MS of 3 in negative ion mode. Assignments: m/z
= 2129.8726 [Cu15(SR′′)6Cl10]− (calcd m/z = 2129.8718), m/z =
2527.6428 [Cu19(SR′′)6Cl14]− (calcd m/z = 2527.4636), m/z =
2431.7378 [Cu18(SR′′)6Cl13]− (calcd m/z = 2431.5574), m/z =
2327.6748 [Cu17(SR′′)6Cl12]− (calcd m/z = 2327.6667), m/z =
2229.7747 [Cu16(SR′′)6Cl11]− (calcd m/z = 2229.7683), m/z =
2
to the same value. In all fits, the value of S0 was fixed at 0.8, in
accordance with our previous analyses of Cu(I) standards and Cu-
based clusters,26,27 and ΔE0 was refined as a global fit parameter.
Uncertainties are shown in parentheses; values without uncertainties
were fixed during curvefitting.
́
−
́
2031.9645 [Cu14(SR)6Cl9] (calcd m/z = 2031.9734), m/z =
1932.0714 [Cu13(SR′′)6Cl8]− (calcd m/z = 1932.0750), m/z =
major peaks at ca. 1.8 and 2.3 Å in R-space. The first peak
represents scattering from the light atoms (Cl and S)
coordinated directly to Cu, while the second peak represents
Cu−Cu scattering. Both features are more intense for 1, whose
EXAFS also contains a prominent long-range path at ca. 3.8 Å.
For all three nanoclusters, scattering involving nearest-
neighbor Cu−Cl, Cu−S, and Cu−Cu paths was simulated
using the “Atlas-sphere” [Cu12(SR)6Cl12]6− core present in
clusters 2 and 3. For the ligand-based paths, the expected
coordination numbers are N(Cu−Cl) = 1.0 and N(Cu−S) =
0.5, which have nearly identical average distances of 2.27 and
2.28 Å, respectively. These similar pathlengths led us to
combine the scattering paths for all ligands into a single Cu-L
path in the EXAFS fit. The expected nearest-neighbor
coordination number N(Cu−Cu) is 2.0, at an average distance
of 2.76 Å; however, there is a large range in the crystallo-
graphically determined Cu−Cu distances (see above). To
account for this variation, EXAFS data were fitted with two
different Cu−Cu paths, following a previous successful
approach.26,27 The FEFF model50 also predicts significant
contributions from a variety of single-scattering paths at ca. 4.0
Å, which we modeled using a long Cu−Cu path.
1831.0859 [Cu12(SR′′)6Cl7]− (calcd m/z = 1831.1843).
The fluorescence spectrum of 3, recorded for the solid and
excited at 365 nm, reveals a broad peak at 650 nm (Figure
S20). We also briefly examined the chemical properties of
complex 3. Similar to complex 2, it is insoluble in alkanes,
Et2O, benzene, toluene, CH2Cl2, and MeCN. It is soluble in
THF, although the cluster appears to partially decompose in
that solvent upon standing at room temperature for 5 h, as
evidenced by the deposition of a white powder and a bleaching
of the yellow color. Complex 3 also reacts with pyridine to
form 4, which was isolated in 95% yield after workup.41
X-ray Absorption Spectroscopy Characterization.
Previously, we demonstrated that X-ray absorption spectros-
copy is a valuable tool for the structural characterization of
copper nanoclusters.24,26,27 In particular, we showed that the
XANES edge energy is highly sensitive to the average Cu
oxidation state in Cu nanoclusters.24,26,27 Building on this past
work, we measured the Cu K-edge XANES and EXAFS of
nanoclusters 1 (synthesized using dibenzyl ether as the
solvent), 2, and 3. The XANES spectra of nanoclusters 1, 2,
and 3 feature edge positions at 8980.7, 8981.1, and 8980.5 eV
(Figure S27), respectively. These values are essentially
identical to those measured for the Cu(I) coordination
complexes [CuCl(PPh3)]4 (8080.9 eV) and CuCl (8981.9
eV),24,26 and corroborate our assignment of 1, 2, and 3 as
Cu(I)-containing nanoclusters with no Cu(0) character. If 1, 2,
and 3 did have some Cu(0) character, we would expect to
observe edge positions at lower energies (comparable to
Satisfactory fits were achieved for all three nanoclusters. For
example, for nanocluster 2, the curve fit gives a Cu−L path
length of 2.240(2) Å (N = 1.2(2)), and the combined value of
N(Cu−Cu) is 1.9(6). These parameters are in good agreement
with the FEFF-predicted paths for the “Atlas-sphere” core,
[Cu12(SR)6Cl12]6−. A similarly good fit was achieved for
nanocluster 3. For nanocluster 1, the curve fit gives a Cu−L
pathlength of 2.246(6) Å (N = 1.8(3)), while the combined
F
DOI: 10.1021/acs.inorgchem.9b01140
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
nanocluster 1. Finally, the prominent feature at ca. 4 Å in the
EXAFS of [Cu14H12(phen)6(PPh3)4][Cl]2 is reproduced well
by a near-collinear multiple-scattering path (Cu−Cu−Cu, N =
6, ∠ 160.1°). Overall, the spectrum of Cu14 exemplifies the
EXAFS expected for a Cu14 nanocluster with strong Cu−Cu
bonding, and is very different from the EXAFS of 1, 2, and 3,
supporting our conclusion about the structure of 1.
Comparison to Other Reported Copper Thiolate
Nanoclusters. As mentioned in the Introduction, several
thiolate-protected Cu APNCs with partial Cu(0) character
have been reported in the past few years, including
[Cu15(GSH)4], [Cu9(SC6H4-p-F)7], and [Cu9(SC6H4-p-
Br)6].15,17 Many of these low-valent nanoclusters were
reportedly formed by direct reaction of a Cu(II) salt with an
alkyl or aryl thiol, which acts as both reducing agent and
capping ligand. On the basis of the reactivity we report here,
we now believe that these previous reactions do not result in
the formation of low-valent Cu APNCs. Instead, we suspect
that they lead to formation of Cu(I)-containing thiolate
clusters, similar in formulation and structure to complexes 1, 2,
and 3. Given the apparent thermodynamic stability of the
“Atlas-sphere” structure type, as revealed by the structures of 2
and 3, as well as the structures of [Cu12(SR)6X12][CuX] (X =
Cl, Br; R = CH2CH2NH3), [Cu12(SR)6Cl12][CuCl]5,
[Cu12(SMe)6(CN)6], and [Cu12E6L8] (E = S, Se; L =
phosphine),37,38,52−55 it is likely that many of these complexes
also feature a [Cu12(SR)6]6+ core. That being said, other core
structures are also possible, including [Cu4(SR)4] (R = 2,6-
(Me3Si)2C6H3, 2,4,6-iPr3-C6H2),56,57 [Cu4(SR)6]2− (R = Me,
Figure 6. Comparison of Cu K-edge EXAFS for (a)
[Cu14H12(phen)6(PPh3)4][Cl]2 and 1; and (b) 2 and 3. All spectra
are shown as FT magnitudes in nonphase corrected R-space (points).
Parameters for the curve fits (solid lines) are shown in Tables 1 and
S4. Spectra are offset vertically for clarity.
58−65
i
Et, Pr, Ph, p-Cl-C6H4, o-tBu-C6H4),
[Cu5(SR)6]− (R =
tBu, 2,6-Me2-C6H3, 1-adamantyl),64,66−68 [Cu5(SR)7]2− (R =
Me, Ph),62,69,70 [Cu6(SR)6(μ6-Br)] (R = 1-(thiolato)-
triptycene),71 [Cu8(SR)8] (R = 2,4,6-iPr3-C6H2),57,72
[Cu8(SR)6Cl6]2+ (R = CH2CH2NH3),55 and [Cu12(SR)12]
(R = 2-(Me3Si)C6H4).73
value of N(Cu−Cu) is 2.0(5). Most significantly, these
parameters agree well with those determined for 2 and 3,
and demonstrate that a single “Atlas-sphere” structural model
can be used to describe the EXAFS of all three nanoclusters,
albeit with slight differences in EXAFS intensity (which likely
arises from perturbations of the core due to the different outer
surface environments). These findings further reinforce our
hypothesis that nanocluster 1 is an “Atlas-sphere”-type cluster,
and not a low-valent, Cu(0)-containing nanocluster as
originally surmised.
For further comparison, we also recorded EXAFS data for an
authentic Cu14 cluster, [Cu14H12(phen)6(PPh3)4][Cl]2, which
we synthesized and structurally characterized in 2015.51 In the
solid state, [Cu14H12(phen)6(PPh3)4][Cl]2 features a signifi-
cantly shorter average Cu−Cu distance than is found in either
2 or 3, making it a reasonable model for the Cu14(SR)10
structure proposed by Zhang and co-workers. Its EXAFS
spectrum contains a broad signal with multiple, overlapping
components centered at ca. 2 Å (Figure 6a). The fit was
conducted using contributions from Cu-L (L = N, P)
scattering, as well as three distinct Cu−Cu single-scattering
paths (Table S4). In particular, the curve fit gives Cu−N and
Cu−P pathlengths of 2.07(1) and 2.30(1) Å, respectively,
while the combined value of N(Cu−Cu) is 4.1(5). These
parameters are in good agreement with those extracted from
the X-ray crystallographic analysis. More importantly, though,
the N-weighted average Cu−Cu EXAFS pathlength is 2.60 Å,
which is close to the value of 2.55 Å found for bulk Cu metal,24
and much different from the Cu−Cu pathlengths measured for
The reactivity of Cu(I) and Cu(II) salts with thiols and
thiolates is actually well explored.74 Despite this long history,
there is no crystallographically authenticated example of this
reaction resulting in formation of a Cu(0)-containing product.
For example, Kroneck and co-workers monitored the reaction
of [Cu(MeCN)4][ClO4] with a variety of thiols in MeCN/
H2O. These reactions produce thiolate-containing Cu(I)
coordination polymers exclusively.75 In no case did they
observe reduction of Cu(I) to Cu(0). Similarly, the reaction of
[Cu(MeCN)4][PF6] with HSC6H4-o-SiMe3 results in for-
mation of the Cu(I) nanocluster, [Cu(SC6H4-o-SiMe3)]12.73
More recently, Donahue and co-workers found that reaction of
CuCl with [n-Bu4N][Cl] and NaSR (R = 1-(thiolato)-
triptycene) results in formation of the monometallic Cu(I)
“ate” complex, [Cu(SR)2]−.71 It is also useful to survey the
reactivity of Ag and Au salts with thiols. For instance, reaction
of AgNO3 with RSH/NEt3 in MeCN resulted in formation of
[Ag(SR)]n oligomers.76,77 The reaction conditions are similar
to those used in our study, yet no reduction to Ag(0) was
observed, despite the fact that Ag(I) is a much stronger oxidant
than Cu(I).78 Similarly, reaction of AgNO3 with PhSH/
[NMe4][Cl] in MeOH/MeCN yields a series of AgI(SPh)
“ate” complexes.79 Again, no reduction to Ag(0) is observed.
With respect to Au(I), which is a stronger oxidant than either
Ag(I) or Cu(I),78 reaction of H[AuCl4] with excess RSH in
water results in formation of [AuI(SR)]n in excellent yields,80
although in this case, reduction to metallic gold can be
observed if the reaction mixture gets too hot. Similarly,
G
DOI: 10.1021/acs.inorgchem.9b01140
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
reaction of Na[AuCl4] with 3 equiv of RSH in EtOH also
results in formation of [AuI(SR)]n.81 This procedure is
compatible with a wide variety of R groups, including Bu
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.9b01140.
■
S
n
and C12H25 (which were employed in the current study).
The well-known photochemical properties of Cu(I) clusters
further buttresses our argument that the material isolated by
Zhang and co-workers is a Cu(I)-containing “Atlas-sphere”
nanocluster and not the mixed-valent nanocluster, Cu14(SR)10,
that was original proposed. For example, the “Atlas-sphere”
clusters, [Cu12E6L8] (E = S, Se; L = phosphine), are strongly
luminescent, with measured PL quantum yields of up to
90%.52−54 In fact, many Cu(I)-containing clusters are known
to be photoluminescent,13,82−89 including many Cu(I)-thiolate
and Cu(I)-thiolate/halide clusters.13,83,87−89 For example,
[Cu(SR)]n (n = 2, 4, 7; R = p-S-C6H4−NMe2)13 features an
emission peak between 480 and 560 nm, depending on its
nuclearity, while [(Cu(StBu))4(dppe)]n (dppe = bis-
(diphenylphosphino)ethane) and [(Cu(StBu))6(bix)]n (bix =
1,4-bis(imidazole-1-ylmethyl)benzene) emit at 603 and 629
nm, respectively.88
Experimental procedures, crystallographic details, and
spectral data (PDF)
Accession Codes
CCDC 1911088−1911089 contain the supplementary crys-
tallographic 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 1223 336033.
AUTHOR INFORMATION
Corresponding Authors
*(T.W.H.) E-mail: hayton@chem.ucsb.edu.
*(S.L.S.) E-mail: sscott@engineering.ucsb.edu.
■
ORCID
Susannah L. Scott: 0000-0003-1161-0499
Trevor W. Hayton: 0000-0003-4370-1424
Notes
CONCLUSION
■
We have examined the reactions of CuCl2 with a variety of
thiols (RSH) under anhydrous conditions. In the cases where
R = n-Bu and R = CH2CH2Ph, we isolated “Atlas-sphere”-type
nanoclusters in good yields. Both nanoclusters are built around
identical [Cu12(SR)6]6+ core structures and both contain
Cu(I) ions exclusively. Neither cluster features any Cu(0)
character. In the case where R = n-C12H25, we generated an
insoluble Cu(I)-containing thiolate nanocluster. The insol-
ubility of this material prevented us from growing X-ray quality
crystals. However, we believe this cluster also features an
“Atlas-sphere” core on the basis of a comparative XANES and
EXAFS analysis. Our conclusion concerning the nature of this
material is further strengthened by our XPS characterization
data, as well as the observation that the “Atlas-sphere”
structure type is a conserved across a variety of thiolate
ligands. Contrary to previous reports, we do not believe that
this material is a mixed valent, Cu(0)-containing nanocluster.
Our conclusions concerning the nature of this material are
also better aligned with previously reported group 11 thiolate
chemistry, which has been extensively studied. In particular,
this past work suggests that the M(0) state is not accessible
without addition of stronger reducing agents, such as NaBH4.
To the best of our knowledge, all previously reported reactions
of Cu(II) salts with thiols have resulted only in formation of
Cu(I)-containing products. Stated differently, thiols alone
cannot reduce Cu2+ or Cu+ to Cu(0). Perhaps most
importantly, it is apparent that the synthesis of thiolate-
stabilized, Cu(0)-containing APNCs is an unsolved synthetic
problem. Their isolation would represent an important
synthetic advance, but these materials remain elusive, in
contrast with the plethora of known thiolate-stabilized Au(0)-
and Ag(0)-containing APNCs. Going forward, we will
continue to pursue the synthesis of Cu(0)-containing,
thiolate-stabilized APNCs. However, their successful isolation
will likely require the development of new ligands and new
synthetic procedures.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
T.W.H. and A.W.C. thank the National Science Foundation
(CHE 1764345) for financial support. Z.R.J. and S.L.S. thank
the U.S. Department of Energy, Office of Science, Office of
Basic Energy Sciences, under the Catalysis Science Initiative
(DE-FG-02-03ER15467). NMR spectra were collected on an
instrument supported by an NIH Shared Instrumentation
Grant (SIG, 1S10OD012077-01A1). ESI mass spectra, diffuse
reflectance spectra, X-ray photoelectron spectra, and fluo-
rescence spectra were acquired at the Materials Research
Laboratory (MRL) Shared Experimental Facilities, supported
by the MRSEC Program of the NSF under Award No. DMR
1720256 and a member of the NSF-funded Materials Research
Facilities Network. X-ray absorption spectra were acquired at
the Stanford Synchrotron Radiation Lightsource, a Directorate
of SLAC National Accelerator Laboratory and an Office of
Science User Facility operated for the U.S. Department of
Energy Office of Science by Stanford University. We thank the
support staff at the MRL and California NanoSystems Institute
(CNSI) for their assistance. This research used resources of
the Advanced Light Source, which is a DOE Office of Science
User Facility under the contact no. DE-AC02-05CH11231.
A.W.C. thanks the Mellichamp Academic Initiative in
Sustainability at UCSB for a summer fellowship. We thank
Alexander Touchton for assistance with the TGA measure-
ment.
REFERENCES
■
(1) Jin, R.; Zeng, C.; Zhou, M.; Chen, Y. Atomically Precise
Colloidal Metal Nanoclusters and Nanoparticles: Fundamentals and
Opportunities. Chem. Rev. 2016, 116, 10346−10413.
(2) Heaven, M. W.; Dass, A.; White, P. S.; Holt, K. M.; Murray, R.
W. Crystal structure of the gold nanoparticle [N(C8H17)4]-
[Au25(SCH2CH2Ph)18]. J. Am. Chem. Soc. 2008, 130, 3754−3755.
(3) Zhu, M.; Aikens, C. M.; Hollander, F. J.; Schatz, G. C.; Jin, R.
Correlating the crystal structure of a thiol-protected Au25 cluster and
optical properties. J. Am. Chem. Soc. 2008, 130, 5883−5885.
H
DOI: 10.1021/acs.inorgchem.9b01140
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(4) Qian, H.; Eckenhoff, W. T.; Zhu, Y.; Pintauer, T.; Jin, R. Total
Structure Determination of Thiolate-Protected Au38 Nanoparticles. J.
Am. Chem. Soc. 2010, 132, 8280−8281.
(24) Nguyen, T.-A. D.; Jones, Z. R.; Goldsmith, B. R.; Buratto, W.
R.; Wu, G.; Scott, S. L.; Hayton, T. W. A Cu25 Nanocluster with
Partial Cu(0) Character. J. Am. Chem. Soc. 2015, 137, 13319−13324.
(25) Cook, A. W.; Nguyen, T.-A. D.; Buratto, W. R.; Wu, G.;
Hayton, T. W. Synthesis, Characterization, and Reactivity of the
Group 11 Hydrido Clusters [Ag6H4(dppm)4(OAc)2] and [Cu3H-
(dppm)3(OAc)2]. Inorg. Chem. 2016, 55, 12435−12440.
(26) Nguyen, T.-A. D.; Jones, Z. R.; Leto, D. F.; Wu, G.; Scott, S. L.;
Hayton, T. W. Ligand-Exchange-Induced Growth of an Atomically
Precise Cu29 Nanocluster from a Smaller Cluster. Chem. Mater. 2016,
28, 8385−8390.
(5) Qian, H.; Jin, R. Ambient Synthesis of Au144(SR)60 Nanoclusters
in Methanol. Chem. Mater. 2011, 23, 2209−2217.
(6) Zeng, C.; Chen, Y.; Kirschbaum, K.; Lambright, K. J.; Jin, R.
Emergence of hierarchical structural complexities in nanoparticles and
their assembly. Science 2016, 354, 1580−1584.
(7) Sakthivel, N. A.; Theivendran, S.; Ganeshraj, V.; Oliver, A. G.;
Dass, A. Crystal Structure of Faradaurate-279: Au279(SPh-tBu)84
Plasmonic Nanocrystal Molecules. J. Am. Chem. Soc. 2017, 139,
15450−15459.
(27) Cook, A. W.; Jones, Z. R.; Wu, G.; Scott, S. L.; Hayton, T. W.
An Organometallic Cu20 Nanocluster: Synthesis, Characterization,
Immobilization on Silica, and “Click” Chemistry. J. Am. Chem. Soc.
2018, 140, 394−400.
(8) Joshi, C. P.; Bootharaju, M. S.; Alhilaly, M. J.; Bakr, O. M.
[Ag25(SR)18]−: The “Golden” Silver Nanoparticle. J. Am. Chem. Soc.
2015, 137, 11578−11581.
(9) Desireddy, A.; Conn, B. E.; Guo, J.; Yoon, B.; Barnett, R. N.;
Monahan, B. M.; Kirschbaum, K.; Griffith, W. P.; Whetten, R. L.;
Landman, U.; Bigioni, T. P. Ultrastable silver nanoparticles. Nature
2013, 501, 399−402.
(10) Yang, H.; Wang, Y.; Huang, H.; Gell, L.; Lehtovaara, L.; Malola,
S.; Hakkinen, H.; Zheng, N. All-thiol-stabilized Ag44 and Au12Ag32
nanoparticles with single-crystal structures. Nat. Commun. 2013, 4,
2422.
(11) Luo, Y.-R., Bond Dissociation Energies. In CRC Handbook of
Chemistry and Physics, 89th ed.; Lide, D. R., Ed.; CRC Press/Taylor
and Francis: Boca Raton, FL, 2009.
(12) Fuhr, O.; Fernandez-Recio, L.; Fenske, D. New Copper
Chalcogenide Clusters with a Selenide Core and a Sulfide Shell. Eur. J.
Inorg. Chem. 2005, 2005, 2306−2314.
(13) Langer, R.; Yadav, M.; Weinert, B.; Fenske, D.; Fuhr, O.
Luminescence in Functionalized Copper Thiolate Clusters −
Synthesis and Structural Effects. Eur. J. Inorg. Chem. 2013, 2013,
3623−3631.
(14) Wang, Z.; Chen, B.; Rogach, A. L. Synthesis, optical properties
and applications of light-emitting copper nanoclusters. Nanoscale
Horiz. 2017, 2, 135−146.
(15) Das, N. K.; Ghosh, S.; Priya, A.; Datta, S.; Mukherjee, S.
Luminescent Copper Nanoclusters as a Specific Cell-Imaging Probe
and a Selective Metal Ion Sensor. J. Phys. Chem. C 2015, 119, 24657−
24664.
(28) Chakrahari, K. K.; Liao, J.-H.; Kahlal, S.; Liu, Y.-C.; Chiang, M.-
H.; Saillard, J.-Y.; Liu, C. W. [Cu13{S2CNnBu2}6(acetylide)4]+: A
Two-Electron Superatom. Angew. Chem., Int. Ed. 2016, 55, 14704−
14708.
(29) Weßing, J.; Ganesamoorthy, C.; Kahlal, S.; Marchal, R.; Gemel,
C.; Cador, O.; Da Silva, A. C. H.; Da Silva, J. L. F.; Saillard, J.-Y.;
Fischer, R. A. The Mackay-Type Cluster [Cu43Al12](Cp*)12: Open-
Shell 67-Electron Superatom with Emerging Metal-Like Electronic
Structure. Angew. Chem., Int. Ed. 2018, 57, 14630−14634.
(30) Yuan, P.; Chen, R.; Zhang, X.; Chen, F.; Yan, J.; Sun, C.; Ou,
D.; Peng, J.; Lin, S.; Tang, Z.; Teo, B. K. K.; Zheng, L.-S.; Zheng, N.
Ether-soluble Cu53 Nanoclusters as an Effective Precursor of High-
quality CuI Films for Optoelectronic Applications. Angew. Chem., Int.
Ed. 2019, 58, 835−839.
(31) This change was made, in part, because we performed our
syntheses in an inert atmosphere glovebox.
(32) Hasan, M.; Bethell, D.; Brust, M. The Fate of Sulfur-Bound
Hydrogen on Formation of Self-Assembled Thiol Monolayers on
Gold: 1H NMR Spectroscopic Evidence from Solutions of Gold
Clusters. J. Am. Chem. Soc. 2002, 124, 1132−1133.
(33) Biesinger, M. C. Advanced analysis of copper X-ray
photoelectron spectra. Surf. Interface Anal. 2017, 49, 1325−1334.
(34) Naumkin, A. V.; Kraut-Vass, A.; Gaarenstroom, S. W.; Powell,
C. J. NIST Standard Reference Database 20, Version 4.1 (web version)
(http://srdata.nist.gov/xps/) 2012.
(16) Lin, Y.-J.; Chen, P.-C.; Yuan, Z.; Ma, J.-Y.; Chang, H.-T. The
isomeric effect of mercaptobenzoic acids on the preparation and
fluorescence properties of copper nanoclusters. Chem. Commun. 2015,
51, 11983−11986.
(35) The redox potentials of organothiols are essentially
independent of the substituent. SeeWhitesides et al. J. Org. Chem.
1993, 58, 642−647.
(36) Janssen, M. D.; Spek, A. L.; Grove, D. M.; van Koten, G. A
Mixed (Arenethiolato)copper(I)/Copper Bromide Aggregate: X-ray
Structure of Octanuclear [Cu8{SC6H3(CH2NMe2)2-2,6}3Br5]. Inorg.
Chem. 1996, 35, 4078−4081.
(17) Ai, L.; Jiang, W.; Liu, Z.; Liu, J.; Gao, Y.; Zou, H.; Wu, Z.;
Wang, Z.; Liu, Y.; Zhang, H.; Yang, B. Engineering a red emission of
copper nanocluster self-assembly architectures by employing aromatic
thiols as capping ligands. Nanoscale 2017, 9, 12618−12627.
(18) Wei, W.; Lu, Y.; Chen, W.; Chen, S. One-Pot Synthesis,
Photoluminescence, and Electrocatalytic Properties of Subnanometer-
Sized Copper Clusters. J. Am. Chem. Soc. 2011, 133, 2060−2063.
(19) Nguyen, T.-A. D.; Cook, A. W.; Wu, G.; Hayton, T. W.
Subnanometer-Sized Copper Clusters: A Critical Re-evaluation of the
Synthesis and Characterization of Cu8(MPP)4 (HMPP = 2-Mercapto-
5-n-propylpyrimidine). Inorg. Chem. 2017, 56, 8390−8396.
(20) Wu, Z.; Liu, J.; Gao, Y.; Liu, H.; Li, T.; Zou, H.; Wang, Z.;
Zhang, K.; Wang, Y.; Zhang, H.; Yang, B. Assembly-Induced
Enhancement of Cu Nanoclusters Luminescence with Mechanochro-
mic Property. J. Am. Chem. Soc. 2015, 137, 12906−12913.
(21) Wu, Z.; Liu, H.; Li, T.; Liu, J.; Yin, J.; Mohammed, O. F.; Bakr,
O. M.; Liu, Y.; Yang, B.; Zhang, H. Contribution of Metal Defects in
the Assembly Induced Emission of Cu Nanoclusters. J. Am. Chem. Soc.
2017, 139, 4318−4321.
(37) Parish, R. V.; Salehi, Z.; Pritchard, R. G. Five-Coordinate Sulfur
in a Polymeric Copper(I) Thiolate Complex. Angew. Chem., Int. Ed.
Engl. 1997, 36, 251−253.
(38) Prichard, R. G.; Parish, R. V.; Salehi, Z. Self-assembling
copper(I) clusters involving electron-deficient, quadruply bridging
thiolate ligands. J. Chem. Soc., Dalton Trans. 1999, 243−250.
(39) Li, D.; Wu, T.; Zhou, X.-P.; Zhou, R.; Huang, X.-C. Twelve-
Connected Net with Face-Centered Cubic Topology: A Coordination
Polymer Based on [Cu12(μ4-SCH3)6]6+ Clusters and CN− Linkers.
Angew. Chem., Int. Ed. 2005, 44, 4175−4178.
(40) Qian, H.; Zhu, Y.; Jin, R. Atomically precise gold nanocrystal
molecules with surface plasmon resonance. Proc. Natl. Acad. Sci. U. S.
A. 2012, 109, 696−700.
(41) Scholz, S.; Lerner, H.-W.; Bolte, M. Chlorotripyridinecopper-
(I). Acta Crystallogr., Sect. E: Struct. Rep. Online 2002, 58, m72−m73.
(42) Brookhart, M.; Grant, B.; Volpe, A. F. [(3,5-
(CF3)2C6H3)4B]−[H(OEt2)2]+: A Convenient Reagent for Gener-
ation and Stabilization of Cationic, Highly Electrophilic Organo-
metallic Complexes. Organometallics 1992, 11, 3920−3922.
(22) Liu, Y.; Yao, D.; Zhang, H. Self-Assembly Driven Aggregation-
Induced Emission of Copper Nanoclusters: A Novel Technology for
Lighting. ACS Appl. Mater. Interfaces 2018, 10, 12071−12080.
(23) Wang, Z.; Chen, B.; Rogach, A. L. Synthesis, optical properties
and applications of light-emitting copper nanoclusters. Nanoscale
Horiz. 2017, 2, 135−146.
(43) Jutzi, P.; Muller, C.; Stammler, A.; Stammler, H.-G. Synthesis,
̈
Crystal Structure, and Application of the Oxonium Acid [H-
(OEt2)2]+[B(C6F5)4]. Organometallics 2000, 19, 1442−1444.
I
DOI: 10.1021/acs.inorgchem.9b01140
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
̈
(44) Pietikainen, J.; Maaninen, A.; Laitinen, R. S.; Oilunkaniemi, R.;
(61) Baumgartner, M.; Schmalle, H.; Dubler, E. Synthesis,
characterization and crystal structure of copper(I) thiolates:
[(C6H5)4P+]2[Cu4(C2H5S−)6]·0.5C2H6O2 and [(C6H5)4P+]-
[Cu7(C2H5S−)8]. Polyhedron 1990, 9, 1155−1164.
(62) Baumgartner, M.; Schmalle, H.; Baerlocher, C. Synthesis,
Characterization, and Crystal Structure of Three Homoleptic
Copper(I) Thiolates: (Cu(CH3S−))∞, [(C6H5)4P+]2[Cu5(CH3S−)7]
· C2H6O2, and [(C3H7)4N+]2[Cu4(CH3S−)6] · CH4O. J. Solid State
Chem. 1993, 107, 63−75.
(63) Fujisawa, K.; Imai, S.; Suzuki, S.; Moro-oka, Y.; Miyashita, Y.;
Yamada, Y.; Okamoto, K.-i. M−S vibrational study in three-
coordinate thiolato compounds (NEt4)2[M(SC6H4-p-X)3] and
(NEt4)2[M4(μ-SC6H4-p-Cl)6]: M = Cu(I) and Ag(I), X = Cl and
Br. J. Inorg. Biochem. 2000, 82, 229−238.
(64) Zeevi, S.; Tshuva, E. Y. Synthesis and X-ray Characterization of
Mono- and Polynuclear Thiolatocopper(I) Complexes: The Effect of
Steric Bulk on Coordination Number and Nuclearity. Eur. J. Inorg.
Chem. 2007, 2007, 5369−5376.
Valkonen, J. Halogenation of tellurium by SO2Cl2. Formation and
crystal structures of (H3O)[Te3Cl13]·1/2SO2, [(C4H8O)2H][TeCl5]·
(C4H8O), [(Me2SO)2H]2[TeCl6], and [Ni(NCCH3)6][Te2Cl10].
Polyhedron 2002, 21, 1089−1095.
(45) Krossing, I.; Reisinger, A. Perfluorinated Alkoxyaluminate Salts
of Cationic Brønsted Acids: Synthesis, Structure, and Characterization
of [H(OEt2)2][Al{OC(CF3)3}4] and [H(THF)2][Al{OC(CF3)3}4].
Eur. J. Inorg. Chem. 2005, 2005, 1979−1989.
(46) Schnaars, D. D.; Wu, G.; Hayton, T. W. Reactivity of
UI4(OEt2)2 with phenols: probing the chemistry of the U−I bond.
Dalton Trans. 2009, 3681−3687.
(47) Nachtigall, O.; Pataki, A.; Molski, M.; Lentz, D.; Spandl, J.
Solvates of Manganese Trichloride Revisited - Synthesis, Isolation,
and Crystal Structure of MnCl3(THF)3. Z. Anorg. Allg. Chem. 2015,
641, 1164−1168.
(48) Stasko, D.; Hoffmann, S. P.; Kim, K.-C.; Fackler, N. L. P.;
Larsen, A. S.; Drovetskaya, T.; Tham, F. S.; Reed, C. A.; Rickard, C. E.
F.; Boyd, P. D. W.; Stoyanov, E. S. Molecular Structure of the
Solvated Proton in Isolated Salts. Short, Strong, Low Barrier (SSLB)
H-bonds. J. Am. Chem. Soc. 2002, 124, 13869−13876.
(49) Hazin, K.; Serin, S. C.; Patrick, B. O.; Ezhova, M. B.; Gates, D.
P. [HL2][P(1,2-O2C6Cl4)3] (L = THF, DMF): Brønsted acid
initiators for the polymerization of n-butyl vinyl ether and p-
methoxystyrene. Dalton Trans. 2017, 46, 5901−5910.
(65) Kohner-Kerten, A.; Tshuva, E. Y. Preparation and X-ray
characterization of two-coordinate Cu(I) complex of aliphatic thiolato
ligand: Effect of steric bulk on coordination features. J. Organomet.
Chem. 2008, 693, 2065−2068.
(66) Dance, I. G. Formation and X-ray structure of the hexa(t-
butylthiolato)pentacuprate(I) monoanion. J. Chem. Soc., Chem.
Commun. 1976, 68−69.
(50) Ankudinov, A. L.; Ravel, B.; Rehr, J. J.; Conradson, S. D. Real-
space multiple-scattering calculation and interpretation of x-ray-
absorption near-edge structure. Phys. Rev. B: Condens. Matter Mater.
Phys. 1998, 58, 7565−7576.
(67) Bowmaker, G. A.; Clark, G. R.; Seadon, J. K.; Dance, I. G. The
formation and structural chemistry of the hexa(μ-t-butylthiolato)
pentacuprate(I) cage anion with triethylammonium and tetraethy-
lammonium cations. Polyhedron 1984, 3, 535−544.
(51) Nguyen, T.-A. D.; Goldsmith, B. R.; Zaman, H. T.; Wu, G.;
Peters, B.; Hayton, T. W. Synthesis and Characterization of a Cu14
Hydride Cluster Supported by Neutral Donor Ligands. Chem. - Eur. J.
2015, 21, 5341−5344.
(68) Fujisawa, K.; Imai, S.; Kitajima, N.; Moro-oka, Y. Preparation,
Spectroscopic Characterization, and Molecular Structure of Copper-
(I) Aliphatic Thiolate Complexes. Inorg. Chem. 1998, 37, 168−169.
(69) Dance, I. G. The hepta(μ2-benzenethiolato)pentacuprate(I)
dianion; X-ray crystal and molecular structure. J. Chem. Soc., Chem.
Commun. 1976, 103b−104.
(52) Dehnen, S.; Fenske, D.; Deveson, A. C. [Cu12S6(PnPr3)8] and
[Cu20S10(PnButBu2)8]: Two sulfur bridged copper clusters with Cu-S
cluster cores of known compositions but new structures. J. Cluster Sci.
1996, 7, 351−369.
(70) Dance, I. The Hepta(μ-benzenethiolato)pentametallate(I)
dianions of copper and silver: Formation and crystal structures.
Aust. J. Chem. 1978, 31, 2195−2206.
(53) Yang, X.-X.; Issac, I.; Lebedkin, S.; Kuhn, M.; Weigend, F.;
̈
̈
(71) Ferrara, S. J.; Mague, J. T.; Donahue, J. P. Synthesis and
Structures of Cuprous Triptycylthiolate Complexes. Inorg. Chem.
2012, 51, 6567−6576.
Fenske, D.; Fuhr, O.; Eichhofer, A. Red-luminescent biphosphine
stabilized ‘Cu12S6’ cluster molecules. Chem. Commun. 2014, 50,
11043−11045.
̈
̈
(72) Yang, Q.; Tang, K.; Liao, H.; Han, Y.; Chen, Z.; Tang, Y.
(54) Eichhofer, A.; Buth, G.; Lebedkin, S.; Kuhn, M.; Weigend, F.
Luminescence in Phosphine-Stabilized Copper Chalcogenide Cluster
MoleculesA Comparative Study. Inorg. Chem. 2015, 54, 9413−
9422.
i
Synthesis and X-ray crystal structure of [Cu(SC6H2 Pr3)]8. J. Chem.
Soc., Chem. Commun. 1987, 1076−1077.
(73) Block, E.; Gernon, M.; Kang, H.; Ofori-Okai, G.; Zubieta, J.
Coordination chemistry of sterically hindered thiolate ligands.
Preparation and structural characterization of the oligomeric
homoleptic complexes [Cu(SC6H4-o-SiMe3)]12 and [{Ag(SC6H4-o-
SiMe3)}4]2 and a comparison to the structure of the cadmium
mononuclear species (Et4N)2[Cd(SC6H4-o-SiMe3)4]. Inorg. Chem.
1989, 28, 1263−1271.
(55) Salehi, Z.; Parish, R. V.; Pritchard, R. G. A polymeric cationic
copper(I) complex involving a quadruply bridging, zwitterionic
thiolate ligand: {[Cu8Cl6(SCH2CH2NH3)6]Cl2}. J. Chem. Soc., Dalton
Trans. 1997, 4241−4246.
(56) Block, E.; Kang, H.; Ofori-Okai, G.; Zubieta, J. The crystal and
molecular structure of a tetranuclear copper thiolate cluster,
[Cu{SC6H3-2,6-(SiMe3)2}]4. Inorg. Chim. Acta 1990, 167, 147−148.
(74) Blower, P. J.; Dilworth, J. R. Thiolato-complexes of the
transition metals. Coord. Chem. Rev. 1987, 76, 121−185.
(75) Vortisch, V.; Kroneck, P.; Hemmerich, P. Model studies on the
coordination of copper in enzymes. IV. Structure and stability of
cuprous complexes with sulfur-containing ligands. J. Am. Chem. Soc.
1976, 98, 2821−2826.
(76) Tang, K.; Aslam, M.; Block, E.; Nicholson, T.; Zubieta, J. Steric
control of aggregation in neutral silver(I) thiolates, [AgSR]n. Crystal
and molecular structures of [AgSCH(SiMe3)2]8, a discrete molecular
biscycle of weakly interacting [AgSCH(SiMe3)2]4 units, and of
[AgSC(SiPhMe2)3]3 and [AgSC(SiMe3)3]4, discrete molecular mono-
cycles containing linearly coordinated silver(I) and doubly bridging
mercapto sulfur donors from novel sterically hindered thiolate ligands.
̈
̈
(57) Schroter-Schmid, I. S. J.; Strahle, J. Synthese und Struktur von
Thiolatokomplexen des einwertigen Kupfers: Tetrameres und
Octameres [CuSC6H2(iPr)3]. Z. Naturforsch., B: J. Chem. Sci. 1990,
45, 1537−1542.
(58) Dance, I. G.; Calabrese, J. C. The crystal and molecular
structure of the hexa-(μ2-benzenethiolato)tetracuprate(I) dianion.
Inorg. Chim. Acta 1976, 19, L41−L42.
(59) Coucouvanis, D.; Murphy, C. N.; Kanodia, S. K. Metal-
mercaptide chemistry. The synthesis and structural characterization of
the [Cu(SC6H5)3]2‑ anion. A rational synthesis and the structure of
the [Cu4(SC6H5)6]2‑ cluster. Inorg. Chem. 1980, 19, 2993−2998.
(60) Dance, I. G.; Bowmaker, G. A.; Clark, G. R.; Seadon, J. K. The
formation and crystal and molecular structures of hexa(μ-
organothiolato)tetracuprate(I) cage dianions: bis-
(tetramethylammonium)hexa-(μ-methanethiolato)tetracuprate(I)
and two polymorphs of bis(tetramethylammonium)hexa-(μ-benzene-
thiolato)-tetracuprate(I). Polyhedron 1983, 2, 1031−1043.
A
comparison with the nonmolecular structure of
1
[Ag4{SCH2(SiMe3)}3]n . Inorg. Chem. 1987, 26, 1488−1497.
(77) Dance, I. G.; Fisher, K. J.; Banda, R. M. H.; Scudder, M. L.
Layered structure of crystalline compounds AgSR. Inorg. Chem. 1991,
30, 183−187.
J
DOI: 10.1021/acs.inorgchem.9b01140
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(78) Bratsch, S. G. Standard Electrode Potentials and Temperature
Coefficients in Water at 298.15 K. J. Phys. Chem. Ref. Data 1989, 18,
1−21.
(79) Dance, I. G. Crystallization and structure of bis-
(tetramethylammonium) octakis(benzenethiolato)hexaargentate(I),
extending the series of cages [M4(SPh)6]2‑, [M5(SPh)7]2‑,
[M6(SPh)8]2‑, and [M12(SPh)16]4‑. Inorg. Chem. 1981, 20, 1487−
1492.
(80) Battisti, A.; Bellina, O.; Diversi, P.; Losi, S.; Marchetti, F.;
Zanello, P. Preparation, Structure and Reactivity of Polynuclear
Gold(I) Phosphanyl Alkanethiolates. Eur. J. Inorg. Chem. 2007, 2007,
865−875.
(81) Al-Sa’ady, A. K. H.; Moss, K.; McAuliffe, C. A.; Parish, R. V.
̈
Mossbauer and nuclear magnetic resonance spectroscopic studies on
‘Myocrisin’, ‘Solganol’, ‘Auranofin’, and related gold(I) thiolates. J.
Chem. Soc., Dalton Trans. 1984, 1609−1616.
(82) Kyle, K. R.; Palke, W. E.; Ford, P. C. The photoluminescence
properties of the copper(I) clusters Cu4I4A4 (A = aromatic amine) in
solution. Coord. Chem. Rev. 1990, 97, 35−46.
(83) Knotter, D. M.; Blasse, G.; Van Vliet, J. P. M.; Van Koten, G.
Luminescence of copper(I) arenethiolates and its relation to
copper(I) luminescence in other complexes. Inorg. Chem. 1992, 31,
2196−2201.
(84) Ford, P. C.; Vogler, A. Photochemical and Photophysical
Properties of Tetranuclear and Hexanuclear Clusters of Metals with
d10 and s2 Electronic Configurations. Acc. Chem. Res. 1993, 26, 220−
226.
(85) Ford, P. C.; Cariati, E.; Bourassa, J. Photoluminescence
Properties of Multinuclear Copper(I) Compounds. Chem. Rev. 1999,
99, 3625−3648.
(86) Wang, X.-L.; Qin, C.; Wang, E.-B.; Su, Z.-M.; Li, Y.-G.; Xu, L.
Self-Assembly of Nanometer-Scale [Cu24I10L12]14+ Cages and Ball-
Shaped Keggin Clusters into a (4,12)-Connected 3D Framework with
Photoluminescent and Electrochemical Properties. Angew. Chem., Int.
Ed. 2006, 45, 7411−7414.
(87) Maiti, B. K.; Pal, K.; Sarkar, S. Flexible CuI−Thiolate Clusters
with Relevance to Metallothioneins. Eur. J. Inorg. Chem. 2007, 2007,
5548−5555.
(88) Li, Z.; Li, X.; Lin, P.; Du, S. Self-assembly of 1D Coordination
Polymers Containing Copper(I) tert-butylthiolato Clusters: Structural
Characterization and Properties. J. Cluster Sci. 2008, 19, 357−366.
(89) Troyano, J.; Perles, J.; Amo-Ochoa, P.; Martínez, J. I.;
́
́
Concepcion Gimeno, M.; Fernandez-Moreira, V.; Zamora, F.;
Delgado, S. Luminescent Thermochromism of 2D Coordination
Polymers Based on Copper(I) Halides with 4-Hydroxythiophenol.
Chem. - Eur. J. 2016, 22, 18027−18035.
K
DOI: 10.1021/acs.inorgchem.9b01140
Inorg. Chem. XXXX, XXX, XXX−XXX