The trinuclear copper(I) thiolate complexes[Cu3(NGuaS) 3]0/1+ and their Dimeric Variants [Cu6(NGuaS) 6]1+/2+/3+ with biomimetic redox properties

Article abstract of DOI:10.1002/anie.201008076

A mixed-valent redox-active copper thiolate complex is formed in the reaction of [Cu(MeCN)₄]PF₆ with a CPh₃ thioether by a combination of homo- and heterolytic cleavage of the S-CPh ₃ bond. In its oxidized state, the hexanuclear copper sulfur cluster (see picture) has the same average metal oxidation state as the dinuclear copper thiolate center of cytochrome c oxidase or N₂O reductase. Copyright

Full text of DOI:10.1002/anie.201008076

DOI: 10.1002/anie.201008076
Copper Sulfur Clusters
The Trinuclear Copper(I) Thiolate Complexes[Cu3(NGuaS)3]0/1+ and
their Dimeric Variants [Cu6(NGuaS)6]1+/2+/3+ with Biomimetic Redox
Properties**
Adam Neuba, Ulrich Flꢀrke, Wolfram Meyer-Klaucke, Marco Salomone-Stagni, Eckhardt Bill,
Eberhard Bothe, Petra Hꢀfer, and Gerald Henkel*
Dedicated to Professor Wolfgang Kaim on the occasion of his 60th birthday
As the active participant of various electron-transport chains,
the element copper plays a central role in biology.[1] This
privileged position can be traced back to specific redox
properties originating in the unique interplay between
demands of d9 and d10 copper atoms towards coordination
geometries and ligand fields. In this respect, sites for mono-
nuclear coordination (e.g., in azurin and plastocyanin) are
conditioned by matrix effects of the protein surroundings.[2]
Similar matrix effects are experienced by dinuclear systems,
such as CuA present in cytochrome-c oxidases or N2O
reductases, which contain copper atoms bridged by two
thiolate donor functions.[3]
Artificial reconstruction of these biologically active
copper sites to model their characteristic properties in the
laboratory failed to date because of difficulties in replacing
the natural matrix effects by suitable other influences. This
problem also holds for model complexes of CuA within
cytochrome-c oxidases or N2O reductases,[4] which—in spite
of similarities with respect to coordination numbers and
ligand fields—often differ very significantly from their
archetypes in their redox properties and the degree of
stretching of their central {Cu2S2} rhombus.[5] In addition,
there are numerous other examples of dinuclear thiolate
complexes which differ even further from the natural CuA.[6]
Searching for solutions to the problem of (biological)
matrix packaging[7] we have prepared new thiolate ligands
from peralkylated guanidine residues to model the biological
N,S donor set and to control the reorganization energies of
the corresponding copper complexes as they pass through
different metal oxidation states.
In the course of these investigations, we have also
encountered polynuclear complexes with rigid geometries.
We must assume that these complexes can only respond to
changes in individual metal oxidation states by undergoing
very small distortions.
In a detailed study, we have examined the influence of the
guanidine thiolate ligand NGuaSꢀ on the structural and
electrochemical characteristics of its copper complexes and
found that CuSPh reacts with NGuaS–SGuaN giving the
cyclic trinuclear CuI complex [Cu3(NGuaS)3] (1) after reduc-
tive splitting of the disulfide bridge by thiophenolate ions
(Scheme 1a and Figure 1). Complex 1 can be electrochemi-
[*] Dr. A. Neuba, Dr. U. Flꢀrke, Prof. Dr. G. Henkel
Fakultꢁt fꢂr Naturwissenschaften
Department Chemie, Universitꢁt Paderborn
Warburger-Strasse 100, 33098 Paderborn (Germany)
Fax: (+49)5251-60-3423
E-mail: biohenkel@uni-paderborn.de
Dr. W. Meyer-Klaucke, Dr. M. Salomone-Stagni
EMBL-Outstation Hamburg
Scheme 1. Syntheses of 1 (a) and 2(PF6)2 (b).
Gebꢁude 25A, Notkestrasse 85, 22603 Hamburg (Germany)
Dr. E. Bill, Dr. E. Bothe, P. Hꢀfer
Max-Planck-Institut fꢂr Bioanorganische Chemie
Stiftstrasse 34–36, 45470 Mꢂlheim an der Ruhr (Germany)
cally oxidized to the monocation 1+ at ꢀ0.320 V (reference
Fc/Fc+; Fc = [(C5H5)2Fe]). The associated reduction wave of
the quasi-reversible process occurs at ꢀ0.640 V. Though we
were not able to characterize the electrochemically oxidized
species further, indications of its structure emerged from the
analysis of a trinuclear complex of empirical formula [Cu3-
(NGuaS)3I] (1I), which we obtained in the course of inves-
tigations using CuI in place of CuSPh. The core of complex 1I
(Figure 2) is arranged in the same way to that of 1 (see below)
as a strongly distorted Cu3S3 heterocycle, but is characterized
[**] We thank the German research council (DFG) and the Federal
Ministry of education and research (BMBF) for continuous support
of our work. A.N. thanks the University of Paderborn for granting a
doctorate scholarship. We thank HASYLAB for providing beamline
E4 within the scope of the project I-20090150 and Dr. Dariusz A.
Zajac for his support during the measuring time. NGuaS=
=
o-SC6H4N C(NMe2)2.
Supporting information (experimental details) for this article is
available on the WWW under http://dx.doi.org/10.1002/anie.
201008076.
Angew. Chem. Int. Ed. 2011, 50, 4503 –4507
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4503

Communications
a mean edge length of 2.654 ꢀ. They are connected by m2-S
bridges from the three thiolate groups and coordinated in a
distorted trigonal-planar manner. Each copper atom is part of
a five-membered chelate ring with a S-Cu-N angle of 88.68
(average). The S-Cu-S angles vary more and are 151.5(2),
145.6(2), and 126.5(2)8 for Cu(11), Cu(13), and Cu(12),
respectively. The trinuclear complexes [Cu3(SC6H4NMe2)3]
and [Cu3(SC6H4CH(Me)NMe2)3] with comparable ligand
donor sets have different S-Cu-N chelate and S-Cu-S angles.[8]
Reaction of the thioether NGuaS-CPh3 with [Cu-
(MeCN)4]PF6 (Scheme 1b) leads to the complex cation
[{CuI2CuII(NGuaS)3}2]2+ (2), which could be isolated as the
hexafluorophosphate salt. This cation formally represents the
dimeric variant of the oxidized trinuclear compound 1+
(Figure 5). The mechanism of the complex formation is not
completely understood. We suppose that in the first step CuI
ꢀ
induces a heterolytic cleavage of the S CPh3 bond followed
by reaction with the thus generated guanidine-thioate ions to
form multinuclear precursor complexes (possibly also in form
of compound 1). In the next step, thiyl radicals, as inter-
mediates in a homolytic splitting of other thioether molecules,
could initiate partial oxidation of these complexes and their
transformation or dimerization to the isolable mixed-valent
hexanuclear species 2. The rearrangement associated with the
oxidation of 1 to 1+ would favor the first linking step between
two trinuclear complexes through the formation of a m3-S
bridge and subsequently would result in a reorientation of the
nitrogen donor functions in the resulting hexanuclear com-
plex.
Figure 1. Structure of [Cu3(NGuaS)3] (1) in the crystalline state.
Our hypothesis that a homolytic thioether splitting is also
occurring finds support in the formation of compound 3,
which is isolated as a by-product and whose existence is
compatible with the appearance and the supposed reactivity
of intermediate triphenylmethane radicals (see Scheme 1b).
The higher oxidation state of the copper in 2(PF6)2 in
comparison to the situation in 1 emerges not only indirectly
from the charge balance in the crystal, but is also detected
directly from the energy of the CuK edges in the correspond-
ing X-ray absorption spectra. The experimental values of
8980.1 eV for 1 and of 8981.5 eV for 2(PF6)2 confirm the
interpretation derived from the crystal structural analysis
unequivocally. Besides the shifting of the absorption edge
which reflects the change of the mean oxidation state of the
copper ions, 2(PF6)2 shows, in comparison to 1, increasing
intensity in the shoulder region of the absorption edge at
8980 eV presumably caused by the higher number of sulfur
donor atoms.
Compound 2(PF6)2 can be recrystallized from acetonitrile
without decomposition. In the crystal structure all the copper
atoms are identical, in agreement with complete valence
delocalization.[9] The UV/Vis/NIR spectrum shows a distinc-
tive absorption band at 1117 nm (Figure 3, black curve) as
well as a further transition at 960 nm partly hidden by the first
band. The 1117 nm band has an extinction coefficient of e =
6.9 ꢁ 104 mꢀ1 cmꢀ1 with a full width at half maximum (FWHM)
of Dn1/2,exp. = 1400 cmꢀ1. This value remains far below the
value of 4130 cmꢀ1 which according to Hush is the base for
weakly coupled mixed-valent systems.[10] Consequent, 2
should represent a class III system (that is, fully delocalized)
Figure 2. Structure of [Cu3(NGuaS)3I] (1I) in the crystalline state.
by three chemically distinct copper atoms. While the copper
center with a S2N2 donor set and the coordination number
four is assumed to be CuII, the two copper atoms in trigonal
coordination environments with S2N and S2I donor sets,
respectively, are monovalent. Apparently, 1I is a mixed-
valence complex in which the different metal oxidation states
are localized. Presumably, the conditions in the electrochemi-
cally generated species 1+ are comparable, because the
separation of about 320 mV between the redox waves
suggests a chemically rearranged complex with localized CuI
and CuII centers.
As we can show in this work, the dimeric variant of 1+ is a
complex with complete valence delocalization. The passage
through different metal oxidation states is likely not associ-
ated with rearrangement processes, because the separations
between the redox waves are at DE = 71 and 75 mV, very
close to the thermodynamically required value (59 mV).
[Cu3(NGuaS)3] (1, Figure 1) crystallizes in the monoclinic
space group P21 with two independent molecules in the unit
cell. The copper atoms form a nearly equilateral triangle with
4504 www.angewandte.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2011, 50, 4503 –4507

purpose, complexes 2ox and 2red were coulometrically gener-
ated at ꢀ258C, independent of each other, from 2 in
quantitative reactions and characterized by their UV/Vis/
NIR spectra (Figure 3).
The spectrum of 2ox shows an intensive absorption band at
1145 nm which compared to the band of 2, is less intense and
has a small red shift. In the reduced species 2red this band is
even less intense and shifted to 1332 nm. Based on the large
extinction coefficients as well as the experimentally obtained
and calculated FWHMs (2ox: Dn1/2,exp. = 1450 cmꢀ1, Dn1/2,calcd
=
4090 cmꢀ1; 2red: Dn1/2,exp. = 1810 cmꢀ1, Dn1/2,calcd = 3790 cmꢀ1),
2ox and 2red also belong to valence-delocalized class III
systems with y!y* transitions. Compounds 2 and 2ox also
have sulfur-based ligand-to-metal charge transfer (LMCT)
transitions at 420, 530, and 640 nm, after reduction to 2red
these bands become very weak.
Figure 3. UV/Vis/NIR spectra of 2 (black), 2ox (red), and 2red (green)
(ꢀ258C, CH2Cl2).
According to the results of SQUID and NMR spectro-
scopic measurements, 2(PF6)2 behaves diamagnetically. The
electrochemically generated derivatives 2ox and 2red should be
paramagnetic species. This assumption was confirmed by
means of EPR measurements (2ox: g? = 2.06 and gk = 1.98;
according to the classification of Robin and Day.[9] The
observed absorption band is therefore assigned to the y!y*
transition in the [{CuI2CuII(NGuaS)3}2]2+ core. The ratio
Dn1/2,exp./Dn1/2,calcd of 0.33 indicates a fast electron transfer on
the time scale of solvent molecule movements.[11] Our
interpretation is also confirmed by the fact that the absorption
band at 1117 nm shows no solvent or temperature depend-
ence (Figures S10–S12 of the Supporting Information).[10g,h,11]
Like the trinuclear complex 1, the dimeric variant 2 also
has interesting redox properties. The cyclovoltammogram in
dichloromethane (Figure 4) shows two reversible redox
couples, one at + 0.296 V (DE = to 71 mV), the other one at
ꢀ0.652 V (DE = 75 mV; all potentials versus Fc/Fc+). Coulo-
metric measurements confirm two one-electron redox pro-
cesses. These results demonstrate that the stability range of 2
2
red: giso = 2.02). EPR spectra of 2ox and 2red show no hyperfine
splitting consistent with a valence delocalization over all the
copper atoms.
The complex cation 2 (Figure 5) is a molecular wheel with
one {Cu6S6} hub and a virtual axis. This hub consists of three
diamond-shaped {Cu2S2} units, which are linked to each other
ꢀ
by a total of six Cu S bonds. The result is a second set of three
other {Cu2S2} diamonds, which share common Cu–S edges
with the diamonds of the first set. These edges extend in
approximately parallel directions to the virtual axis of the
wheel.
Interestingly, the structural archetype of the {Cu6S6}
framework of 2 is seen in the metal–sulfur scaffoldings of
the hexanuclear sulfide–halide complexes of iron with
composition [Fe6S6X6]3ꢀ/2ꢀ (X = Cl, Br, I), for which the
term prismane cluster has been adopted.[12] In this complex
extends from the mixed-valent Cu+1.5 state (2ox: [CuI3CuII -
3
(NGuaS)6]3+) to Cu+1.33 (2: [CuI4CuII (NGuaS)6]2+) to the
2
reduced Cu+1.17 species (2red: [CuI5CuII(NGuaS)6]+). From the
difference of the redox potentials for 2, a comproportionation
constant Kc of 1019.8 can be calculated in complete accordance
with expectations for class III systems.[10g,h,11]
The proof of copper-based redox processes can be
provided by spectroelectrochemical measurements. For this
Figure 4. Cyclovoltammogram of 2(PF6)2 at 258C in CH2Cl2.
Figure 5. Structure of [Cu6(NGuaS)6]2+ (2) in the crystalline state.
Angew. Chem. Int. Ed. 2011, 50, 4503 –4507
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
4505

Communications
type, the sulfur atoms occupy the corners of an elongated
Keywords: copper sulfur complexes · cytochrome-c oxidase ·
enzyme models · electron transfer · mixed-valent compounds
.
octahedron, whilst the metal atoms form a metal-deficient
cube that can be derived from a regular one by removing two
corners along a body diagonal. The elongation of the sulfur
octahedron takes place along this body diagonal, which at the
same time coincides with the virtual axis of the {Cu6S6} hub.
An interesting variation of paddle-wheel like complexes
with {Cu6S6N6} cores, in which the six copper atoms are
arranged in an approximately octahedral manner, is found if
1,1-bifunctional N,S donor ligands are used.[13] This variant
contains only monovalent copper and has—compared to 2—a
slightly modified {Cu6S6} hub allowing for Cu···S contacts
parallel to the virtual axis of the wheel which are now much
longer than covalent bonds. Most probably, the very short
N···S distance in the ligand prevents chelate ring formation in
this case, which is a typical feature of 2 with its 1,2-
bifunctional N,S donor ligands. Interestingly, in a recently
described hexanuclear CuI compound containing 1,3-bifunc-
tional S,S-donor ligands, a {Cu6S6} core portion similar to that
in 2 is present. The basic structural difference between this
compound and 2 lies—besides the different metal oxidation
state—in the chemical identity and the arrangement of the
exogenous bound ligand donor functions which in the CuI
compound belong to the same Cu3S3 ring as the bridging
thiolate sulfur functions contrasting the situation in 2.[14]
The individual {Cu2S2} unit of 2 is a structural model for
the core portion of the CuA center of cytochrome-c oxidases
(and N2O reductases), and the oxidation state of the copper
atoms in the oxidized form 2ox coincides with the oxidized
form of the biological system.[15] This similarity also applies to
the Cu···Cu distance of 2.598 ꢀ which is only slightly shorter
in the biological system. The coordination environment of the
copper atoms within the {Cu2S2} diamond is completed by two
nitrogen donor functions of the exogenously bound guanidine
ligands, which take the place of two histidine residues of CuA,
and by two other sulfur donor functions from neighboring
diamonds. These sulfur donors take over the role of ligands
from the second co-ordination sphere of CuA and replace
secondarily bound methionin sulfur and carbonyl oxygen
donor functions.
[1] a) Metal Ions in Biological Systems, Vol. 13 (Ed.: H. Sigel),
Marcel Dekker, New York, 1981; b) Bioinorganic Chemistry of
Copper (Eds.: K. D. Karlin, Z. Tyeklꢂr), Chapman and Hall,
New York, 1993; c) Handbook of Metalloproteins, Vol. 2 (Eds.:
A. Messerschmidt, R. Huber, T. Poulos, K. Wieghardt), Wiley,
Chichester, 2004.
[2] D. B. Rorabacher, Chem. Rev. 2004, 104, 651 – 697, and refer-
ences therein.
[3] a) S. Iwata, C. Ostermeier, B. Ludwig, H. Michel, Nature 1995,
376, 660 – 669; b) T. Tsukihara, H. Aoyama, E. Yamashita, T.
Tomizaki, H. Yamaguchi, K. Shinzawa-Itoh, R. Nakashima, R.
Yaono, S. Yoshikawa, Science 1995, 269, 1069 – 1074; c) M.
Wilmanns, P. Lappalainen, M. Kelly, E. Sauer-Eriksson, M.
Saraste, Proc. Natl. Acad. Sci. USA 1995, 92, 11955 – 11959; d) K.
Paraskevopoulos, S. V. Antonyuk, R. G. Sawers, R. R. Eady, S. S.
Hasnain, J. Mol. Biol. 2006, 362, 55 – 65.
[4] a) R. P. Houser, V. G. Young, Jr., W. B. Tolman, J. Am. Chem.
Soc. 1996, 118, 2101 – 2102; b) W. B. Tolman, J. Biol. Inorg.
Chem. 2006, 11, 261 – 271; c) R. K. Chadha, R. Kumar, D. G.
Tuck, Can. J. Chem. 1987, 65, 1336 – 1342; d) A. F. Stange, E.
Waldhꢃr, M. Moscherosch, W. Kaim, Z. Naturforsch. B 1995, 50,
115 – 122.
[5] a) G. Henkel, A. Mꢄller, S. Weißgrꢅber, H.-F. Nolting, G. Buse,
T. Soulimane, G. C. M. Steffens, Angew. Chem. 1995, 107, 1615 –
1619; Angew. Chem. Int. Ed. Engl. 1995, 34, 1488 – 1492; b) N. J.
Blackburn, S. de Vries, M. E. Barr, R. P. Houser, W. Tolman, D.
Sanders, J. A. Fee, J. Am. Chem. Soc. 1997, 119, 6135 – 6143.
[6] a) Y. Ueno, Y. Tachi, S. Itoh, J. Am. Chem. Soc. 2002, 124,
12428 – 12429; b) A. I. Uraev, I. S. Vasilchenko, V. N. Ikorskii,
T. A. Shestakova, A. S. Burlov, K. A. Lyssenko, V. G. Vlasenko,
T. A. Kuzmenko, L. N. Divaeva, I. V. Pirog, G. S. Borodkin, I. E.
Uflyand, M. Yu. Antipin, V. I. Ovcharenko, A. D. Garnovskii,
V. I. Minkin, Mendeleev Commun. 2005, 15, 133 – 135; c) R. P.
Houser, J. A. Halfen, V. G. Young, Jr., N. J. Blackburn, W. B.
Tolman, J. Am. Chem. Soc. 1995, 117, 10745 – 10746; d) S. Itoh,
M. Nagagawa, S. Fukuzumi, J. Am. Chem. Soc. 2001, 123, 4087 –
4088; e) W. Rammal, C. Belle, C. Beguin, C. Duboc, C. Philouze,
J.-L. Pierre, L. Le Pape, S. Bertaina, E. Saint-Aman, S. Torelli,
Inorg. Chem. 2006, 45, 10355 – 10362; f) N. Roy, S. Sproules, E.
Bothe, T. Weyhermꢄller, K. Wieghardt, Eur. J. Inorg. Chem.
2009, 2655 – 2663; g) N. D. J. Branscombe, A. J. Blake, A. Marin-
Becerra, W.-S. Li, S. Parsons, L. Ruiz-Ramirez, M. Schrꢃder,
Chem. Commun. 1996, 2573 – 2574; h) S. Torelli, M. Orio, J.
Pecaut, H. Jamet, L. Le Pape, S. Menage, Angew. Chem. 2010,
122, 8425 – 8428; S. Torelli, M. Orio, J. Pecaut, H. Jamet, L.
Le Pape, S. Menage, Angew. Chem. 2010, 122, 8425 – 8428;
Angew. Chem. Int. Ed. 2010, 49, 8249 – 8252.
Though by use of terminally bound thiolate ligands, we
veer a little bit away from CuA, but it must be noted that 2
with the structural characteristics of its {Cu2S2} diamonds, its
metal oxidation stage and its electronic and electrochemical
properties resembles the biological CuA site more closely than
any other compounds known to date.[16] Thus we succeeded
for the first time in solving the problem of biological matrix
stabilization to produce the desired redox properties of CuA
by suitable steric restrictions within a synthetic model
complex.
Apart from this biologically motivated question, the
hexanuclear compound 2 with its unique ability to undergo
one-electron-transfer steps between valence delocalized
states within the series [Cu6(NGuaS)6]3+/2+/1+ is a unique
functional system in copper–sulfur cluster chemistry.
[7] X. Xie, S. I. Gorelsky, R. Sarangi, D. K. Garner, H. J. Hwang,
K. O. Hodgson, B. Hedman, Y. Lu, E. I. Solomon, J. Am. Chem.
Soc. 2008, 130, 5194 – 5205.
[8] a) M. D. Janssen, J. G. Donkervoort, S. B. van Berlekom, A. L.
Spek, D. M. Grove, G. van Koten, Inorg. Chem. 1996, 35, 4752 –
4763; b) M. Knotter, G. van Koten, H. L. van Maanen, D. M.
Grove, A. L. Spek, Angew. Chem. 1989, 101, 351 – 352; D. M.
Knotter, G. van Koten, H. L. van Maanen, D. M. Grove, A. L.
Spek, Angew. Chem. 1989, 101, 351 – 352; Angew. Chem. Int. Ed.
Engl. 1989, 28, 341 – 342; c) D. M. Knotter, H. L. van Maanen,
D. M. Grove, A. L. Spek, G. van Koten, Inorg. Chem. 1991, 30,
3309 – 3317.
[9] M. B. Robin, P. Day, Adv. Inorg. Chem. Radiochem. 1968, 10,
247 – 422.
[10] a) G. C. Allen, N. S. Hush, Prog. Inorg. Chem. 1967, 8, 391 – 444;
b) N. S. Hush, Prog. Inorg. Chem. 1967, 8, 391 – 444; c) N. S.
Received: December 21, 2010
Revised: January 13, 2011
Published online: April 11, 2011
4506 www.angewandte.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2011, 50, 4503 –4507

Hush, Electrochim. Acta 1968, 13, 1005 – 1023; d) N. S. Hush,
Coord. Chem. Rev. 1985, 64, 135 – 157; e) B. S. Brunschwig, C.
Creutz, N. Sutin, Chem. Soc. Rev. 2002, 31, 168 – 184; f) C.
Creutz, B. S. Brunschwig, N. Sutin, J. Phys. Chem. B 2005, 109,
10251 – 10260; g) C. Creutz, Prog. Inorg. Chem. 1983, 30, 1 – 73;
h) D. M. DꢆAlessandro, F. R. Keene, Chem. Soc. Rev. 2006, 35,
424 – 440.
J. Zubieta, J. Chem. Soc. Dalton Trans. 2000, 559 – 567; g) C.
Wycliff, A. G. Samuelson, M. Nethaji, Inorg. Chem. 1996, 35,
5427 – 5434; h) C. Wycliff, D. S. Bharathi, A. G. Samuelson, M.
Nethaji, Polyhedron 1998, 18, 949 – 958; i) S. Kitagawa, M.
Munakata, H. Shimono, S. Matsuyama, J. Chem. Soc. Dalton
Trans. 1990, 2105 – 2109.
[14] R. C. Luckay, X. Sheng, C. E. Strasser, H. G. Raubenheimer,
D. A. Safin, M. G. Babakina, A. Klein, Dalton Trans. 2009,
4646 – 4652.
[15] P. M.H Kroneck, W. A. Antholine, J. Riester, W. G. Zumft,
FEBS Lett. 1989, 248, 212 – 213.
[16] The literature describes a complex with a Cu–S skeleton of eight
edge-sharing {CuI2S2}-diamonds, which arrange themselves sym-
metrically around a local axis (T. Kawamoto, N. Ohkoshi, I.
Nagasawa, H. Kuma, Y. Kushi, Chem. Lett. 1997, 553 – 554).
Recent studies on a variant modified in the periphery of the
ligand revealed an average oxidation state of + 1.125, which can
electrochemically be increased to + 1.25 or reduced to + 1.00.
However, the averaged oxidation stage of + 1.5 achieved by us
could not be realized within these systems (T. Kawamoto, M.
Nishiwaki, M. Nishijima, K. Nozaki, A. Igashira-Kamiyama, T.
Konno, Chem. Eur. J. 2008, 14, 9842 – 9845).
[11] a) D. E. Richardson, H. Taube, Coord. Chem. Rev. 1984, 60,
107 – 129; b) R. J. Crutchley, Adv. Inorg. Chem. 1994, 41, 273 –
325; c) A. W. Bott, Curr. Sep. 1997, 16, 61 – 66.
[12] a) M. G. Kanatzidis, W. R. Hagen, W. R. Dunham, R. K. Lester,
D. Coucouvanis, J. Am. Chem. Soc. 1985, 107, 953 – 961; b) W.
Saak, G. Henkel, S. Pohl, Angew. Chem. 1984, 96, 153 – 154;
Angew. Chem. Int. Ed. Engl. 1984, 23, 150 – 151.
[13] a) C. Yue, C. Yan, R. Feng, M. Wu, L. Chen, F. Jiang, M. Hong,
Inorg. Chem. 2009, 48, 2873 – 2879; b) M. Du, R.-Q. Zou, R.-Q.
Zhong, X.-U. Qiang, Inorg. Chem. Commun. 2007, 10, 1437 –
1439; c) E. Lꢇpez-Torres, M. A. Mendiola, C. J. Pastor, Inorg.
Chem. 2006, 45, 3103 – 3112; d) Y. Bai, G.-J. He, Y.-G. Zhao, C.-
Y. Duan, D.-B. Dang, Q.-J. Meng, Chem. Commun. 2006, 1530 –
1532; e) L. J. Ashfield, A. R. Cowley, J. R. Dilworth, P. S.
Donnelly, Inorg. Chem. 2004, 43, 4121 – 4123; f) J. A. Garcꢈa-
Vꢂzquez, J. Romero, A. Sousa-Pedrares, M. L. Louro, A. Sousa,
Angew. Chem. Int. Ed. 2011, 50, 4503 –4507
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org 4507