Aggregation control of copper(I) thiolates through substituent size and ancillary chelate ligands: Closely related mono-, di-, tri- and tetranuclear complexes

Article abstract of DOI:10.1016/S0020-1693(01)00535-7

The choice of thiolates and of ancillary nitrogen chelate ligands N ^∧ N determines the aggregation state of copper(I) thiolate compounds [(RS)_xCu_y(N ^∧ N)_z]^k. Starting from electrogenerated [(RS)Cu]_n, the species obtained and structurally characterized include (i) mononuclear (RS)Cu(Me₄phen), Me₄phen = 3,4,7,8-tetramethyl-1,10-phenanthroline, with 2,6-diorganophenyl thiolates RS^-, (ii) dinuclear [(μ-RS)Cu(Me₂phen)]₂, Me₂phen = 2,9-dimethyl-1,10-phenanthroline, with R = phenyl or o-tolyl, (iii) trinuclear (μ-RS)₃Cu₃(Me₄phen)₂ with R = mesityl, (iv) tetranuclear (μ-RS)₄Cu₄(bpy)₂ with R = 2,4,6-i-Pr₃C₆H₂, and (v) the tetranuclear dianion [(μ-RS)₆Cu₄]^2- where the added chelate ligand N ^∧ N = bis(2-imidazolyl)ketone occurs in the [(N ^∧ N)₂Cu]⁺ counterions. The new trinuclear (μ-MesS)₃Cu₃(Me₄phen)₂ exhibits an unsymmetrical Cu₃S₃ six-membered ring in which the dicoordinate copper(I) center has a nearly linear configuration (angle S-Cu-S 173.93(13)°). Both tetracoordinate copper(I) atom sites exhibit a characteristic distortion from a tetrahedral towards a trigonal pyramidal CuN₂S₂ arrangement which is reminiscent of the geometry observed for the rhombic variants of type 1 Cu centers in blue copper proteins.

Full text of DOI:10.1016/S0020-1693(01)00535-7

www.elsevier.nl/locate/ica
Inorganica Chimica Acta 324 (2001) 336–341
Note
Aggregation control of copper(I) thiolates through substituent size
and ancillary chelate ligands: closely related mono-, di-, tri- and
tetranuclear complexes
Andreas F. Stange, Axel Klein, Karl-Wilhelm Klinkhammer, Wolfgang Kaim *
Institut fu¨r Anorganische Chemie, Uni6ersita¨t Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart, Germany
Received 23 March 2001; accepted 6 June 2001
Abstract
‚
The choice of thiolates and of ancillary nitrogen chelate ligands N N determines the aggregation state of copper(I) thiolate
compounds [(RS)xCuy(N N)z]k. Starting from electrogenerated [(RS)Cu]n, the species obtained and structurally characterized
‚
include (i) mononuclear (RS)Cu(Me4phen), Me4phen=3,4,7,8-tetramethyl-1,10-phenanthroline, with 2,6-diorganophenyl thiolates
RS−, (ii) dinuclear [(m-RS)Cu(Me2phen)]2, Me2phen=2,9-dimethyl-1,10-phenanthroline, with R=phenyl or o-tolyl, (iii) trinu-
clear (m-RS)3Cu3(Me4phen)2 with R=mesityl, (iv) tetranuclear (m-RS)4Cu4(bpy)2 with R=2,4,6-i-Pr3C6H2, and (v) the tetranu-
‚
‚
clear dianion [(m-RS)6Cu4]2− where the added chelate ligand N N=bis(2-imidazolyl)ketone occurs in the [(N N)2Cu]+
counterions. The new trinuclear (m-MesS)3Cu3(Me4phen)2 exhibits an unsymmetrical Cu3S3 six-membered ring in which the
dicoordinate copper(I) center has a nearly linear configuration (angle SꢀCuꢀS 173.93(13)°). Both tetracoordinate copper(I) atom
sites exhibit a characteristic distortion from a tetrahedral towards a trigonal pyramidal CuN2S2 arrangement which is reminiscent
of the geometry observed for the rhombic variants of type 1 Cu centers in blue copper proteins. © 2001 Elsevier Science B.V. All
rights reserved.
Keywords: Copper compounds; Crystal structures; Phenanthroline ligands; p/p Interactions; Thiolates
1. Introduction
c oxidase [9] where dinuclear ‘CuA’ centers are bridged
by two m-Cys− groups [6]. In addition, metalloth-
ioneins, phytochelatins as well as copper transport,
storage and regulatory proteins typically contain sev-
eral Cu(I) binding cysteine functions [5,6]. Especially
after the dinuclear bis(cysteinato)-bridged arrangement
of the CuA center had been established by crystallo-
graphic and spectroscopic efforts [9], the variable [5,10]
aggregation state of such species has become an inter-
esting topic.
The structures and chemical properties of copper(I)
thiolates have been reviewed recently [1]. These species
have an interesting chemistry in their own right but are
of a wider interest also because of their uses in synthetic
chemistry [1,2] and materials science [3], because of
their luminescence [4,5] and their occurrence in organ-
isms [5,6]. Copper(I) bound by deprotonated cysteine
has been established for the reduced states of blue
copper proteins which contain mononuclear type 1 Cu
centers with electron transfer function [6,7]; it also
occurs in oxidase enzymes such as nitrous oxide reduc-
tase [8] or the terminal respiratory enzyme cytochrome
Previous studies on the structures of compounds
containing copper(I), aromatic thiolates and ancillary
‚
chelate ligands N N, e.g. of the 1,10-phenanthroline
type, have shown a remarkable variety, including
‚
mononuclear species (RS)Cu(N N) [11], dinuclear sys-
* Corresponding author. Tel.: +49-711-685 4170/71; fax: +49-
711-685 4165.
E-mail address: kaim@iac.uni-stuttgart.de (W. Kaim).
‚
tems [(m-RS)Cu(N N)]2 [12] and tetranuclear com-
‚
pounds such as [(m-RS)6Cu4][(N N)2Cu]2 [13] or
0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(01)00535-7

A.F. Stange et al. / Inorganica Chimica Acta 324 (2001) 336–341
337
‚
(m-RS)4Cu4(N N)2 [14]. Continuing with our program
of a greyish powder. Anal. Found: C, 49.89; H, 5.01.
Calc. for C9H11CuS (214.80 g mol−1): C, 50.01; H,
5.16%.
to combine sulfur and unsaturated nitrogen ligands at
copper centers for approaching biological copper sites
we now report that we can complement this series by a
missing link,
a
new trinuclear species (m-RS)3-
2.1.3. (v-MesS)3Cu3(Me4phen)2 (I)
‚
‚
Cu3(N N)2 (I), R=mesityl and N N=Me4phen=
3,4,7,8-tetramethyl-1,10-phenanthroline. The factors
determining the degree of aggregation will be discussed.
A suspension of 30 mg (0.063 mmol) (MesS)-
Cu(Me4phen) as obtained from [(MesS)Cu]n and
Me4phen [11] in 20 ml acetone was heated to reflux for
6 h. The red solution was cooled down slowly and after
3
days 17 mg (72%) of brown (m-MesS)3Cu3-
2. Experimental
(Me4phen)2·0.5C3H6O could be isolated. Anal. Found:
C, 63.12; H, 5.90; N, 4.88. Calc. for C59H65Cu3-
N4S3·0.5C3H6O (1146.00 g mol−1): C, 63.41; H, 5.98;
2.1. Syntheses
1
N, 4.89%. H NMR (CD2Cl2): l=2.12 (s, 3H, Mes-4-
CH3), 2.19 (s, 6H, Mes-4-CH3), 2.25 (s, 6H, Mes-2,6-
CH3), 2.32 (s, 12H, Mes-2,6-CH3), 2.49 (s, br, 12H,
Me4phen-3,8-CH3), 2.73 (s, br, 12H, Me4phen-4,7-
CH3), 6.85 (s, 4H, Mes-H), 6.89 (s, 2H, Mes-H), 8.18
(s, br, 4H, Me4phen-5,6-H), 8.49 (s, br., 4H, Me4phen-
2,9-H) ppm.
2.1.1. General procedure
All preparations and measurements were performed
under an atmosphere of dry argon in dried solvents.
2.1.2. 2,4,6-Trimethylthiophenolatocopper(I)
[(MesS)Cu]n
A
solution of 3.0 ml 2,4,6-trimethylthiophenol
MesSH [15] in 100 ml acetonitrile was electrolyzed at a
copper anode for 2.5 h (25 V, 20 mA) [16,17]. An
amount of 131 mg (2.06 mmol) copper was dissolved
during that process. The colorless precipitate was col-
lected and washed with acetonitrile and diethyl ether.
Drying under vacuum yielded 395 mg (89% rel. to Cu)
2.2. Crystallography
Single crystals of I·0.5C3H6O were obtained from the
reaction mixture. X-ray diffraction was carried out with
a Syntex P21 instrument using graphite monochromated
Mo Ka radiation (u=71.073 pm). The data were cor-
rected for Lorentz and polarization effects. The struc-
ture was solved by direct methods using the program
Table 1
Crystal data and structure refinement parameters for I·0.5C3H6O
packages SHELXTL-PLUS [18] and SHELXL-93 [19]. All
non-hydrogen atoms were refined anisotropically, hy-
drogen atoms were introduced at calculated positions
with coupled isotropic temperature factors. Further
information is summarized in Table 1.
Empirical formula
C59H65Cu3N4S3·0.5C3H6O
1146.0
triclinic
Formula weight (g mol−1
)
Crystal system
Space group
Unit cell dimensions
a (pm)
b (pm)
c (pm)
(
P1
1049.8(4)
1616.6(5)
1812.5(5)
67.24(2)
3. Results and discussion
h (°)
i (°)
83.20(3)
85.61(3)
2.8150(16)
1
1.359
3.1. O6er6iew
k (°)
V (nm3)
Z
Previous efforts to combine copper(I) centers, ring-
substituted aromatic thiolates and bidentate nitrogen
donor ligands N N have already led to a variety of
spectroscopically, electrochemically and structurally
characterized products [11–14,16,17,20].
Dcalc (Mg m−3
)
v (mm−1
F(000)
)
1.278
1188
‚
Crystal size (mm)
[ Range (°)
Index ranges
0.2×0.2×0.15
1.95 to 24.00
05h512, −185k518,
−205l520
8834
‚
‚
1/x[(RS)Cu]x+N N“(RS)Cu(N N)
(1)
Number of reflections
Number of independent
reflections
Data/restraints/parameters
Goodness-of-fit
‚
8816 [Rint=0.0322]
R=2,6-Ph2C6H3, 2,4,6-Me3C6H2 (Mes); N N=
Me4phen; coordination number 2+1.
electrolysis
2RSH+2Cu+2N N ꢀꢀꢀꢀꢀꢁ [(m-RS)Cu(N N)]2+H2
(2)
8016/0/677
1.056
R1=0.0857, wR2=0.1909
R1=0.1679, wR2=0.2298
687 and −611
‚
‚
R [I\2|(I)]
R (all data)
Residual electron density
‚
(e nm−3
)
R=o-tolyl=2-MeC6H4, N N=phen, Me2phen; co-
ordination number 4.

338
A.F. Stange et al. / Inorganica Chimica Acta 324 (2001) 336–341
‚
‚
‚
3(RS)Cu(N N)“(m-RS)3Cu3(N N)2+N N
(3)
‚
R=Mes, N N=Me4phen; coordination numbers 2
and 3+1.
6RSH+6Cu
electrolysis
+4N N ꢀꢀꢀꢀꢀꢁ [(m-RS)6Cu4][Cu(N N)2]2+3H2
‚
‚
(4a)
‚
R=o-tolyl, N N=bik; coordination numbers 3 and
4.
‚
‚
[(RS)Cu]4+2N N“(m-RS)4Cu4(N N)2
(4b)
‚
R=2,4,6-i-Pr3C6H2, N N=bpy; coordination num-
bers 2 and 4.
Fig. 1. Molecular structure of (m-MesS)3Cu3(Me4phen)2 in the crystal
of I·0.5C3H6O.
Table 2
Selected distances (pm) for I·0.5C3H6O
Cu1ꢀN11
Cu2ꢀN21
Cu1ꢀS1
Cu2ꢀS2
Cu3ꢀS1
214.5(7)
212.4(8)
241.0(3)
240.1(3)
216.0(3)
373.3(2)
301.4(2)
Cu1ꢀN12
Cu2ꢀN22
Cu1ꢀS3
Cu2ꢀS3
Cu3ꢀS2
Cu1···Cu3
212.2(7)
212.8(7)
225.7(3)
224.8(3)
215.5(3)
271.5(2)
Cu1···Cu2
Cu2···Cu3
Table 3
Selected angles (°) of I·0.5C3H6O
N11ꢀCu1ꢀN12
N12ꢀCu1ꢀS1
N12ꢀCu1ꢀS3
N21ꢀCu2ꢀN22
N22ꢀCu2ꢀS2
N22ꢀCu2ꢀS3
S2ꢀCu3ꢀS1
77.1(3)
102.2(2)
136.4(2)
78.2(3)
104.4(2)
121.7(2)
173.97(13)
82.68(10)
N11ꢀCu1ꢀS1
N11ꢀCu1ꢀS3
S1ꢀCu1ꢀS3
N21ꢀCu2ꢀS2
N21ꢀCu2ꢀS3
S2ꢀCu2ꢀS3
106.5(2)
111.6(2)
114.62(10)
103.1(2)
127.4(2)
115.23(10)
72.67(9)
111.94(12)
As illustrated by Eqs. (1), (2), (4a) and (4b) these
systems can be obtained either by electrolysis of N N
‚
and thiol-containing mixtures with copper as sacrificial
anode [12,16,17] or by reacting chemically or electrolyt-
ically obtained oligomers [(RS)Cu]x [10,21] with the
bidentate ligands [11,12]. The latter procedure (1) was
used to prepare (MesS)Cu(Me4phen) which has been
spectroscopically, electrochemically and structurally
Cu1ꢀS1ꢀCu3
Cu2ꢀS3ꢀCu1
Cu2ꢀS2ꢀCu3
1
characterized [11]. The H NMR spectrum showed only
The trinuclear species contains an unsymmetrical six-
one species present in CD2Cl2, in contrast to other,
related systems which exhibit association equilibria in
solution [14,16].
membered ring [(m-RS)Cu]3 with one two-coordinate
‚
(Cu3) and two tetracoordinate (i.e. N N chelated)
copper(I) centers (Cu1, Cu2). The intraring metal–
metal distances are long and quite variable (Table 2),
illustrating the asymmetry and the absence of signifi-
cant d10–d10 interactions. As a consequence of the
almost linear S1ꢀCu3ꢀS2 arrangement (cf. below) the
ring adopts a ‘half-chair’ conformation.
Although there are no special intermolecular contacts
in the crystal of I·0.5C3H6O, there is evidence for weak
intramolecular inter-substituent p/p interactions be-
tween neighboring (S-)mesityl and (Cu-)Me4phen p sys-
tems. The smallest non-bonding distance between
carbon atoms of the largely parallel oriented sub-
stituents is 347.5 pm (C21···C222)—a still significant
3.2. Synthesis and structure of
(v-MesS)3Cu3(Me4phen)2 (I)
Prolonged heating of (m-MesS)Cu(Me4phen) in ace-
tone was now found to cause partial loss of the biden-
tate ligand, producing
a new trinuclear species
(m-MesS)3Cu3(Me4phen)2 (I) according to Eq. (3). The
structure of the hemi-acetonate I·0.5C3H6O could be
determined by X-ray crystallography, the pertinent data
and structural results are summarized in Tables 1–3.
Fig. 1 shows the structure of the molecule in the crystal.

A.F. Stange et al. / Inorganica Chimica Acta 324 (2001) 336–341
339
value considering the multiple substitution of the
arenethiolate and phenanthroline p systems with methyl
groups. This interaction appears to be retained in solu-
tion where the broadened signals from Me4phen and
the high field shifted resonances for the two Me4phen-
neighboring mesityl groups indicate p/p contact.
In agreement with the different coordination num-
bers, the angle S1ꢀCu3ꢀS2 is approaching linearity at
173.97(13)° whereas the SꢀCuꢀS angles at the four-co-
ordinate metal sites lie at about 115°. Similar observa-
tions have been made for (m-RS)4Cu4(bpy)2 which
contains two four-coordinate and two-coordinate cop-
per(I) centers [14].
As has been noted on previous occasions [6,22] there
is a conspicuous tendency for the distortion from an
approximately tetrahedral to a trigonal-pyramidal ge-
ometry at CuIN2E2 sites (E=S, P, As; coordination
number 3+1). This distortion also characterizes the
special arrangement found for type 1 copper centers in
blue copper proteins [6,7]: typically, two N-donor lig-
ands (His) and one S− donor (Cys anion) are bound at
about 210 pm distance to form the base of an approxi-
mate trigonal pyramid whereas the apical donor (often
S from Met) is weakly coordinated at about 280 pm
distance (Scheme 1).
In I the apical bonds of the approximately trigonal
pyramidal copper coordination sites are between Cu1
and S1 and between Cu2 and S2. In both cases the
bonds are about 15 pm longer than those between Cu1
and S3 or Cu2 and S3 (ca. 240 vs. ca. 225 pm, Table 2).
Correspondingly, the NꢀCuꢀS3 angles are relatively
large (average: 124.1°) in comparison to NꢀCuꢀS1 or
CuꢀNꢀS2 (average: 104.1°). The unique S3–thiolate
which bridges two tetra-coordinate copper centers ex-
hibits not only the strongest metal–sulfur bonding, it
also shows a larger CuꢀSꢀCu angle of 111.94(12)° in
relation to the 72.67(9)° (at S1) or 82.68(10)° (at S2).
The latter two angles are particularly small because of
the intraring compensation for the adjacent ‘linear’
S1ꢀCu3ꢀS2 arrangement.
The tendency towards a trigonal pyramidal distortion
at Cu1 and Cu3 is further quantified by the very
different angles between the CuꢀS bonds and the corre-
sponding NꢀCuꢀN plane at each copper(I) center.
These values are 109.1° (S1) versus 138.8° (S3) at Cu1
and 107.8° (S2) versus 137.1° (S3) at Cu2. At ꢀ=
648.7° (Cu1) and 649.8° (Cu2) the sums ꢀ of the bond
angles XꢀCuꢀY lie between the 657° calculated for an
ideal tetrahedron and the value of ꢀ=630° expected
for a pure trigonal pyramid. The distance between the
copper atoms and the N,N,S3 plane is 69.4 pm for Cu1
and 69.5 pm for Cu2; somewhat smaller values of
30–45 pm were found for type 1 copper centers in blue
copper proteins [23].
3.3. Comparati6e discussion of structures
Considering the generally variable coordination ge-
ometry of copper(I) [24] with its d10 configuration and
especially the well-established tendency of copper(I)–
thiolate systems to form large aggregates of variable
size which can engage in association/dissociation equi-
libria [5,10,21] it is remarkable how the substitution at
aromatic thiolates and the nature of the added chelate
‚
ligand N N can lead to different aggregation forms.
The use of structurally flexible and weakly donating
bidentate ligands such as bik or bpy has given rise to
‚
tetranuclear species. With N N=bik and the sterically
less demanding o-tolylthiolate a ‘standard’ cluster an-
ion [(m-RS)6Cu4]2− is formed which is well known from
the copper thiolate chemistry [25] and which exhibits a
coordination number three at the CuS3 centers; the
‚
N N ligands are relegated to coordinate to the Cu+
counterions (4a) [13]. Using bpy and the very bulky
2,4,6-triisopropylphenylthiolate, a mixed system (m-
RS)4Cu4(bpy)2 with two four- and two two-coordinate
copper centers has been crystallized (4b). In solution,
this species shows signs of dissociation into smaller
fragments [14].
With the more rigid 1,10-phenanthrolines the typical
‚
products are monomers (RS)Cu(N N) and dimers [(m-
‚
RS)Cu(N N)]2 [11,12,17,20a]. Monomeric species
‚
(RS)Cu(N N) were obtained through combination of
rigid bidentate 1,10-phenanthroline ligands and steri-
cally demanding thiolates such as (tert-BuO)3SiS− [20a]
or 2,6-disubstituted arenethiolates [11]. The dimers were
shown to exhibit a very flexible geometry of the (m-
RS)2Cu2 core; strongly folded [17] or planar arrange-
ments [12] with very variable angles at the d10 metal
centers were observed. We have now shown that the
neutral chelate ligand can be partially lost in a thermal
reaction upon which the system can stabilize in a
‚
trinuclear form (m-RS)3Cu3(N N)2. As in (m-
RS)4Cu4(bpy)2 [14], the metals avoid coordination num-
ber three and opt for either two- or four-coordination.
With only methyl-substitution at the p systems there is
a possibility to stabilize this arrangement I through p/p
interaction; another kind of ‘secondary interaction’ to
stabilize unusual copper(I)–thiolate structures would be
intramolecular hydrogen bonding [26].
A comparison of the bond parameters of the phenan-
throline ligands-containing monomers, dimers and the
Scheme 1. (3+1)-Coordination arrangement at type 1 Cu centers in
proteins (left) and at Cu1 and Cu2 atoms in I (right).

340
A.F. Stange et al. / Inorganica Chimica Acta 324 (2001) 336–341
‚
Scheme 2. Aggregation state variations in the system [(RS)xCuy(N N)z], y=1–4.
low-coordinate, avoiding the coordination of the biden-
tate ancillary ligands.
new trinuclear system 1 reveals the possibilities for
structural flexibility: At about 211 pm the CuꢀN bonds
‚
are ‘normal’ for I and [(m-RS)Cu(N N)]2 but highly
variable with about 197 and 217 pm for the monomers
‚
4. Supplementary material
(RS)Cu(N N) where a 2(N,S)+1(N%) coordination ar-
rangement leaves the Me4phen ligand highly unsymmet-
rically bound [11]. The CuꢀS bonds are short at about
215 pm for essentially dicoordinate copper in
X-ray crystallographic files for (m-MesS)3Cu3-
(Me4phen)2 are available from the authors on request.
‚
(RS)Cu(N N) [11] and I (Cu3), longer at about 230
‚
pm in [(m-RS)Cu(N N)]2 with tetracoordinate copper
Acknowledgements
[12,17] and variable (225, 240 pm) for Cu1 and Cu2 in
I with the 3(N,N%,S)+1(S%) coordination. Incidentally,
a 2(N,N%)+2(S,S%) coordination for copper(I) with a
nearly linear NꢀCuꢀN% axis and weakly bonded
thioether (i.e. neutral) S donors has been observed
recently in [Cu(mmb)2]+, mmb=1-methyl-2-(methylth-
iomethyl)-1H-benzimidazole [27].
This research was supported by the Deutsche
Forschungsgemeinschaft (DFG) and by the Fonds der
Chemischen Industrie (FCI). We thank Dr. W. Schwarz
for the X-ray diffraction measurements.
Summarizing, the new trinuclear (m-MesS)3Cu3-
(Me4phen)2 may be viewed as the missing link, espe-
cially between the dimers [(m-RS)Cu(N N)]2 with tetra-
References
‚
[1] M.D. Janssen, D.M. Grove, G. van Koten, Prog. Inorg. Chem.
46 (1997) 97.
[2] (a) A. Pichota, P.S. Pregosin, M. Valentini, M. Wo¨rle, D.
Seebach, Angew. Chem., 112 (2000) 157; Angew. Chem., Int. Ed.
Engl. 39 (2000) 153;
coordinate copper(I) and tetranuclear (m-RS)4Cu4(bpy)2
[14] with two tetra- and two two-coordinate metals. An
attempt to rationalize these various structural options
has to involve the sterical demand of the thiolate and
the flexibility of the bidentate ligand. Increasing bulki-
(b) D. Ohlmann, C.M. Marchand, H. Gru¨tzmacher, G.S. Chen,
D. Farmer, R. Glaser, A. Currao, R. Nesper, H. Pritzkow,
Angew. Chem. 108 (1996) 317; Angew. Chem., Int. Ed. Engl. 35
(1996) 300;
(c) M.D. Janssen, R. van der Rijst, A.L. Spek, D.M. Grove, G.
van Koten, Inorg. Chem. 35 (1996) 3436.
‚
ness of RS and rigidity of N N favor smaller coordi-
nation numbers at the metal, however, the preferred
aggregation state (Scheme 2) is more difficult to predict:
higher aggregation may be achieved even with bulky
thiolates if at least some of the metal centers remain
[3] W. Hirpo, S. Dhingra, A.C. Sutorik, M.G. Kanatzidis, J. Am.
Chem. Soc. 115 (1993) 1597.

A.F. Stange et al. / Inorganica Chimica Acta 324 (2001) 336–341
341
[4] (a) F. Sabin, C.K. Ryu, A. Vogler, P.C. Ford, Inorg. Chem. 31
(1992) 1941;
[17] R.K. Chadha, R. Kumar, D.G. Tuck, Can. J. Chem. 65 (1987)
1336.
(b) V.W.-W. Yam, C.-H. Lam, W.K.-M. Fung, K.-K. Cheung,
Inorg. Chem. 40 (2001) 3435.
[5] (a) K. Fujisawa, S. Imai, N. Kitajima, Y. Moro-oka, Inorg.
Chem. 37 (1998) 168 (and references therein);
[18] G.M. Sheldrick, SHELXTL-PLUS, An Integrated System for Solv-
ing, Refining, and Displaying Crystal Structures from Diffrac-
tion Data, Siemens Analytical X-Ray Instruments Inc.,
Madison, WI, USA, 1989.
(b) A.C. Rosenzweig, Acc. Chem. Res. 34 (2001) 119.
[6] W. Kaim, J. Rall, Angew. Chem. 108 (1996) 47; Angew. Chem.,
Int. Ed. Engl. 35 (1996) 43.
[7] E.I. Solomon, D.W. Randall, T. Glaser, Coord. Chem. Rev.
200–202 (2000) 595.
[8] K. Brown, M. Tegoni, M. Prudeˆncio, A.S. Pereira, S. Besson,
J.J. Moura, I. Moura, C. Cambillau, Nat. Struct. Biol. 7 (2000)
191.
[9] (a) S. Iwata, C. Ostermeier, B. Ludwig, H. Michel, Nature 376
(1995) 660;
[19] G.M. Sheldrick, SHELXL-93, Program for Crystal Structure De-
termination, University of Go¨ttingen, Go¨ttingen, 1993.
[20] (a) B. Becker, W. Wojnowski, K. Peters, E.-M. Peters, H.G. von
Schering, Polyhedron 11 (1992) 613;
(b) O.P. Anderson, K.K. Brito, S.K. Laird, Acta Crystallogr., C
46 (1990) 1600.
[21] (a) I.G. Dance, Polyhedron 7 (1988) 2205;
(b) J.R. Dilworth, J. Hu, Adv. Inorg. Chem. 40 (1993) 411;
(c) E. Block, H. Kang, G. Ofori-Okai, J. Zubieta, Inorg. Chim.
Acta 167 (1990) 147.
(b) T. Tsukihara, H. Aoyama, E. Yamashita, T. Tomizaki, H.
Yamaguchi, K. Shinzawa-Itoh, R. Nakashima, R. Yaono, S.
Yoshikawa, Science 269 (1995) 1069;
(c) T. Tsukihara, H. Aoyama, E. Yamashita, T. Tomizaki, H.
Yamaguchi, K. Shinzawa-Itoh, R. Nakashima, R. Yaono, S.
Yoshikawa, Science 272 (1996) 1136;
[22] (a) C. Vogler, W. Kaim, H.-D. Hausen, Z. Naturforsch., B 48
(1993) 1470;
(b) M. Schwach, H.-D. Hausen, W. Kaim, Inorg. Chem. 38
(1999) 2242;
(c) M. Sieger, C. Vogler, W. Kaim, A. Klein, M. Wanner, J.
Fiedler, unpublished results.
(d) P.M.H. Kroneck, W.E. Antholine, D.H.W. Kastrau, G.
Buse, G.C.M. Steffens, W.G. Zumft, FEBS Lett. 368 (1990) 274;
(e) W.E. Antholine, D.H.W. Kastrau, G.C.M. Steffens, G. Buse,
W.G. Zumft, P.M.H. Kroneck, Eur. J. Biochem. 209 (1992) 875.
[10] (a) I.G. Dance, Polyhedron 5 (1986) 1037;
(b) R.V. Parish, Z. Salehi, R.G. Pritchard, Angew. Chem. 109
(1997) 276; Angew. Chem., Int. Ed. Engl. 36 (1997) 251.
[11] A.F. Stange, T. Sixt, W. Kaim, J. Chem. Soc., Chem. Commun.
(1998) 469.
[23] (a) E.T. Adman, S. Turley, R. Bramson, K. Petratos, D. Banner,
D. Tsernoglou, T. Beppu, H. Watanabe, J. Biol. Chem. 264
(1989) 87;
(b) N. Kitajima, K. Fujisawa, Y. Moro-oka, J. Am. Chem. Soc.
112 (1990) 3210.
[24] C.E. Holloway, M. Melnik, Rev. Inorg. Chem. 15 (1995) 147.
[25] (a) I.G. Dance, G.A. Bowmaker, G.R. Clark, J.K. Seadon,
Polyhedron 2 (1983) 1031;
(b) I.G. Dance, J.C. Calabrese, Inorg. Chim. Acta 19 (1976) L41;
(c) D. Coucouvanis, C.N. Murphy, S.K. Kanodia, Inorg. Chem.
19 (1980) 2993;
[12] A.F. Stange, E. Waldho¨r, M. Moscherosch, W. Kaim, Z. Natur-
forsch., B 50 (1995) 115.
[13] A.F. Stange, W. Kaim, Z. Anorg. Allg. Chem. 622 (1996) 1118.
[14] D. Ohlmann, C.M. Marchand, H. Scho¨nberg, H. Gru¨tzmacher,
H. Pritzkow, Z. Anorg. Allg. Chem. 622 (1996) 1349.
[15] P.J. Blower, J.R. Dilworth, J.P. Hutchinson, J.A. Zubieta, J.
Chem. Soc., Dalton Trans. (1985) 1533.
(d) J.J. Vittal, Polyhedron 15 (1996) 1585.
[26] A.F. Stange, K.-W. Klinkhammer, W. Kaim, Inorg. Chem. 35
(1996) 4087.
[27] M. Albrecht, K. Hu¨bler, S. Zalis, W. Kaim, Inorg. Chem. 39
(2000) 4731.
[16] A.F. Stange, PhD Thesis, Universita¨t Stuttgart, 1996.