Halide-controlled construction and structural determination of a series of thiolato-bridged 16-nuclear copper(I) clusters from benzothiazoline

Article abstract of DOI:10.1246/cl.2012.334

Treatment of [Cu(CH₃CN)₄]⁺ with 2-(4-dimethylaminophenyl) benzothiazoline in the presence of halide ions (X = Cl^-, Br^-, and I^-) gave [Cu₁₆L ₁₂X]³⁺ (L = (C₆H₄NMe ₂)CH=N- (C₆H₄)S^-) with a spherical Cu16S12 structure, while similar treatment in the absence of halide ions afforded [Cu₈L₈]²⁺ with a cyclic Cu ₈S₈ structure.

Full text of DOI:10.1246/cl.2012.334

doi:10.1246/cl.2012.334
334
Published on the web February 29, 2012
Halide-controlled Construction and Structural Determination of a Series
of Thiolato-bridged 16-Nuclear Copper(I) Clusters from Benzothiazoline
Yusuke Takino,1 Nobuto Yoshinari,1 Kiyoshi Tsuge,2 Tatsuya Kawamoto,3 and Takumi Konno*1
1Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043
2Department of Chemistry, Graduate School of Science and Engineering, University of Toyama,
3190 Gofuku, Toyama 930-8555
3Department of Chemistry, Faculty of Science, Kanagawa University, Hiratsuka, Kanagawa 259-1293
(Received December 5, 2011; CL-111164; E-mail: konno@chem.sci.osaka-u.ac.jp)
Treatment of [Cu(CH3CN)4]+ with 2-(4-dimethylaminophen-
¹
yl)benzothiazoline in the presence of halide ions (X = Cl ,
¹
¹
Br , and I ) gave [Cu16L12X]3+ (L = (C6H4NMe2)CH=N-
¹
(C6H4)S ) with a spherical Cu16S12 structure, while similar
treatment in the absence of halide ions afforded [Cu8L8]2+ with a
cyclic Cu8S8 structure.
Over the past decades, thiolato-bridged multinuclear copper
species have attracted considerable attention not only in the field
of inorganic chemistry because of their intriguing structural
versatility,1 but also in the field of biological chemistry because
of their relevance to structural models of copper-containing
metalloenzymes.2 To date, a large number of thiolato-bridged
copper compounds with different nuclearities and electronic
states have been prepared,3,4 thanks to the diversity of
coordination geometries and oxidation states for copper ions in
combination with the diversity of bridging modes for thiolate
groups. In some cases, the structures of this class of compounds
have been controlled by external factors such as reaction ratios,
ancillary ligands, and reaction solvents.3 However, this is almost
limited to low-nuclearity systems, and the finding of an external
factor that leads to the rational construction of copper species
with a high nuclearity is a current concern in thiolato-bridged
copper chemistry. In our successive study on the reactivity of
2-substituted benzothiazolines toward transition-metal ions,5
we have recently found that the reaction of copper(II) with
Scheme 1. Synthetic routes of 1, 2, 3, and 4.
copper structures are rationally expanded by halide ions
(Scheme 1).7
The reaction of [Cu(CH3CN)4]PF6 in acetonitrile with
equimolar 2-(4-dimethylaminophenyl)benzothiazoline in chloro-
form gave a brown solid, which was crystallized from a mixture
of methanol and chloroform to produce black crystals 1 in a
satisfactory yield.8,9 Compound 1 was confidently assigned as a
2
equivalents of 2-(4-dimethylaminophenyl)benzothiazoline
affords a unique thiolato-bridged 8-nuclear copper complex,
¹
¹
[Cu8L8]+ (L = (C6H4NMe2)CH=N(C6H4)S ), which is convert-
PF6 salt of [Cu8L8]2+, based on its absorption spectrum that
ed to [Cu8L8]2+ under aerobic conditions with retention of its
cyclic-ladder Cu8S8 core structure.6 In this reaction, 2-(4-
dimethylaminophenyl)benzothiazoline acts not only as a pre-
cursor of ligand but also as a reducing agent of copper(II) to
produce [Cu8L8]+, in which the copper ions virtually exit as a
+1 oxidation state with one electron being delocalized over the
Cu8S8 core. This is indicative of the possible formation of
[Cu8L8]+/2+ from the reaction of copper(I) with equimolar 2-(4-
dimethylaminophenyl)benzothiazoline, which prompted us to
investigate this 1:1 reaction. While this reaction gave [Cu8L8]2+
as a major product, we found the formation of a novel thiolato-
exhibits a characteristic intense near-infrared band at around
1220 nm,6 besides its 1H NMR spectrum (Figure 1a) and
elemental analysis.10 On the other hand, a similar crystallization
procedure from chloroform led to the production of red
microcrystals 2 as a minor product, together with black crystals
of 1.8 When the mixture of 1 and 2 was treated with methanol,
only 2 was dissolved to give a dark red solution, from which
single crystals of 2¢6MeOH suitable for X-ray crystallography
were obtained.8
The structure of 2¢6MeOH, determined by X-ray analysis,
revealed the presence of a twelfth of complex cation and a
¹
¹
bridged 16-nuclear copper(I) cluster with a central Cl ion as a
quarter of PF6 anion, besides solvated methanol in the
minor product when chloroform was used as a solvent. Notably,
asymmetric unit.11 The entire complex-cation of 2 ([Cu16L12-
¹
this compound was effectively formed by adding Cl ions. In
Cl]3+) contains sixteen Cu atoms, twelve iminothiolate ligands
¹
¹
this paper, we report on these intriguing results, together with
the preparation and structural characterization of analogous
(L = (C6H4NMe2)CH=N(C6H4)S ), and one central Cl ion.
Considering the total charge of the complex-cation and the
monoanionic nature of the iminothiolate ligand, each Cu atom
in 2 is assigned to have a +1 oxidation state. As shown in
¹
¹
16-nuclear copper(I) compounds with a central Br or I ion,
which demonstrate for the first time that thiolato-bridged
Chem. Lett. 2012, 41, 334-336
© 2012 The Chemical Society of Japan
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335
structure. In 2, each L ligand bridges four Cu atoms using ¯3-
thiolate and ¯1-imine groups. The coordination geometry of CuI
atoms in 2 is best described as distorted ClS3 trigonal pyramid
and NS2 trigonal plane for those in the tetrahedral [Cu4Cl]3+
core and the [Cu3L3] ring-units, respectively.
Unlike the absorption spectrum of 1, no near-infrared band
is observed in the absorption spectrum of 2 in acetonitrile. This
is compatible with the assignment of the +1 oxidation state for
all Cu atoms in 2, with the lack of electron(s) delocalized over
the S-bridged core structure.6 In the 1H NMR spectrum in
acetonitrile-d3, 2 exhibits a single set of signals (nine 1H
aromatic and one 6H methyl proton signals) for twelve L ligands
in the complex (Figure 1b), suggestive of the retention of the T
symmetric structure found in the crystal.8 Consistent with this,
the ESI mass spectrum of 2 in acetonitrile gave a cluster of
signals centered at m/z 1372, the calculated mass and the
isotopic distribution of which match well with those for
[Cu16L12Cl]3+ (Figure S1).8
Figure 1. 1H NMR spectra of (a) 1 in 1,2-dichloroethane-d4
and (b) 2, (c) 3, and (d) 4 in acetonitrile-d3 at 0 °C (aromatic
proton region).
To check whether 2 is formed in preference to 1 in the
¹
presence of a sufficient amount of Cl ions, an acetonitrile
solution of [Cu(CH3CN)4]PF6 was treated with equimolar 2-(4-
dimethylaminophenyl)benzothiazoline dissolved in chloroform
in the presence of excess Bu4NCl.8 As a result, only a red
powder of 2 was produced in a moderate yield from this
solution.14 In addition, 2 was obtained in a higher yield by the
reaction of [Cu(CH3CN)4]PF6 with 2-(4-dimethylaminophenyl)-
benzothiazoline in a stoichiometric ratio of 4:3 in the presence of
¹
excess Bu4NCl.8 These results imply that a Cl ion acts as a
template for the construction of the spherical Cu16S12 structure
¹
in 2. The template effect due to Cl was confirmed by the
1H NMR spectroscopy of the 4:3 reaction solution of [Cu-
(CH3CN)4]PF6 and 2-(4-dimethylaminophenyl)benzothiazoline
1
in methanol-d4/acetonitrile-d3. That is, the H NMR spectrum
before adding Bu4NCl showed complicated, multiple proton
signals, while a single set of signals for 2 appeared dominantly
1
in the H NMR spectrum after adding Bu4NCl (Figure S2).8
When [Cu(CH3CN)4]PF6 was treated with 2-(4-dimethyl-
aminophenyl)benzothiazoline in a 4:3 ratio by adding Bu4NBr or
Bu4NI, instead of Bu4NCl, a reddish powder 3 or 4 was obtained
in a reasonable yield.8 The elemental analyses of 3 and 4 were in
agreement with the formulas for [Cu16L12X]3+ (X = Br for 3,
X = I for 4),15,16 and the presence of Br or I atoms in 3 or 4 was
confirmed by the X-ray fluorescence spectrometry. In addition,
the 1H NMR spectrum of each of 3 and 4 in acetonitrile-d3 gives
a single set of signals, the chemical shifts of which are very
similar to those for 2 (Figures 1c and 1d). Judging from these
results, together with the absence of intense near-infrared bands
in the absorption spectra, 3 and 4 are assigned a spherical
copper(I) structure analogous to 2. This was unambiguously
confirmed by single-crystal X-ray analyses.17,18 The overall
structure of the complex-cation ([Cu16L12X]3+) in each of 3 and
Figure 2. Perspective views of (a) the tetrahedral [Cu4Cl]3+
core, (b) the hexagonal [Cu3L3] ring, (c) the overall structure of
[Cu16L12Cl]3+, and (d) the double-layer structure accommodat-
ing a chloride ion in 2. H atoms are omitted for clarity. Cu:
brown, S: yellow, Cl: green, C: gray, N: blue.
Figure 2, the complex-cation consists of a tetrahedral [Cu4Cl]3+
¹
core, in which a central Cl ion is bound by four Cu atoms in
a tetrahedral geometry (Cu-Cl = 2.4991(5) ¡), and four outer
[Cu3L3] units, in which three Cu atoms are alternately bridged
by three S atoms from three L ligands to form a hexagonal ring
(av. Cu-S = 2.290(14) ¡). The four [Cu3L3] ring-units, which
are connected with each other through Cu-N bonds (2.004(2) ¡),
are in a tetrahedral arrangement, and they bind to the tetrahedral
[Cu4Cl]3+ core through Cu-S bonds (2.3287(6) ¡). This binding
fashion completes a unique T symmetric cluster structure with a
diameter of ca. 21 ¡, in which a spherical Cu16S12 layer that
¹
¹
4 is very similar to that in 2, except the presence of Br or I in
¹
place of Cl in 2 (Figures 3 and S3).8 As expected, the Cu-X
¹
bond distances increase in the order X = Cl (2.4991(5) ¡) <
¹
¹
¹
accommodates a Cl ion is covered by an organic layer. As far
Br (2.5819(4) ¡) < I (2.6589(8) ¡). However, the differences
are rather small relative to those in the ionic radius between the
as we know, 2 is the first structurally characterized thiolato-
bridged copper(I) cluster having a 16 nuclearity.12 Note that
there exist six sets of intramolecular ³-³ interaction (3.63(2) ¡)
between N,S-bridging phenyl rings and pendent phenyl rings in
the organic layer,13 which appears to support this spherical
¹
¹
¹
halide ions (Cl = 1.81 ¡, Br = 1.96 ¡, and I = 2.20 ¡).19 In
addition, the distances between the central halide ion and the
center of each Cu3S3 ring in 2 (3.007(1) ¡), 3 (3.001(2) ¡), and
4 (3.025(5) ¡) are essentially the same. Thus, the size of the
Chem. Lett. 2012, 41, 334-336
© 2012 The Chemical Society of Japan
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336
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Supporting Information is available electronically on the CSJ-
Journal Web site, http://www.csj.jp/journals/chem-lett/index.
html.
Figure 3. Perspective views of the Cu16S12X core structure in
(a) 2, (b) 3, and (c) 4. Cu: brown, S: yellow, Cl: green, Br: red-
brown, I: purple.
Cu16S12 sphere is little affected by the accommodated halide ion.
This is most likely due to the outer organic layer, the size of
which is predetermined by the multiple intramolecular ³-³
interactions.
6
7
In summary, we showed that 2-(4-dimethylaminophenyl)-
benzothiazoline readily reacts with copper(I) ion in the presence
of chloride ions to form the novel 16-nuclear copper(I) cluster
having a central chloride ion, [Cu16L12Cl]3+. This cluster was
found to possess a unique spherical double-layer structure, in
which the organic layer covers the inner Cu16S12 spherical
framework. The presence of bromide or iodide ions afforded
analogous spherical clusters with a central bromide or iodide
ion. While a number of discrete multinuclear species that
accommodate a halide ion in the center have been pre-
pared,1a,4a-4d,20 reports on the construction and structural
determination of a series of multinuclear compounds with a
chloride, bromide, or iodide ion are quite rare.4d Finally, it
should be noted that a similar reaction in the absence of halide
8
9
Calcd for 1¢2CHCl3: C, 47.58; H, 3.99; N, 7.28%. Found: C,
47.63; H, 4.09; N, 7.36%. Yield: 75%.
10 The exclusive production of 1 by the crystallization from
methanol/chloroform is likely in part due to the high solubility
¹
of 2 in methanol, as well as the lack of Cl ions in this solution.
ꢀ
11 Crystal data for 2¢6MeOH, Cubic, Fd3c, a = 43.5328(8) ¡,
¹3
V = 82499(5) ¡3, Z = 16, T = 200(2) K, Dcalcd = 1.528 g cm
,
ions gave only the cyclic 8-nuclear copper cluster, [Cu8L8]2+
.
188243 reflections measured, 3942 independent (Rint = 0.136),
R1 = 0.056 (I > 2·(I)), wR2 = 0.165 (all data).21,22 CCDC-
855296.
This demonstrates that halide ions act as a template for the
construction of [Cu16L12X]3+ and that the 16- and 8-nuclear
copper structures are controlled by the presence/absence of
halide ions. Halide-controlled construction of thiolato-bridged
copper clusters with use of other benzothiazolines is currently
underway in our laboratory.
12 A similar spherical Cu16S12 framework, which possesses a
Se2¹ ion in the center, has been found in [Cu20Se(SPh)12-
(OAc)6(PPh3)4].3c
13 C. A. Hunter, J. K. M. Sanders, J. Am. Chem. Soc. 1990, 112,
5525.
14 Calcd for 2¢7H2O: C, 46.22; H, 4.18; N, 7.19%. Found: C,
46.19; H, 4.14; N, 7.20%. Yield: 40%.
15 Calcd for 3¢9H2O: C, 45.44; H, 4.19; N, 7.07%. Found: C,
45.47; H, 3.91; N, 7.03%. Yield: 74%.
This work was supported in part by Grants-in-Aids for
Science Research (No. 23107517) from the Ministry of Educa-
tion, Culture, Sports, Science and Technology of Japan.
16 Calcd for 4¢2CuI¢2H2O: C, 42.73; H, 3.67; N, 6.64%. Found:
C, 42.44; H, 3.64; N, 6.60%. Yield: 67%.
ꢀ
References and Notes
17 Crystal data for 3¢6MeOH, Cubic, Fd3c, a = 44.0618(6) ¡,
¹3
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,
215493 reflections measured, 4090 independent (Rint = 0.058),
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855297.
ꢀ
18 Crystal data for 4¢6MeOH, Cubic, Fd3c, a = 44.2098(16) ¡,
¹3
V = 86408(9) ¡3, Z = 16, T = 200(2) K, Dcalcd = 1.487 g cm
,
196933 reflections measured, 4139 independent (Rint = 0.149),
R1 = 0.070 (I > 2·(I)), wR2 = 0.208 (all data).21,22 CCDC-
855298.
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Chem. Lett. 2012, 41, 334-336
© 2012 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/